Oh, all right. It's kind of nice hearing my voice on a nice, loud sound system. Well, all right. So welcome to the growth crash course. I will be teaching you how to do growth, whether you're an early stage startup or you are an early stage startup, early or later stage startup. Moving on. So I'll go really quickly over where I worked. So Corembase, Angelus, Strava, Haven, Airbnb. Haven was a tiny seven-person startup. And I think when you think about growth, it's really nice to know exactly how large the companies you are working with. So what worked at Haven, when it was a seven-person startup, is very different from what I was working at Airbnb. Working at Coinbase, where I'm working in Web 3 in crypto, is very different from when I worked at Strava. So the nice thing about growth is that once you start learning about growth, you can take those learnings and move it somewhere else and generalize it and kind of adapt it to fit the correct niche. So I'm a product manager. So obviously, I had some goals with this talk. And the goal is basically this. One, I want to make sure that everybody is a pretty solid foundation of how to do growth across multiple channels. And the second one was that I wanted to make sure that I provided concrete examples and insights every single step of the way. I think this is super important because when you talk to people about growth, it's really easy to go very, very high level. And most people aren't able to provide very, very deep insights onto what's worked for them and what doesn't work for them. So hopefully, you get that. So the very first thing that I'm going to tackle, this is really boring, what is growth? So all companies grow, but startups are defined by growth. And I like to use growth with a capital G. And I define it by the process in which you are very intentional about growing. This is the things that you do in order to get more people onto your platform to get them to re-engage, to get them to perform very, very high intent things. So the very first thing I like to actually, so this is the agenda. I'm going to talk about funnel optimization. Then I'm going to go to acquisition, virality, and then activation and engagement. And I like to start with funnel optimization because this is a very fundamental growth concept. And I think everybody here has heard of it. Everybody's almost done it. But it's very applicable to all areas of your product, not just growth. And it's a really nice way in order to kind of dip your feet into growth if you've never done it before. And I like to break it down to three steps. First one, break down your product into discrete steps. This is the user journey. This is how people are going through things. The second one is discovering the inefficiencies. And the third one is to fix them. Step one and step three are super, super easy. It's not difficult in order to break it down to steps. And then it's very easy to fix them outside the engineering problems. But the hard part actually is figuring out where the inefficiencies are. So in order to do that, my favorite place to start working on growth, if you've never done it before, is sign up and onboarding. Because sign up and onboarding is already a natural funnel. There are steps that your user has to go through in order to onboard. And there's a very, very, very clear goal that they need to go through. So on top of that, every user that goes through onboarding is high intent. If they're on onboarding, they want to get to your product. And you want them to get to the end, which means that any change you make is going to have a very, very, very high impact. And the funny thing is is that for as key as this is, almost every company I've ever worked with, sign up and onboarding is very under-optimized. And it kind of makes sense because when you're a smaller company, or sorry, if you're an earlier-stage startup, you're trying to build things as quickly as possible. So you're going to build out your onboarding funnel, and then you're going to move on to building out the actual product.  So because of that, it's usually really complex in order to fix, but it has really, really high return. So with that, I'm going to walk you through how we did it at AngelList. So these slides are really small, but step one, if you remember, is to break everything down into discrete steps. So we break this down into pre-onboarding, onboarding, and post-onboarding. So for pre-onboarding, you hit the home page. Fine, you go, hit, sign up, and then you enter the onboarding process. Then this is a seven-step process in order for you to actually finish. So what do we do next? Try to figure out what the inefficiencies actually are, in which case, the very first thing we do is you look at amplitude. So we have gone ahead and built out the instrumentation in order to see what steps users are going through and where the actual drop-offs are. So from this step, we know that our onboarding funnel had a 30% conversion rate, and it was a pretty big drop in between some steps. Then after that, I'm going to steal Holly Lou's saying where data kind of lights up the room, but it doesn't tell you where to move it. So even if you know where things are bad, you don't exactly know what you need to fix, in which case, then you start to rely on different things. So we used full story in order to look at user sessions. You can see how users are clicking around, what they're doing, and then on top of that, we also did some UXR interviews in order to figure out in order to get actual feedback on how customers were using the product. And what we found out was that at the very top of the page, you can see we have this very, very, very vague bar that just kind of fills up. And because it just fills up, you don't know what steps you're going through, you don't know how much time you need, you don't know how close you are to finishing it. Users are very confused about the title. They're confused about a lot of things just from looking at all the feedback that we had. So this is what we ended up doing. So what we did was we went ahead and made it a little bit more clear about what steps you need to go through. We went ahead and made the steps a little bit more concrete, and we added some nice little messages to say, save and continue, because that means that they are not losing where they are. But the most important thing that we did, and it's not on the slides, I apologize, is that we reduced the number of fields that you actually need to go and input. So I think one of the things that we found out was that we asked for your location four times. So that's like, where do you work? Where do you live? San Francisco, San Francisco, San Francisco. So what we did is we just consolidated it into one single field. And that way, the less field the user has to fill out, the less chance that you introduce friction, and they don't make it through. The last thing that we did was actually very interesting in that you can go ahead. So you need to upload your resume at one point. We took the resume, we moved it to the very end of the funnel, because when you need to upload a resume, that's a very, very, very high amount of friction. You have to go find it on your desktop and upload it. And by moving it to the very end, the interesting thing is that because you go through all these steps, answer all of these questions, is that you're so invested in finishing the onboarding process that you're going to go ahead and upload the resume anyways. Whereas if you had the resume up first, and you're like, ah, this is too much work. I'm not going to do it. So by doing all of that, we increase conversion rate from 30% to 60%. And the more important thing is, is not only did more people convert, they actually started doing more job searches. And this is super important, because not only are users finishing the funnel, they're performing something else that is very, very intentful. All right, now we're going to move on to acquisition, in which case, I will be talking about SEO and paid marketing. Everybody talked a little bit about conversion and optimization. So we're going to move on a little bit from there. So SEO is really nice, because it's free user acquisition. Whereas with paid marketing and performance marketing, you have to go and pay for it, right? And in times of where it's a bear market or you're hitting a recession, SEO gets a little bit more attention, just because it's free. You don't need to pay for it. And for SEO to work as an acquisition strategy, it's a function of both quantity and quality. You want to have a lot of pages, and the pages need to be very, very high quality. By high quality, there's an SEO saying, content is king. The more content you have on the page, the more successful your pages are going to be in the Google search results. And I usually break this down into two different steps, either programmatic or contents. We're going to go with programmatic first. So programmatic basically means let's go and generate as many decent pages as possible. They don't be great pages, but they don't be great pages. They could be kind of OK pages. But you're really good for quantity over quality, because what you're trying to do is you're trying to generate as many pages as possible to bring as many keywords as possible. And this is a very scalable strategy. And it minimizes the amount of risk that you have to invest in SEO. But it's not an option for every single company. So you have to think about whether or not this is going to work for you. So to look at Airbnb, Airbnb has a lot of city pages, right? Places in San Francisco, places to stay in Helsinki, places to stay for every single city in the world. Zillow, lots of house pages, Instacart, a lot of product pages, Zapier, a lot of integration pages. You can see how this would work out. And as an example, I worked with this company called Spot Angels. And what they do is they provide parking information for specific cities. And what we end up doing is we created these pages so they can make for places to park near the Statue of Liberty, places to park near Golden Gate Park. And by creating all these pages, they went in three months from 60 visitors a month to 100,000. And the only thing that's limiting them is the amount of information that they have in order to create more pages. But why don't we take a look at somebody that does not a great job at it? So if you look at Ramp, they have these pages called Travel and Expense Management in whatever industry, right?  This is the first page. T and E, which means nothing to me, for logistics companies. And then the second one is for prop tech companies. Look at these pages. Nothing is really different about them except maybe they use a different image, and the header is a little bit different. And what ends up happening is Google has no idea what these pages are. So if you Google management software for real estate companies, it shows management solution for e-commerce. Google has no idea what these pages are. These are terrible SEO pages. And their programmatic strategy isn't particularly working. But let's move on to content. So content is fun because you've got to be very, very targeted on the keywords that you want to rank for.  But it's really high risk because it doesn't always work. And you're putting a lot of effort into creating very, very high quality content. So if you do want to pursue content, this is the general rule of thumb. It's that you probably want to start with blog posts and landing pages. I usually try to start off with trying to rank for keywords. I get about 250 searches a month just because the competition is going to be lower. And usually lower volume keywords are going to have a much higher user intent. So they will convert more. And then once you get that going, then you can target bigger keywords after 1,000 plus, 2,000 plus, et cetera. But for all of SEO results, you should see them in about one to three months. I think a lot of SEO experts will say, oh, it'll take like six months to a year. They're lying to you or they're not that great at SEO. Moving on, paid marketing. Paid marketing is fun because it's very, very easy to spin up, which also means it's super easy to lose money. So if you're going to do this, you need to be very careful and very thoughtful about your strategy. And this is also used to the first acquisition channel for a lot of different startups. So I would say that if you want to do paid marketing, you should do this when you make money or you are charging. Because paid marketing is entirely about how efficiently you are able to spend. Your customer acquisition cost cannot outweigh the LTV. If it costs more money to acquire a customer than the customer's worth, then you're just going to be bleeding cash. So you need to know these two numbers in order for you to actually do this efficiently. So for small startups that want to try doing this, my biggest piece of advice is try out different channels because you don't know what works depending on where you are. So Google is always a really, really good place to start. It's always fantastic. This is how they make all their money. Facebook has been great but recently not so good. Twitter's never been good, especially with the recent news. Maybe it will be even worse. So I would maybe not do Twitter. And I find influencer marketing to be pretty interesting now. But really, what you're trying to do when you're doing performance marketing, you need to know exactly where your customers are and go and try and buy ads there. So if you are a, let's say, more developer API-focused company, buying ads on Stack Overflow is probably going to be much more efficient than anything you do on Google, Facebook, Twitter, or influencer marketing. And then for the larger companies out there, this is a study that we did at Airbnb. So this is a quote from our head of performance marketing. If you guys don't know what branded searches are, it's searches that have your brand name in it, right? So for Airbnb, Airbnb, San Francisco. Airbnb, Helsinki. People are typing in your branding keyword in order to navigate around your website. And what Airbnb ended up finding out was that it's not super incremental. It's about 15% incremental that you're getting. But it was ridiculously efficient, which means that it was really cheap in order to buy the keywords and then get users onto your website and actually bring in money. So there's always this fight on whether or not branded search conflicts with SEO. And what we found in Airbnb was that it was really fine in order to have both of them coexisting. And my favorite thing to talk about is virality just because it's pretty deep. So virality can go to referrals, word of mouth, social sharing, things like that. Mostly be focusing on referrals for this talk. And it's fun because it's one of the most nuanced channels that you can actually go into because you can grow your user base super, super quickly and they will advocate for you, which is really, really cool. But it needs to be very thoughtfully created because a lot of bad things could happen because it kind of relates back to the customer acquisition costs that I was talking about earlier, where if it costs you more in order to get a referral than your users are generating, then you'll just start blading money. Yeah, I actually just talked about this. I think the only thing I wanna say here is probably the last bullet point, copying other successful companies may not be the best idea because referrals is really weird in that your company's positioning, what your customers are like is gonna have a really, really big difference on what an effective referral strategy is going to be. So I'm gonna talk about Robinhood because Robinhood is probably the best at virality period that I've worked with and I really like their referral program. So the first step for Robinhood, or I guess for anything, is that when you have a referral program, you need to figure out how a user's gonna get there. If a user doesn't know where to go, they're not gonna be able to actually refer anybody. So if you look in the upper right, it says Rewards, that's how you get to their referral program. But the interesting thing about this is that I think like three or four years ago, with Uber, Lyft, and Airbnb to substitute for their referral program, we didn't use Rewards, it just said free $15 and users would click on it in order to discover the actual referral. So anyways, this is one thing that you can optimize is how do users go ahead and actually find out how to get to your referral program. The next step once you get there, this is fun, is this page says, invite friends, pick your free piece of stock. And when you think about referrals, there's three different ways to look at it. It's either selfish, altruistic, or quid pro pro, which is you scratch my back, whatever. But the way that Robin does this, it's very, very selfish because what it says is that you get the free piece of stock, not the other person. And that's an interesting thing because what we found at Airbnb was that the quid pro pro works a lot better saying, oh, you get $5 and your friend gets $5 as well, worked a lot better in terms of messaging as well as the strategy. So for Robinhood, what we can assume here is that the users are pretty selfish and this is fine. Like I'm not, being selfish isn't a bad thing, but this is what they found. So if you go get the link and you share it, the first thing you see that, like let's say I sent to my friend Holly, Holly goes and looks at it and it says, your free stock is waiting for you. Again, they're playing back into the selfish bit. It was like, oh, you need to go get this free stock. And then the other thing is that it says, Brian invited you to join 18 million plus people Robinhood. This is just social proof, sometimes it works, sometimes it doesn't. This is pretty nice. I do want to point out their CTA, which I know is a micro optimization, but it's just fun, right? It says claim your free stock, which is very, very different to a user than get your free stock because claim means that you already own it, you just need to grab it where get it feels like it's a little bit more of an activation energy. So they've definitely optimized the hell out of this page and it's very interesting to see what they've done. So then it says join your way, but first your email, they ask you to input your email and you hit continue. And then when you hit continue, it takes you to just the sign of page. It doesn't do anything. Like if you look up, they ask me my first name, my last name and then my email address again. But by getting your email address here, what they get is now they can go and email you saying, hey, you forgot your referral. Remember to go claim your free stock because now they have your email address.  So I would say that for the most part, Robin Hood's referral strategy is pretty solid. The only thing that I would really worry about is how they go and look at their email address because if you ask for the email address back here, just fill it back in once you hit the sign up page. And then I ran one referral strategy at Haven and Haven was a fintech company. You can go and store a bunch of money in the bank. And we did it so that every single time you refer to a friend, you would get an extra 0.25% of APY up to 4%. If you don't work in fintech, a 4% APY is ridiculous. That's a lot of money. But this didn't work and it didn't work because there was absolutely zero dopamine hit for getting 0.25%. What really works is do not delay the dopamine hit. People want money or a monetary equivalent. If you can give them money, if you can give them $10 for signing up, give them $10. If you can give them $15 in Uber credit, give them $15 in Uber credit. But really the monetary reward is what drives referrals. And if you do not give people money, it's just not going to work. Be thoughtful in your reward system. Again, I mentioned the selfish, altruistic, and quid pro quo. Think about how you want to position yourself in your brand when you do that. And referrals is really, really, really good early on. But I would say as you get bigger and you hit market saturation, you do need to revisit referrals in order to figure out the incrementality of this. And then the last thing I want to talk about is activation and engagement. In specifics, I'm going to focus on both email and push. So for push and email, there's different levels of urgencies based on the different channels. So for push, push is annoying. It's like, oh, this is a problem that you need to go look at immediately. Whereas email is a little bit more delayed, so you can go and take your time with it. So be more selective when you send out push notifications because you can push for a lot of user interactions, but you can also get them to unsubscribe if they find it too annoying. And the other thing that you should definitely be thinking about is you should be thinking of everything in terms of user life cycles, right? So everybody knows if you're going to send an email, send it to specific messaging to people that are 18 to 25 and 26 to 32. But it's much less about thinking about that than more like, where are your users in the life cycle of your product? A user that signed up a week ago is expecting very, very different things than users that signed up six months ago. So if you haven't defined user life cycles, I would 100% do it because not only is it helpful for other areas of growth, it's going to be very helpful as you go figure out this push and email strategy as well.  I don't think, if a user unsubscribes, I don't think there is a way to get them to read, subscribe back to an email or push on a vacation. People just, people don't like emails.  So be very, very careful in how you're doing this and if you're annoying the hell out of your users because you don't want to do that.  Be very careful how you're storing your user data and how you're sending out emails and make sure you don't break into the laws because it will get very, very, very expensive. So the biggest tip that I have that I got from my friend was that you need to send users the right content at the right time. And this is really important, especially when you think about low and 10 emails. So low and 10 emails are emails where you send users an email and hope they do something when they didn't ask for it. And this didn't work at Airbnb because like what a low and 10 email looks like, it says take the trip less traveled and they gave me a bunch of suggestions. One, I didn't ask for a trip. I'm not planning for a trip and me going for a trip is not related to Airbnb at all because traveling is rare. Traveling doesn't happen all the time. And even if we show nice listings, the user quality is gonna be super low and the conversion is gonna be super low. So what you end up doing is you're just spamming your users with like, hey, look, check out this cool thing that we have and they're gonna be like, well, I don't really care about this and they're gonna leave. They don't travel because they see nice listings. They travel because they want to. So if you look at this email, it's just not a great email to be getting. Instead, what I like to focus my time on is on event-based emails. This is where you see the most success because this is where users have engaged and shown intent. So like if somebody is on your platform and they're interacting and they're doing something, like send them emails based on that information. So I think like the most recent one I got that was useful is this eBay one because I was looking at climbing shoes and I forgot about it and just left it alone and then I went and continued to do something else. But eBay knows that I looked at this climbing shoe. They know that I'm interested in this on some sort of level and now that there's only one left, they send me an email saying, hey, come back to it. Why don't you go look at this shoe again? And like this is actually helpful because I have shown interest in this. I want to know when this shoe is going to be available and now they've told me that, oh, there's only one left. So these event-based emails are really, really critical in order to engage with the users because you're providing a lot more information to them than you would with like these really terrible low-income emails. Nobody cares about this. People care much more about this. So lessons, push notifications I've learned should be pretty consistent sends. Like if you were able to send consistent, valuable push notifications, then people will find value out of it and they won't unsubscribe from the performance-intentful action. The best time to engage with the users is right after they sign up because they've shown a lot of intent. They know exactly what they want from your product. They've done something, now you can start walking them through the process of what you need to do in order to get the most value out of your product. Taiwan Platform matters for users whenever you engage with them, right? This goes back to the user life-cycle stuff that I was talking about and you should send things that matter. And the next slide is actually my favorite slide. I interviewed my friend that worked, was a PM at Airbnb on emails. So the first tip she gave me, don't send fluff garbage, which is pretty obvious. But then everybody likes to go off my subject lines. She's like, subject lines don't need to be short and don't waste a ton of your time on this, test like three.  So if the most relevant email you can get, you're sending is Friday at 5 p.m., send that email. So in conclusion, grocery lay done as foundation, it can always be optimized later. And this is a really important thing to be thinking about is that you can go and spin up your SEO thing right now and let it sit around for a couple of weeks or a couple of months or even a year or two and that's fine.  If you're in an early stage startup and you spend too much time, you know, like optimizing running A, B tests, you're gonna get lost in the weeds. And I've seen tons of companies get really lost because they wanna go and test everything. As a small startup, the point of your product, what you wanna be doing is you wanna launch things as quickly as possible, right?  You need to have a checkout button. So if you're a small company, don't get too lost in the optimization, running A, B tests, launch things and launch them quickly. And yeah, the last thing that I wanna go over is my favorite thing about growth is that you should ship fast and learn quickly. You should always be iterating. And if you ever fail, that's fine because failure is how you learn. The biggest problem I find with growth teams is once people are scared to fail, that's when your company starts to stagnate. So as long as you go and are always trying to learn from everything that you launch and every experiment that you run, you're in pretty good shape. And that's it. Thank you for your time. Hopefully that was pretty helpful.


So, today I am going to discuss intracesional variation and intracesional oscillations. Now, what is intracesional variation? Intracesional variation is variation on the super synoptic time scales. Synoptic time scales are up to 5 days or so, typical of synoptic scale systems. Intracesional variation involves variation over a larger scale than synoptic, but not as larger seasonal or monthly. Now, we have seen that the fluctuations between the active spells and weak spells or breaks is an important feature of intracesional variation of the monsoon. The other important feature of the intracesional variation of the monsoon is northward propagations of the cloud band or rain belt from the equatorial region on to the Indian region. So, this is the first feature. These are the active weak spells which we have of course, discussed in great depth and this is the rainfall over central India you remember and this is the long break that occurred in 72. But notice that this was a in fact a drought year, but even in a good monsoon year we do have fluctuations between active and weak spells. So, active and weak spells are features which are found in every year every monsoon season, but outbreaks of this kind do not occur in every monsoon season. We have already looked at that the other feature is northward propagations of the band starting from the equatorial region and moving northward. So, this as you remember is from satellite MSU at 90 degrees for one specific year 1986. So, this is the other feature and you also see here active and weak spells here. This is a weak spell and this is an active spell and these are the northward propagations. So, these are the two major features on the intracesional scale that we see. Now, northward propagations we have seen are a basic feature of the variation of cloud bands or rain belts in every summer monsoon season irrespective of whether it is a good monsoon season or a poor monsoon season. So, you have 3 years 73, 74, 75, 74 was a drought, 75 was a good monsoon year and irrespective of whether it is a drought or not these northward propagations always occur this is of course at 90 degrees. We also see if we look at just 75 and look across the Indian longitudes we see that these northward propagations are coherent across the longitudes. Now, we have also seen this was during the season, but we have also seen that seasonal transitions that is spring to summer as well as summer to autumn are characterized by northward propagations this is something we have seen. So, this is the seasonal transition from spring to summer and that is characterized by northward transition propagations and you can see that the post monsoon season or the seasonal transition from the summer monsoon to the fall are also characterized by northward propagation. These propagations occur at intervals of 2 to 6 weeks except in the case of transition seasons when they can occur in rapid succession this is from the original paper by Sikha and Gadgil and what you can see is that by and large the period between 2 propagations is of the order of 40 days or so this is one propagation this is the other one. But occasionally you will see that they occur in quick succession like this one and here this is during the onset phase say in 75 you saw one propagation it went there got finished and another got generated in quick succession. So, often in transition phases you see these propagations occurring in quick succession like here and here, but otherwise typically the period between them is of the order of about 40 days. Now this implies you see that this band is moving northward from the equatorial Indian ocean across the Indian peninsula. So, if the band is moving this means that there will be a correlation between the south and north and that is seen here that if we look at correlation with lag. So, black arrows correspond to one week lag then a band that is here you will see this is correlated with this with a one week lag. Similarly, this rainfall over here is correlated with this rainfall over here is correlated with this rainfall here correlated with this rainfall here correlated with this which is just saying that these are all manifestations of the northward movement of the band. Even with a two week lag you see of course rainfall here is correlated with this here also is correlated with this and here all are correlated with this because in two weeks it will have moved that much more. So, typical length of arrows will be much more. So, actually these northward propagation that we see are manifested as lag correlations in rain belts or in rainfall over the subdivisions and so it will be useful to if we can predict northward propagation because we would then be able to predict the rainfall. Now, we have seen that if for some reason the northward propagation are suppressed in the onset phase it leads to a hiatus in the progress of the monsoon. If the mechanisms leading to these propagation is understood and models can simulate or predict them they could be the basis for predictions of important phases of the monsoon such as the onset phase and revival from bricks. So, we see not only during the inter-seasonal variation between active and brick do the propagation play a role particularly in revival from long bricks, but they are also important in the transition phases which we have seen and variability in the northward propagation if suppose it suppressed in that transition phase we will see examples of this. In fact, then we have then we have actually what is called a hiatus in the phase can you just stop edit edit this for a minute I will switch off my mobile and come we will start again we have noted before that two distinct approaches have been adopted in the study of inter-seasonal variation in the first the more traditional approach the focus is on special events such as breaks in the monsoon or special features of some systems such as the propagation of the TCZ. The major features of these events are studied with analysis of data and attempts are made at simulation of these events by models in order to understand the underlying mechanism. So, the focus in the first approach is on these events in the second approach which is the one adopted in most of the recent studies the variation is viewed as a superposition of waves or modes or special patterns which are called inter-seasonal oscillations. Structure and evolution of these modes is investigated in detail for further understanding and generating predictions. So, this is an alternative approach that people adopt. So, we have so far in our description of the event of active week cycles or of northward propagation use the traditional approach. Now, let us look at the second approach namely of inter-seasonal oscillations. So, what are the observations the important time scales of variation of the rainfall over the Indian region during the summer monsoon have been identified in the past 3 decades as the 10 to 20 day or quasi bi-weekly scale and 30 to 50 day scales in addition to the synoptic scale. Peaks corresponding to these scales are clearly seen in the spectra of rainfall and wind and the 30 to 50 day mode is seen also. So, you see here this is spectrum this is rainfall over the central Indian region this is from a paper by Goswami and what you see here is this is from 75 to 85 and 15 to 25 and this is a peak corresponding to 15 days this is a peak corresponding to 40 days and all these correspond to the synoptic scale peaks corresponding to synoptic scale this is as far as rainfall is concerned. Now, if you look at the zonal wind over Arabian sea then the picture is somewhat different if you look at the Bay of Bengal zonal wind it is different and the wind anomaly meridional wind anomaly also the modes are somewhat different, but the typical modes that are observed in rainfall are seen in this spectrum. Now, this 30 to 50 day mode which we first encountered as a mode in which northward propagations occur of the TCG from the equatorial Indian Ocean to the monsoon zone. In fact, happens to be a mode which is seen over a large part of the tropics and is called the madden Julian oscillation. So, this is a very important feature of tropical circulation and convection the madden Julian oscillation or MJO this is an oscillation on the scale of 30 to 50 days. Now, what you saw were spectra here from Goswami's paper. Now, what you see here is our spectra derived by Webster and this is the eastern equatorial Indian Ocean for which you see the variance you see a very clear peak in the around say 30 days or so very clear peak in the spectrum and for the Bay of Bengal you have a peak around 32 days or so, but also another around 8 or 10 days. In fact, there is a lot of variance all the way up to quasi biviquely period over the Bay of Bengal. So, these are spectra based on OLR. Actually for different regions Bay of Bengal eastern Indian Ocean or equatorial Indian Ocean, but the eastern part then this is the western Ghat area, this is the central Indian and this is the Gangetic plain. So, and this is Cambodia. So, for these regions Webster, Hoyas and Webster have actually done frequency analysis and wavelet analysis and what you see here is summer average wavelet spectrum for GPCP rainfall for different regions and the first is EIO which you had seen earlier the OLR spectrum. This is very very similar you see a very clear mode around 32 days or so most of the energy is in that mode. Now, if we look at Bay of Bengal and the region is shown here then you see again a very similar kind of thing to what we saw earlier in the spectrum of winds that there is a peak here around 32 and a very broad peak going all the way from 4 days to about 10, 12 days or so. This is the characteristic spectra of this region, but you notice that the spectra do vary from place to place. So, although it may be useful to look at modes, the way these modes are superposed in different regions is definitely different. So, interpretation of these modes and the role they play at different places has to be investigated properly before we can see what the implications are for fields like rainfall. Now, this is central India and this is very interesting this is very different for example, from EIO where here the maximum variance seems to be in the synoptic scale and then there is a steady decline with not much variance in the 30 to 50 day mode. Same story for the western Ghat region actually here it is much flatter than central India and you have variance in all frequencies up to about 2 months or so. Now, Cambodia again is somewhat similar to central India in that you get a decreasing variance with increasing period very similar to western Ghat and the genetic plane is more similar to western Ghat whereas, central India and Cambodia are similar and neither of them have too much variance in the 30 to 50 day mode. This is the genetic plane and you see most of the variance is flat up to about 2 weeks and then decreases rapidly here. So, this is to be borne in mind when we look at the different modes. Now, let me talk a little bit about Madden Julian Oscillation because like Enso on the inter-annual scale Madden Julian Oscillation is a very important phenomena on the inter-seasonal scale in the tropics. So, Madden Julian Oscillation MJO named after its discoverers is the largest element of the inter-seasonal super synoptic variability in the tropical atmosphere. It is a large scale coupling between atmospheric circulation and tropical deep circulation rather than being a standing pattern like Enso it is a travelling pattern and propagating eastward approximately at 4 to 8 meters per second through the atmosphere above the warm parts of the Indian and Pacific oceans. This overall circulation pattern manifests itself in many ways most clearly as anomalous rainfall. Again the comparison with Enso is instructive because local effects on Peruvian fisheries were discovered long before the global structure of the pattern was recognized in Enso whereas, with Madden Julian Oscillation it is the global pattern that has been first discovered. So, the MJO is characterized by an eastward progression of large regions of both enhanced and suppressed convection and maybe it will be good to look at this and then we go back and see what is happening. See this is going this is the way a cycle of a Madden Julian Oscillation evolves. Now this is this is 60 20 degrees is this is 60 degrees is. So, Indian longitudes are around here and it goes right this is the date line and it goes all the way around the globe till 10 degrees here 10 degrees east. So, that is on the coast of Africa. So, this is the equatorial region MJO is an Oscillation of convection over the equatorial region primarily and this is a typical pattern for the other hemispheric winter. So, you have convection beginning somewhere near the Indian ocean western Indian ocean this is the convection here. Now you see convergence into the convection divergence are loft. So, this is one cell this is the convection cell the air that is ascending in the convection is descending here. So, you have wet here and dry here. Now this system moves eastward with time. So, the next will be here it has got intensified then it is here is now over Indonesian region now it is over west Pacific and now it has come close to the date line and just east of the date line is the last time it is seen as a active convection after that it disappears. So, it is a phenomena which involves eastward propagation of convection and the associated circulation from about the western equatorial Indian ocean to just past the date line about 140 degrees west. So, the MJO is characterized by an eastward progression of large regions of both enhanced and suppressed tropical rainfall observed mainly over the Indian ocean and the Pacific ocean. The anomalous rainfall is usually first evident over the western Indian ocean and remains evident as it propagates over the very warm waters of the western and central tropical Pacific. This pattern of tropical rainfall then generally becomes nondescript as it moves over the cooler ocean waters of the eastern Pacific which is what we have seen except perhaps for region of warmer water west of the west coast of central America. But occasionally reappears at low amplitude over the tropical Atlantic and higher amplitude over the Indian ocean. The wet phase of the enhanced convection and precipitation is followed by a dry phase. Each cycle lasts approximately 30 to 60 days because of this pattern MJO is also known as the 30 to 60 day oscillation or intracisional 30 to 60 day intracisional oscillation. So, this picture is actually from the original paper by Madan and Julian who discovered this. Now, these are the typical variables used in MJO analysis. You have this cloud system here associated with rainfall and you have cyclonic vorticity here this is the U 850 then you have convergence here divergence aloft and this will imply that low OLR here because it is deep clouds and high OLR and clear skies here where there is descending motion. So, here you have upper level convergence and divergence at the lower level and the opposite holds here. So, this is then the schematic picture here you have cyclonic vorticity at the lower level over the region where it is raining anti cyclonic aloft. So, convergence here divergence aloft and the opposite holds over the region to the east where you have dry conditions and so you have convergence at upper levels and divergence at lower levels with no rain no clouds. So, this is the schematic picture that you have. So, it is an intracisional time scale phenomena 40 to 60 days. It is a planetary scale as you have seen it goes all the way from about 50 degrees east to 140 degrees west almost half way around the globe. Convection has multi scale structure this is important and it is it has a tendency to be equatorially trapped. However, we have to remember that although the eastward propagation that you I just showed is a characteristic of northern hemispheric winter. In northern hemispheric summer we have seen that there is northward propagation over the Indian longitudes on the same time scale. So, this MJO can be thought of as having a north eastward propagation and there is significant interannual variability as well. So, let us now look at what the winter MJO pattern looks like and this is the rain forcing and what you have here these are composites composite rainfall maps derived from merge satellite in situ and in situ measurements separated by 10 days. So, this corresponds to minus 20 days minus 10 days 0 day 10 day and 20 day and what you see here is these are negative anomalies of rainfall these are positive anomalies of rainfall. So, you can see here that this is a positive anomaly of rainfall that has appeared now it has moved east from here to here and intensified. Now it moves further east here and is moving east here and now it here it has moved all the way to the west specific. So, you see a very clear eastward propagation here if you want to look at dry conditions also dry anomalies also you will see they also move eastward from here up to here and another has formed here now. So, what you see here is a clear eastward propagation and see also that this is more or less restricted to the tropical eastern hemisphere. So, you see the action is between around 50 east or so to about 140 east from 140 east the other half of the thing tropical atmosphere is not affected by MGO and this is an MGO life cycle composite from GPCP again and you will see very similar things this is rainfall and you see the rain band propagating very nicely and this is from November to April this are the different phases of MGO as they say phase 1, 2, 3, 4, 5, 6 and so on. Now I must mention that madden Julian oscillation has been extensively studied over the last two decades. So, what I will do in this lecture is give you only some introduction and it will not be possible to go into great detail. In fact, an entire course can be given now on inter seasonal variation and madden Julian oscillation because there is that much literature that has been published in the last 10 and 20 10 or 20 years ok. Now, this is the summer one and let us start again it is composites of rainfall let us start with here remember yellow is positive rainfall anomaly and blue is negative. So, here a rain band has appeared and everywhere here there is deficit. Now the rain band moves northward, but also eastward you can see it has moved north, but also eastward and again it has moved north and intensified eastward and again further north and intensified eastward and now further north even further north, but it is very weak here and has become strong here this is what they consider as a north eastward propagation, but it is somewhat of a figment of the imagination I believe because if you look at actual propagation you do not see too much of north eastward movement it is much more a clean northward movement and eastward movement in the equatorial region ok. The MJO undergoes strong seasonal cycle in both strength and latitudinal locations its primary peak season is austral summer or fall when the strongest MJO signals are immediately south of the equator the second peak season is boreal summer when its strongest signals are north of the equator. The synaptic scale disturbances move westward while the large scale convection in which they are embedded move eastward. Now this is the thing that I talked about earlier that there is an interaction between different scales of convection and it is very interesting that in the larger scale convection synaptic scale convection is embedded and what we saw earlier was an organized convection on a much larger scale which moves eastward, but the individual synaptic scale disturbances actually move westward and we can see that and this is from Zhang's paper this is actually zonal wind at 850 HPA and this is the rainfall precipitation and this is all average from 10 south to 10 north and what you can see here is very clear eastward propagations here you can see here clear eastward propagation and here as well. So, this is clear eastward propagation which characterizes the MJO this is the eastward propagation, but look at precipitation also you see very clear eastward propagation exactly at the same time remember this is time and this is latitude longitude. So, an arrow like this implies eastward propagation however an arrow which is at right angles to this would imply westward propagation and that is what you see here see these are individual systems which are moving to the west which you can see here and here which are literally at a very large angle almost right angle to the eastward propagating systems and this is the westward propagation of the synaptic scale systems. So, life is a little bit complicated because of this multi scale problem, but the large scale convection certainly moves eastward in MJO. Now, over the Indian region 10 to 20 day mode is associated with westward propagation and 30 to 50 day mode with northward propagation. We have seen that the onset phase comprises of northward propagation of the TCG from the equatorial Indian Ocean on to the monsoon zone and westward propagation of systems from the bay across the monsoon zone this is what we have seen very clearly in our lectures on the onset phase. So, the transition also involve both the modes in a way both northward and westward propagation. We have also seen that revival from breaks occurs either by westward propagation of the systems from the bay which can often be attributed to westward propagation of systems from the west specific or by northward propagation of the equatorial ITC. Thus both modes are important components of the monsoon and its variability and this has to be borne in mind because people have got carried away with MJO and the 30 to 50 day mode which involves northward propagation and not paid as much attention to the westward propagating quasi by weakly mode which plays an equally important role in the monsoon. Now, this is just to illustrate that actually the modes have considerable inter annual variation and you see that here 79 has very large amplitude fluctuations 88 much smaller amplitude 96 higher frequency than 88 and so on and so forth and that is a characteristic of the tropic the eastern hemisphere wherever MJO occurs. So, much about the intracesional oscillations and the intracesional variation now. So, we have some idea of the nature of these variation and oscillations question is what are the mechanisms that lead to that. So, the major features of the mechanisms are over the Indian region are fluctuations between active spells and weak spells or breaks and northward propagation of the TCG at intervals of 2 to 6 weeks. An in depth discussion of these mechanisms believed to be responsible for these features requires a detailed exposition of the model studies which is beyond the scope of these lectures because in these lectures I have really not referred to models at all. So, here I shall only elucidate the processes believed to be important, but at the end references to the large number of reviews are also provided. So, that people who are interested in going in depth in the mechanisms can refer to those papers. Now, occurrence of active week cycles is found to be a ubiquitous feature of the TCG although the time scales vary in different regions that is to say over all the monsoonal regions of the world where TCG occurs it fluctuates. But the periods of active spells and weak spells vary from place to place. For example, active spells tend to be of shorter duration over the African region then the Indian monsoon zone during the northern hemispheric summer. And we will now see examples of this and what you see is for different years again the lower regions are plotted. So, this is 2009, 2010, 2011 and 12 and this is all in the African region 10 east for JJA. And what you see is that typically only for a few days things are active and it is a highly fluctuating phenomena with a high frequency of fluctuation compared to the Indian region. This is the African case and this is what we had in our paper where we have drawn actually the bands cloud bands. And what you see here is again there is a considerable variation from year to year. See in 76 you got much longer active spells over the African region then in 75 and you got very big dry spells in 83 here for example. So, there is considerable inter annual variation but the typical scales time scales of active and weak spells vary a great deal from region to region. Now, if we go to Africa for southern Africa for December, January, February that is northern winter again you have fluctuations between active spells and weak spells or breaks but these happen to have be characterized by much longer time scales than the one over west Africa at 10 east. Now, this is the variation over 100 west and this is over the Pacific region and over South American region and again you see that the time scales are somewhat different but the fact that you will never have a cloud band persisting through a season is a characteristic of all regions. Now, this is 90 degrees east and December, January, February. So, this is the Indian ocean and again you see a great deal of variation from year to year and fluctuations are always there. This is 70 west so this is South America. South America you seem to have much more much longer active periods and less of a fluctuation compared to say Africa and this is again the same thing that you get you tend to get longer active periods but there are occasions in which you get large breaks also. So, no matter where you go every monsoonal region there are fluctuations in the TCG and therefore, active spells and weak spells and they are characterized by different time scales. Now, over the Indian longitudes there are two favorable locations for TCG, one over the Indian monsoon zone and the other over the warm waters of the equatorial Indian ocean in our summer. So, northward propagation of the TCG from the equatorial Indian ocean to Indian monsoon zone occur at 2 to 6 weeks with a dominant time scale of 40 days. Now, we looked at satellite data and we showed that bimodality that is existence of two favorable zones is a special feature of the Asian summer and winter monsoon regimes. So, this feature that we seen over the Indian region is not seen everywhere it is a special feature of Asian summer and winter monsoon regime while poleward propagations of the TCG are occasionally seen over other regions. They appear to be a basic feature of the TCG only over the Asian summer monsoon zone. Thus we expect the mechanisms leading to active week cycles to be related to the intrinsic features or dynamics of the TCG such as cloud radiation feedbacks. Why is that because they occur over every zone every region over which the TCG occurs we see fluctuation. So, they must be related to some intrinsic feature of dynamics of the TCG such as cloud radiation feedback. On the other hand special features of the Asian monsoon zone are likely to be important for poleward propagations of the TCG. So, let us look at what can lead to fluctuations of the TCG. We have seen the deep clouds over their existence to the presence of vertical moist instability which we call CAPE. This is the available potential energy convective available potential energy CAPE which is a measure of that instability. Initially the presence of clouds will lead to intensification of organized convection leading to an active phase. However, CAPE gets depleted in active phases because of the mid tropospheric heating by the clouds and surface cooling because of rainfall and less radiation reaching the surface. So, what is happening is that the instability which is in the atmosphere is slowly getting eaten up by convection because mid tropospheric heating occurs. So, and also cooling of the surface occurs thus there is a negative feedback between organized convection and vertical stability which leads to the weakening and eventual demise of the system. Once the system disappears again CAPE builds up which is the recharge and convection can be triggered if the dynamical conditions are favorable. Now fluctuations in the intensity of the TCG have been attributed to such feedbacks of the dynamical thermo dynamical system characterizing the TCG. In the paper by Sikha and Gargil in 1980 they talked about the fluctuations of the TCG and they suggest the following that in a simplified form the action of clouds may be represented as follows. Initially when the ITCG is getting established near the radiative source we expect a positive feedback from clouds because the latent heat released in the clouds leads to the intensification of the ITCG by Sikha. So, initially we will see that clouds release heat and we have already looked at a conditional instability of the second kind. The release of heat by clouds leads to intensification of the cyclonic vorticity and which in turn leads to intensification of the convergence and more clouds. So, initially there is a positive feedback between the clouds and the cloud system. However, over long time scales the negative impact of the increased albedo dominates the positive effects of increased absorption of long wave radiation and a negative anomaly of radiative heat flux will appear. In fact, Monin has a very nice description of how a TCG would oscillate over the ocean. He says the surface of the ocean in our case the moist continent will cool and begin to cool the atmosphere. Downward motions will develop in the atmosphere and the clouds will begin to disappear. With a decreased amount of clouds the ocean again land in our case will undergo an increased warming. The conditions with which we began will be established and the whole process will be repeated. Such a process could lead to fluctuations between active and weak spells in the monsoon. So, there are feedbacks which are negative feedbacks which can lead to these kind of fluctuations. Now, Krishnamurti and Balmay attribute the prominent 10 to 15 day periodicity they found in the fluctuations of all the components of the monsoon system they studied including rainfall to the mid tropospheric warming associated with clouds. Thus it appears that the fluctuations of the TCG and hence the monsoon could arise from feedbacks involving clouds. The first observational experiment over the Indian seas under the Indian climate research program was Bob Max conducted during July August 1999. This was under the leadership of Bhatt. During Bob Max high resolution measurements of the vertical profiles of temperature and humidity from which reasonable estimates of Cape and vertical moist stability could be obtained were made over the North Bay. The composite profiles of temperature and specific humidity for active and weak phases of convection over the Bay from these observations are consistent with the theory that vertical moist instability builds up in the weak phases and gets depleted in the active phases. So, you have here the profile of the potential temperature you see here that this is a convective phase and this is an average and this is a clear phase. So, what is happening is that once the clouds start building up you see here warming this is the warming of the mid troposphere that Krishnamurti and Balmaine others talked about and there is also cooling of the surface. So, what happens is that the stability instability decreases. A surprising observation was the short time required for recovery from low values characterizing the active spins. In fact, this was totally unexpected it was found that Cape decreased by 2 to 3 kilowatt per kilowatt joule per kg per gram during convective episodes, but recovered in one or two days. The quick recovery of Cape suggests that the thermodynamic conditions become favorable for convection within two days of its cessation. This is for the Bay of Bengal and may actually explain why is it that the Bay of Bengal is one of the most fertile oceans as far as genesis of cloud systems is concerned they occur at where genesis occurs at very high frequency over the Bay and this quick recovery of Cape may have something to do with it. Now, so this is the feedback on the vertical moist instability. Now, similar theories have been proposed for the MGO which again is an oscillation which involves convective dynamic feedbacks and they consider that three phases occur. One is the destabilization phase in which the instability of the atmosphere builds up through radiative cooling of the upper atmosphere, surface warming and development of a shallow boundary layer cumulus clouds. So, this corresponds to what we call the weak phase. Then convective phase occurs with heavy precipitation cooling of the surface and moistening of the surface of the upper troposphere in which the instability decreases rapidly and the restoring phase in which strong winds keep the surface cool and high clouds associated with high humidity stabilize the atmosphere. In fact, so you have three phases of this and feedback similar to what I discussed earlier have been proposed and there was another observational experiment called jasmine and in that they reported that the feedbacks that could that operated in the intracisional oscillation in fact involved these three phases destabilization, convection and the restoring phase. Now, analysis of observations by Kembal, Cook and Weir has shown that that after a passage of a Madden-Julian oscillation mid level moist static energy builds up with a drying of the mid troposphere and this energy this is the charging and this energy is consumed during the passage of a Madden-Julian oscillation this is the discharge. So, you can see that throughout very similar kind of things have been proposed and details of this can be found in many studies, but whether these feedbacks help us to actually predict the fluctuations as is yet to be determined northward propagation. So, we think we know something about how the fluctuations of the tropical convergence on occur northward propagation. Northward propagation of cloud bands during April to October emanate from the equatorial Indian Ocean culminate in the monsoon zone or the head bay and are characterized with speeds of about 1 degree per day. At the culmination of each propagation the TCG persists over the monsoon zone for several days and this is something we have seen that we have this is the culmination for example, here these are quick propagation then this is the culmination at the end of the onset phase and you can see that the TCG just fluctuates in the same place with of course, some fluctuations in intensity, but it is around the same region here similarly here at the end of the northward propagation it just occurs here and similarly here and so on and so forth. So, at the culmination of each propagation the TCG persists over the monsoon zone for several days thus there is an active phase of the monsoon at the end of the each poleward propagation in which the TCG fluctuates around the monsoon zone of 20 degrees north or so you can see it fluctuates around 20 degrees north or so. Now, this phenomena was explained by a class of zonally symmetric models which are very very simple models with one continental cap north of 18 degrees. So, zonally symmetric means it is a sphere in which there is no variation with longitude right. The atmosphere does not vary with longitude at all it varies only with latitude and the continent is a cap north of 18 degrees north. Now, but these models actually was a hierarchy with increasing complexity and they have yielded increasingly realistic simulations of the intracisional variation of the TCG over the Indian longitudes during the summer monsoon. See the first model to similar poleward propagations of the TCG was a simple two-level zonally symmetric model developed by Webster and Chow and what it did is the following. Now, what we are seeing here is only the axis of the rain belts and this is the observation for 1975 at 90 degrees east and this is what the model showed remember that the model has a continent up to 18 degrees beyond 18 degrees north. So, from the northern pole till 18 degrees is a continental cap and this is the ocean and what you can see is it generates lot of northward propagations. In fact far too frequently secondly while remember now southern tip of India is around 8 north. So, the observed propagations actually a originate from the equatorial Indian ocean not from land, but in the model the oil originated the land ocean boundary and occur at very frequent intervals. So, the simulated propagations were restricted to the region over the continent whereas, the observed propagations are across the equatorial ocean and the continent and were far more frequent than observed. So, this was a problem with this model and then we started working on this and what Srinivasan realized is that one has to incorporate the thermal inertia of land and we should also have a realistic SST distribution. Once these two were incorporated then we got somewhat more realistic propagations. Now, this again is the observed one this is the old thing with the simple model when you incorporate thermal inertia of land then you see that the propagations have become less frequent much less frequent than these and you are also with realistic SST you are also getting genesis over the ocean which also means that propagations are not restricted to land anymore they occur over both ocean and land. So, the next complexity in the model told us that now in all these simulations at the culmination of each propagation the TCG over the continent disappeared you can see it just moves north and disappears that is true with all these, but if you look at observations actually there is this active spell here which occurs at the culmination of northward propagation which is not simulated in any of those. Thus the active phase of the monsoon at the end of each poleward propagation in which the TCG fluctuates over the monsoon zone around 20 north was not simulated. A realistic simulation of all important features was obtained by the model developed by Nanjunya Airtel which was more complicated and what you see here is in fact you see very clearly two favorable zones and you see very nice propagation and most important is at the end of the propagation there is a very clear active spell which was absent in all the earlier models. So, now Webster had suggested that hydrological feedbacks leading to cooling of the land surface beneath the TCG that is to a perturbation in the sensible heat flux played an important role in poleward propagation. Obviously, the mechanism based on hydrological feedbacks cannot explain propagation over the ocean. Also, we did an experiment in which we switched off the sensible heat flux totally and still the propagations occurred. So, that suggested that Webster had not got the story right. The mechanism of propagation over land and ocean was identified by Gargill and Srinivas and Srinivas and Airtel and they showed that northward propagations occurred because of the north south differential in total heating arising from the north south gradient in the convective stability and moisture availability which led to maximum convective heating being northward of the maximum. So, what happens is this is W vertical velocity and vertical velocity is maximum here but the convective heating associated with the system is actually maximum slightly to the north of where it is W is maximum where the rain is. Now, if that happens then there is more heating to the north and lower pressure will occur to the north and the rain system will move to the north. So, this is the mechanism of poleward propagations that this mechanism was responsible for the propagations in the model was shown with an experiment in which the convective heating in the model was taken to be independent of the north south gradient in the convective stability and moisture availability. So, what we do is to test whether indeed it is this gradient of instability that is responsible we change the model to say that this kind of gradient has no longer effects the convection in the model and in that experiment what you saw was that there were no propagations at all. So, another this is the advantage of working with models that one can propose theories and they are they can be verified with model experiments. Now, same mechanism was shown to operate for propagations that is simulated in the model of Nanjindai et al. Simulation of the active phase with the TCG persisting over the continent and the culmination of the poleward propagation was found to be associated with anchoring of the TCG in the surface trough which is very interesting because this is exactly what is observed. Now, there are alternative theories like Lau and Lau who studied vorticity disturbances in the Bay of Bengal, Philippine Sea and South China Sea and they tried to understand north west movement in terms of rotation of the horizontal vorticity vector by the equator and gradient of vertical velocity and I do not want to get into detail of this people who are interested can look at the paper, but they basically say that about the center of convection if the upward velocity is higher southward then it results in tilting lifting of the vorticity vector which results in vertical component of the vorticity in north of the center of convection and this results in low level convergence to the north. So, this is another mechanism by which you could get convergence to the north of the rain belt where the rain belt has to move. In fact, different hypothesis for mechanisms responsible for meridional propagation have been reviewed in these two papers. Now, there are also studies on scale selection and prediction of inter-seasonal oscillation. Again, this is something that we are not equipped to go into in this lecture series because we have not discussed in detail about Kelvin waves and Rossby waves and so on, but there are major review papers for people who are interested. I should also mention that Krishnamurti et al have shown that interaction of the MJO time scales characteristic in the SSD fluctuation with tropical disturbances arising out of instabilities around the synoptic time scales in the constant flux and boundary layers leads to a large amplification at the MJO time scales. So, this is an interesting idea of scale interaction. How synoptic scale systems can give intensification of the MJO time scale and using continuous space time wavelets Shankar and Anju they have shown that the dominant spatial scale related to these latitudinal variation is about 30 degrees and the associated temporal scale is 30 to 40 days. So, many hypotheses have been proposed for these propagations and they are all discussed in various details. So, what I have tried to do here is to give you a flavor for the kind of processes that may be important in the two major features that we saw of inter-seasonal variation over the Indian region active week spell fluctuations and northward propagation. Thank you.