Now, in the last lecture, we have seen the nature of monsoon variability as analyzed from rainfall data. Today, we will begin with looking at what monsoon variability looks like from measurements from satellites, the eye in the sky. And then we will look at the Indian monsoon, the seasonal variation of surface and so wind and so on and then develop the background required for understanding the various theories we have on mechanisms. Now, so let us first look at monsoon variability through the eye in the sky. In fact, satellites have contributed enormously not only to our understanding of the monsoon variability, but also to the elicitation of the basic system responsible for the monsoon. You know the physics of the mean monsoon. Now, even if one is interested only in the rainfall over the land region that is only over the rainfall over the Indian region, it is important to know about what is happening over the tropical oceans. Now, why is that? Because almost all the cloud systems which give rainfall over the Indian region are actually born over the warm parts of the tropical oceans, warm our Arabian Sea, Bay of Bengal, Equatorial Indian Ocean and Equatorial Pacific Ocean and warm parts of West Pacific are the breeding regions if you wish for the cloud systems which actually give us rainfall. Now, earlier without satellites, we did not really have good data on what was happening over the oceans. Now, with satellites it is possible to literally see the cloud systems over the entire tropical belt several times a day and in fact, some of us do that we see every day what is happening over the world. Now, this has had a major impact on our understanding of the monsoon and also on its variability and I believe in the ability to predict various facets of the monsoon and its variability. Now, at first when meteorological satellites came in the data we had actually were images. You know photographs taken by cameras from satellites and in these images clouds appear as white blobs because lot of sunlight gets reflected from the tops of the clouds. So, now if we look at a typical image that we got in that time which is what we will see in the next slide it is an image of an active monsoon day a day on which lot of rainfall occurred in the monsoon zone and it happens to be 8th of July 1973. So, what you see here is what the satellite actually generated it is a satellite image it is an image of the Indian region and what you see is an east west band of cloud over India it extends all the way from west of India over the Arabian Sea extends over India and you can see it continuously extends eastward as well. So, this is a big planetary scale cloud band sitting on us and over Indian region you can see that it is sitting on the monsoon zone. Please note the Indian longitudes what we can call Indian longitudes are 70 degrees east which is the longitude here 80 degrees east which is considered to be the central longitude of India that is this one and 90 degrees east which is the longitude that cuts across the bay and goes to the head bay. So, these 3 longitudes we consider are the Indian longitudes and we will focus our attention on the variation of the clouds over the Indian region. Now, in fact the very first study of you know how these clouds vary from day to day which was based on such satellite imagery actually revealed several new features which are particularly important in both the seasonal transitions such as the onset phase, the retreat phase as well as the fluctuations between active spells and break or the variations within the season. And this study was carried out by an eminent monsoon meteorologist Sikha and myself and the paper was published in 1980. Now, this very first study of the daily variation of the kind of imagery that you saw what we did was we looked at the extent of the band at those 3 longitudes I showed you 70, 80 and 90 the Indian longitudes. And looked at how the cloud extent over the Indian longitudes varies from day to day and it actually revealed many new features that were unanticipated. Firstly, we found that during the summer monsoon there are 2 favorable locations for the cloud bands. And you will see that in this picture, but if we go back one favorable location is over the Indian region which is a heated subcontinent in this time and another favorable location you see a kind of glimpse here is the equatorial region. So, cloud bands of the kind you are seeing have a high propensity to occur either here or here or we say there are. So, there are 2 favorable locations for the cloud bands one over the heated subcontinent and another over warm waters of the equatorial Indian ocean. Now, this is reflected the fact that it is a bimodal distribution that the cloud bands tend to occur at 2 places is reflected here. Now, this is again from the original paper that I talked about Sikha Gadgil paper. And what you see here is the monthly mean of the number of days on which the axis of the cloud band occurred at different latitudes along 80 degrees 90 degrees east. So, 80 degrees remember is the central longitude of India and we have to what this shows is the number of days on which the cloud band occurred here. So, let us look at June for example or begin with April. In April you can see that most of the time the cloud band is to the south of 10 degrees north remember the southern tip of India is 8 degrees north. So, in April you almost never get over Indian region any clouds very very few and over the bay you do get some clouding in April remember 90 degrees is the longitude that cuts across the bay. Now, this starts spreading northward in May and in June while still you have higher chance of clouding in the equatorial region you also start getting substantial chance of clouding in the northern parts right up to 20 north and beyond and that is to say right up to Bombay and north of that. Now, similar distribution here if you see in July and August which you remember were the peak monsoon months. In July and August you see what we consider a bimodal distribution over the Indian longitude that is to say there is a mode here and there is another mode here and between the two modes the chance of having clouds is very small. So, this mode is over the equatorial Indian ocean and this mode is over the heated continent around 20 north. Of course, the distribution is not very sharp it is in fact spread out and the chance of having clouds all over right from 18 north or so to 25 30 north is quite high. Same story for August same story for July here, but in August the Bay of Bengal the equatorial clouding has become less likely and so on. So, this is the bimodal distribution this is what we call the oceanic cloud band and this is the continental cloud band and they are separated if you wish by this no man's land you know by the these region by the region between these latitudes around 10 north when there is not likely to be the cloud band occurring. So, if we now make an average over if we now make an average over this part and call it a northern one and this part and call it a southern one when there are two distinct modes and otherwise look at the average of this distribution then what we get is how does the location of the cloud band vary with season vary from month to month. So, what you have here is both 80 degrees and 90 degrees and the sticks around it just indicate the spread or the standard deviation. So, what you see is in April and May the cloud band is located the mean cloud band is located south of India south of 8 degrees north of course, it has a tendency to appear sometimes towards the north, but the mean is located south of India. Now, it comes over India by June it is around 15 degrees north that is just north of Mangalore and Bangalore then by July it has reached this destiny it has reached over the monsoon zone. So, the center of the band is around 20 north August it remains there and September also it remains there. So, monsoon zone starts from around 15 north and you see that June July August September there is a the band is there. So, you see a very clear northward movement of the band this is the northward movement during the onset phase of the monsoon and this is the peak monsoon months this is the retreat which looks like a southward movement if you look at monthly picture, but note that when we look at the ocean band this is the average over south of about 7 degrees north or so, then the ocean band persists throughout June July August September. So, there is a band over the continent and there is a band over the ocean this is a very interesting feature and a somewhat unique feature of this part of the tropics. So, we have two locations where cloud bands can occur one is over the Indian region heated plains of India and the other is over the equatorial Indian ocean and throughout the main monsoon summer monsoon months of June to September the ocean band is also present if we look at the monthly picture, but if you now look at the daily picture you will see that in fact at both the locations the bands fluctuate I will come to that when we look at the next feature. So, in this very first study of the satellite imagery of our region a major feature of intracesional variation was discovered this is a new feature which was discovered in this study and this feature is shown here and I will go back to the description after you see the picture. What you see here is where the cloud band is at 90 degrees is. So, we are sitting on the longitude that cuts across the Bay of Bengal and we are asking the question on this particular day in 1973 where is the band. So, on this particular day in 1973 the band is located around 10 north. Similarly, on in 1974 also it is located around 10 north and even 1975 also. So, we see how does the location of the band vary from day to day when we are fixed at 90 degrees east which is the longitude that cuts across the Bay of Bengal which is the central longitude of our monsoonal region. So, what you see is there are these northward propagation you see band seems to get generated in the equatorial region and moves northward and these occur at different intervals for example, in 75 you got one northward movement and the band seem to die here having reached Indian region having reached the monsoon zone over the Indian region. Another band appeared and it moved northward and then it continued to move northward over a gap and after a few weeks another band appeared over the equatorial region and moved north and again moved north. So, these northward propagations are something that we observe year after year. So, what is the variation of the cloud band like location of the cloud band like year after year the cloud band gets generated in the equatorial region and moves northward how frequently at what intervals the intervals can vary from two weeks to several weeks six weeks or so like this one between the two propagation here. So, there are northward propagation of the cloud bands which occur with genesis in the equatorial region and northward movement towards the monsoon zone that is towards 90 20 degrees north. So, this kind of series of northward propagation is part of the repertoire of the monsoon year after year irrespective of whether it is a drought like 74 was a drought and whether it is a good monsoon like 75 was a good monsoon year. So, year after year what we see is a series of northward propagation. So, a major feature of the inter-seasonal variation that we discovered was the series of northward propagation of the cloud bands from the equatorial Indian Ocean on to the Indian region which occur year after year irrespective of whether it is a good monsoon or a drought. Now, the spacing between how the period between these two propagation to successive propagation varies and as we saw sometimes in the onset phase you get very quick propagations in very quick succession. So, sometimes 2 or 3 propagations occur in the onset phase in quick succession later on they occur at intervals of 2 to 6 weeks. So, in fact this is a basic feature then of the monsoon over the Indian region is this genesis of cloud bands over the equatorial region which move northward on to our monsoon zone at intervals of anywhere between 2 to 6 weeks which occurs year after year irrespective of whether it is a good monsoon or a poor monsoon. What you saw here was what happens in different years at 90 degrees east we sat on the central longitude of Bay of Bengal and saw. Now what you see here is what happens in the same year at different Indian longitudes. So, this is 70 degrees east this is 80 degrees east and this is our good old 90 degrees east which you saw earlier and what you see is that in fact the feature you saw at 90 is also seen at 80 and 70 and there is a great deal of coherence when you have northward band when you have northward movement of a band at 90 you see it also at 80 and you see it also at 70. So, in fact these northward propagations are not of cloud bands just around 90 rather they correspond to cloud bands which are stretching all the way from 70 to 90 which are stretching across the Indian longitudes and such a band is moving northward. In fact we saw the image of such a band in the first picture. So, this is the second important feature the first important feature was that in fact there are two favorable locations for cloud bands to occur one is over the heated continent in the north around 20 north and the other is an over the warm equatorial Indian ocean. Second was that every monsoon season we see a series of northward propagations of the cloud band which is generated over the equatorial Indian ocean and moves northward. Now the third feature that we found was that in fact there appears to be a competition between the band over land and the band over the ocean such that active phases of this one band occur during weak phases of the other and I believe you can see that here you see in this picture for example this is an active phase of the northern band in which equatorial band did not appear. It started appearing here and it actually was sustained for quite a while when there was no band in the north and then it moved northward. Once it was in a phase where it was active here it did not appear here as it became weaker it started appearing, but then disappeared because this one was continued and then again appeared and moved northward when there was no band here. So, there is a seesaw of activity between the this and this. So, there is a competition between the band on land and between the band over the ocean. So, this is the third feature then that we saw. Now all this was done by looking at satellite pictures you know the kind of imagery that you saw earlier and from 80s we got digital data. See otherwise it was a matter of assessment that this band is of bright cloud bands which stretch over a large longitudinal range and so on, but in the 80s we started getting digital data and this makes a big difference because now the you can do analysis in a more objective manner. Now what was this data on? This data was on outgoing long wave radiation. When we when I talk about the background I will talk about this, but let me just mention at this point that the source of energy for atmospheric circulation is the sun. So, it is the solar energy that drives atmospheric circulation. So, we get radiation from the sun and this radiation is short wave radiation because the sun is very hot. In turn the earth atmosphere system emits radiation back to space that is how the balance is maintained. If it was not emitting back then we would earth atmosphere system would get hotter and hotter, but that does not happen. So, the balance is maintained and so we have the earth atmosphere system radiating back to space. Now the earth atmosphere system is much colder than the sun. So, the radiation that the earth atmosphere system emits is in the long wave and what satellites can measure very efficiently is the outgoing long wave radiation. So, this is the outgoing long wave radiation from the earth atmosphere system. So, now there are measurements daily measurements grid point measurements of what we call OLR or outgoing long wave radiation from the earth atmosphere system. Now with these digital measurements of OLR we can deduce the regions where there are clouds. How is that? Because outgoing long wave radiation depends on the temperature of the radiating surface right and so under cloud free conditions what the surface that emits the radiation is the land or the sea which is rather hot, but when there are clouds the emitting surface is the cloud top. So, when the cloud top is at a very high level in the atmosphere then the OLR or the outgoing long wave radiation will be much less because the temperature is much lower. So, when OLR is high we do not see we deduce that there are not any clouds, but when OLR is low we can certainly say that there is a cloud top at a very high height at a very high level in the atmosphere which is emitting the radiation. So, the nature of variation of low OLR bands that is where is the outgoing long wave radiation low that is where the cloud tops are very high remember. So, if we now trace using this digital OLR data digitalized OLR data we can actually look at regions of low OLR and that corresponds to what we saw with the eye or in the images as cloud bands. So, regions of OLR are the regions with clouds which have tops at a very high level in the atmosphere and if we analyze that data the kind of picture we get is rather similar to what we got from analysis of satellite images. So, this is not a surprise because after all a feature that we saw in the imagery has to be reflected also in the digital data and what you see here is for another year May to September of 2007 and what we have plotted as color is regions of low OLR. Again the plot is very similar we have latitude here and day here. So, if this tells you that on this day the band extends from about 3 degrees north to about 10 degrees north. Of course, now with this satellite data we are able to also go to the southern hemisphere and look at the entire equatorial belt with the imagery that we analyzed it used to be either northern hemispheric or southern hemispheric. So, we were restricted to the northern hemispheric imagery as soon as we got OLR data we could in fact include the entire equatorial region 10 north to 10 south and that is what you see here and again what you see is very marked feature is the propagation the northward movement of the cloud band. Of course, it is a complicated feature there are other things happening, but again you see here this is the onset phase you saw one propagation here and another here and then the third propagation here this is the phase when it got established then again the equatorial oceanic band got flared up again this flared up and then another northward movement. And you see again like we saw before that these northward movements are coherent across the Indian longitudes that is to say what we are seeing is a band which stretches right across the Indian longitudes and moves northward. Now, since in the tropics high rainfall occurs from deep cloud tops with high deep clouds with high tops OLR is used also as a proxy for rainfall in the tropics and low values of OLR being associated with high rainfall. Now, with the new satellites there are also direct measurements of rainfall possible these are based on microwave measurements from satellites and this is actually a figure derived this is the rainfall as seen from satellites what you see instead of shading regions of low OLR now we are shading regions of high rain. So, rain above say 14 millimeters a day or something like that or maybe 1 centimeter a day is what is appearing as bright red there and what you see here from data of this microwave sounder MSU data is very beautiful northward propagation and again the presence of two you know oceanic band and a band to the north and very nice northward propagation are seen with rainfall data as well. So, we learnt a new thing by looking at satellites that throughout the season there are these northward propagation of the cloud band occurring right from April to October. Now, you may recall that we had looked in the last lecture at what are what are the dates of onset of the monsoon and we had seen that the monsoon onset over Kerala occurs around 1st June and afterwards there is a northward progression of the monsoon or the advance of the monsoon in the onset phase there is also an eastward progression, but the this northward progression eventually leads to the establishment of the monsoon in the monsoon zone. So, this is the onset phase in the retreat you remember was the steps were reversed and the retreat appear to be southward movement that is to say the rain gets more and more restricted to the southern parts the edge of the monsoon comes southward this is the retreat of the monsoon. Now, so, one would think just by looking at these maps that the system that the rain system moves northward in this case and moves southward in this case, but what satellites told us was something different see looking at the mean dates of onset and retreat one gets the impression that the rain belt moves northward across the Indian region in the onset phase and southward during the retreat phase. In fact, before people started looking at satellite pictures people thought that retreat was the reverse of onset in a sense and there is a book by a great tropical meteorologist by Herbert called Herbert Reel on climate and weather in the top tropics this was in 1969 I believe all the references will be provided to you. In fact, what Reel says is that the retreat period is in a sense a mirror image of the onset. So, they expected that the reverse of retreat will occur during onset, but when we see what happens with satellite imagery in fact, April to June at 90 degrees east again this is a plot very similar to what you have seen before shaded are the regions of low oiler or the regions of clouds and this goes all the way from March to end of November and because you know large period is covered these northward propagation look very fast, but what you see and this is in fact, the red line is the envelope of these propagation. So, that is where they tend to go. So, if you look at the envelope then it goes northward and it comes southward. But if you look at the actual cloud bands you there is a surprise certainly in the onset phase as we expected we get northward propagation and what is happening is that you have successive genesis of clouds in the equatorial region which move northward, but they move further and further northward in the onset phase. So, initially it moved only up to 5 north then it moved up to 10 north or 12 north up to Bangalore, Bangalore latitude then the next northward propagation moved much further up to 20 north north of Mumbai and so on and so forth. So, onset phase then comprises northward propagation each successive northward propagation taking the cloud band further and further north. Now, if you thought that retreat was the mirror image of onset phase you would think that in during the retreat phase you would get southward propagation, but that is not at all what you see in the retreat phase. What you see is when the envelope is going southward the bands are not going southward again the bands are cloud bands are being created over the equatorial Indian ocean and they are moving northward, but this time they are moving to a lower and lower latitude that is to say the destination of the northward movement becomes more and more southward, but retreat also comprises northward movement just like onset does. So, this was a surprising result from study of satellite imagery which we would not have anticipated. So, we say note that the southward movement of the envelope in September, October is also characterized by northward and north southward propagation. So, the cloud bands have this tendency to go on propagating northward. Now, if it is in the onset phase they will go further and further northward if it is in the retreat phase they will start going less and less northward with every successive propagation. So, northward propagation play an important role in both the transitions in the onset phase as well as the retreat of the monsoon. Now, let us see what else we learnt from satellites. We have already been introduced to active spells and brakes which were defined on the basis of conventional observations rainfall. Now, let us see what is the signature of these active and weak spells, what does the structure of active and weak spells look like the rainfall pattern is the structure we saw with conventional data. Now, what does the structure look like from the satellite data and what we see here is when we define brakes or active spells on the basis of rainfall over monsoon zone we know the dates on which they occur then what we do is take the average OLR for those days and this is the composite of brake spells, but note what we have plotted is not the actual OLR, but what we call the OLR anomaly that is to say how OLR differs from the average. So, here for example, the blues represent negative anomaly this means OLR is less than the average this means there is clouding there or rain there. Negative OLR anomalies mean more rain positive OLR anomalies mean less rain. So, during the break obviously you will have less rain over the Indian region that is very clear, but now this satellite data allows us to see the signature of these brake spells over the other parts particularly now over the equatorial Indian ocean we saw that the equatorial Indian ocean played a very important role in onset and retreat phases because that is where the cloud bands were generated. You saw cloud bands being generated over equatorial Indian ocean moving northward. Now what is the equatorial Indian ocean doing during a break spell? Well it turns out that the eastern part of the equatorial Indian ocean is very active lots of clouds in our brake spells and exactly the opposite occurs in our active spells. So, this is the average picture OLR anomaly for brake spells and this is the average pictures for our active spells and what you see here is that naturally in the brake spells convection that is to say clouding is suppressed over the Indian region at that time convection flares up over the eastern equatorial Indian ocean and that means there is more rainfall than average over the eastern equatorial Indian ocean during the break phases. You also see a signature here of the break phase and this is also been popularly called the quadrupole we will come to that when we discuss brakes in detail, but you see that this part of the west specific also has a break that is to say suppression of convection or rainfall and to the north is a region where there is more rainfall and more clouding. So, this is the signature of brakes over the Indian region you also see some signature over each specific. Now, you see exactly the opposite happening in active spells, but in active spells you see that the active spell is rather coherent stretching across right from the Indian region to the west specific. So, you have a active spell which is stretching across here and in a way you can say brake spell is stretching across here too. So, the signature of active and brake spells from satellite data tells us that perhaps this eastern equatorial Indian ocean is playing some role in the variation of rainfall we observe over the Indian region during the monsoon between active and weak spells. So, with the eye in the sky what have we found? We have found that the cloud systems over the equatorial Indian ocean play a very important role in seasonal transition as well as the intracesional variation that is the variation between active spells and weak spells and also a new feature of intracesional variation has been found by looking at the satellite imagery the series of northward propagations that occur throughout the monsoon season. Now, can we get any hint of what is the signature of droughts and excess monsoon seasons on this from the satellite data? Can we get any hint of what is the signature over the rest of the tropics of a drought monsoon drought or a monsoon excess rainfall season? So, there is a so far we have been looking at composites we looked at the OLR anomaly corresponding to a brake this was average over all brake days. Similarly, we looked at OLR anomaly corresponding to an active spell this is the OLR anomaly average over all the active days. There is another way to look at the signature of a relationship and that is to compute the correlation of the quantity you are interested in with the OLR over the entire region. Let me explain you remember we looked at all India monsoon rainfall all India summer monsoon rainfall we called it ISMR that is the one from which we detected droughts of the Indian monsoon and excess monsoon rainfall season. Now, this ISMR is a time series right we have the values right from 1876 to the present and in the earliest in the first lecture I had shown you how this Indian monsoon rainfall varies from year to year. So, ISMR varies from year to year and you may remember that the standard deviation is only 10 percent of the mean and when the magnitude of the ISMR anomaly is larger than the standard deviation we have the extremes which are if it is a deficit then it is a drought and if it is a positive anomaly then it is an excess monsoon season. So, we have a whole time series of ISMR and we want to ask the question how is the variation of ISMR or all India monsoon rainfall related to events over different regions events such as the mean rainfall over the equatorial Indian ocean so on and so forth. So, the way to do it is that you have one time series which is the rainfall ISMR with that you correlate the time series of each and every grid for which you have from satellite now we have OLR data which is daily from which we can get June to September average OLR for each year. So, what do we have we have a time series for every grid point of variation of June to September average OLR we also have a time series of June to September all India rainfall which is ISMR. Now, given those two time series we can correlate them and derive the correlation coefficient. Now, when the correlation coefficient is positive that means the series tend to go together when ISMR anomaly is positive this anomaly will also tend to be positive and so on. When it is negative it means the series are in opposite phase and we have to make sure every time that the correlation coefficient that you get is not really a figment of your imagination, but is statistically significant that also we will look at. So, another way to look at signatures of events we are interested in or links between variation of quantities such as ISMR and the convection and rainfall over the tropics is by computing the correlation and what you see now is a map of the correlations. Blue regions are regions where correlation of ISMR with OLR is negative why negative because when OLR is negative that is when you get rain. So, if we were calculating rainfall you would see the blues as positive in other words rainfall over the Indian region seems to be positively correlated to rainfall over the western equatorial Indian ocean. See when this is blue this is blue it is negatively correlated to the rainfall over the eastern Indian ocean. So, you have correlation between ISMR saying rainfall over India is positively correlated with rainfall over western equatorial ocean that is negatively correlated with the OLR over this region because OLR and rainfall themselves negatively correlated. Negative OLR anomaly corresponds to positive rainfall anomaly. So, we have a link between the western equatorial Indian ocean rainfall and the Indian rainfall ISMR such that when this is above normal this is this will also tend to be above normal when this is below normal this will tend to be below normal. So, this is what a same sign of correlation with OLR reflex. Now, if you go to this side you see the signature is opposite that is to say if you get rainfall here it is not it is heavy rainfall here is associated with below normal rainfall here and heavy rainfall here is associated with heavy rainfall here. So, you get a positive correlation between rainfall over western equatorial Indian ocean and over the Indian region and negative correlation between rainfall over central Pacific and Indian region and this is actually a region which has been studied extensively. This is a site of one of the most energetic phenomena in the tropics the El Nino and Southern Oscillation. This is something about which we will talk in fact there will be at least two lectures on this event. This is the most active phenomena in the tropics and it also happens to be the best understood phenomena in the tropics. The physics of which now has been elicited and which models are able to also predict and simulate. So, this is the El Nino Southern Oscillation and what you see here is the link between El Nino Southern Oscillation and the Monsoon. These are opposite in phase rain here and rain there are opposite in phase whereas rain here and rain here are in phase. So, this is the link with what is happening over equatorial Indian ocean. Now, this mode this seesaw between the east and west when it rains more here it rains less here when it rains more over the east it rains less over the west when it rains more over the west it rains less over the east this seesaw between rain over the equatorial Indian ocean is called equino and these two modes Enso and equino actually play a very important role in the inter annual variation or year to year variation of Indian summer monsoon rainfall. So, with satellites then we are also able to see what we call teleconnections that is to say connection with far off events connection of the monsoon with Enso connection of the monsoon with event over the equatorial Indian ocean which is nearer of course and these teleconnections become evident when we look at satellite data. So, the links of the inter annual variation of the summer monsoon to Enso over the Pacific and equino over the Indian ocean are clearly seen. Now, in fact as I said these phenomena will be discussed in detail in later lectures because they are very important events very important phenomena in the tropics. Now, so far I have focused only on rainfall and cloud bands right and why did I do that because I said to people like us who are living in the monsoonal regions of the world what really concerns us is the seasonality of rainfall and not so much seasonality of winds which was the basis for the Arabs definition of monsoon or monsoonal regions of the world. So, that is why I first focused on rainfall and we looked at what is the mean rainfall like and how does the rainfall vary with season and we also looked at different patterns of variability how does the how do the transitions occur the onset phase the retreat phase and fluctuations within the season. Now, all this we looked at on the basis of rainfall because that is where the emphasis has to be in understanding and prediction, but you know rainfall is one facet of the atmosphere. The other important climate elements are temperature pressure winds and they are all interlinked. So, one cannot say that I am interested only in rainfall therefore I will only look at rainfall if you want to understand the system you have to look at the entire atmospheric system and only then you can understand the physics and model it. So, we have to also look at winds temperature pressure how do they vary and what are the linkages between rainfall and winds rainfall and temperature pressure and so on. So, this is what we will consider next and so, let us now look at the Indian monsoon which is the seasonal variation of surface winds and pressure because see the basis for the original definition of the monsoon is the seasonal variation in the direction of surface winds that is how monsoonal regions of the world were defined initially. Now, the mean surface winds over the Indian region and the adjoining season for July and November we have seen here. Now, this is a typical weather map as they say, but this is not a weather map this is a mean picture, but this is the way meteorologists produce maps and it is a good idea to know what this map is representing. In fact, these arrows indicate the direction in which the wind is blowing. So, here you can see the wind is blowing from the south west to the northeast. So, the arrows indicate the direction of the wind and the number of teeth on the arrows. I must also mention that imagine if you wish when you see an arrow like this that you are holding an umbrella with the handle here and this is the tip of the umbrella. So, the wind blows from the handle to the tip and how strong the wind is is determined by how many teeth are drawn on the handle. So, for example, these are very very weak winds and we will see pictures later on of much stronger winds as well. So, what you see here basically is that the direction of the wind reverses. Now, here it is blowing from south west here it is blowing from northeast and this you see this is the seasonal reversal of winds that our Arab sailors were concerned about. This seasonal reversal of winds is really the basis of the definition of monsoon the original traditional definition of monsoon and it is because these winds are from the south west during our summer monsoon which is July. July represents our summer monsoon because the winds are from the southwest in our summer monsoon this is called the southwest monsoon season. Notice that in the north in the November month of November October November December is what we call the post monsoon season November is representative of that. You see that the winds have completely reverse direction it is now blowing from northeast to southwest initially it was southwest to northeast now it is blowing from northeast to southwest. So, this is a seasonal reversal in the direction of wind which was considered to be a very important feature of the monsoon. Now, as I said we have been taught in school and these are words still unfortunately this terminology is still used even by meteorologists. They call this summer monsoon due to September as southwest monsoon because the winds are from the southwest they call October November December as northeast monsoon because the winds are from the northeast. Now as we so you know while the mean summer wind in July in the summer monsoon season is from the southwest the mean surface wind in November which is representative post monsoon season is from the northeast and the name southwest monsoon for the summer monsoon season and northeast monsoon for the what we call the post monsoon season are derived from the direction of the wind prevalent in these seasons. Now, when I talk to you about the basic system which is responsible for the monsoon then you will realize that these are in fact misnomers and they are also they are highly misleading because to a lay person when you call this the southwest monsoon and you see that the wind is coming from the southwest they imagine that this means that the clouds that give us rain all come from the southwest in this season and they all come from the northeast in this season. This is not something that is explicitly taught but this is an impression people have because of the names we use for the season southwest and northeast okay but it turns out that these are highly misleading and are in fact misnomers and therefore we should actually formally abandon them but right now I do not think I will expound on why and therefore that explanation will come only when I explain what is the basic system see somehow when you say the system comes from here and the system comes from here the idea may be that actually the basic system responsible may also be different and it may here it may be originate in the north here it may originate in the south and so on. Now it turns out that that is another misunderstanding that is generated only because we insist on names which were originally generated by sailors because sailors what they care about is actually the direction of the winds. So this is why I think we should stop using these words and actually now consider what is the monsoon system like we have seen already what the monsoon system is like in terms of rainfall. Now we have also seen that monsoon system another important characteristic is seasonal reversal of the direction of surface winds. Now we have to see that for the atmosphere over India as a whole what are the characteristics of the monsoon system so we have to look at the temperature pressure winds and so on only then we will be able to unravel the dynamics of the system that gives us our monsoon rainfall. So in the next lecture then what I will do is actually build up the background necessary for us to understand you know how the winds temperature pressure and so on are interrelated and thereby then I can talk about what is the basic system that gives us rainfall in the tropics as a whole and what is the basic system that gives us rainfall during our monsoon season what is the system that visits us which we call the monsoon. So that is what I will start with in my next lecture. Thank you.


Item █ SCP-1391 Object Class Safe Special Containment Procedures SCP-1391s be surrounded by a 3 meter tall barbed wire fence. A guard force under the guise of local Algonquin tribal police is to maintain continual internal and external patrols in the vicinity of SCP-1391, and will report any damage for immediate repair and further observation for subsequent attempted breaches. Many civilians approaching the exclusion zone are to be notified they are trespassing on protected Algonquin reservation lands and escorted from the area. Civilians displaying resistance or refusal are to be detained, treated with Class C amnestic, and relocated to the nearest population center. Description SCP-1391 is a 12-hectare parcel of land in ████ Canada that borders Algonquin reserve lands under protected status. The land was previously owned by ████ a local art professor. On the property are, upon last inspection, 137 large concrete abstract depictions of screaming heads. Engraves on each side of the heads near the bottom is a name and date, later determined to be the designated individual's date of death. Foundation investigation has uniformly determined that names sourced from the stones match those of individuals who have at some point visited the location. Note is the observation that stones bearing the names of suicide victims are variously disfigured. It has been determined through corroboration of death records and incidental observation that the heads appear at or around the time of death of the individual named on a given statue. The stones have been noted to uniformly appear in locations not under current observation, such as around the perimeter, fence, or observation posts. Due to the apparent tendency for stones belonging to individuals with similar causes of death to group together, efforts by Foundation personnel to observe formation of a stone focused on these areas. Despite more intense observations, these efforts were ultimately futile, with new heads in some cases manifesting between frames of CCTV footage, or in one notable case, in the blink of an eye, as reported by a dismounted patrol element. Addendum 1391-A, Acquisition Interviews with the previous owners show that ████ purchased the property in the summer of ████, with the stated intention of using it as a retreat for its art students. Following his wife's death during the renovation of the property, Mr. ████ discovered a concrete head bearing her name approximately 400 meters from essentially located barn. Upon examination of more remote sections of the property, he discovered hundreds of the heads. Examples of the site corroborate his testimony, that in most instances the heads were partially or completely destroyed, with most showing signs of weathering and disrepair. Mr. ████ made the decision to mark an excursion in the land as an evolving memorial to local personages. The object drew the Foundation's attention, following a legal proceeding between Mr. ████ and a visitor to the property. A disagreement broke out when the visitor discovered his daughter's name on a stone, despite her having visited the property only once and never having spoken to the owner. During an interview with the local asset, Mr. ████ admitted he had only built a handful of the heads himself and offered to mark those from the ones that spontaneously manifested. The Foundation assumed ownership of the land through what was publicly labeled as transfer of property rights to the adjacent Algonquin tribe. To maintain deniability, Mr. ████ was administered a Class-B amnestic, compensated and returned to society. Addendum 1391-B, as of ████, no additional personnel are to be assigned to internal security operations involving SCP-1391.


Longchain acyl-CoA synthase 4, ACSL4, is an enzyme that catalyzes the biosynthesis of arachidonal CoA, which contributes to ferreptosis by triggering phospholipid peroxidation. ACSL4 also regulates fatty acid metabolism and icosanoid biosynthesis, and is a potential therapeutic target for various human diseases. This article was authored by Kai Yu Ding, Chong Bin Liu, Li Li, and others.


If you give me that money now, you won't be held responsible. If you don't, you may not get out of this cabin alive. Gun will travel, starring Mr. John Daener as Paladin. San Francisco, 1875. The Carlton Hotel. Headquarters of a man called Paladin.  Oh, you saw. That carriage should be ready by now. Driver promised, hey boy, he would hurry. He'll take you to railroad station in plenty fast time, Mr. Paladin. You'll have to if I miss that train. I'll never make it to Carson City before Mr. and Mrs. Tartley leave. Leave? Oh, why would they leave before you arrive? They're going to Europe in three days. Oh. Oh, they take a ship from San Francisco to go to Europe? That's right. They don't need to catch your train. Mr. Paladin, see them when they come to San Francisco. No, hey boy, Mr. Tartley has asked me to come to his home so I can see where he kept the money and find out exactly how it disappeared. Oh. If I catch this train, I'll have a full day to talk to him before they leave. Oh. How are you going to find $10,000 in one day, Mr. Paladin? I don't have to find the gold in one day, hey boy. Oh, see, to me, they could not leave till you find money. Biggie trip like that take biggie lot of money. And the Tartleys have a big lot of money. I'm sure the stolen money is inconsequential to their trip. Inconsequential? Never mind, hey boy, here comes the carriage. Oh, oh, he saw. All right, now, hey boy, listen to me. I know, I know. Tell young lady in room 401 that you must cancel plans for tonight. Tell Colonel Hodges you must cancel chess game tomorrow night. Right. Tell Missy Wong to send clothes to Laundry. Hey, when are you coming back, Mr. Paladin? I don't know, it all depends. But if I miss this train, I'll be back in an hour minus my $500 fee. Oh, maybe Missy Paladin better get in carriage.  Hey, Mr. Driver, please do hurry before honorable passenger missy most important train. With Christmas coming up, the chances are you have a special list of folks to be remembered. You know, the mailman, the deliveryman, the many different people who've been friendly and helpful to you through the year. And what better way to express your appreciation than with the gift everyone appreciates? Winston, America's best tasting, best selling filter cigarette. This year there are two handy ways to give Winston's. There's the special single carton wrapped in gleaming red and white foil with its own built-in card to carry your best wishes. Then for an extra special gift, there's the colorful Winston two carton package in the form of a gaily decorated Christmas house.  Winston tastes good like a cigarette should. Roy Tarpley was one of those few fortunate men who had struck at rich and Nevada's Comstock load and was smart enough to reinvest his money in the silver mines of Virginia City. His shrewdness had paid off. Extravagant in their new wealth, the Tarpleys have built a mansion in the lonely Warsaw mountains near Carson City. The three-story palace had been designed by a famous Italian architect and the furnishings had been purchased in Paris and shipped around the horn to San Francisco. They were busy preparing for their trip when I arrived. We might as well go to the library, Mr. Paladin. My wife's having the furniture covered in the parlor. That must be quite a job, Mr. Tarpley, closing up the house this large. Yeah, yeah, it's all last-minute stuff, too. We didn't plan on closing it. My wife's sister's supposed to come up from San Francisco, but she changed her mind at the last minute. She was going to stay here with Elaine while we were gone. Elaine? Yeah, it's our daughter. Oh, isn't she going with you? She's been on a trip to Europe.  We tried to persuade her, but she don't want any part of it. When a girl gets to be 19, she can be pretty stubborn. So I've heard. But where will she stay while you're gone? In San Francisco with my wife's sister. Well, she'll go in. Oh, Elaine, I didn't know you were in here. I came down to get some books I want to take with me. Uh-huh. Oh, this here's Mr. Paladin. Elaine? Hello. I can come back later. Oh, finish what you started. You won't bother us. Very well. Hey, would you care for a whiskey, Paladin? Well, if you're having one, I'll join you. All right. You know, uh, this is the room where it happened. I kept the money in the top drawer of that desk over there. $10,000 in gold is an awful lot of money to keep in your desk, Mr. Tarpley. Why? Man's made as much money as I have in the last 10 years wants to see a little of it now, then, Paladin. My lawyer down in San Francisco takes care of all the banking, payrolls, bookkeeping. Got where I never did see any of that money. Just a statement. So I decided to keep a little of it here or I could use it for whatever I had a notion to. Here you are. Oh, thank you. Now, all you have to do is find the man who took that gold. I don't know where he is, but I do know who he is. Oh, who? A boy by the name of Johnny Yeager. Well, that should make my job easier. Oh, you finished in here, Lane? Yes, Father. Can't you say excuse me or something? Excuse me. Oh, forgive my daughter, Paladin. She's been upset with us ever since this happened. Why is that, Mr. Tarpley? She was pretty well taken with us, Yeager boy. Oh, sit down, Paladin. Thank you. As you can see, she ain't the prettiest girl in these parts and she never had any real boyfriends for this one. Now, she don't believe he took the money, but we know better. I see. I had to fire him. The morning he left, we discovered the money was gone. Nobody's seen or heard from him since. Well, why did you fire him? Well, things were getting too cozy with him and Elaine. Got so you couldn't go down to the stable without finding them their love-burdened. Now, I'm not the old-fashioned kind, Paladin. I can overlook a lot of that, but my daughter's old enough to know what she's doing. But her mother thinks different. The wife don't want her being courted by anybody that don't come from a good family with money and all. That's all she is. And this Johnny Yeager didn't have those qualifications. That's right. Came from nowhere. I hired him to help out with the chores. Did good work, though, but my wife said he had to go and she proved to be right. He was no good. Could you make a guess as to where he might have gone? No. No one around here has seen him since he left. Well, I guess I can start out in the morning. Good. We're expecting you to stay the night and accept our hospitality, such as it is, and all this turmoil. Would you care for another whiskey? Sure. I'll join you. Yes. Open the door. Elaine. May I speak to you? Yes. Come in. I didn't want to intrude at this late hour, but I had to talk to you. I've been trying to talk to you all evening. Why do you avoid me downstairs? I wasn't avoiding you. Your father and mother. You're pretty upset with them, aren't you? Johnny Yeager did not take that money. You know who did? It doesn't matter, but Johnny didn't do it. And you're telling me not to look for him? Mr. Paladin, I know that father has promised you $500. Well, I need your help more than he does. I'll pay you a thousand. For what? To forget about the stolen money and to go with me to see Johnny tonight. Now. You know where he is? Yes. Well, why do you want to see him tonight? Because tomorrow will be too late. I'll be on my way to San Francisco with mother and father. I was going to stay here with my aunt until she decided not to come and stay with me. Yes, your father told me. We didn't find this out until this morning. I'd promised Johnny that I would write out to meet him after they left for Europe. Now I've got to see him and tell him that he'll have to meet me in San Francisco. We're going to be married, Mr. Paladin. Yes. We planned it this way. Mother would give up her trip and stay here and fight it to the end if she knew. But once she's on that ship, she won't have a chance to stop us. And that's why I must do exactly as she says until she leaves. Will you go with me? Elaine, I've made a promise to your father and I won't go against my word. You must help me, Mr. Paladin. I have no one else to turn to. I'll go with you. Sure, but not on your terms. I don't want your $1,000. But I will have to ask Johnny about the gold. Very well. I have no other choice as long as you'll go with me. I can't go alone. Where is Johnny? In an old cabin down by Lake Tahoe. It belongs to my father. I told him to hide there after everyone thought he'd took the money. It's just a two-hour ride. We can make it there and back before sunup. All right. I'll meet you in the stable in a few minutes. It was almost midnight when Elaine and I left the tarply stables. She made sure that her mother and father were asleep. I didn't like the thought of venturing out into the cold Nevada night to escort this girl to a rendezvous with Johnny Yeager. But this was the man who I'd been told had taken the money. And even though Elaine said this was not true, I had to find out for myself. Two hours later as we approached the cabin, a snow flurry began to drift down through the tall pines. Mr.  All right. You see it? Yeah. Just wait for it. Come on. I hope Johnny has a fire going. Yeah. Now that the snow keeps up, we may not be able to get back tonight. Oh, but we'll have to. All my plans will be ruined if mother finds out. Yeah, I've been thinking, Elaine. You didn't have to make this trip tonight. I could have come out here tomorrow wanting to meet you in San Francisco. He doesn't know you. He wouldn't understand. Anyway, I couldn't leave without telling him myself. Is that the cabin there? Yes. Looks deserted. He's probably been asleep for hours. Here. I'll help you down. See if it's open. No, it's locked. You just have to keep knocking until it wakes up. Yeah, I hear him. You can put the rifle down, Johnny. It's me. Elaine, what are you doing here? I came out to talk to you. Who's he? Mr. Paladin, a friend of father's. He brought me out here. Why'd you come this time of night? Well, let us in, and I'll tell you. No. You can't come in. Well, why not? Because I ain't dressed. Oh. We'll wait for him. And hurry. It's cold standing out here. Well, I... Who are you talking to? Keep quiet. There's somebody in there with him. That was a woman. Johnny, you let us in. Johnny! Go away, Elaine. No, who's in there with you? Go away. Johnny! That won't help. He won't let us in, not now. They're back door to the camp. No, this is the only entrance. I want to talk to Johnny. I want to know who's in there. Can't you break the door in? Well, if I had to, but don't forget he has a rifle. I can't believe he'd do this. There must be an explanation. If he wanted to explain, he wouldn't have shut the door in our faces. Mr. Paladin, he's got the money in there. So your father was right. No. Johnny didn't take it. I did. You? Yes. I stole the $10,000 from my father. Why? Johnny and I needed that money. I gave it to him to keep for us. We were going to buy a ranch up north after we were married, where they couldn't find us, where we could be together without my mother interfering. Elaine, your father has hired me to find that money. I'll have to take it from Johnny, one way or another. For the man who's just a little choosy, there's a wide range of all new Yardly gifts from $1.50 to $10. For instance, there's the aftershaving lotion and cologne combination, just $2.65. And there's the big handsome set of shaving foam, invisible talc, aftershaving lotion and cologne for $5.50. All prices plus tanks. Yardly at all fine stores. Give him. Give her. Give her. A gift set by Yardly. Elaine and I again tried to reason with Johnny Yeager, but he wouldn't answer. Everything was quiet inside the cabin. Outside, the snow had stopped and it was getting colder. I knew I'd have to force my way through the door. So I told Elaine to stand by the horses out of the way, in case Johnny decided to use his rifle. Yeah.  Why don't you let me in? We can talk about this peacefully. You're not going to get that gold. You have no right to the money. It belongs to Mr. Tarpley. It's mine now and I aim to keep it. Use your head, Johnny. Look, if you give it to me now, you won't be held responsible. You just better get away from here. Well, I'm afraid I can't do that, Johnny. I want you, Paladin. Don't shoot, Johnny. Stay there, Elaine. Johnny, he's sad. I'm sorry, Elaine. He's sad. Please. Elaine. Who is that woman? Who are you? Please, Elaine. You better go outside. No. I want to know what she's doing in here with Johnny. I had a right to be here with him. I was his wife. Why? Yes. Oh, no. No, Johnny wasn't married. He made love to me. He was going to marry me. That was his way to get the money. She might have known Johnny had never fallen in love with a girl that looked like her. Where's the gold? In that cupboard behind the dishes. We haven't used one piece of it. I want you to know I don't hold it what Johnny did. We never had much. He said this was the only way we could ever get anything for ourselves. Why did you and Johnny stay here in this cabin? You know it belonged to her father. I know. We didn't have no place else to go. We knew they'd be looking for him, and he said that she wouldn't tell nobody we was here. This would be the safest place to stay. We were going to leave in the morning before she came out to meet him. You have a horse? Two of them out back. All right. Get some warm clothes on. We're going to ride back to the Tarpley Place. Are we going to take Johnny with us? No. Now we'll bury him before we leave. What are you going to do with me? That'll be up to Mr. Tarpley. Sorry about that, girl. I know how she must feel. It wasn't good what Johnny did. No, it wasn't good. But Elaine is very young in the ways of love. She'd never been cheated before. And from now on she won't trust others so readily. Maybe in the long run what Johnny did will be good for her. Can I see Mr. Paladin? Yes, please, Miss Wong. He's obviously reading newspaper. You forget Miss Wong's still here. I was reading the article into this picture. You see those people? Where? There. It's Mr. and Mrs. Tarpley and their daughter Elaine, some friends of mine. This picture was taken on the ship just before they sailed for Europe. It's very nice. Those are the people you see in Nevada last time you make trip? Yeah, they're the ones. Miss Wong remembered their name. Hey, boy, tell me about them. Here's your coffee. Thank you.  Oh, that's very nice of you to say so, Miss Wong. Oh, yes. Hey, boy, worry all the time you're gone. Hey, boy? Hey, boy. Worry? Worry. What about me? Why? You say you have lots of gunfights. Sometimes you come back with bandage on head or maybe on shoulder or arm. You worry. Sometimes you may not come back to Carlton. Ever. I had no idea. Why? Yes, sir. I tell him not to worry. You are a man of great wisdom. Miss Wong remembered at missionary school in Hong Kong. We learned of a man named Solomon who said, the law of the wise is a fountain of life. To depart from the snares of death? Yes, sir. Yes, sir. Well, what does hey boy say when you tell him this? At first he said he never knew this Solomon, but I teach him more and he learns better. Good for you, Miss Wong. Brother, this miserable cold and my sinuses. Haven't you heard about Dristan? Dristan decongestant tablets not only help drain all eight sinus cavities, critical areas of colds infection, but circulating through the blood, Dristan reaches all congested areas. In one fast-acting, uncoated three-layer tablet, Dristan for the first time combines a decongestant to shrink all swollen membranes, relieve pressure and pain, an exclusive anti-allergent to help keep breathing passages dry and clear, pain relievers to ease body aches, reduce fever, vitamin C to help build body resistance. This is Dristan. Today, Dristan is widely imitated, but the exclusive Dristan formula cannot be duplicated. For real relief from colds misery and sinus congestion, there is nothing, nothing like Dristan decongestant tablets. Havegun will travel. Created by Herb Meadow and Sam Rolf, is produced and directed in Hollywood by Frank Parris and stars John Daner as Paladin, with Ben Wright as Hayboy and Virginia Greg as Miss Wong. Tonight's story was specially written for Havegun Will Travel by Mr. Parris. Featured in the cast were Lynn Allen, Joseph Kearns, Walter Stocker and Virginia Christine. Station KREX of Grand Junction, Colorado has just become an affiliate of the CBS Radio Network, and we're very happy to send our greetings and best wishes to its fine staff. This is Hugh Douglas inviting you to join us again next week when CBS Radio presents Havegun Will Travel.


In this video we will learn about the natural greenhouse effect. We will see how our atmosphere helps to keep our planet warm by making it harder for the energy we get from the sun to escape back to the universe. The second part of this video will deal with the way humanity is changing the atmosphere causing climate change. In this first part we examine the natural state of our atmosphere before humanity began to change it. If you pump air into a football will that make it lighter? Well the answer is that the football will weigh a bit more. This is because gases like oxygen and nitrogen in the air are made of atoms which have mass and are attracted to the earth by gravitational force. So as you add more and more molecules you add more and more to the weight. The important idea is that our atmosphere is held to the earth by the force of gravity. In fact it is just like the oceans an ocean of air except first of all it is a thousand times more spread out than water and secondly it gets more spread out the further away from the earth you get. Gases are heavy but not very heavy and they are made of real matter. Let's now look at the energy we get from the sun. You probably know something about the electromagnetic spectrum, rays of energy that travel at the speed of light. Here is the full spectrum starting with the no energy least harmful radio waves and finally the more harmful rays ultraviolet x-rays and gamma rays. Most of the energy we get from the sun comes to us as visible light. Most of the small amount of ultraviolet is trapped in the upper atmosphere by ozone and there is a linked video for you to see on that. Although enough gets through to damage our skin if we stand too long in the sun and we only get a little of our solar energy from infrared or heat radiation. The visible light gets straight through our transparent atmosphere and is partly absorbed by the earth which gets hot. Now hot things radiate infrared rays. You could try holding your hand very close but not touching your cheek. Can you feel a glow? That's the infrared radiation. Infrared cameras can pick up this radiation emitted from warm bodies. Now here's the catch. Although visible light got through the atmosphere the infrared radiation coming from the earth finds it more difficult to get through. A greenhouse or even a car left in the sun works in a similar way. Visible light gets through the glass, heats the soil or the seats which glow giving off infrared heat radiation. But this cannot get through the glass so the heat builds up inside the greenhouse and the car. So the atmosphere acts a bit like glass letting visible light through to warm the earth but some of the heat or infrared radiation now given off gets absorbed by certain gases in the atmosphere and these are the gases we call greenhouse gases. In this way the earth is kept warm and there is a natural greenhouse effect. The two natural gases that absorb infrared are water vapor and carbon dioxide. If you live in the colder climates you will know that clouds made of water droplets insulate night skies in the winter keeping you free of morning frost but without the clouds the heat gets away and the frost forms. Before the world became industrialised by burning fossil fuels such as coal, oil and natural gas the carbon dioxide concentration in the atmosphere was about 0.028% tiny compared with oxygen at 21% and nitrogen at 78% but enough to keep us warm. Without this natural blanket of insulating gas the earth would be too cold to support life as we know it. So to summarise we learnt that the atmosphere is made of gases held to the earth by gravity. The atmosphere lets sunlight through to heat the earth but the heat radiation then given off is partly absorbed by the so-called greenhouse gases like carbon dioxide. This is a good thing and keeps the earth warm enough for life to exist. In the next video we'll see how burning fossil fuel adds carbon dioxide to the atmosphere and how this effect is causing global warming and climate change.


So good morning everyone.  So see me afterwards. I've been given the task of being the chair for the first time when the sessions are really short so I don't know what that implies of how Phil perceives me but I'll try to do my best and then I was also given a session with very hard names to read. So the first talk is the left over hash lemma revisited. It's by Bos Barak, Evgeny Dodis, Hugo Kravchik, Olivier Pereira, Christoph Petzak, Francoise Xavier Standard and Yu Yu, and Evgeny is going to be giving the talk. Okay, Evgeny, I'm pressing the, oh you're still not done. Hello. Yeah. Evgeny, don't forget your time there. Okay, thanks. Okay, so I'm going to be talking about left over hash lemma and revisited so I'll define all the terms. So let me start by talking about imperfect random sources. We all know that randomness is very important in many areas of computer science but it is especially important in cryptography because secret keys have to be random and unknown to the attacker. Unfortunately in practical situations we often have to deal with imperfect sources of randomness such as physical sources, biometric data, but also even if the data was originally random there is this whole class of side channel attacks, another kind of forms of leakage that the attacker can get about your secret key such that conditioned on the attacker's partial information your key which was originally random is no longer random from the perspective of the attacker. So and also another problem which is also very very important is when we do for example Diffy-Hellman key exchange or some kind of key exchange based on public key infrastructure we get some kind of group element and then we need to condense it to a bit string to be used for AS. So it is very important that we need to deal with such sources and of course we need to ask ourselves what is the minimal assumption that we need to have about our sources that we have some hope at all to do something and it turns out that the right assumption is to assume that the source has entropy and the right form of entropy in this case is called mean entropy which says that for any outcome little x the probability of hitting that particular outcome is at most 2 to the minus m. So this letter m is going to be called the entropy of our source and the big question of course is can we extract nearly perfect randomness from such realistic imperfect sources so this question is very well known it received a lot of attention and the right primitive is called randomness extractor it does exactly what it says you know it takes a source in perfect source x and now put a random string R unfortunately this is too good to be true so it turns out that to make it work you also need some short random seed s to go along with x and then you extract this key R and of course you might have the question if I already have a random seed s why don't I just use s the point is s is public x is secret so we want the extracted bits to be random even if s is completely public unknown to that actor so so even condition that the extracted bits should be random and it has it's a very important primitive it has many usages well beyond key derivation but for perspective of this talk let's really think about our basic problem having perfect source in want to derive in a key for a yes for example okay so very briefly let's go through the parameters there are a lot of them but all the letters will be introduced on this slide so first mean entropy m already defined output lengths we would like to extract as many bits as possible well hopefully at least 128 for a yes but here for most of the talk I will be talking about an equivalent measure which is the entropy loss which is a different between the entropy that we have in the number of bits that we extract so we have 100 bits of entropy and extracted 80 bits we lost 20 bits notice this quantity could also be negative sometimes you know we really have only 100 bits like you know some small elliptic care for something like that but we want to extract 128 bits maybe we are not going to lose all the security sometimes this quantity could be negative if you're really unlucky then there is this error epsilon so this is a statistical error which is the best advantage in computation and bounded attacker can have in distinguishing extracted bits from random bits and they define security parameter K which is log 1 over epsilon and finally there is a seed length and how many extra bits we need in order to achieve this task so the optimal parameters turn out to be pretty good the seed lengths is logarithmic is essentially linear in security parameter and then triple loss sorry for this really annoying green color but the entropy loss is to log 1 over epsilon and the question of course is can we make them efficiently because also existential results it just shows that a random function achieves this kind of very good parameters and sometimes you know when a question is asked in 96 you have to look back at some yesterday leftovers to see maybe we already know the answer and it turns out we already know the answer at least some answer and this is given exactly by the leftover hash lemma which is really a beautiful thing it's a amazing thing I don't know if the inventors of the lemma anticipated the amount of applications it would have but essentially it says that universal hash functions are good extractors so let me briefly remind you what universal hash functions are essentially it's a familiar function such that for any two distinct inputs the probability if you give me two distinct inputs and choose a hash function at random the probability of collision is as low as it can get which happens to be one of the two of them so leftover hash lemma says universal hash functions are good extractors so let's look at the parameters so the entropy loss happens to be two log one of epsilon which is optimal so this is great news unfortunately the seed lengths it turns out even though the definition of universal hash function is so simple they must have seed lengths at least linear in the source length so we have some physical I don't know some kind of noise which is like one megabytes long or something like that we need a seed lengths of one megabyte or something like that so this is not so good and but on the other hand despite this there are a lot of advantages it's very simple to construct universal hash functions the order of magnitude faster than cryptographic hash functions so they're like very very fast if you know what you're doing and they also have some nice algebraic properties which were recently used for designing public key cryptosystems resilient to leakage and so on but the cons unfortunately the first cons is kind of forbidden the seed lengths is large but also argues that even the entropy loss is pretty large so I'm going to explain both of those disadvantages of the leftover hash lemma in a second this is roughly speaking the two parts of our talk we're going to improve both of those disadvantages of this beautiful invention of leftover hash lemma so let's start with the first one improving the entropy loss like this guy has pretty severe entropy loss so we'll try to kind of improve it and the setting of leftover hash lemma so let's ask two questions the first question we'll ask it is it important because I already told this like such a small entropy loss who cares well the answer is definitely yes especially if you talk to practitioners because many sources of randomness they just do not have this two log one of the absolute say hundred sixty or two hundred bits of extra random randomness lying around like biometric physical sources and even when we control the source like if you want to do a different helman key exchange on the elliptic curve so the smallest possible size we can control the size but we still need the size to be large enough to extract randomness so here we don't want to like unnecessarily increase you know the size of a elliptic curve like 320 bits or something like that so this is like very important even when we control the source in some sense and also the other motivation is in practice we all you know as a theoretician we all love leftover hash lemma but in practice people are just going to use some you know hash function like shave without understanding that it wasn't designed to be randomness extractor we had a paper at crypto 5 about the soundness of this idea and this idea you know if you really make this heuristic random or a class assumption such extractors actually very good I will put a formula a little bit later but just trust me I put it in quotes that cryptography this idealistic non-existing cryptographic hash functions have no entropy loss so we have a steep competition we have a triple loss to log one of epsilon this guy have no entropy loss so as an end result practitioners of course you know even as all of torque has lemma is so beautiful they just say you know we don't care let's just use cryptographic hash functions and you know don't worry about anything everything is fine so our goal at least initial goal would be to reduce is probably reduces to log one of epsilon entropy loss of leftover hash lemma and to make it closer to no entropy loss of heuristic extractors so the second question is a well it's a great goal you want to compete with random oracle good luck but you know you just told us that this is optimal so how can we improve to log one of epsilon if it's already optimal it turns out the proof of optimality of this entropy loss is if you care about all kinds of possible computation and boundary distinguishes do kind of everything in cryptography actually we care intuitive about a restrictive class of distinguishes at least when for the task of key derivation which will be the point of the stock so informally and I'll make it a little bit more precise is the kind of distinguishes that we care about meeting a cryptographic definition is we have some kind of signature scheme or something like that is a distinguisher who plays a game between the attacker and a challenger some well-defined game like this is essential for stability or something like that and the distinguisher output one of the attacker ones again so there is some restrictions there is some kind of structure on this distinguisher so maybe the low bound doesn't apply so to make it less abstract let's look at the case study let's say key derivation for signatures of max so here we know that the signature is secure with ideal keys and what we would hope is that the probability suddenly if I plug instead of ideal key I plug the extracted key the probability doesn't jump up too much from epsilon to epsilon prime so the key inside is that in the ideal model essentially the distinguisher almost never outputs one because if he outputs one the signatures and secure in the ideal model so we shouldn't use it extracted randomness definitely we shouldn't use it even this perfect randomness so in this case a distinguisher for example is very restricted because we know that it almost never outputs one so maybe we can circumvent the slow bound and improve it and indeed this is what our results are so let me first formalize the setting and then briefly state our results so we have this application P which needs a V bit secret key R in the ideal model we just sample a uniform key in real model we'll apply the extractor where the min entropy of the source will be V plus L plus entropy loss and you would like to have good results so we need to assume that the application was epsilon secure in the ideal model and we would like to conclude that the application is epsilon prime secure in the real model and with this kind of notation it's pretty straightforward to translate the left over hash lemma didn't put the parameters but trust me the bound becomes that epsilon prime is that most original security and the security drops by this factor which is turns out to be exactly the statistical distance that we are talking about so our result says that for a wide range of application speed which I'll define in two slides from now the security is improved in particular there is an extra term epsilon under the square root this is kind of an improved bound so the moral is you might extract more if you know why you're extracting which is a special kind of case of a general philosophy in life if you know what you're doing you can get better results so you can have applied it for the setting of left over hash lemma so let's give me a brief comparison between all the bounds and you know take a look at the paper because you know just trust me those of the bounds so this is the bound of the standard left over hash lemma which kind of says that if you want comparable security the entropy loss has to be at least two log one of epsilon which is exactly what I said and this bound unfortunately is also not minimal if you need to extract more than what you have even if you have a super secure tourism minus million secure application you know suddenly all this tourism minus million security is lost you know when you have no entry you know when L is equal to zero so random oracle heuristic it turns out we kind of do this bound but this turns out to be the right bound for the random oracle heuristic which is much better in multiple terms so in particular as I told you it suffices to have even when L equals to zero you already get comparable security and when L goes you know becomes more than zero you essentially reach epsilon and it's also suddenly which is what we expect it is meaningful even when L is lesser equals than zero which is what we expect because suddenly the application doesn't become completely insecure and just just like when you turn the switch for example the first bit of the key is always zero but the rest is truly uniform you kind of know that you will lose it most a factor of two so it's nice that we borrow a little bit from the application even if we extract more than what we have and here this is our result and this is how we so we didn't quite match the heuristic you know random oracle model but we at least made headway they're kind of halfway in between we already achieve comparable security when L is log one of epsilon and just like this bound our bound is meaningful for L lesser equals than zero for example for no entropy loss maybe we don't get fantastic security but at least we get something like square root of epsilon all right so very briefly which applications are all unpredictability applications so whenever the attacker has to forge something or you know output kind of a long string like max signature one with function and so on also prominent in most surprising result which we don't have time to talk about is we actually show that this holds for essentially all important in this ability applications not all but most like chosen plenty chosen cypher to execute encryption scheme something called weak to the random functions unfortunately doesn't work for all for example doesn't work with pseudo random functions trim cypher's and one time pad which in some sense is expected but I want to make a very quick note it is okay you know if you use one of those rad applications but you use it as a building block for a green application for good application it's fine so it's okay to derive AS key even though AS is a PRP which is red but you want to design you know derive it to get a Mac or an encryption scheme this is fine we only care about the final application and a simple observation is if you care about red applications which sometimes you know some people do here is a quick simple trick that you can kind of first extract a key for a weak PRF and compose it related to the random point and because weak PRF is green you get a key which is good for all applications including this but not one-time pad because they use a computational primitive so essentially I can cover all applications the cost is meaningful it's one extra call to AS and the seed becomes a little bit longer because I need to contain the random point all right so let me move to the second part of the talk which is improving the seed length so the approach I'm going to define an approach which I call expands and extract so first let's recall that the best seed length for left over hash lemma is order of security parameter unfortunately left over hash lemma I just told you requires a really big kind of seed so what do we do if you want to have a short seed and we need a big seed apply pseudo random generator so the idea is we'll assume we have a pseudo random generator G we have it has a short seed S but then we'll expand it and apply left over hash lemma on top of it so now we have a very short seed and so this is very friendly to like streaming sources you know the source can come online and it can result in very fast implementations because both stream side percent universal hash functions are blazingly fast so the hope is that the extracted bits of pseudo random because you use you know computational assumption but this is fine but the question is is this idea sound so at first it appears almost as a triviality of course it sounds to use a pseudo random generator it's you know otherwise you break to the generator but the trivial implication is actually not what we want if you think about it it only tells you that the extracted bits of pseudo random even if I give you the long pseudo random seed but I don't want to give you a long pseudo random seed because then I might as well have a long random seed I want to what I want is that the output looks random even if you use a short seed which is used to expand the big seed so it's not so obvious and indeed our first observation is that under a well established assumption from public e cryptography called decision of the helmet assumption there exists a pseudo random generator in fact a very natural pseudo random generator and a universal hash function again relatively natural universal hash function which is there for an extractor such that this thing not only is it false but it is as false as it can get we can distinguish this probability almost one on any source even uniform distribution on any source so therefore unfortunately our brilliant idea is not sound in general okay so this is the first thing but I'm not going to stop here despite this bad news I'm going to have some good news the first good news is we are going to show that it is okay to extract small number of bits more specifically despite this counter example which I didn't show you it is okay to extract the number of bits which is roughly speaking log of this of the security of the pseudo random generator a bit more formal it means that the pseudo random generator should be secure against you know attackers who run on time exponential in the number of out the bits it's not the thing which is kind of subtle but was very surprising remember I told you that we expect to settle for computational security it turns out here we actually still get statistical security so we use a computational assumption of pseudo random generator in a weird part of the proof but we get a regular extractor you know standard extractor this way and you know there are drops of square root of epsilon but that's a little bit of a technicality but still it's somewhat of a surprising result so the corollary is that if you want to extract logarithmic number of bits from the you know like one coin flip you want to decide if you go to a soccer game or to an opera that's okay or if you assume exponentially strong pseudo random generators it's okay to extract even linear number of bits unfortunately if you look at the seed lengths at best it has to be log of the security of pseudo random generator which turns out to be this and if you want this seed lengths there are already very simple relaxations of universal hash functions called almost universal hash functions which already achieved so it's great that we use this big hammer of pseudo random generators but you know it's surprising that the result still works given our counter example but the parameters on the seed lengths are still not the greatest so I'm not going to stop here so the most surprising result which is the last thing that I'm going to tell you will show that the expending the extract approach is secure in this hypothetical world which is called mini-crypt so let me explain this result and also convince you why we should care about this result so the counter example we had it used the you know very simple assumption natural assumption DDH assumption but that's an assumption from public key world and here we extract keys for AES and so on so it's kind of weird why we used a public key assumption for a counter example so the world mini-crypt is one of these beautiful worlds of russian and paliazza where they assume that symmetric e cryptography is possible but public e cryptography is impossible just as a sort of experiment and our theorem says that in this hypothetical world the public encryption doesn't exist but to the random generators exist this approach is always secure and this is true for any number of extracted bits so you don't need like logarithmic number or something but of course just as we expect now we need to sample settle for efficiently sampleable sources which is fine and also for computational security which is fine which is what we were hoping from the beginning and it's similar in the spirit to some other beautiful results of this kind but arguably simpler so let me actually now you know we have this one line theorem I'll expand it to a three line theory which I can prove in one minute so the tile doesn't yell at me so the theorem so what are we trying to prove we try to prove that expanded as an extract approach is secure and mini-crypt so we prove it by contradiction so I assume not I assume there exists an efficiently sampleable source and some pseudo random generator and some distinguisher who can tell it apart right so the approach is insecure we need to get a contradiction the contradiction in the wealth of mini-crypt means we need to build a public encryption which would be a contradiction right so this is a statement and the public encryption is really simple the secret key is a seed for pseudo random generator the public is an output of a pseudo random generator and to encrypt a bit here is what I do if I want to encrypt one I send a random string if I want to encrypt zero I sample my source acts I apply extractor to accent public key and sends output how do I decrypt that's of course a big question and here I assume this hypothetical distinguisher who actually now knows a short seed and now he can precisely distinguish encryptions of zero from encryption of one and semantic security follows from a trivial observation because if you don't know the secret key only know the public key security trivially follows from the security of pseudo random generator alright great so why do we care about this result it's kind of a weird result who cares about mini-crypt so here is a corollary which is an equivalent restatement of the theorem it says that let G be a pseudo random generator and I assume there exists no public key encryption of very restricted form the secret key is a seed s the public key is g of s this encryption should have pseudo random ciphertext and exact security should be you know exactly essentially exactly the security of our PRG then we know that the expand as an extractor approach is secure with this pseudo random generator right and I argue and this is the last thing before conclusions that that practical PRGs like a yes or stream ciphers built from is unlikely to yield such a restrictive and remarkable public encryption first we don't even have a black box construction known of this very restrictive kind and it is possible from what we know that even if public encryptions exist maybe public encryptions are you know in general much less secure than symmetric encryptions and even practice for a say you know the keys are like 2,000 bits for a yes is 128 bits so it's kind of conceivable that forget about this restricted form we cannot even achieve this okay and it would be I think overall if you think about a yes to build such a thing from us would be like really remarkable okay so the moral is that we give formal evidence and expect an extract approach might be secure as practice is actually used stream ciphers so the summary is we show that we can improve large enter billows and seed lengths of LHL for enter billows we go from 2 log 1 of epsilon to log 1 of epsilon for a lot of green applications but using the strictest WPRF we can use any application and the seed lengths essentially the important result that it seems our approach seems to be practical for all pseudo random generators which don't imply a public encryption scheme and the paper is available on internet. Thank you very much, okay so we don't have time for questions because we ran over a little bit so where is the person


Hello everyone this is Amit Dan of amitdan.com you're watching one of my one-minute AI series videos and in this series I would ask Alexa and Google Assistant the same question to see how do they respond so usually I ask the same question more than one time because I've noticed that Google Assistant comes up with different answers usually like you know it has two to three answers for the same questions and then it keeps repeating so I'm going to ask the same question more than two times to see if you know the change the answers and today's question is going to be starting right now so I'll start with Alexa first. Alexa what do you eat? while I appreciate great food and drink my good taste is better reflected in the company I keep thanks for asking me here's another fun thing try asking me to tell you a joke okay so now we'll ask Google Assistant okay what do you eat? I'm a big fan of reading recipes but I'll be honest I haven't figured out how to eat yet okay so we'll ask Alexa again what do you eat? while I appreciate great food and drink my good taste is better reflected in the company I keep okay so you can see that you know Alexa has the same answer for this question so just ask Google Assistant again okay what do you eat? I'm always hungry for knowledge okay so you can see that you know Google Assistant has a different answer this time so we'll try again to see you know whether the Google Assistant keeps repeating from the first answer or there's another answer this time okay Google what do you eat? I'm always hungry for knowledge okay so you can see that you know for this question Google Assistant has two different answers and Alexa has only one answer so that was today's part thank you for watching this video forget about subscribing this channel forget about liking this video there will be more videos coming up so I'll see you shortly thank you


We're here yesterday, but we're not sick, we're all right here in the car, sir. So everyone knows we're a ceasefire right now, we're currently getting the hardest part painted up a little bit, but we're easier to see. The refires, so I need to go back for that brief. Loading make ready that five-round magazine in a prone, supportive position. This is your zero confirmation that the 300-meter target got five rounds, no time limit. Four is good. That's the end of your target recognition phase. Go ahead and get in the prone, supported firing position. Secure one five-round magazine, load and make ready. This will be your zero confirmation shooting at the 300-meter target. Safety's right here. Safe fire. Action releases right there. One ready. You can shoot at anything out there. What do you want to shoot at? Which one? Left and short. The bead, yeah. So, do you look through the sign? See the bead? You see? Now wait till... Bring your head to the shotgun. Press that, leach over. Now you can actually... It's on safe. You press that four, it's on five. Not the trigger, just press the button right there. And then press it, hold it, there you go. I'll be the target. You use the press that button? I'll keep you around, bro. Grab your home one way or another. More to safety. Safety off. Good. Now use the action bar. Try to go from underneath. Yeah, there you go. Perfect. Now get up on the aim. Good job. Lock it back. Now forward. There you go. Lock it back. And again. Again.