 It's my pleasure to introduce our next lecturer, Nina Mani-Joseph. Nina is a faculty in the Earth and Climate Science Department at the Indian Institute of Science Education and Research, IACR and Pune. Formerly Nina did a postdoc at the Jet Propulsion Lab in Pasadena, California and was also a research associate in the Indian Institute of Tropical Meteorology, Pune prior to that. She studies large-scale atmospheric circulation systems, their interactions and predictability. She's done a lot of work on verification of intracesinal predictions as well as understanding the monsoons and its variability from intracesional to multi-decadal timescales. And she also studies interaction of multiple climate modes such as ENSO and MJO and monsoons. Thank you, Nina, for accepting our invite and look forward to your lecture. Yeah, thank you, Anish. Can you hear me? Yeah. Okay. Thanks. So it's not full screen. Thank you, Anish and Judith for the invitation and it's a great colloquium which is going on. So today I'll talk about monsoon ISO and its predictability. So I'll have to turn off my video to save the bandwidth. Okay. So this is the outline, basically. So I'll give you an introduction to monsoon main state. Then I will talk a bit about monsoon intracesional oscillations, how it is different and how the different scales of variability are present over the monsoon domain. Then I'll discuss a bit about the theories of north of propagation mechanism and how the MISO evolves from the winter state to the spring and to the summer state, how the difference in MISO evolution is happening and a little bit about ocean fluxes, the role of ocean fluxes in MISO initiation. Then I think a part of the lecture I have kept aside to discuss about how the MISO is simulated in GCMs, how we define the MISO indices for understanding prediction skill or predictability. So I think many of you must be familiar with the Asian summer monsoon system. So it is basically this is, these are the main states what you observe during the summer over the Asian monsoon domain, Indian Ocean and the Asian monsoon domain. So you can see in contrast to the winter state where you have most of the conviction and precipitation confined to the equatorial region, there is a distinct propagation or there is a spread of conviction to the landmass over the monsoon domain. There is a reversal of bins from Easterlies to Westerlies, that is what we call the monsoon flow. And you can see the low-level jet over here and it is associated with the shift in the ITC or the shift in the location of the ITC from the winter to the summer hemisphere. And it is evident in the SST pattern during DJF as compared to the SST pattern during DJSO here in the right-hand side. So you can see there is a total change in the background condition from summer to winter. So this change in background condition in this particular monsoon domain leads to a lot of variability in the S2S timescale or even shorter timescales. So these are the different scales of variability what you observe. So you can focus over the Asian monsoon domain. So this was shown as a global figure. So you can see there is a strong variance in the 10 to 2 to 10 day that is the synoptic timescale. This is what we call the quasi-bi-weekly timescale, the 10 to 20 day. Also there is significant variance and there is a very strong signal in the 20 to 60 day timescale of what we call the MISO or the ISO timescale. And related to all these high frequency variability, when you look at the intranural variability, the monsoon variability in the intranural timescale is less than 10 percentage of the mean. So it is much smaller as compared to the intracesional variability. So that is the importance of S2S timescales for the monsoon region as a whole. So how does that change in the background conditions from winter to summer? How does that impact the propagation of ISO over this region? So we know that we have been hearing about the MGO in the previous lectures, the eastward propagation of convection along equitably trapped about like five meter per second. And it has got certain circulation and convection features. And what happens during summer over this region is that it has a more complex evolution of intracesional anomalies in convection as well as in circulation. So in addition to some eastward propagation along the equator, what we have is a northward propagation over the monsoon domain in convection and circulation fields. And in addition, we have something what we call the quasi bi-weekly oscillations, which falls in a 10 to 20 day. Again, it is also in a subsesional timescale. So what we have here is that due to the seasonal cycle and boundary conditions, what we have here is the MGO convection, what starts off here in the equatorial Indian Ocean propagates eastward, then it spreads the anomalies, spreads into an elongated band, and part of it moves northward and part of it continues eastward. So we're kind of a northwestward propagation over the monsoon domain and in our propagation along the equator. So and this extends all the way and you finally get this elongated band of convection extending all from the Indian monsoon domain towards the rest of the perspective. So this is a signal, this is a like the final image what reflects like what is the convective band of convection what we observe during our summer monsoon active state. And along with that, something what we have, there is a strong signal of variability in the quasi bi-weekly timescale that is 10 to 20 day timescale. So these are associated with westward propagation of convection and circulation fields from the western Pacific to all the way up to 70 east that is the Arabian Sea. So that propagation is basically like it's got a shorter spatial scale and it has the structure of the greatest meridional mode of equatorial-rospy waves but it is slightly shifted by the main background state. So it probably gets best for like 4.5 meter per second from the western northwest week or east Asian monsoon domain towards the Indian monsoon. So these two modes of intracesinal variability is what drives or what impacts the convective activity over the land mass over the Indian land mass which we which is very important because that gives rise to the active and break phases of monsoon, Asian monsoon and the Indian monsoon. I'm just focusing on the Indian monsoon for now. So these shows the variations in the rainfall during a season for different years. So you can see it happens in spells. So there are active spells followed by periods of like lull, there is no precipitation, there's like again an active spell and so forth. So some years you can have many number of active spells, some years few. So you can say that the more the number of active or active rainfall conditions we have a good monsoon here. So basically this meso defines so this figure on the right shows a mesoactive phase over the Indian monsoon domain and this is a break phase over the Indian monsoon. So it's a product of both these not just the 30 to 60 day the north propagating and the 10 to 20 day best for propagating mode and also like a lot of synoptic scale disturbance is also contribute to that. So necessarily like what we have is this strength of the meso activity basically defines the strength of the seasonal mean monsoon. So if you have more number of active dates and it can even lead to extreme conditions in seasonal mean monsoon like floods of droughts. So that is and more than the predicting the seasonal mean state often it becomes important to predict like what happens like two weeks in advance over the monsoon domain like for agricultural practices and a lot of practical applications. So how this so as I said like multiple scales that is very crucial for the ISM domain. So what do you have this convective envelope of V-SISO which kind of encompasses a lot of meso scale convective systems. So the category of meso scale convective systems like low blows and depressions and cyclones and you have easterly waves. So all that account for a large fraction of the total amount of monsoon precipitation. So this is what shows that this like shows that it's kind of a building block for the monsoon ISO and monsoon ISO or the meso kind of helps in clustering this active systems like the low pressure systems along the region of like you know positive or convictive active phase of meso all this monsoon low pressure systems align. So the frequency of occurrence as well as the tracks and the number or the genesis of low pressure systems are controlled by meso. So you can see this very important like graphic which basically shows how this low frequency meso variability is in fact interacting with the other two scales of variability the diner then the synoptic scale of variability and it is these interactions not much is like we don't have a very clear picture about like how these interactions take place. So a lot more to explore in that direction but these interactions are very critical for understanding monsoon as well as for predicting the monsoon and as well as predicting the meso. So based on this now we talk a bit about like how what do we understand about meso northward propagation. So there are based on the some some mean dynamic and thermodynamic states many northward propagating mechanisms have been proposed some of them have listed very few of them have listed there are some more studies so land surface heat fluxes into the planetary boundary layer can play a role in destabilizing the atmosphere ahead of conviction which can lead to the northward shift of convective zones so that is one of the earlier theories with the problem was like more than more of the meso northward propagation you observe not over the land but over the oceans. And another theory is that conviction thermal relaxation feedback mechanism that is resulting in the standing oscillation between the land and the there is a monsoon drop zone and the equatorial Indian ocean. So convective activity will result in an increase in the static stability which can express convection and by dynamical and radiative relaxation processes it can decrease the moist static stability and further bring the system to an unstable state so that kind of relaxing feedback between convection and radiative processes gives rise to an oscillating standing oscillation between equatorial region and the monsoon drop. And the third theory is the Rossby wave emanation from the eastward propagating equatorial convection there is a convective front which is moving along the equator and the Rossby wave response to that is seen as a northwestward propagating signal which we see as the northward propagating signal in convection. And some theories are related to the ocean atmosphere interactions which can give rise to surface latent heat fluxes feedback with winds and which can lead to increase SSD the north of convection leading to the moisture convergence in the potential boundary layer and leading to for convection to further move northward. So and these are all set up theories and that which is based on internal dynamics of the atmosphere now the propagation happens through internal atmospheric dynamics such as vertical shear induced, meridional vorticity asymmetry and meridional vorticity advection and convective momentum transport. So these are some very good papers which I would recommend any of you who are interested in this MISO to refer. And there is a very good review by Kikuchi I have referred to here which gives a overall idea about like most of the aspects related to MISO. So now what we are looking at is the patterns of wind shear and meridional the gradient and the humidity gradient. So the patterns of mean wind shear that is U 200 minus U 850 meridional wind 200 minus 850 and this is a lower surface meridional wind component. So what we have is vasterlies in the lower troposphere and easterlies in the upper troposphere that gives rise to a very strong easterly vertical wind shear. So that's what you see here and you have a very southerly component of wind in the lower troposphere which again gives rise to a strong shear here and this is a strong meridional wind in the lower levels. And if you look at the humidity pattern so you can see that it's a very strong high values of humidity over the land region especially over this Bay of Bengal and western Pacific region and this you can see not just in the lower troposphere but also in the like middle to upper troposphere up to the middle troposphere. So this is the two important concept like mean features which is very important for MISO propagation as per the theory proposed by Jian and like several other studies which followed up also like agree that vertical wind shear is a very important component for MISO propagation. So what we have is a strong vertical wind shear over the monsoon domain. So there is a deep convection in the northern hemisphere in the presence of meridional vertical shear. So the convection is associated with baroclinic divergence and negative baroclinic vorticity and associated with this convection there is a negative divergence gradient north of convection there is positive vorticity gradient and opposite in the south of convection. So in the presence of this vertical wind shear there is an adpiction of mean baroclinic divergence which generates two barotropic vorticity anomalies positive barotropic vorticity anomalies to the north of convection. So this can lead to boundary layer convergence and finally lead to precipitation to that is the system will move northward by this advection and generation of barotropic vorticity to the north of the convection center. So that is the importance of vertical wind shears apart from vertical wind shear and the dynamical process is associated with it moisture perturbation in the boundary layer is also considered a very important factor for meso northward propagation. So positive moisture density so you have seen positive gradient in moisture and you have southerly winds. So positive moisture tendencies can lead to can help in the propagation of meso northward. So let's see how this so this is a reason study which talks about how the system changes from like the pattern what you see for interest is no lower anomalies from winter to spring to summer. So you know how this change how this change happens over the Indian Ocean domain. So you can see this this iso meridional propagation is driven by large scale environmental conditions and vertical wind shear meridional the gradients in humidity and static stability fields are important. So what we have here if you look at what happens in spring that is April to me you can see a strong component of northward propagation over the Bay of Bengal but not much signal is there over the Arabian Sea but once the monsoon sets in there is a June meter June period there is significant northward component in Bay of Bengal as well as Arabian Sea which indicates that first there is a northward propagation bills over the Bay of Bengal and later it spreads over to the Arabian Sea and finally the whole system the Rosway wave someone's structure kind of sets in. So how this happens we'll try to see based on like the vertical wind shear and the meridional gradient in humidity. So seasonal variations in surface moisture plays a major role in regulating the northward propagation of convection over the Bay of Bengal in spring which means that so you can see this contours are the vertical wind shear and this easterly vertical wind shear is mostly like south of 10 degree north the strongest shear is not hit or reached to the northern part of the Indian Ocean. So but you can see over Bay of Bengal there is a strong gradient in humidity so already the Indian land region because of the summer conditions there is a strong humidity values are present over the northern Bay of Bengal and this part then so there is a strong gradient in humidity and in the later part what we have in the once monsoon has set in you can see the vertical wind shear has extended all the way up to the 20 degree north latitude strong values in vertical wind shear and strong gradients in humidity. So we can assume that vertical wind shear even though it is not that strong the strong gradients in humidity of Bay of Bengal is kind of supporting northward propagation in spring but for the Arabian Sea it is not yet like the gradient in humidity is not supported and finally when the monsoon sets in both the gradient in humidity as well as the vertical wind shear is helping in the northward propagation of the Arabian Sea and the final setting of the convective northward propagation of Meso. So goodbye half the time. So yeah six to ten minutes. Okay So the role of oceans is nothing to be argued about because you can see this is the mean SST pattern so it's basically this very strong SST anomalies more than 28 degrees Celsius which is driving the Meso northward so that plays a very important role in terms of the strong positive SST anomalies help in destabilizing the troposphere prior to Meso convection and interest rates in our variability through feedbacks, divergence and can lead to changes in SST anomalies. Changes in fluxes can also produce changes in interest in SST anomalies. Apart from that there are like ocean dynamical processes which is again less explode over the Indian Ocean domain which can give rise to strong SST anomalies over the region. So how the models simulate the Meso northward propagation as you can see this is the observation this is the sort of models as part of the Cassiope project you can see there is the strong signal of northward propagating convection is simulated not by many models mostly it's kind of a stagnant signal or a slower signal as compared to what you've seen observed but still it's good it's good in a few models. So here are the two quantities which we think was very critical for northward propagation unfortunately this is the northward propagation skill score based on these patterns on the y-axis and on the x-axis you have vertical wind shear and vertical and the meridional winner of the zonal and meridional winds what you've shown here so it doesn't like really bring out a very strong correlation between these two at least for the vertical shear of meridional and some significant value is observed but that's not very robust. So and one thing which is which can be said about like how the models simulate the northward propagation is like if you the model can simulate the north south tilted rain band then the northward propagation is generally good in this model so it's the skill of simulating the north south tilted rain band and this skill in the northward propagation one can lead to the other so you can see that those two are related in the models and so I think I will quickly summarize like skip this part so there are different monitoring metrics just like the RMM for the especially for design for the MISU because the RMM is kind of captures only the symmetric structures about the equator there have been like recommendations of using multiple metrics based on conviction as well as circulation fields for real-time monitoring and forecast skill estimation or for the MISU so you basically try to find the error that is the error between like initial conditions are closed by initial conditions that is sensitive to an initial conditions will give you an estimate of potential predictability and like the correlation between the prediction predicted and the observed indices so you just project your refocus on to any of these EOF or the combined EOFs whatever is recommended by the indices and you measure this differences or pattern similarity you can get an estimate of predictability so in the contemporary models these are the estimates of prediction skill in the different models you can get like two to three weeks and in terms of dynamic prediction skill and ensemble mean prediction skill is going up to like 30 days in some models even higher in the recent S2S refocus so these are based on two different indices again but there is a lot of scope for further improvement of predictability in terms of S2S forecast so we have about like five weeks predictability range five to seven weeks is what is predicted by many of the previous studies so that is what we have about like how much we can predict the MISU in by the contemporary forecasting systems so and the point is the prediction skill associated with MISU is relatively lower by the same forecasting systems about like five to ten days it is lower as compared to the MGO forecasting skill so there's something really wrong with how we like are simulating or predicting the summer mean state over this region so the take home messages would be the small MISUs are more complex than the MGO it exhibits northward and westward propagating modes in addition to underlying MGO eastward propagation there can be like independent northward propagation which is not associated with the eastward propagation many models simulate the MISU northward propagation that may not be for the right reasons and relatively lower predictability is associated with the MISU than the MGO and understanding the scale interactions is essential for predicting in the S2S stamp scales over the months in domain so there's multiple scales which is I think very crucial and understanding oceanic processes is another factor which we really need to work upon so I think I'll take questions now thank you great thanks a lot Nina it was super interesting