 The key focus of today's talk is on ocean warming and the specific role of Indian Ocean on regulating the tropical variability, especially of the monsoon, also possibly on the ENSO. In fact, the most recent issue of science is a special issue on the changes in the ocean, especially considering the warming in the ocean. If you look at the effect of the greenhouse warming on the radiative forcing and the heat absorbed by the different air system components, you can see a picture like this which came out from IPCC. And you can see more than 90% of the heat has been absorbed by the oceans, a large share by the surface ocean or the upper ocean and large share by the deeper ocean. And the other earth system components like the land atmosphere and the ice comes up to less than 10%. So the oceans have been warming and this warming is uneven. So there is an even warming in the ocean. That's one point. The other key point is that the warming across the different earth system components is also uneven as you can see here. So this has a large potential to change the tropical variability, for example, the monsoon. And that's the focus of our study. So we have some questions which has been already answered where has all the heat gone? You can see here. Where in the ocean, we will see that in the coming slides. And why is the Indian Ocean warming anomalously? We'll get into those points and whether it has any links with the El Nino. And then this uneven warming has a potential, as I told, to change the tropical variability. It can change the temperature gradients over different regions and affect the monsoon. And also whether this warming has any impact on the end. So we also compare the effect of warming in the Indian Ocean and the Atlantic Ocean on the ENSO activities. So quite a handful of studies have looked into the warming in the oceans and they found out that the Indian Ocean has been warming monotonously for a long time. If you remember the talk by Clara Dessar in the first day, she remarked that though there is large multidicatal variability over the other oceans like the Pacific and the Atlantic, the Indian Ocean is not showing a detectable multidicatal variability. And in fact, it does mean showing a monotonous trend. And if you look at the Indian Ocean for the past 50 years, you can see that the seas of the temperatures have been warming monotonously. This is the annual SSC trend during the last 50 years. And one of the significant impact is on the expansion of the warm pool. So these colors stand for different periods, 50 to 60, 75 to 85, 98 to 2008. You can see that the warm pool has been expanding gradually. And this for 28 degrees Celsius, 28.5 degrees Celsius, 29 degrees Celsius. So obviously this can possibly change the dynamics over the region. And if you extend that period to 100 years, again I will call Dessar here, she has shown that the Indian Ocean has been fairly having good records over the western Indian Ocean because of the trade routes over here from the Mediterranean to the maritime continent. So you have good data here. Well, of course, there is some uncertainty over the regions over the Pacific. So if you look at the past 100 years, mind you, this is for the summer period. I'll tell you why. You can see there isn't much large warming over the Pacific. There is some warming over the Atlantic. And there's a large warming over the Indian Ocean, mostly over the equatorial Indian Ocean with significant warming over the west. And this warming goes up to 1.2 degrees Celsius. That's quite large compared to global surface warming of up to 0.85 degrees Celsius during the past century. It's a large warming, right? And why summer? If you look at this picture, this is the seasonal cycle of sea surface temperature over the Indian Ocean. And the blue to red goes from the early period to the late period. So the difference between them shows the extent of change. You can see it is during summer that the warming is most prominent. So we are taking the summer period. Also it coincides with the monsoon period, the boreal summer. So, yeah. So this is the focus of our study. And if you look at this plot, this is the climatology of sea surface temperature of the Indian Ocean. You can see the Wampool and the cooler western Indian Ocean. And this red is the time series of the relatively cooler western Indian Ocean. This is for the rest of the Indian Ocean, Wampool region. So earlier there is to be a sea surface temperature gradient between the western Indian Ocean and the Wampool region. But over time, this gradient has been nullified because of the extensive warming over the western Indian Ocean. So does that have an effect on the monsoon? And why is the Indian Ocean warming monotonously like this? And so earlier studies have pointed out different reasons for Indian Ocean warming. One is that the weak winds over the Indian Ocean triggers a warm SST and this further triggers a local air sea interaction. But one of the interesting factors we found is the effect of Elino, specifically the asymmetry and skewness in and so forth, which you will see here. So this is a picture of the mean conditions during summer. You can see the Wampool region. And this is the mean walker circulation during the same situation. And if you look at this, this is the Indian Ocean region. You can see the Westerlies. These Westerlies are part of the south Westerly monsoon winds, which bring the moisture from the ocean to the land. And we have prepared the Elino Composites for the circulation and the SST anomalies and also the Lanina Composites. And if you compare the Elino and the Lanina, you can see along with the Elino, you have warming over the western Indian Ocean, because the Elino changes walker circulation and induced easterly anomalies over the eastern Indian Ocean. But you don't get a similar response to a Lanina. You have some anomalies, but they are very insignificant, because the winds, the changes in the winds are nominal. So there is asymmetry in the ends of forces. You have Elino, Lanina, Elino, Lanina in the Pacific. But the response in the Indian Ocean is more towards the Elino side. Along with that, there is a skewness in this foreseeing. And here, there are many figures. I don't want you to get confused. So better to look at this time series from 1900s to 2012. The red stands for the East Pacific Sea surface temperature anomalies. And the green stands for the anomalies over the western Indian Ocean. You can see whenever there is a Elino, you have a peak in the western Indian Ocean. But whenever you have a Lanina, you don't see a similar dip in the SSD anomalies. But that is not the point here. If you look at the first 50 years, the number of Elinos are few compared to the next 50 years. The number of Elinos have gone up. Not only that, the magnitude of the Elinos have gone up. So you have seven Elinos here compared to 12 Elinos. And if you take an average of the strongest Elinos, just to clarify, the Elinos are when the red line goes above the standard deviation, above the dashed line. And you can see most of the Elinos in the first 50 years go up to one degree Celsius on an average. But most of the Elinos in the recent period goes up to two degrees Celsius on an average. So that means along with the asymmetry in the ends of forcing, there's a skewness towards more positive events over the Pacific, which will down more warm SSD anomalies over the Indian Ocean. And as you know, the Indian Ocean is a landlock region. And it triggers local air sea interaction, which will keep the sea surface temperatures persistent over the region. And so you have warm Indian Ocean. It should increase the convection like Chauh et al. has shown. It should increase the convection over the region. And that's what many studies have shown. These are from the observations with increases of the temperature, the cloud thickness and the height of the clouds, the occurrence of the clouds at high. All these increases with increases of the temperature. So one of the Mansun drivers is increasing. And the other Mansun driver sees the land-sea temperature difference. So during summer, the land is generally warmer, lately warmer than the ocean. And many of the observations and model simulations shows that over the Northern Hemisphere, the land is warming faster than the ocean, which you can see here. Over the Northern Hemisphere, the land is the red color show in Greece warming compared to the oceans. And this is the land-sea temperature difference over most of the Northern Hemisphere. And this shows a tremendous increase. So these two factors should ideally mean more rainfall. But is that what is happening for the Mansun? No. And if you look at the trends in the Mansun rainfall, these are the trends from the Indian Meteorological Department data. And these are the trends from the group precipitation. And you can see both of them show robust weakening trends over the central Indian region. And if you look at the last-scale picture, you have a weakening trend from the south of Pakistan to central India to Bangladesh. So mostly over the central South Asia, the rainfall is weakening. But you won't get a similar picture if you take the oil in the rainfall, which doesn't represent the regional features. So why is it weakening? We tried to correlate with the Indian Ocean, the sea surface temperature anomalies. And the top panel shows the same picture as the trends. And the bottom panel shows the correlation with the Indian Ocean SSD anomalies. We have, in fact, mixed and matched the SSDs and the rainfall. Here is the Hada SSD with AMD-RAIN. And this is the ER SSD with the group precipitation. Both of them shows significant reduction in the rainfall over the central Indian region or the central South Asian region. And this is much similar to the trends, which means they are well associated. But we don't know which is forcing which. We have to look at the causal relationship. And in fact, we are interested in this horseshoe pattern from Foothills of Himalayas to the central India. You can see the similar pattern in the trend as well. Now, if you zoom into the temperature trends over the South Asian region, you will see a different picture. We have seen the land-sea temperature is increasing over the northern hemisphere. But that is not the case here. If you look at the, only at the South Asian domain, you can see us, we saw before the ocean is warming much faster than the land. In fact, over the land, there is suppressed warming or some cooling during summer, where while the rest of the northern hemisphere is warming, the Indian region is showing some cooling and also the Indian Ocean is warming tremendously. And this land-sea contrast is more important for the Mansun onset. So once you have the Mansun rains over the land, it cools down the land and the land-sea temperature gradient over the surface is no more functional. But what keeps it functional? It's the latent heat release from the surface of the land. You have more release of the heat to the atmosphere. So once the onset has happened, it's the tropospheric temperature difference between the land and the ocean, which keeps it working. And if you look at the trends in the tropospheric temperature as well, it has weakened over the time. You can see much warming over the ocean at the troposphere. And similarly, there is some cooling. And this warming over the ocean is connected with the warming over the Indian Ocean. Because the warming over the Indian Ocean can increase the convective activity up to the upper troposphere and change the trends over the upper troposphere. But you have a cooling here. We don't know why this cooling is. We'll look into some factors. But generally, the land-sea temperature difference has been weakening. You can see that in the time series also over the surface and over the upper troposphere. And someone asked about the circulation. You can see that over the Indian Ocean region, there is enhanced convection. So there is ascending motion here, which is shown by the red. And to compensate that, there is a right subsidence over the Indian region, which weakens the circulation towards the land associated with the Indian Ocean. And we did some sensitivity studies. We imposed NS warming over the Western Indian Ocean. And this represents all Indian Ocean because the warming over the West is in phase with the warming over the equatorial Indian Ocean. And we saw the response. You get more, the colors are the rain. You get more rain over the convection and rain over the Indian Ocean. But you get a weakened rainfall as a response over the Indian land mass. And interestingly, we were much surprised that it's like a horseshoe pattern, as you see in the observations. And similarly, we get similar changes in the circulation as well. Enhanced convection over the ocean, but decreased our subsidence over the land. And we cannot miss the aerosols. Many studies have shown that the suppress warming over the Indian land mass could be due to the effect of aerosols. But we are not sure because the present day models, they are unable to show the exact impact of the direct and indirect effect of aerosols over the Indian land mass. And for the upper tropos, we're calling some studies, including Chow et al study, they have shown that there are stratosphere-troposphere interactions which could result in some cooling. So there are other factors also included in this. And for the future, see if I future projections are just further warming of the Indian Ocean. But will the monsoon increase further? Or will the monsoon decrease further? Well, these future projections also suggest increased monsoon rainfall. But it is to be noted that these models fails to reproduce the present day monsoon. So we should be with this pinch of salt that we should consider these semify future simulations. And coming into the effect back on the end, so we did some simulations by suppressing the variability over the Indian Ocean, and also some simulations by suppressing the variability over the Atlantic Ocean in the second panel. So the first panel shows that when you suppress the Indian Ocean variability, the end saw increases, the end saw variability increases. And the second panel also shows that if you suppress the variability over the Atlantic, the end saw also increase. But the increase is more for the Indian Ocean. I will quickly go into some of these slides. And it also, other than suppressing the end saw variability, the Indian Ocean warming also can shorten the lifespan of end saw. So the first one is the reference run. And the second one is the run with the Indian Ocean suppressed. And the third one shows the Atlantic Ocean suppressed. So if you have the normal Indian Ocean variability, the end saw goes on for a shorter period. But if you have it suppressed, the end saw lasts for a longer period. That's the point from this figure. And yeah, to summarize, we see that there is a strong monotonous warming without any detectable multi-decadal variability in the Indian Ocean, specifically over the Western Indian Ocean. And it has links to the asymmetry and skewness in the end saw forcing. And the potential impacts are it weakens the South Asian monsoon by changing the circulation and lancet thermogradient and also dampens the ends of magnitude and the cycle. Thank you.