 Now, we come to the end of this series of lectures on monsoon and its variability. I began this lecture series with a discussion of what the monsoon means to the life in a monsoonal region such as ours and why I consider the study of the monsoon the most enjoyable and worthwhile of a scientific endeavours. Monsoon in common parlance is the system associated with large scale rainfall over the region. The focus of the lectures is the summer monsoon season June to September in which most of the rainfall occurs over the Indian region and this is the pattern of rainfall over the Indian region and this is the monsoon zone where the large scale system, monsoon system gives rainfall during the season. This is of course, the west coast associated with orography and northeast also. Now, the major features of monsoon variability are interannual variation of the Indian summer monsoon rainfall and you see we have a great deal of data 1876 till present and this is the nature of interannual variability with droughts and excess monsoon years occurring with differing frequencies in the decades. So, this is a major feature of monsoon variability that we have looked at on the interannual scale. On the intracesional scale two special features are one is fluctuations between active spells and weak spells which which you see year after year and active spells and a break such as the one you see here. So, fluctuation between active and weak spell is another important feature of the sub seasonal or intracesional variation of the monsoon and this is the rainfall anomaly composite corresponding to a break spell you see rainfall is huge deficit all over here and is above normal over southern tip of the peninsula and northeast Himalayan foothills. This is the active spells rainfall anomaly which is almost a mirror image of the breaks. Another important feature that we looked at on the sub seasonal scale is the northward propagation of cloud bands or rain belts emanating from the equatorial Indian Ocean and moving propagating northward up to the monsoon zone. Now, these propagations play a very important role we have seen in the seasonal transitions that is the onset phase from spring to summer as well as the retreat phase from summer to fall. In fact, they also play a very important role within the season after the system is established over the monsoon zone in revival from the breaks. Now, this is so far as the major features of variability that we want to understand model and predict. One of the things I covered at considerable length in this lecture series was what is the basic system responsible for the monsoon because this is something that we are taught from high school onwards and what we are taught is unfortunately not the right model. We are taught that the monsoon is a gigantic land sea breeze but I have shown here in these lectures that it is in fact, the monsoon the large scale monsoon rainfall is associated with a planetary scale system you see this is the cloud band associated with a tropical conversion zone which is stretching across the monsoon zone over India and continues across up to the west Pacific. So, this is monsoon is associated with the seasonal migration of tropical conversion zone which is a planetary scale system and it is not a local response to land sea contrast. The fact that this region is hotter than ocean will make a difference to the amplitude of the seasonal migration but the basic system is not a land sea breeze the basic system is a system which gives rainfall all over the tropics. So, this is an important thing that we learnt during the course of these lectures that the monsoon is associated with a planetary scale TCC and its variability on intra seasonal and inter annual scales is linked to the variability of convection over the tropical and Pacific and Indian ocean. You already saw in that picture that in fact, the monsoon is not restricted the system is by no means restricted to the Indian longitude it extends all over here and we have also seen that it has links with the surrounding seas because almost all the systems that give us rain are generated over here or over the equatorial Indian ocean. So, there are links obviously it is the variability of inter seasonal and inter annual scales of the Indian monsoon is linked to variability of convection over the tropical Pacific and Indian ocean. Now, that brought us to the question of what is the variability of convection governed by? Everybody knows that the sea surface temperature is a very critical parameter of the ocean as far as clouding or convection over the oceans is concerned. This is because sea surface temperature determines how much water vapor is in the air near the surface of the ocean. Now, an interesting result that we discussed in this lecture series was that in fact, the relationship between rainfall and sea surface temperature is highly non-linear in rainfall tends to be suppressed below a threshold and above a threshold there is a large variation in rainfall for a given SST range with little relationship between the rainfall and the SST. So, this is a particular relationship and we saw which is actually valid over the global tropics and we saw the implications of this for the seasonal migration of the inter tropical conversion zone over Pacific Atlantic and so on and thereby finally, determined the monsoonal regions of the world. We discussed another important phenomena which is El Nino Southern Oscillation for two reasons it is the most energetic element of the variability of the tropical atmosphere over the Pacific and secondly it is something about which the there has been a phenomenal gain in understanding modeling and prediction from about the 90s onwards. So, this is why I dwelt at considerable length on how this came about how this revolution in our understanding of ENSO came about and that was one reason is to take try and take lessons from you know how progress was made in understanding of ENSO to try and understand how we will go further in our understanding of the monsoon itself. The second reason is ENSO is known to be linked to monsoon. So, these were the two reasons for dwelling at length on ENSO and this is the El Nino as you see this is one phase of ENSO and this is La Nina where the cloud system is located over West Pacific in El Nino it stretches right across the Central Pacific and La Nina corresponds to warming of the equatorial belt El Nino corresponds to warming of the equatorial belt La Nina implies cooling here more than average and warming here. There is another interesting phenomena we looked at and which was the equatorial Indian ocean oscillation if you look at the outgoing long wave radiation anomaly patterns you see that often there is a seesaw in convection between East equatorial Indian ocean and West equatorial Indian ocean. For example, in this year there is excessive convection over E I O suppressed over W E I O opposite is the case here where we have excess convection over W E I O and suppressed over E I O. This phenomena oscillation is known as the equatorial Indian ocean oscillation and we showed that in fact, it is true that the most important link of ISMR or the Indian summer monsoon rainfall is to ENSO, but it is also linked to equinoe equatorial Indian ocean oscillation and if we take indices of these two phenomena in fact and plot all the extremes of ISMR all the droughts and excess rainfall season then you see a very clean separation between droughts and excess rainfall season and this is a very surprising result it seems to say that extremes of such a complex system are mainly governed by two modes equinoe and ENSO, but this understanding also then can lead us into some ideas as to how to predict monsoon extremes with models. Now why are extremes important? I talked as I said at length about monsoon variability in agriculture and I also gave one lecture on monsoon agriculture and GDP. The result of that study which was a quantitative assessment of the impact of monsoon on agriculture and GDP was as follows. This is the food grain production impact on food grain production and rainfall anomaly and what you see is that the relationship is highly non-linear that if you have a ISMR anomaly of a given magnitude say minus 10 you will get a large deficit of food grain production, but a positive anomaly of the same magnitude plus 10 does not really give as large advantage of having more rain as the disadvantage of having less rain. So, it is a highly non-linear thing and the this is for food grain production but the same relationship holds for GDP as well. Now in fact we showed in that lecture that this kind of you know farmers not being able to reap benefit of good monsoon years, but suffering the losses due to poor monsoon years. This asymmetry can be to some extent mitigated if prediction of extremes are available. So, this leads us to the importance of prediction of extremes asymmetry in response as I mentioned larger amplitude for deficit ISMR than positive ISMR anomaly to rectify we need prediction of extremes. So, that brought us to the question how good are the predictions of extremes with state of art coupled models. Now, we find that they are reasonable but not good enough. So, in fact this is an example of state of the art coupled models in the European community and black is the observed and rest are different models and these are the different extremes 61 was a very large excess here and 88 and so on and so forth. We show in the showed in that lecture that vast majority of the extremes are now simulated by the models simulated in the sense at least they are getting the sign of the ISMR anomaly right, but there are two years 83 and 97 in which all the models are giving huge false alarms. They are predicting droughts for 83s several of the models and all the models are predicting deficit when actually it was an excess monsoon year for 97 which was a strong El Nino year all the models are predicting droughts whereas, it turned out to be above normal. So, these are two years in which things went wrong and then we discussed why they went wrong and diagnose the problem that the problem had to do with the models not being able to simulate the link with equino although they simulated well the link with and so. So, given that kind of an analysis we came to the conclusion that if now we pursue this path of trying to fix where all models irrespective of their parametrizations and scheme other numerical schemes and so on are going wrong if we can fix those years then the performance of the model will indeed improve and our hope was that we will get there in a few years. So, this is a very brief summary of the kind of things that I have covered in the lectures in the beginning I thought 40 lectures would be lot of lectures and I should be able to cover most of the important facets, but at the end I find that I regret that I have not been able to cover one major topic in this lecture series namely I have not been although I did spend some time in defining the monsoonal regions of the world and so on I have not had a chance to discuss monsoon and its variability over other parts of Asia or the Asian monsoon and its links with the Indian monsoon. Now this is a very important topic I also could not cover the monsoon over Africa, South America and so on. So, this will have to be left as it is, but on the whole I am pretty satisfied with what I have been able to cover and I have learnt a lot in preparing for this lecture series and very much hope that you will also learn something from it. Thank you.