We have prepared some background now about the ocean to start learning about one of the most fascinating phenomena in the tropics namely El Nino and Southern Oscillation. So, today's will be the first set of first of a set of lectures on El Nino and Southern Oscillation. So, the most dominant phenomenon in the inter annual that is to say year to year variation of the tropical ocean atmosphere system is the El Nino Southern Oscillation that is Enso over the Pacific. Now Enso has been a major focus of studies of the tropical atmosphere ocean system and there have been a large number of papers including reviews and excellent books on the theme which should be referred to for an in depth insight what I will give is an introduction to this very fascinating phenomena. So, the three books I strongly recommend is first is El Nino La Nina and the Southern Oscillation by George Philander, Academic Press this came out in 1990 subsequently he wrote another book semi popular on our affair with El Nino Princeton University Press 2004 and a recent book which is actually meant as a text book for graduate level which also includes the mathematical part the mathematical modeling part is El Nino and Southern Oscillation phenomena by Saracic and Cain. So, I recommend these books and in fact these three players these three authors Philander, Cain and Saracic have been major players in actually unraveling the mysteries of the El Nino and particularly its physics in the last two decades. So, it is very nice that they have written those books and I strongly recommend that readers who are interested or excited by this phenomena should go to these original books. Now, what is El Nino? The name El Nino means child Jesus in Spanish and it was originally given to the warm seasonal current that appears off the coast of Peru around Christmas when it moderates the low temperatures of the eastern tropical Pacific Ocean. Now, we just mentioned that one gets a warm current on the coast of Peru what you see here is the difference between the boreal summer or June, July, August sea surface temperature SST and the DJF which is December, January, February. So, these are this is the difference between the two temperatures. So, it tells you how much warming or cooling has occurred between the boreal summer JJA and DJF. Now, notice that this is a negative sign here these are all blues. So, off the coast of Peru and Ecuador what you are getting is large negative changes. What does that mean? That means that SST-DGF is getting warm relative to SST-JJA. So, SST-DGF is warm relative to SST-JJA so a warming is occurring off the coast of Peru. So, there is a warming of SST in DJF relative to that of JJA over eastern parts of the tropical Pacific in the southern hemisphere of the coast of Peru and Ecuador. This is the warming and such a warming also occurs over the eastern parts of the tropical Atlantic and the southern hemisphere. You see this here also one gets a warming in December, January, February relative to the June, July, August situation. Now, so every year there is a warming of the ocean off the coast of Peru in around Christmas, December, January, February relative to what it was in the boreal summer June, July, August. Now, this is a annual phenomena. However, every few years this current is more intense than normal penetrates unusually far south and brings heavy rains to the otherwise arid coasts of Ecuador and Peru. So, what you are saying is something that used to occur annually in some years comes with a much larger magnitude penetrates much deeper and lasts much longer. And this used to be called an year of abundance because you get such heavy rains in what is really a desert part. Now, remember this is just to remind you this is Peru and Ecuador on the map here near the hump here of South America. And this is the mean temperature that use mean precipitation annual mean precipitation. And what you see here is that all of them are 20 centimetres of below very, very little rain over the year. So, this is the arid region to which El Nino brings rain and that is why it used to be called year of abundance. However, this connotation that it is associated with child Jesus that means it is a good thing and that it is also associated with year of abundance has now changed over the years. Why is that? Because the warm SST anomaly is associated with reduced upwelling that is to say reduced nutrients in the surface layer and hence disappearance of fish and birds on which the economies of Ecuador and Peru have now become dependent. So, El Nino which was named after an event which was as welcome as child Christ has become a dreaded phenomena. Now, I will show you why this happens. See this is what we have seen before. This is of course, the circumpolar current and this is the gyre we were talking about earlier. This is the anticlockwise gyre in the southern hemisphere and this is the Peru current and you know that the winds here along the South American coast are parallel to the South American coast. So, you get a lot of upwelling here and we have also seen that the nutrients in the ocean are maximum in the deep water. So, upwelling leads to replenishment of nutrients supply of lot of nutrients to this region which leads to lot of growth of phytoplankton, zooplankton fish and also birds that feed on the fish. So, these are the regions of upwelling you get similar region here as well. So, the rocky islands along the coast of Peru provide nesting sites for these goanna birds you can see one of them here and in the absence of an El Nino event the birds are highly productive because you know in the absence of an El Nino event cold water with full of nutrition has come up and so the surface layers are very rich in nutrition they give rise to a lot of phytoplankton, lot of zooplankton, a lot of fish particularly anchovies and therefore, make it an ideal situation for these birds who feed on anchovies goanna birds. So, in the absence of an El Nino event the birds are highly productive consuming a large quantity of fish primarily anchovies that are in the surface layer of the E specific ocean. Now, this is converted into guano which are bird droppings that are used now as fertilizer for agriculture. So, this is a major source of income for Peru and Ecuador on a regular basis they can export and use this fertilizer for agriculture. Now, with the coming of an El Nino what happens that upwelling decreases you get much warmer seas and with the much warmer seas there is not enough nutrition and that means that their fish numbers decline and become inaccessible to guanos. So, there is a big negative impact on the production of guano the bird droppings that come during an El Nino and this is why now El Nino is considered as a phenomena to be dreaded because of the large negative impact on the economy. Now, I should mention that originally El Nino was defined as a warm event namely along the coast of South America particularly Peru and Ecuador. But now what we refer to as an El Nino is of a much larger spatial scale phenomena which is characterized by warm anomalies see these are the anomalies around Peru and Ecuador of 1.2 degrees or so which we had which was associated with the original definition of El Nino. But we will come to this since the events of 1957 and so on it came to be realized that El Nino is not restricted to the coast of South America on the contrary the warm anomalies extend to over a very large region here where this is now this is 150 ways this is 180. So, this is the date line so you have warm anomalies extending up to the date line very high SSD anomalies positive SSD anomalies extending right up to the date line. So, now we what we call an El Nino is not something that is restricted to the coast of South America, but rather something that occurs in the equatorial regions of the central and east specific this part is central specific and this part is east specific. So, now what we refer to as El Nino is a much larger scale phenomena. Now, in some years cold anomalies of SSD are observed over that same region where we observed warm anomalies for during an El Nino and that you can see here. So, this is the same El Nino picture you saw and this is a La Nina event the dashed lines are all cold anomalies and you can see that the same region over which we had warm anomalies during El Nino now there are cold anomalies during what are called cold events and you know El Nino means a boy child. So, La Nina is a girl in Spanish. So, El Nino is a boy and La Nina is a girl. So, these cold events are called La Nina in fact a term coined by George who George Philander who happens to have a Spanish speaking wife. So, so we have two phenomena here the warm and the cold warm being El Nino and cold being La Nina and eastern and central tropical Pacific exhibit an irregular cycle of warming and cooling remember it is a cycle, but it is not a regular cycle like a pendulum it is an irregular cycle of warming and cooling oscillating between warm events El Nino and the cold events La Nina with the period ranging typically between 2 to 7 years. So, the period of the oscillation is not fixed it is an irregular oscillation and the period is typically between 2 to 7 years. So, now what happens during El Nino and what happens during La Nina during El Nino the eastern Pacific as well as central Pacific warm we have seen this and can warm to such an extent that the temperature across the entire tropical Pacific assumes an almost uniform temperature and you see that here see this is the El Nino and what has been done is that the region above 26 or so this is 27, 28. So, above 27 the region has been shaded and what you see is a river of warm water flowing right across the Pacific here. So, this is the El Nino story and this is 26. So, what you see here is a is the cold event. So, what what has happened in this the region above 26 has been shaded. So, 28 is here. So, this is 26 and this is 28. So, this whole region has become above 28 the 6 whereas, during La Nina in fact the region is all above 26 in a relatively narrow belt, but the region above 28 is much more restricted. See here the region above 28 is right across the Pacific here whereas, here the region above 28 is restricted to this part of the Pacific. So, this is why SSD note that SSD greater than 28 degree centigrade is the threshold for convection which we have considered before and which I will consider discuss again later. So, what is happening is the entire ocean has become warm during El Nino and this part of it is colder than usual during La Nina. This is another example and what you see here again is a El Nino of 1997 a more recent one one of the strongest El Nino's of the century and again you see this is the 28 degrees isotherm here and there is a whole stretch of water that is above 28 here whereas, during La Nina this is of 1988 what you see is that the 28 degrees isotherm is just around here. So, the warm water is just around west and central Pacific and here it is not above 28 anywhere this is the La Nina case. Now, that the temperature of the specific is close to that of the western Pacific indicates that the warm phase of Enso is due to a failure of the eastern Pacific to stay cold. We had seen why the eastern Pacific stays cold, but what seems to be this is on the mean, but what seems to be happening is that in some years on some occasions the east specific does not stay cold that is to say the temperature that is to say the temperature becomes close to that of the western Pacific and this is to be kept in mind. So, this is a major departure from the mean and before we can understand this major change from the mean circulation let us discuss what we know about the mean state of the tropical Pacific and the atmosphere above it. So, when we understand the physics of the mean state we will be able to understand what happens during the El Nino and La Nina. So, let us look at the mean climate of the tropical Pacific first the most important characteristic of the tropical Pacific is the large variation between west specific and east specific. So, let us first consider the ocean component and this is something we have seen before that the SST irrespective of the season shows an extremely large variation between west and east. You see in particular this part is cold irrespective of the season and this part is warm irrespective of the season. So, on the whole west is much warmer higher SSTs than the east and SSTs become somewhat comparable only over very very small portion in boreal winter which is December, January, February over somewhat larger portion in June, July, August, but there is no doubt that the west is different from the east there is a large variation between west and east. We have noted before that the extent over which we get warm water over the west is much larger than that over the east. So, there is a major variation in SST. Now, SST is higher over the western equatorial Pacific than the eastern one and that warm SSTs will occur over a region of a larger latitudinal extent over the west western relative to the eastern oceans is only to be expected from the cold equator word currents over the eastern ocean. We have talked about this before that currents emanating from the poles are coming towards the equator near the eastern boundaries near eastern Pacific and that is why it is colder and the latitudinal extent of warm water is less. And this is something you see here these are the cold currents. So, this is the cold current coming here and that whereas, this is a warm current going this way and this is why we have a much larger extent of warm SSTs over west than east. Now, low SSTs of the South American coast in the southern hemisphere arise not only from the fact that you have cold currents coming from high latitudes in there, but also arise from the strong upwelling occurring in association with winds which are northward and parallel to the South American coast throughout the year. And this we will show in the following slides. So, what do we find see we find here you see this is the region you see the winds are all going northward here. This is the within this red circle that I have marked and they are very strong winds as you can see they are all greens. These are wind vectors and the magnitude is large. So, you have strong winds coming from the south to the north blowing parallel to this coast. And this happens in June, July, August also just as it happened in December, January, February again in the same place you have very high winds coming from the south to the north during June, July, August. Now, what happens when we have winds going parallel to the coast of South America? What happens is this leads to Ekman transport to the left that is to say towards the west because this is in the southern hemisphere. So, there is Ekman transport westward in this direction away from the coast. Now, if the wind is pushing the water away from the coast in the Ekman layer then it has to be balanced by upwelling along the coast because the water that is pushed away in the Ekman layer away from the coast has to be replaced by water coming from below the Ekman layer which is to say upwelling along the coast. And if you have upwelling since the lower water is colder you will get lower SSDs along the coast. So, we expect in fact low SSDs along the coast here simply because coast of South America because of the upwelling that is generated by winds which are going parallel to this coast from south to north. But notice that the cold tongue stretches from the coast of South America right up to about 150 west you see this is the cold tongue here and it is there in both the seasons June, July, August as well as December, January, February. There is a cold tongue which is along the equator this part of the equatorial Pacific that is the eastern Pacific eastern and central Pacific also has a cold tongue at the equator that is very nicely seen by another kind of map this is a map of the anomaly SSD anomaly at each latitude relative to the SSD average over all longitudes. So, what is the anomaly at each longitude relative to the SSD average over all the longitudes there. So, if we take this particular longitude of the coast of Peru then you see that there is a huge negative SSD anomaly relative to the zonally average SSD of this latitude. So, equatorial cold tongue is also very nicely seen here in this kind of a picture. So, you see the Pacific you have a huge anomaly negative anomaly of the SSD relative to the rest of the regions in the same latitudinal belt both of the coast of America as well as in the equator. So, these are the upwelling regions notice also there are upwelling regions here of the coast of Africa as well. So, we have seen then that there is a very prominent in addition to the coastal region here there is a prominent belt of cold water along the equator equatorial cold tongue. Now, why do we have cold water along the equator see this again has to do with the winds the winds along the equator are westward let us see that see along the equator the winds you know these are the trade winds. So, they are all going from east to west these have the easterly components south easterly in the northern hemisphere in the southern hemisphere and north easterly in the northern hemisphere, but both have an easterly component easterly is going from east to west. So, the winds along the equator then are going from east to the west. Now, the winds along the equator are westward. So, how will the Ekman transport be in the oceanic region to the north and south of the equator. So, let us consider this region here. Now, if this is the equator and we are slightly to the north of the equator the winds are westerly anyway as we have seen. So, since we are now in the northern hemisphere the Ekman layer will push water to the right that means it will push water to the north. Similarly, in the southern hemisphere the Ekman layer transport will be to the left of the winds that is to say towards the south. So, what is happening is if we look at the equator water to the north of the equator is being pushed northward by the wind driven Ekman layer whereas, water to the south of the equator is being pushed southward by the wind driven Ekman layer and because of this you know there is water is being lost from the surface layer by this divergence that is forced water going north in the northern hemisphere water going south in the southern hemisphere. This water has to be replenished somehow and the way it is replenished is again by upwelling of the deep water. So, the water that is going north and south is replaced by water which comes from below the Ekman layer here and again water from the below the Ekman layer will be colder from then that in the Ekman layer. So, what you get is low SSD's right along the equator and that is the equatorial tongue that you have seen. So, the cold tongue extending along the equator from east to central pacific is attributed to such equatorial upwelling. Now, supply of nutrients associated with upwelling leads to concentration of phytoplankton over the region of equatorial upwelling and even higher concentration of the coast of Peru and Ecuador and nowadays satellite pictures show very beautifully where the extra phytoplankton are. What you see here is high phytoplankton concentration induced by coastal upwelling this is the one and this one here is the phytoplankton concentration induced by equatorial upwelling. So, this is the equatorial upwelling and this is the coastal upwelling where you have highest concentration of Peru and Ecuador. So, you see the result of you see the impact of upwelling on the phytoplankton and hence on the rest of the food chain in the ocean. So, this is an important thing to remember. Now, so far we have seen the sea surface temperature variation from east to west, but there is more to this east to west variation than surface properties alone. In fact, we have seen in the last lecture that thermocline is the region of the ocean the layer of the ocean in which the temperature decreases very rapidly from that near the surface to that of the bottom or deeper layers of the ocean. So, thermocline you remember is the layer in which there is a very sharp decrease in temperature and another feature of the Pacific ocean sure is the variation of the thermocline from east to west. So, what we see is a market variation from east to west in the region depth of the thermocline. Now, this is the depth of the thermocline you can see it these are actually temperature this is now equatorial belt 140 to 100 west and just to give you a feel for what we are going to keep encountering these kind of longitudes now 100 40 is to 100 west. Just to give you a feel for what they imply I have drawn for you on a map of SST it turns out where is 140. So, 140 cuts across the west Pacific here it cuts across Australia this is 140 east and this is 100 west. So, this is clear ocean or at 100 west and this is the equator. So, along the equatorial region we take if you wish how does temperature vary with depth right from west to east from 140 to 100 west and what you see is here. So, at 140 which is in the west Pacific what you find is that the ocean is very warm. In fact, you see this is 28 this is 29. So, it is very very warm and below that this is the thermocline. The thermocline is between 100 and 250 meters in which the temperature is decreased very rapidly from about 26 to about 14. So, this is 16. So, this shaded region is the thermocline which is between 100 to 200 meters roughly over the west Pacific and we can go now this is the date line and roughly the same story as we start going east toward what is happening. See the colder water is coming higher. So, the thermocline is rising and you can see that here at the surface itself this is 27, 26, 25. So, the surface of the ocean is getting colder and colder and actually the thermocline is rising. So, the thermocline is very shallow over eastern Pacific and it is deep over western Pacific. There is a deep layer of warm water over western Pacific below which the thermocline is whereas, eastern Pacific the cold water has come to the surface. So, there is a very large variation from west to east not only in the sea surface temperature which you see in the top part here, but also in the depth of the thermocline in the depth of this warm layer also there is a large variation. This is very shallow thermocline is very shallow in the east and very warm in the west very deep in the west. So, deeper thermocline in the west and shallower thermocline in the east is what we see. Now, why do we get a deep thermocline in the west? This is attributed to the prevalent easterly winds. We have seen that the winds along the equatorial region or in the tropical Pacific are is have an easterly component. So, because the winds are to the west they will move the surface water westward along the equator. Along the equator the winds will push the surface water towards the west Pacific. Since the pressure at any point so the winds are pushing the water there. So, what will happen that means the sea level will rise over the west Pacific relative to the east Pacific. So, now if the sea level rises remember that if one considers a point in the ocean then the pressure at any point in the ocean is the weight of the total column of the water above it. This is hydrostatic balance. So, the larger the amount of water over that point the higher will be the pressure. So, what happens is over the west Pacific if we consider same height or same depth in the ocean then the pressure over the west Pacific will be higher than pressure over the east Pacific that is to say the pressure gradient is going from west to east. So, it is opposing the wind stress. So, the piling of the water will continue until a point at which the pressure gradient force which is in the opposite direction to the wind balances the westward wind stress. So, the result of the piling up of the water is that in the ocean there is a pressure gradient which goes from the west to the east. Now similar thing is seen also in the Atlantic because we have similar winds in the Atlantic with easterly component north east in the northern hemisphere south east in the southern hemisphere throughout the year. So, that also leads to east west variation in the Atlantic, but if you notice here January, February, March the thermocline is tilting this way again it is shallowing in the east deeper in the west, but in other seasons like June, July, August it is even more deep in the west then it is in the east. So, there is considerable variation of this tilting of the thermocline in the east west direction with season in the Atlantic. Now, it should be noted so far we are talking of the mean state right in the mean the SST is much higher over the west than the east in the mean the thermocline is deeper over the further west specific than the east specific, but you know what is the mean state ever observed. In fact, it should be noted that most often the Pacific is either in the warm state or the cold state El Nino or La Nina with brief periods in which neither are seen. So, although the mean or normal condition can be defined statistically because we can always average all the data and find out what the mean is it is not often observed because the mean is the mean of two states which are totally different. So, you have this is the sea surface temperature going from 100 west to going along along the equator from 140 is to 100 west and along a line from 0 naught to 100 west and then to the South American coast. So, this is the sea surface temperature variation along the equator and then along a line which sort of is going slanting towards the South American coast from about this and what you see here is this is the warm water here this is warm and this is cold and this is South American coast and you see here this is an El Nino because the warm water has come right up to South American coast whereas, this is a La Nina in which the cold see the warm water has retreated to the west specific side and the cold water has spread much more. So, what you see is events of warm and cold alternating very often. So, this is 28 degrees and this is 24 degrees. So, you get El Nino and La Nina alternating and you see that often here and the mean state is observed only for brief periods in between these two states that has to be kept in the mind. Now, what happens during El Nino and La Nina to the thermocline we have seen that the thermocline tilts with the in the mean the thermocline is deeper in the west than the east. So, what happens during El Nino and La Nina is schematically shown here see this is the thermocline this is west specific and what you see here is the sea surface temperature in colors. So, during El Nino actually the thermocline which is normally shallow here has become slightly deeper. So, the thermocline is deeper in the east during El Nino than normal whereas, during La Nina it has become more shallow and when it has become deeper you see that the warm water extending all the way from west to east and during La Nina when the thermocline has become very shallow the warm water is restricted to part of the western central pacific. So, we have two important changes between the warm phase and the cold phase first is of course, the sea surface temperature on the basis of which we defined the warm phase, but second which is a very important thing is this thermocline tilt which is much more during La Nina the tilt is much more during La Nina than the mean whereas, it is much less during El Nino than the mean. So, this is an important thing to remember and we see that here often to trace where the thermocline is oceanographers use the depth of the 20 degrees centigrade isotherm and that is given here these black patches correspond to a depth less than about 70 meters. So, these are all depth less than 70 meters. Now, you see here this is a case where the depth this is 120 meters and this is 100 meters. So, what has happened this is 80 meters here the other solid line is 80 meters. So, what has happened is that during El Nino the 20 centigrade 20 degree centigrade isotherm has become much deeper right this is simply showing that the thermocline is deeper during El Nino. So, the cold isotherm has become deeper whereas, during La Nina it has become very very shallow. So, that is the surfacing of the cold thermocline during La Nina and you see that here in the SST as well that this is during El Nino when all the SST is warm throughout whereas, during La Nina you see that 27 degrees isotherm has come all the way here to almost 100 and beyond 180 east. So, this is El Nino and La Nina cycles. Now seasonal variation. So, what is the seasonal variation over the Pacific unlike the Atlantic the thermocline of the Pacific as measured by the depth of the 20 degrees isotherm hardly varies with season. So, what you see here is this is the now these are the calendar months and this is again going from east to west in the Pacific and basically these are just vertical lines which is saying it is hardly varying with season. The thermocline depth hardly varies with season over the Pacific, but over Atlantic we saw much more variation. However, that is not true of the sea surface temperature we have already seen sea surface temperature does vary with season and we can now see it in here. Now, what you see is a snapshot of the mean SST for January, April which is the boreal spring, July boreal summer and October which is the austral spring. Now, what you see is actually you can see very easily that in January it is see the warm thing is almost touching Australia here. It is at its southern most location this is the warm SST belt, but throughout of course this part remains cold. The southern hemisphere and equatorial region over this part remains cold January, April, July and October that is a permanent feature that does not change. But this belt of warm water that does show a change and you can see between January where it is more to the south and July now you see it has shifted northward. So, that the it has gone north of the tip of Australia as well. So, there is a northward shift of the belt. Secondly, you see a major change in the northern hemisphere in the east specific in January it is all cold all below 27.5 remember yellow and orange and so on correspond to temperature above 27.5. So, January this part entire is specific is cold and west specific is warm here, but from April onwards you begin to see warm ocean here, but only in the northern hemisphere in the east specific not in the southern hemisphere because of the upwelling caused by winds. So, this blob that you see here of warm water is there from April is there in July, but remember it is only in the northern hemisphere and is in October as well it is very strong in April relative to October. So, there is considerable variation in SST you see that also over Indian ocean and we will look at it in greater detail when we discuss the coupled Indian ocean atmosphere system and you see this is January when it is to its southern most location and not as high SST, but by April this is one of the hottest regions of the world Indian ocean and you see that it is warm over a very large latitudinal extent relative to the Pacific and by July the monsoon has set in and you see still there is warm water here, but Pacific is now much warmer and October again now SST is weakening, but the specific region remains hot. Now, however it is now slowly moving to the south. So, over east specific the SST is low except in small patches in January we have seen this. However, during April to October ocean is warmest along the coast of America from about 5 degrees to 20 degrees north and warm in a thin belt around 5 degrees north. So, what happens from here on April onwards SST is high here and in a thin belt around 5 degrees north here same thing here July you see it is hot here much warmer and along a thin belt it is just above 27.5 and a very very thin 28 degrees here. So, there is a thin belt connecting this rather large region of warm SST is here and much larger region of warm SSTs over the west specific is connected by a thinner belt of warm SSTs. Now, we go to the mean atmospheric circulation and convection over the tropical Pacific. Now, the main tool we use for this is the OLR of course, the outgoing long way radiation measured by satellite which is a very robust measure and for which measurements are available for a very long time very stable OLR data from 82 onwards to date. So, already more than 30 years. Now, in the boreal as well as austral summer the SST and hence the air temperature is higher over the west specific than the east we have seen this. What this? This is now the mean sea level pressure because remember now we are looking at features of the atmosphere over the Pacific and pressure is low greens means low and this means it is higher. So, for both the seasons pressure is lower over the west specific then it is over the east specific. So, first let us consider the boreal winter that is December, January, February season which is generally the focus of most of the discussions of ENSO because they generally begin with a discussion of the boreal winter. Now, the mean surface wind and divergence in February this was derived by Rasmussen carpenter by collection of a huge data set including ship data is here. Now, these are the mean winds and you can see here very clearly. See, these are the winds from south to north which cause the coastal upwelling and these are the winds which are northeasterly from the northern hemisphere, southeasterly from the southern hemisphere which have converging over the equator. So, as far as the atmosphere is concerned these are now belts of convergence. So, there is a very strong belt of convergence here and this is called there is a convergence belt here that you can see going this way this is called the south specific convergence zone and in addition this is called south specific convergence zone SPCG and in addition you see just here around five north there is another zone of convergence of these winds. So, these were the two zones of convergence and remember zones of convergence are important because if you have zones of convergence that means the air has to ascend and this is moist tropical air. So, if it ascends with sufficient velocity then you can get condensation and rainfall you can get a tropical convergence zone. So, the mean OLR pattern again we are looking at boreal winter now first what does it show? This is the mean OLR pattern and remember lighter shades are from about 240. So, on monthly or seasonal scale less than 240 watts per meter squared outgoing long wave radiation indicates deep convection presence of deep convection and as you go to darker and darker shades you are getting deeper and deeper clouds clouds which are taller and therefore, emitting less and less radiation. So, now what you see here is there is one band this we call the ITCG inter tropical convergence zone and in addition to that there is the SPCG this is the south specific convergence zone. So, for February then you see in fact the ITCG over the Indian Ocean is also nicely seen here. So, you have an ITCG extending from the Indian Ocean going along here and in addition to that another convergence zone SPCG note there is nothing in this whole region no organized convection no organized deep convection in the east specific. So, what we saw was that convergence zone over the western and central part with the axis tilting southeastward from 150 is this is associated with the belt of low OLR delineating the south specific convergence zone. So, here we can I have marked the convergence zone here see this is the convergence zone tilting this is the convergence of air remember it is tilting this way it is going southeast word in this way. So, from the winds we can derive that there is a convergence zone here and there is another convergence zone which is all along here. So, now the convergence here we see, but the convergence here we do not see as a low OLR region and that is what we will see here though low OLR belt around the equator the ITCG stretching eastward from the Indian Ocean is over the region of convergence. So, this is the region of convergence here and of course, we saw the convergence only for the Pacific. So, that corresponds to this zone here and we had this tilted zone here which was of convergence which is actually now showing deep clouding here this is the south specific convergence zone. But on the other hand over the region of convergence over east and central Pacific that is to say this part here east and central Pacific also there was a zone of convergence what we saw was what came over this zone of convergence and this zone. But over this zone we do not see any low OLR region at all you see here that zone was around here five north or so, but you do not see any low OLR region OLR is above 240 over the entire region. So, the OLR pattern for the boreal winter is seen to be similar to that of the February with SPCG stronger than the ITCG over the west Pacific and no low OLR region. So, we have here SPCG we have the ITCG which is coming all the way from the Indian Ocean here this is the ITCG SPCG is stronger stretching more and there is no low OLR region at all over this region the rainfall pattern. So, actually there are this is the precipitation rate from CMAP data this is the precipitation in millimetres per day and the scale is down here. Now, what you see is bright green and red is reasonable rainfall what you see is a lot of rain occurring over this Indian Ocean ITCG and over SPCG this is part of the ITCG here and this is the ITCG convergence stretching here and where you did not see much of a low OLR region. Now, you are seeing some rain occurring this is between 5 and 6 millimetres per day. So, there is some rain occurring now what you see below is omega at 500 HPA that is to say half way up in the troposphere mid troposphere is the air rising or sinking you can see air is rising very much strong ascent here where we already saw low OLR this region here including over southern parts of Africa this is the African monsoon. So, you see air rising here and air is also rising to some extent here where there is weak rain. So, although there are no regions of deep clouds no low OLR region there is region of weak rain and weak ascent stretching right across the Pacific. So, over the east specific in the southern hemisphere there is a strong descent of air and no rainfall. So, over the east specific here this is a strong descent of air and there is no rainfall. So, if you look at the equatorial region then what you are getting is strong ascent over the west strong descent over the east this is the picture that you see in the equatorial region and also in the southern hemispheric tropics. So, there is strong descent of air over the east. So, along the equator the air rises over the warm western part and sinks over the eastern part of the Pacific ocean. So, this is what is happening here and so, air is rising here and sinking here and so, there is east west variation of organized convection over tropical Pacific we have seen this. There is a T C G over the west specific which we have seen here in the OLR picture as well. This is the huge tropical conversion zone comprising two of them actually over the west specific and this is over the warm oceans. So, the surface of the western Pacific is warm with the SST well above the threshold warm regions tend to have lighter air above these regions as the air is warm by the surface. Now, warm air is light since the surface pressure is the total weight of the air above it the surface pressure tends to be smaller above warm tropical regions. So, you have warm air over the west specific and surface pressure is lower. So, moisture from surrounding higher pressure regions converges over the warm water and rises. The moisture in the rising air condenses and the heat of condensation raises the air further. So, you have in fact convection deep convection triggered here because of convergence which is generated by this pressure difference here which in turn is generated by the sea surface temperature gradient. So, if the underlying SST is warm enough the crowds can reach the top of the atmosphere leading to organized deep convection. Remember this is the way we had analyzed how tropical convective zones arise. So, the rising limb of the atmosphere is located over the low pressure region above the warm water of the west specific. The heating of the air column associated with organized convection over the west specific contributes to enhancing the east west pressure gradient and hence the winds. So, you have in addition to the surface temperature gradient which is warm in over the west we also have heating over the west once the clouds are triggered. So, this will enhance the pressure gradient. Now, winds across the surface of the tropical specific we know blow westward into the region of low pressure. The rising motion in the warm region reaches the tropopause and returns eastward aloft completing the circuit. So, this tropical specific wide circuit of air proceeding westward at the surface rising over the which I will show here. So, this circuit of air which at the surface is proceeding towards the west specific then rising here in the deep convection generated over the west specific then moving towards the east and sinking over the eastern specific. Now, this kind of circulation here is called walker circulation, Birkenness called it walker circulation and this is an east west circulation. Remember we have seen Hadley circulation which is a meridional or north south circulation. This is an east west overturning if you wish which is called the walker circulation. This walker circulation is a very important part of the boreal winter. Now, in the next lecture I will consider the mean state of the tropical atmosphere over the Pacific India the seasons. Thank you.


Hi friends, I'm Scott Hanselman and I want to welcome you to Visual Studio Community. It's an IDE and it runs on Windows, sure, but it actually does a lot more than you might realize. So I want to take a moment and show you some of the stuff. It's not just about Windows and C-Sharp, it's in fact really, really powerful. You can make Windows applications, you can make them in C-Sharp, you can make them in Visual Basic, you can make them in F-Sharp. You can do pretty much anything you want in the world of Windows apps and games. Another reminder that Visual Studio is free for open source and small teams. You can check it all out at visualstudio.com. You can also do mobile development, Android, iOS, Windows. You can do both native and hybrid app development. Here I've actually got a Cordova application running. This is my Apache Cordova application that I'm working on inside of Visual Studio using JavaScript. I can run this inside of the Android emulator. This is a free Android emulator that runs on Windows and I've got full interactive debugging and all of the Apache Cordova tools that you're used to using. I can write node applications, node.js tools for Visual Studio, extend Visual Studio and Visual Studio community, and lets you have intelligent code completion and interactive debugging profiling tools, works with I-OJS, Node.js TypeScript, CSS, and HTML. We've also got Python. Python and Visual Studio, it's just an add-on. It lets you have both C, Python, PyPy, IronPython, and more. In fact, right here is a Django web project. I'm actually in the middle of running this Django application. IntelliSense, syntax highlighting, debugging, all on Windows in the same IDE. Once you learn Visual Studio, you know Visual Studio. You're going to feel comfortable no matter what language you're deciding to use. Maybe you're going to create a game. Maybe you're going to use Unity and it's going to integrate with Visual Studio. You can write DirectX games. You can use them with the top game engines that are available. Right here, I've already got Unity running.  We're doing an interactive debugging session with Visual Studio.  Here I've hit a break point. Step through, change my game, keep flying. All in the same IDE that I'm used to using for all my development. You can also build stuff for the cloud. You can build stuff for IoT, whether it be tiny devices in 64K or giant systems in the web in 64 gigs and 64 terabytes of storage. You can host 10 web apps for free. And when you host those web apps and you make those applications, you can use source control like GitHub or Visual Studio Online. Here in the Team Explorer in Visual Studio, I can use Visual Studio Online and Git to keep my source code safe. Or I can collaborate with others using GitHub in the GitHub for Windows. Whatever language makes me happy, I can do it in Visual Studio. C, C++, C-Sharp, VB, F-Sharp, Node, Python, Games, Mobile, Cloud, IoT, it's all there. The best part is that Visual Studio Community is not only free, it's also extensible. We've got over 5,000 different extensions and products that plug into Visual Studio from IDE extensions that allow you to do Arduino development inside of Visual Studio Online to things like web essentials that make the CSS and HTML editor even greater. All of this is in Visual Studio, it's all free and it's available to you. Check out Visual Studio Community. I hope you're as excited about this as I am and I welcome you to our community. Thanks.


Let's estimate what is the success probability for a payment of a certain size to be successful on the channel, and then select the route from me to Andreas that has the highest probability to settle. This change alone was an incredible step forward in getting more speed on the Lightning network. It seems like an understatement to say it, but it's been quite a year. With Bitcoin near new all-time highs, with the first nation state having adopted Bitcoin as legal tender, the explosion of NFTs continued growth in DeFi, and a lot more than that, it's incredibly hard to keep up. So on today's show we're going to check in with one of the most exciting projects, which might have fallen off your radar. Bitcoin is still in development, yet rapidly growing Lightning network, arguably the most anticipated scaling solution for Bitcoin to date. Although there are still some hard problems to solve, things are really starting to heat up, and to help us understand it, we're joined today by a special guest who co-wrote the book on it, Mastering Lightning Network, published by O'Reilly Media, and available for order now. But before we get to that, I'm Adam B. Levine, and this is Speaking of Bitcoin. For today's discussion we're joined by the other hosts of the show, Andreas M. Ansonopoulos. Hello, Stephanie Murphy. Hi. And special guest, Rene Picard. Hi, everybody. Rene, I really appreciate you being here, so I'm looking forward to this conversation, but in the introduction I neglected to mention that Andreas is actually another co-author on the book, which is his third O'Reilly book. He's also the author of Mastering Bitcoin and Mastering Ethereum, and now this most recent book, Mastering the Lightning Network. So to kick us off, Andreas, can you help some of the members of our audience who haven't been with us for years and years and might not be familiar with the Lightning Network? Just from a high level, what is the Lightning Network? The Lightning Network is a second-layer payment network that runs, let's say, on top of Bitcoin, and it enables fast, secure, private, and cheap payments that were previously not possible. A nice way of putting it, which I think Rene came up with this way of putting it, is Lightning is just a different way of using Bitcoin. So Lightning is Bitcoin, Lightning is Bitcoin payments, but it's Bitcoin payments done with a type of smart contract that allows you to execute them really, really fast between two people and route them across the network for very, very low fees or negligible fees, really. OK, great. So I think that that's a great succinct kind of way to think about this. Again, like it's a way that we can take kind of the limited in terms of scalability, right, the number of people who can be using kind of base layer blockchain at any given time, the higher that goes, the harder it is to run those nodes, which makes it so that you can compromise some elements of decentralization by pushing up that transaction throughput too high. Basically, it comes at the cost of some decentralization. So the Lightning network aims to kind of take that reality and then to build layers on top of it that then allow for people to use kind of that base ultra secure layer as sort of the settlement layer, which kind of eliminates the need to on top of it use, you know, a service like Coinbase or something like that, who's actually going to custody your stuff. Ultimately, you're going for the lower prices in terms of the lower cost for higher throughput, while at the same time, you're keeping the non custodial characteristics that makes Bitcoin so kind of compelling from so many kind of different angles. Is that a good summary? Yeah, let's look at some specific numbers. Now, people who are familiar with Bitcoin payments know that when you make a payment with Bitcoin, if you need it to be confirmed because it's something you're buying that requires the security of a confirmation or several confirmations, then you're looking at waiting on average 10 minutes per confirmation per block until that payment is finalized. And you can make a payment as small as you want down to one Satoshi with Bitcoin and as big as you want up to 21 million Bitcoin. But you're going to pay a fee. And with today's network fees can range anywhere from a dollar to five dollars, depending on how busy the network is at the moment. And of course, that changes a lot with the price of Bitcoin and the capacity of the network and things like that. But you don't generally make a three dollar cup of coffee purchase on Bitcoin on chain anymore, because not only are you going to need to wait 10 minutes, which for a three dollar cup of coffee, you don't really need a confirmation, but you're going to end up paying about a dollar in fees. And your transaction is going to be public for all the world to see your payment is going to be visible on the public ledger. Now, let's compare that to the Lightning Network. Now, you can make a payment as small as a thousandth of a Satoshi. That's the smallest payment you can do on the Lightning Network. Although for practical terms, that gets rounded up to a Satoshi. A Satoshi is one hundred millionth of a Bitcoin. So it's a fraction of a penny. And instead of taking 10 minutes for full final settlement with Lightning, you have your funds, your payment completely cleared anywhere between one and 10 seconds after you send it. So a second, two seconds is very common.  If that takes Lightning payments, you press pay on your wallet and you'd better be holding the cup underneath the spigot because beer starts shooting out within a second or two. So the payments actually are surprisingly fast. The point that beer was spilt, the fee you pay for that is somewhere between a hundredth of a penny to a tenth of a penny for a payment maximum I've seen was a couple of pennies on the US dollar. So just a few hundred Satoshis, a few thousand Satoshis at worst. And then that payment is completely private. It's between you and the recipient. And no one else really knows is coming for you or going to the recipient and no one sees it as a permanent recording on the ledger. I'm simplifying, of course. There's a lot of nuance to all of these things. But it's a radical improvement on the user experience of Bitcoin. So it's faster, it's cheaper and it's also more private. So what are kind of the reasons why everybody isn't using this today? Well, mostly because it's still new. You need a special wallet to use it. And the wallet interfaces were really quite clunky. The other thing is that until now, routing your payment across the network is sometimes challenging. But that's one of the things that Renee is here to talk about today, which is a way of making payments even more fast and effective with an invention of his called Picard Payments. So we'll talk about kind of some of the challenges of the Lightning Network, as well as some of the solutions and how it's very rapidly evolving. You got to remember this is new. It's still a bit clunky. The interfaces are still maturing. But already it is very usable. All right. So this is all new stuff. It's definitely one of the things that's new to me because, you know, I don't have a lot of technical experience. So how would someone like me, who's kind of more of an average user than a power user, use the Lightning Network right now? I would say the first thing would be to get a wallet. Renee, which one would you pick? I would pick anyone. I mean, I run my own notes, so that's probably not the suggestion that I would make to Stephanie. I guess for the casual user, there is a lot of either custodial wallets that run out of the box or semi-custodial solutions that work. I think Phoenix Wallet usually is a good choice for Android users. I think they're coming out with an iPhone version. I'm not sure if it's out yet. Yeah, I would say Blue Wallet or Phoenix Wallet are great first choices. These are wallets that either do just Lightning or they do both Bitcoin and Lightning and they're semi-custodial. So you have control of the keys, but they may help you with routing and other facilitated services. OK, yeah, that was going to be my next question is what is the level of custodialness, I guess, and explain that. OK, so first I have to get a wallet and then I don't need to run my own node to be able to do this. I can just start using a wallet. That's correct. The wallets are lightweight wallets that use the neutrino protocol to talk to a Bitcoin node and they may also use some services such as routing services by the wallet vendor or the wallet maker in order to assist wallet payments, but you don't need to run a node. It's just an app on your smartphone. OK, and then do I need to put in any the channels need to be sort of greased, if you will, right, with like funding? Is that right? Well, in the early wallets, you had to fund a channel, make a channel and do all of that by yourself. But one of the nice things about the newer wallets is that they make a lot of that complexity disappear. Part of that is because they offer some services in the back end to help you do that. So both Phoenix and Blue Wallets, for example, and you should look there, there's lots of wallets out there now. You don't have to even see channels. You don't look at channels at all. You just fund it. So you move Bitcoin to it, generate a Bitcoin address, move Bitcoin to it. And now you have Bitcoin in your lightning wallet, and it manages the channels automatically for you. OK, and so what if I didn't want to send at first? What if I had nothing in my wallet and I wanted to receive what I still have to fund it, or can I just receive? Well, that's where the service comes in. You can just receive and they'll fund a channel for you on the other end and charge you a small commission. I think last time I checked it was something like a 1% commission. That's if you don't have any funded channel already. OK. And it depends, of course, on the size of the payment. I mean, if you wanted to receive one Satoshi, it doesn't make sense to open the channel with you and to charge you 1% of the commission, but it's reasonably cheap. OK, well, that sounds pretty good and easy. What are the problems with it right now, if any? Really a lot about learning and how smooth these wallet interfaces are. The other problem is, of course, the network is still growing. And as a result, it's not always easy to make a payment. So when you try to make a payment, sometimes the payments will fail and they'll fail because your wallet isn't adequately connected to the network. You don't have funded channels. It's unable to find a route to your recipient, et cetera, et cetera. But those problems are gradually going away. So you see less and less of that as time goes by and the network gets better connected. Just to give you for reference, right now the network consists of some 12,000 nodes that have some 50 or 60,000 channels between them. OK, so please forgive me if these are like kind of basic questions, but you can tell that I haven't had much experience with this. But I think some people want to know. So sometimes if you try to send a transaction over the Bitcoin network and you don't include a high enough fee, let's say, it can get stuck and it'll be stuck until it gets unstuck, which can be for hours or days. So what about in the Lightning Network? If you try to send a payment and it fails, does it fail right away? Or does it tie up your transaction for a while? Hopefully it fails right away in most cases, it should, right? Because if you do something like not including enough fees, the routing note will basically immediately reply to you and say, hey, I want out the payment you have to add a fee or if the routing note doesn't have the liquidity, it will tell you, I cannot forward this payment. There are situations and circumstances because it's a decentralized network where a note is just unresponsive and you just don't get feedback. The time that you might have to wait is much more limited than Bitcoin because in Bitcoin, I think I heard cases where people literally waited for three months until the mempool cleared. This cannot happen in Lightning, but you might have to wait quite a bit. OK, well, that sounds better that it should fail right away instead of waiting potentially up to three months. OK, I think one of the interesting things about the Lightning Network is that it opens up all of these new application possibilities that happen because you're kind of exploring this new dimension of time and space. So in terms of space, the size of the transaction is so small that you can effectively do transactions that are infinitesimal amounts. So you could pay, let's say, a tenth of a penny, which is an amount for which there is no even copper coin in the United States. Right? You can't buy anything for that kind of money. So we've seen applications, for example, where people have to pay that kind of amount to post a message in a form to participate in a chat.  You can't sock-pop it and spam the form because while for the average person, a tenth of a penny to post the message is nothing, if you wanted to do it at scale, then it's not nothing. It's something. And so it becomes an anti-spam measure. Or you could use it to play a very, very simple game where you could have tiny Lightning payments as part of the game. So it opens up these possibilities with micro payments, not just micro payments for content, micro payments for gaming, but also micro payments for various applications and services that you wouldn't really consider payable, where it becomes almost like a spam control measure. Yeah, to me, it almost sounds like an improvement in every way. Like why would you not use this, except that the usability maybe isn't quite there yet for someone like me who doesn't have a lot of experience. No, I fully agree. That's the question I've been asking myself. Why would you not use this? That should be the slogan of the Lightning Network. The Lightning Network. Why not use it? So the onboarding might be a little bit rough. But other than that, once you are just out paying, I think the people in El Salvador right now where, you know, they had this adopting Bitcoin conference, I think most people paid a lot of things just with Lightning Network all the time. And I basically didn't hear anybody complaining that it wouldn't work for regular payments, like doing a cab or buying coffee, buying a meal, even paying the hotel. Conference tickets could only be bought with a Lightning Network. And these things, I mean, this is how money should work. You see somebody, you want to pay them, they show you QR code. You hit pay and a couple of seconds later, the payment is settled. Everybody's happy. It's just incredible. And the more widespread it is used and the more people they use it densely in a specific environment, the more usable it becomes.  Once you've onboarded and funded the wallets, which requires a Bitcoin transaction to do the channel open in the beginning. Once you've done that, then the more people actually using Lightning and moving Lightning funds back and forth and creating a closed loop economy, the more usable it becomes, the easier it becomes, the more easily the payments are routed, the more liquidity is available on the network, the more connectivity is available on the network. So we've been talking about the Lightning Network for a long time. I think I first heard about it in 2016, which is five coming up on six years ago, which doesn't feel like it was that long ago on the one hand. And also, yeah, it feels like we've been waiting kind of a long time for this thing to roll into reality in a way that's as impactful as the sort of technology of Bitcoin and cryptocurrency broadly that sort of underlies it. One question that I have is in the past, I feel like we've talked about this and it's been like, well, the network isn't ready for it, not the Lightning Network, but the Bitcoin network, the Bitcoin protocol needed to have upgrades that were made to it that would then make it so that we could really kind of see the full vision for Lightning roll out. Now, I think, and correct me if I'm wrong here, that there were some pretty significant elements of that that came into play with the recent taproot upgrade over the summer, notably Schnorr signatures. But am I correct about that? And I guess where I want to go with this question is on the one hand, what have we accomplished already, right? What upgrades have come to Bitcoin that have resolved some of those issues we've talked about in the past? And on the other hand, is there anything else that we're waiting for? Are we waiting for the next generation taproot? Or is it really just kind of an implementation and maturation, right? As these improvements sort of propagate out to the network, as new wallets are built? I mean, that's kind of what it is. Like talk about where we've come from and where we're going from a technology standpoint, please. So I guess the most important upgrade that happened to the Bitcoin network was the sacred upgrade. Because without going into the technical details, it would just not have been secure to open a channel if we didn't have the sacred upgrade. So basically, we couldn't really bootstrap the lightning network without it. And then you mentioned the taproot and Schnorr signatures upgrade. And that's a great one, because it enables us to have a much cleaner way of routing payments and of delivering payments with more privacy with a technique that is called PTLCs. That stands for point time lock contract in contrast to the HTLCs that we're currently using the hash time lock contracts. So this is really great. And everybody who is a lightning developer is really excited about this because things are just getting a little bit easier for us once we have implemented it. But right now, lightning developers actually really struggling and discussing how to use this Bitcoin upgrade to actually implement that stuff. So the concepts are out. Everybody knows how to do this on principle, but we haven't specced it out yet. One of the discussions on that particular point is what do we do first? And I think the recent conference where you participated, Renee, correct me if I'm wrong. From what I read in the transcript and notes, a lot of the debate was, do we do it all in a big bang upgrade where a whole bunch of things get upgraded at the same time? Or does this get rolled out incrementally with smaller changes that can be absorbed more readily by the network? That was kind of the essence of the debate. Yeah, that was a huge part of the debate because one thing that is problematic with this upgrade is that as of now, PTLCs and HTLCs are not compatible in routing. So if you want to send a payment along a route, either every channel supports PTLCs or every channel supports HTLCs, but you cannot mix them. So you really have to think about how to upgrade this, how to make this backwards compatible. And these are just engineering challenges. I wanted to also mention with respect to future Bitcoin upgrades. There is actually a lot of Bitcoin development right now being driven by the necessity of Lightning Network. A lot is related to fees and how the mempool is being managed. But there is another consensus level upgrade that the Lightning developers are wishing for, which is the any-pref-out upgrade or previously known as Secach No Input, which would allow us to have the L2 payment channels, which is a new channel design that is much cleaner than the current payment channel design and would allow us to not have this penalty that if something goes wrong, we lose our Bitcoins on the Lightning Network, which is one of the downsides that some people might have experienced in the past. Let's be more clear. If something goes wrong, the person who tried to cheat most likely loses their Bitcoin, which is the penalty mechanism. So within a payment channel, in order to ensure that someone can't cheat in the payment channel, there is a penalty mechanism. So if they try to cheat, you can publish a penalty transaction and take the entire balance of the channel. That's how it currently works. A cleaner mechanism would be that you simply don't let them cheat in the first place. A more of a can't cheat rather than cheat and you'll get punished. And that's what L2 would enable. And the problem with this cheating is that a lot of this cheating doesn't happen on purpose because somebody wants to try to cheat, but just because the software is so newer, so software might sometimes by accident be incompatible to each other in certain situations that developers haven't seen. And then this is considered to be a cheating attempt and stuff can go horribly wrong. I don't want to spread fear. A lot of these bugs nowadays are completely fixed. But I remember in 2018, it happened to not only me, but also a few friends and yeah. Well, back then it was hashtag reckless to use the Lightning Network and it was part of the design. In fact, that's actually one of the things that I like about the Lightning Network is that innovation on the Lightning Network moves at a much higher speed than in Bitcoin. And that's because the Lightning Network is effectively decoupled from the consensus layer in such a way that you don't need lockstep consensus and interoperability between all of the clients. You don't need them to have identical consensus implementations. They need to be interoperable. And that allows one client to implement a new feature without anybody else implementing it. Kind of incremental improvement, decentralized innovation, opt-in capabilities. And that's created quite a lot of competition between the various Lightning clients and node implementations. Unlike in Bitcoin, where 98% of all nodes are run Bitcoin Core on the Lightning Network, there's diversity. There's three very actively developed clients, node software, one called LND, the Lightning Network Demon developed by Lightning Labs, one called C Lightning written in the C language by Blockstream and one called Eclair written in Java or Scala, rather, by a French company called Async. So there's really quite a lot of competition. And as a result, there's quite a lot of innovation and things move very, very, very fast in this space. And just to add for completeness, these are only the OGs. There's also the Electron wallet written in Python that nowadays has a Lightning implementation. There's Rust Lightning, which I think nowadays is called LDK. There was a very early implementation by a Japanese group called Patar Gaman, I think. And then there is basically forks of other implementations. So there's actually a lot of people playing around with it. How does that landscape compare against the landscape of Bitcoin clients? It feels to me like the Lightning Network ecosystem that you just described there in terms of like interpretations of the protocol is actually more than we have in Bitcoin, at least that I'm familiar with. I can think of three or four off the top of my head, but that's pretty much it. And obviously, Bitcoin's been around for as long as any cryptocurrency has been around since it was the first. So I mean, like, how would you compare the two ecosystems outside of the fact that Lightning is clearly moving faster? Honestly, I would say that, and this is going to irk some people, but I'm going to say it anyway, the development culture and pace of development, the willingness to take risks, the degree of competition, the degree of diversity is much more similar to Ethereum than it is to Bitcoin. The Bitcoin core protocol is conservative by its very nature. It has to be. And it requires lockstep consensus agreement. Otherwise you fall out of consensus and risk losing or being cheated out of funds, which has resulted in almost a monoculture. There's one client, honestly, 90 plus percent is Bitcoin core. There is a go implementation called BTCD, which has a bit of traction. And after that, it's mostly libraries and frameworks that may or may not be very usable. And there aren't that many nodes running these alternative implementations. So it's completely different from Bitcoin. I'm not sure about the Ethereum comparison because I have never looked into that ecosystem. Andreas can say much more about that. But being active with the lightning developers, I have the feeling that still there is a lot of ethos from the Bitcoin community in there. So people are actually cautious about critical changes. And oftentimes as a developer, I have the feeling stuff could move forward a little bit faster. I think the main difference is that the lightning network is driven by a formal specification. So there is the Bolts repository where all of the functionality and behavior of the protocol is being specced out. And then if you have such a document, it's obviously much easier for people to just implement against this document. Whereas in Bitcoin, it was from day one that Satoshi said on the mailing list, I don't want to spec out the white paper. I have a reference implementation and the reference implementation is basically defining the consensus of the network and the protocol. Yeah, the spec is written in C++ and it's called Bitcoin core. So that makes a lot of sense to me because if you look at, again, like at the point that Bitcoin core in its earliest forms comes out, that is the actual proof of concept. That is sort of the idea that was rallied around because to do it hypothetically, people would have said, well, that won't work. So you do it in real life, right? You prove the concept works and you're off to the races. That is in contrast to something like Ethereum. Again, there was an extended period of public discussion, public interest, right? Many, many people participating and as a result, an ecosystem emerges. And it seems like that's much the same with lightning, is that it started from an idea that was then discussed extensively where people can have different ideas about how that idea should actually manifest in reality. And so you create this ecosystem that isn't there if you start from kind of the software as a basis. And again, with the really heavy consensus element, too, that actually makes a ton of sense to me. And it's kind of neat to see that happening on top of Bitcoin. My sense has always been that the lightning network, although it's not a Bitcoin specific system when it's finally done, really does represent a very interesting way for Bitcoin to kind of have its cake and eat it to our Bitcoin users, anyways, and again, like that competitive ecosystem, I'm always in favor of competition, right? It feels like ideas that are conflicting and competing with each other, bouncing off of each other almost always results in kind of more vibrant products that do better to address. It's simply because by nature of having that competition, you get from here to there faster. So I appreciate kind of going down that rabbit hole with me. We talked at the very beginning of the show about Picard payments, and I would like to explore that idea a little bit more. I think we have a decent idea of what kind of the challenges are that we still face as we move forward. So can you kind of talk to us about that specific problem that you're solving there and how you've solved it? Sure. So if you want to make a payment on the lightning network, you have to choose basically a route on how you want the payment to flow through the network. So let's say if I wanted to pay Andreas and I don't have a direct payment channel with him, I could say, hey, I sent something to Adam and ask Adam to forward it to Stephanie and ask Stephanie to forward it to Andreas. And this is in general how payments are being conducted from one peer to another. The problem with this mechanism is that if I select this route via Adam and Stephanie to Andreas, I don't know if Adam actually has enough funds in his channel to forward the payment to Stephanie. And the reason why I don't know this is because I can't often privacy is given as the main reason like we want to protect the privacy of the funds and the channels, but there is a much more important. Well, not sure if it's much more important, but a much more severe technical reason. And that is if I were to know what the channel balance in the Adam and Stephanie channel was, I would have to know it every time the channel updates. And this means I would have to know about every payment that is taking place in the network. And that would have the same poor scaling mechanisms like Bitcoin, where we also broadcast every transaction to every participant, right? So when we create the lightning network in order to scale Bitcoin, we wanted to get rid of this mechanism where we notify everybody about every payment. And for that reason alone, we can't know how the money in a payment channel is actually being distributed. So when I select this route, I don't know if this route is going to be successful or not. That being said, the lightning network as a protocol is by design unreliable, right? I will try to make a payment. It might fail. And then my note software will try another route. Just like the internet protocol is by design unreliable. And the term unreliable from an engineering perspective means something different than the plain English understanding. It means that reliability is built at a layer above. And so failed payments are simply retried until they succeed, just like failed IP packets are simply retried at the TCP layer. Yeah, and that makes sense because you can't know which is the correct channel beforehand because you don't know the balance. Exactly. And I just want to reiterate, I am so happy that Andreas is the co-author of our book because this is literally how the entire writing process went all the time. I was going with some very sophisticated technical detail like the typical researcher nerd and Andreas was like, Renee, we need to break this down. Yes, so the problem is, I don't know if the channel is going to be usable for my payment or not. And if you a year ago or two years ago looked at the scientific literature, you would find basically in every single paper about the Lightning Network, this problem being described. But in every paper would basically say, look, the smaller the payments are, the higher the chances that they succeed. They would always talk about success rate. And I was the first person to turn this around and say, hey, let's start with the success rate. Let's estimate what is the success probability for a payment of a certain size to be successful on the channel and then select the route from me to Andreas that has the highest probability to settle. And this change alone was an incredible step forward in getting more speed on the Lightning Network. That's not the full solution about what pickup payments are about, but that's the first very crucial ingredient. And I'm happy to say that C Lightning is the first implementation that implemented this probabilistic pathfinding. There's a block article written by Christian Decker. I helped them a little bit to evaluate this. And basically the number of attempts reduced by half, the time to complete also almost reduced by half, and the failure rate also reduced by half. So this is just incredible to see. Before you go on, let me just pick at that for a second. Given that we can't know the balances, what metrics are you using when you are estimating the probability? Yeah, so that's an excellent question. I mean, there's obviously an infinite amount of choices that we could do to estimate a probability. What I did is I actually participated in a research work together with my former co-author Sergey, where we tried to probe the Lightning Network and estimate what is currently in a channel. And from that data that we collected, we realized that the probability distribution is basically uniform distribution. What this means is that if there's a channel that has, let's say, 10 satoshis in them, every distribution, zero satoshi on one side, 10 satoshi on the other side, or one satoshi on the first peer and nine satoshis on the other peer, and so on and so forth, has the same likelihood. And we were very surprised to measure this. We expected that this distribution would look very differently. But for all the experiments that we have done so far, this is actually the distribution that we basically measure. And the nice thing about it is that's very easy to quantify in terms of mathematics, and it's very easy to use this as a cost function in our path-finding algorithms. Okay, in the example that you gave, you were listing a hypothetical distribution of 10 satoshis where it could go from zero on one side of the channel and 10 on the other to one on one side and nine on the other and so on. But not every channel has 10 satoshis in it, right? Exactly. They have different amounts, so how do you take that into account? So the main assumption here is that in order for a payment to succeed, it must not fail, right? So a payment, I mean, I know it's obvious, right? But it's easier to start with a failing case. So for the failing case, a payment will fail if on the channel between Adam and Stephanie, there is not sufficient funds, right? So let's assume Adam and Stephanie have a channel of, let's say, 10 satoshi. And I wanted to send, let's say, five satoshi. If Adam has zero satoshi, one satoshi, two satoshi, or four satoshi, these five cases, then the payment fails. But in the other six cases, where Adam has five, six, seven, eight, nine, or 10 satoshi, the payment does not fail, right? So basically when I want to make a five satoshi payment on this 10 satoshi channel, the likelihood for this payment to be successful is roughly one half. I think there's one point that's important to emphasize here, which is we know the initial capacity of the channel because that is created by a Bitcoin on-chain transaction called the funding transaction that is public. That is how it is announced. So when Adam and Stephanie create a channel together, they fund it and they fund the multi-sig address. So we know what the maximum total capacity of the channel is, which is that initial funding. What we don't know is after that initial event, how is that amount distributed between the two channel partners? So we don't know the split, but we do know the sum. And then the probability we have to calculate is what are the probabilities of different splits within that sum? And then the research that you did, Renee, shows that it's basically a flat distribution, that it's equally likely that any distribution occurs. Yes. Okay, and then based on the size of the payment you're sending, you can calculate the probability that it will fail or succeed based on that. Exactly, and one obvious result from this is that the larger a channel is, the higher the success probability is for a payment of a fixed size. And conversely, the larger the payment is, the lower its probability of success on this current lightning network. Exactly. And this leads to a very interesting side topic, which kind of unveils the second big part of Picard Payments. In the last six months, a very, very important capability has been enabled on the lightning network that changes the game. And that capability is called multi-part payments MPP. What this allows you to do is take a payment, split it into parts, and send it across multiple paths simultaneously, but atomically, and then have it essentially reassembled on the other side. That changes the lightning network from almost a stream network to a packet switch network. And if you combine the research of probabilities with the ability to split things into parts, now you have a different problem, which is what should the parts be? And how do you choose the best paths if you're splitting it into parts? Okay, so the flowing word is really a good word because now you're ending up with a flow that's like drops of water that could then coalesce back into a glass at the end. We're ending up with a flow. And actually, even in technical terms, we're ending up with a flow. We're ending up with a so-called minimum cost flow. So we're trying to find a flow through the network that has a minimum cost. And the cost here is the uncertainty of the channels to be able to route the payment, right? The success probability, we can translate this into a cost function. And yes, it's actually historically speaking, very funny. I was very critical of multi-part payments for a long time because while it was always obvious that if you split the payment, the smaller payment becomes more likely to succeed, now you have more channels involved, right? And well, you have to be successful on every channel, right? So you multiply this out, right? And this also lets the probability drop, right? So there is this kind of like sweet spot of how heavily do you split, right? And do you split into equal chunks or do you split into like not so equal chunks depending on which path you use? And yeah, I spent quite some time in the beginning of this year researching this problem. And together with my co-author Stefan Richter we found the provable optimal solution to this problem. Wow, that's really cool. One of the interesting things is that the result was rather surprising. At least it was surprising to me. So in my mind, because the more paths and parts you use, the more complex it becomes, I would assume that if you had a big payment, you'd probably just split it two, three times, maybe four and send it across two or three or four big channels. But Renee, why don't you tell us about your first production experiment and how many parts you split the payment into? Yes, so what Stefan and I did is we basically spun up a new lightning node and we implemented the method and we tried to send a payment of 0.3679 Bitcoin which is quite some amount. That's $20,000. Roughly, yes. And this payment was split into 345 different paths which were sent through the network. And that sounds really like a lot, but what we can see from this probabilistic approach, this is actually the way how we send it with the highest likelihood to deliver this payment. So if we would split more conservatively and have larger chunks, we would actually put more load on the network. Or if we split more aggressively into smaller chunks, we would also put more load on the network because with these larger chunks we would probably fail more often, right? So we would have to do more retries. And also in this split we had payments that were just like 10,000 satoshis and other payments were of size, I don't know, something like 4.2 million satoshis, right? So there was this huge range in which we split the payment to optimally deliver it. And that was just crazy to see and experience because until then everybody was basically like, yeah, the Lightning Network works for a few million Bitcoin, but that's about it. It's like for small payments. And we basically showed, no, it's actually possible to use it for large payments. That's a game changer right there. And it's useful to also understand that when you take a big payment and you split it into 300 and some parts, it doesn't mean that you have to succeed on all of them. It was one of the beauties of the multi-part payments is you spray it out. You basically create this missed flow of payments that go out across 300 plus paths and then you wait. And a few seconds later, you get what, 70, 80% of them get through and then 20, 25% of them don't. Well, great, you take the remainder, you split it again and you send it out. And not only that, but now from the error returns, you now have a better picture about the actual capacity and probability of the channels in between you and the destination than you had just a few seconds ago. So you use the information from the first round. Oh, so it's also like a probe to see, like you get more information through sending the transaction about which channels were successful. Yeah, exactly. Every failure is a learning opportunity. And then you split it up and you just send the rest. The other 20% and 80% of that gets through. And then you send the rest. And finally, after maybe three rounds, the whole amount goes through. This takes a few seconds, maybe even a minute, but you just sent 20 grand over the Lightning Network. So a minute is okay. Yeah, I was gonna ask Renee, did you do like time tests for these larger payments and what did you find there? Like how long did it take basically to send $20,000 over the Lightning Network? So I think for that payment took something like two minutes, but we had very poor conditions. Yeah, but it's better than 10 minutes, right? That's true, that's true. So one thing that is problematic is the optimization problem that we have to solve is computationally very heavy. And we just don't have a very efficient implementation of this. There is no open source code for this. So we basically implemented the algorithm ourselves in the not most efficient version. So there is certainly some way to improve this, right? So we spent quite some time on computation actually and not on sending out onions. And the other thing is the Lightning node that we spun up, we just randomly connected to some nodes. So we didn't particularly try to connect to well-connected nodes. So we had one or two peers that basically had really poor liquidity. We really had to do a lot of retries because as Andreas just explained, we're learning from our prior retries. So this entire thing is basically presented in two papers. The first paper is about probabilistic pathfinding that came out in March this year. And there we also explain how we can update our knowledge and use all the information from prior successes or prior failures. And then the second paper is the optimally payment flows where we only discuss the question about how to split this, right? So all these things together really present the entire system of how to use the Lightning network in this massive way. Are the implications of this requiring a lot of computational power that this wouldn't be something you could do with a smartphone? Is that right? Well, if you wanted to send 20 grants, maybe not. The computational power gets reduced if you want to send a smaller amount. So the computational power grows with the amount. And also there are... I mean, this is the classical thing about science, right? What we now have with this mechanism is we know what is the absolute optimal solution, right? And it was great for us to test that the actual optimal solution is really good enough, right? Because the result could also have been that the optimal solution just is not good, right? And then we would know that this entire technology would have been a nice endeavor to program, but it wouldn't solve our problem because, you know, I mean, we could prove that this is the most optimal way to do this. So what you usually do now is you do integration where you try to approximate the optimal solution in a much more computational, cheaper way. And maybe you lose a little bit of optimality, but therefore you gain a lot of computational complexity. When Renee talks about reducing optimality, basically what we're saying here is, okay, we now know that we can route this amount with this amount of computation and this amount of time. What if we could get 95% as good a result, but 20 times faster? Exactly. Well, that's a great solution, right? Because it's only 5% less optimal, but it's actually 20 times faster. At that point, you move it to your smartphone, right? It opens a whole different door for you. Just to add, this is exactly what I'm currently working on to figure out what are the good trade-offs here to make. I have a question about privacy. Like, is there any way that this lessens privacy on the Lightning Network because there is information that's able to be learned about the channels? And, well, you already know the balance of the channel because it's linked to a blockchain payment, but the distribution of the coins inside the channel, the Satoshis. So I do know the capacity of the channel because it's linked to the blockchain. What I learn while doing a payment is for certain channels, what is the minimum balance that they have or the maximum balance that they have? But that's a principal property of the Lightning Network, right? The Lightning Network in general has this uncertainty about the capacity split into balance values. And whenever you made a payment, even with the old system, you were trying a route. And if the route was successful, you would know for sure that now all those nodes had a certain amount of Satoshis on the other side. So from the very beginning of the Lightning Network, the payment process was always based around this trial and error loop where you basically learn some information. The only thing that I propose is that if we already have to learn this information, we learn it in an optimal way, right? So we quantify this information or the information gained properly. We measure the entropy and then we choose a route where we expect to have the highest information gain, which corresponds usually to the route that has the highest likelihood. So yeah, there is that. But that's a principal thing about the Lightning Network. Every time you make a payment, you learn something about the network. The question is how useful is it that you learn this because obviously the Lightning Network is a very dynamic system and a second later, the channel could already route a payment in the other direction, right? So this information doesn't stay constant. And a certain ground truth named the capacity of the channel is something that you already knew on the blockchain. So yeah, but there's certainly privacy implications here.  They were there before. I'm just using that. Yeah, and very importantly, you're not down to the base layer of privacy where everything is on the public ledger. Keep in mind, if you know that money has moved on a channel or that balances have been split in a different way, that still doesn't tell you who sent it and who received it. Whether that payment was a local payment between Adam and Stephanie, or whether it was simply a payment being routed through Adam and Stephanie's nodes by other people and then routed back in the opposite direction. It doesn't tell you anything about where the payment came from or where it's going, who's paying who, none of that information is visible because the entire network is onion routed. So it uses an onion routing mechanism to hide senders and recipients from everyone, including the intermediaries. So the intermediaries in the Lightning Network, they see a payment coming in. They don't know if that payment is coming from the person who they received it from or someone else sending on behalf. And when they send it out, they just know the next hop. And they don't know how long the path is or where they are on the path. Let's make this more concrete, Andreas, right? I suggested initially to make the payment via Adam to Stephanie to Andreas. So if Stephanie receives the payment from Adam, Stephanie doesn't know it's actually from me. Whereas when Adam moves the payment forward to Stephanie, Adam doesn't know that this payment is actually for Andreas. And when Stephanie sends it to me, Stephanie doesn't know if I'm the final recipient or simply another link in the chain. And I'm just gonna forward it to someone else. You have no idea how long this path is. You have no idea where you are on this path. You have no idea if this is the entire payment or just a part of a payment. So really you learn very little, even about the payments you yourself are transporting or your node is transporting, whether or not you know the balances. Well folks, that is all the time that we have for this episode of Speaking of Bitcoin. A big thanks to Renee Picard for speaking with us today about the Lightning Network. We look forward to having you back on as this continues to develop. Yes, so I'm really happy that you invited me to the show. It was really a pleasure talking with you folks about it. And I want to use the opportunity to thank all the people who have supported my work this year because as you know, I have tried to stay an independent researcher. I open sourced these results even though there was a high commercial interest in them. And it's just amazing to see how generous the Bitcoin community was. I think there was 1.5 Bitcoins coming to my fundraiser. So I have quite some possibilities now in the next months to continue working on this. And in this sense, also thanks to Andreas and Peter who made two very large donations. And this is really just great. So shout out to everybody who is supporting this work. Thank you very much. Today's show featured Stephanie Murphy, Andreas M. Antonopoulos and myself, Adam B. Levine. This episode featured music by Jared Rubins and Girdie Beatz with editing by Jonas. If you have any questions or comments, send us an email at adamatspeakingofbitcoin.show and we'll be back next week with another episode of Speaking of Bitcoin.


What is up everybody, Jason here for JaspysCaseBrace.com. We just sold out another one of these fillers guys, giving away six spots in the MLB repack dual caser with this 23, Bowman Platinum Baseball Blaster number nine. And again guys, I was told for the two fillers, eight and nine that if they sold out tonight we can give away 10 free spots, which we did. I'm getting confirmation in for number 10 that we just posted. I wasn't told to do a third one at that really, really amazing giveaway price, but if I get confirmation and says do it again, I will, but if not, number 10 is gonna be the full spots. That is technically our last filler guys. So here we go guys. Like I said, we'll do the break first and we'll randomize the customer names, just shoot the hits out, then at the end we will all randomize only the customer names and top six get into the repack. But this first dice roll is gonna be for the list of winners. Top 10 get free extra spots, we'll paste them in and then we'll do the break. Roll it. Two and a five, seven times. One, two, three, four, five, six, and seven. Logan, Eugene, Kev, Eugene, Allen, Allen, Eugene, Logan, Allen, and Allen. Oh, is he a Logan? Yeah. I'm so mad. I did my bracket on Tuesday, but it didn't let me finish it because I had to wait for like the 16 seeds to be drawn out. So then Wednesday comes and I'm like yeah, I'll do it when I get home. The Jaspie bracket, right? I'll do it when I get home. I started watching Eastbound and down and I totally forgot to do it. And then when I woke up in the morning, I woke up and I was like, no, I forgot. And now I totally forgot and the game's already had started, so that's a lost cause for me. So yeah, sellin' the Marlins. Da da da da da da da da da da da da da da da da da. Switch scenes. Top six, get in, roll it. Two and a four, six. One, two, three, four. Six times, six, six. Logan, Logan, Allen, Allen, Allen, and Eugene. There you go. All right, we still have to do another filler plus nine full spots, guys. So obviously still a little ways to go, but we're getting there, guys. Appreciate it. Now let's get some other breaks in the baseball section done, guys, that are closer. Especially like that Bowman Inception, that Dynasty, some good breaks up there, guys, at a great, great price, guys. So appreciate it. Number 10's in the store at jazzybyscasebrakes.com.