AS1.18

The Hengudan Mountains, located at the south-eastern fringe of the Tibetan Plateau, reveal exceptionally high biodiversity. It is believed that this feature is linked to past complex interactions between climate, land surface dynamics and plate tectonics in this region. Contemporary topography was formed by plate tectonics, causing surface uplift, and spatially heterogeneous erosion, which shaped the deep river valleys. The non-hydrostatic regional climate model COSMO is applied to study the impact of surface uplift and river incision. Decades-long simulations at horizontal resolutions of 12 and 4.4 km grid spacing are performed. To study the impact of local topography on climate, we consider two idealized experiments with terrains deviating from the present-day topography: In the first experiment, we reduce the topography in a spatially non-uniform way. This altered topography reflects a past potential state of the Hengduan Mountains. In the second experiment, we remove the deep valleys by applying an envelope topography to quantify the effects of deep valleys on the local climate. Both experiments assume that that the large-scale (continental) climate did not change, i.e., the experiments are driven by large-scale reanalysis data. Preliminary results from the coarse-resolution 12 km COSMO simulation indicate that the uplift of the Hengduan Mountains has a strong impact on the summer monsoon over South Asia caused by circulation changes around the uplifted region. The uplift of the Hengduan Mountains strengthens the westerly wind anomalies from the ocean in South Asia and markedly intensifies the precipitation in Indochina and southwestern China. Besides, the cyclonic circulation in the Bay of Bengal extends eastward, indicating an intensification of the East Asian summer monsoon. The diabatic heating in the eastern Tibetan Plateau increases in response to the regional uplift and it is coupled with the increased precipitation in summer through moist processes. On the contrary, the uplift has little impact on the strengthening of the winter monsoon. In the next stage, we will conduct the same simulations at a higher horizontal resolution of 4.4 km, which captures local terrain more accurate. These simulations will use explicit rather than parameterized convection, thereby providing more realistic estimates of heavy precipitation and erosion. Subsequently, we will run the same experiments for the envelop topography. We expect to relate the changes in the frequency and intensity of extreme precipitation to the changes in the local moisture transport and vertical movement in the high-resolution perspective. In the future, the two different topographies along with the modern topography will be used for simulations of two time periods in the past (i.e., the Last Glacial Maximum (21,000 years ago) and a phase in the Late Miocene (∼7 Ma)) and the future climate (2070–2100).

How to cite: Xiang, R., Steger, C., Sørland, S., and Schär, C.: The Impact of Hengduan Mountains Formation on the Regional Monsoon Climate and Extreme Precipitation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6986, https://doi.org/10.5194/egusphere-egu22-6986, 2022.

Regional orography around India exerts a profound control on weather and climate, both in summer and winter as part of the diurnal cycle of convection, as well as in extreme events.  This poster summarizes the key results of the Indo-UK IMPROVE project (Indian Monsoon Precipitation over Orography: Verification and Enhancement of understanding).  IMPROVE considers two focal regions.  The Western Ghats intercept the monsoon flow across the Arabian Sea and receive some of the most frequent and heaviest summer rainfall, including being subject to extremes such as the 2018 Kerala floods.  Meanwhile, the Himalayas play a vital role in separating dry midlatitude flows from tropical airmasses in summer, while suffering extremes in winter due to western disturbances - cyclonic storms propagating on the subtropical westerly jet. 

We examine the impact of orography on the observed convective diurnal cycle and assess its simulation in models at a range of resolutions including convection-permitting scales.  MetUM and WRF model experiments, in addition to DWR retrievals, are used to identify key mechanisms between forcing at the large scale from the BSISO and newly identified regimes of on- and offshore convection near the Western Ghats.  An additional aspect to this work is consideration of a novel Froude number approach for understanding the convective regimes.  Secondly, the role of orography in extreme events is considered, including its interactions between passing tropical depressions or western disturbances.  Finally, land-atmosphere interactions occurring during the diurnal cycle of precipitation in the Western Ghats and Himalayas regions are discussed.  IMPROVE works towards a deeper understanding of orographic rainfall and its extremes over India and uncovering why such mechanisms may be poorly represented in models.

How to cite: Turner, A., Hunt, K., Phadtare, J., Chattopadhyay, R., Das, S. K., Deshpande, S., Fletcher, J., Kalshetti, M., Menon, A., Ross, A., Schiemann, R., Stein, T., and Bhowmik, U.: Orographic rainfall processes in India – results from the IMPROVE project, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12069, https://doi.org/10.5194/egusphere-egu22-12069, 2022.

The onset of the South Asian summer monsoon is characterized by low-level cross-equatorial flow in the western Indian ocean. This flow turns eastward and becomes a zonally oriented jet off the East African coast at around 10^°N, which is called the Somali Jet. The Somali jet is an important factor in the monsoon onset over the Indian region and transports moisture from the Arabian sea, playing a key role in South Asian summer monsoon rainfall. The kinetic energy (KE) of the jet has an increase that is much more rapid (a few days) than the evolution of solar insolation forcing (over a month). With the help of high-resolution reanalysis data, we explore the factors responsible for this rapid increase in kinetic energy. Using calculations of the KE budget we find that KE generation, from the scalar product of geopotential gradient and horizontal winds, has a high correlation with KE itself, and furthermore shows a rapid increase at the time of jet onset. The major contribution of this KE generation comes from the meridional component (-v∂Φ/∂y) , and is confirmed by a decomposition of generation based on EOF analysis. We demonstrate that a dominant balance between the KE generation and KE advection exists, suggesting that the boundary layer at the location of the highest KE generation is advective in nature. Furthermore, we observe that high KE generation occurs in the regime where the local Rossby number is close to 1. The meridional wind (v) is, to a good approximation, linearly proportional to the meridional component of geopotential gradient (∂Φ/∂y), and the latitude at which this relationship between v and ∂Φ/∂y is the strongest coincides with the location of the jet strength maximum (around 10^°N). This strong relationship and consequent abrupt increase of the KE generation diminishes as we ascend the troposphere. Together these findings give rise to an unconventional boundary layer dynamics view of the Somali jet.

How to cite: Masiwal, R., Dixit, V., and Seshadri, A. K.: Rapid intensification of Somali Jet kinetic energy prior to monsoon onset, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8832, https://doi.org/10.5194/egusphere-egu22-8832, 2022.

The Indian summer monsoon (ISM) features an intense rainy season typically lasting from June to September that is responsible for approximately 75% of the total annual rainfall on the Indian subcontinent. Specifically, the Western (WHF) and Eastern Himalayan foothills (EHF) receive very high amounts of precipitation during the ISM season while also being densely populated [1, 2]. Therefore, a better understanding of the processes controlling ISM intraseasonal variability are of great societal relevance.

In our present work we identify and quantify causal relationships at short lead-times (three to nine days) between characteristic remote and local climate patterns and the precipitation over the WHF and EHF in order to uncover the underlying mechanisms. For this purpose we  first apply the so-called response-guided causal precursor detection (RG-CPD) scheme, an algorithm designed to identify causal precursors of a variable of interest [3]. The employed method is based on concepts of information theory and statistical mechanics, and allows to identify strongly interdependent climate patterns associated with the ISM and to distinguish between spurious and truly causal links. Resulting from this, causal effect networks (CENs) summarize the relationships among different climate variables by visually representing the actual direct causal linkages between the different variables, their strength and directionality, and associated time-lag.

Our analysis reveals that WHF rainfall variability is influenced by mid-latitude teleconnections such as the circumglobal teleconnection index. This can be seen in the analysis of the geopotential height at 200 hPa and in the 2m temperature. In addition the mean sea-level pressure of the Indian Ocean and the outgoing longwave radiation act as causal precursors to the rainfall. In general the WHF rainfall seems to be driven by similar precursors as the precipitation on the monsoon trough, which corresponds to a large region on the Indian subcontinent receiving the highest amounts of rainfall [4, 5]. By contrast, EHF rainfall is driven by a different set of atmospheric processes. Specifically, we find a causal driver in the eastern equatorial Pacific manifesting itself in the geopotential height at 500 hPa and the mean sea-level pressure, potentially indicating that intraseasonal tropical variability patterns associated with the Madden-Julian oscillation and/or the Walker circulation might exert a significant influence on EHF rainfall. The obtained results by this study may be relevant for designing improved (statistical) forecasts of monsoonal rainfall activity in the different regions beyond synoptic time scales.

References
[1] Vellore, R., et al., On the anomalous precipitation enhancement over the Himalayan foothills during monsoon breaks, Clim. Dynam., 43, 2009-2031 (2014).
[2] Vellore, R., et al., Monsoon { extratropical circulation interactions in Himalayan extreme rainfall, Clim. Dynam., 46, 3517-3564 (2016).
[3] Runge, J., Causal network reconstruction from time series: From theoretical assumptions to practical estimation, Chaos, 28, 075310 (2018).
[4] Di Capua, G., et al., Tropical and mid-latitude teleconnections interacting with the Indian summer monsoon rainfall: a theory-guided causal effect network approach, Earth Syst. Dyn., 11, 17-34 (2020).
[5] Di Capua, G., et al., Long-Lead Statistical Forecasts of the Indian Summer Monsoon Rainfall Based on Causal Precursors, Weather Forecast., 34, 1377-1394 (2019).

How to cite: Aviles Podgurski, L. E., Di Capua, G., and Donner, R. V.: Causal Drivers and Mechanisms of Monsoon Rainfall Over the Northern Indian Subcontinent, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1759, https://doi.org/10.5194/egusphere-egu22-1759, 2022.

While the traditional view of monsoons as continental sea breezes generated by land-sea contrasts was shown to have serious limitations, several competing alternative frameworks look promising. Within this debate, it remains unclear if the surface temperature contrast matters at all for the monsoon precipitation, and why there is a non-linear intensification of precipitation intensity with surface temperature forcing.

Idealised studies such as aquaplanets often help improve our understanding of basic mechanisms. But there are very few idealised simulation studies of monsoons at high resolution. Therefore, to determine if monsoon non-linearities with surface forcing come from convective processes, dynamical feedbacks, or from non-linearities in the forcing themselves, we devise a modular framework to simulate idealised monsoons at convection-permitting resolution with the WRF model, in a domain based on an aquapatch (mini-aquaplanet), but in which we can gradually add more realistic components, such as an interactive land surface. The model is forced by a season-dependent meridional contrast of surface temperature, with comprehensive physics and rotation. We compare a series of aquapatch experiments with increasingly intense smooth sea surface temperature forcings with another series including land with increasingly sharp surface temperature contrasts at the land-ocean interface.

By relating forcing to responses, we aim to describe the non-linearity of the relationship between surface temperature gradient (or surface Moist Static Energy (MSE) gradient, or low-level wind), and precipitation intensity (or monsoonal precipitation surface area, or monsoon onset timing). This should help clarify the actual role that surface temperature and MSE gradients play in controlling monsoon precipitation, and could potentially hint at the effect of climate change on monsoons.

How to cite: Colin, M., Haerter, J. O., and Dixit, V.: Relationship between surface thermodynamic contrasts and precipitation intensity in idealised monsoon simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12004, https://doi.org/10.5194/egusphere-egu22-12004, 2022.

The Tropical Rain belts with an Annual cycle and Continent Model Intercomparison Project (TRACMIP) ensemble includes slab-ocean aquaplanet controls and experiments with a highly idealized narrow equatorial continent. In the control simulation, the rain band moves between hemispheres over the annual cycle, so that the annual-mean state displays a broad ITCZ straddling the equator. The introduction of the continent causes an equatorial cold tongue to develop off the western coast and, correspondingly, dry anomalies and a split in the oceanic ITCZ.  The oceanic cooling is initiated by the advection of cold, dry air from the winter portion of the continent, but it persists and is amplified by positive feedbacks. In the long wave (LW) feedback, a colder SST leads to drier and colder air, reduced downwelling LW flux, and enhanced net surface LW cooling. On the equator, the wind, evaporation, and SST (WES feedback) also contributes to the establishment and maintenance of the cold tongue.  The annual mean signal over the ocean is dominated by the continental winter cooling and drying because warm, humid anomalies in the summer hemisphere are restricted to the continent by anomalous surface convergence.   Over land itself, aside for the timing of rainfall’s seasonal progression (i.e., the rainy season occurring close to the time of maximum insolation) the continental rain band remains in an ITCZ-like regime akin deep-tropical monsoons, with a smooth latitudinal transition, a poleward reach only slightly farther than the oceanic ITCZ's, and a constant width throughout the year. The confinement of the monsoon to the deep tropics, especially in the western portion of the continent, is the result of advection of dry, low moist static energy air–a process known as ventilation. Contrary to much previous literature, though, we find that ventilation is not achieved by the mean westerly jet aloft bringing colder oceanic air over the continent, but by the anomalous low-level meridional circulation, which brings dry air from the subtropical portion of the continent equatorward. Because the anomalous circulation is in turn a response to the convection anomalies, we conclude that the limiting mechanism for the monsoon is coupled and sensitive to the surface properties of the land. 

How to cite: Biasutti, M. and Voigt, A.: Ventilation revisited: how dry continental air splits the ITCZ and stops the monsoon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3137, https://doi.org/10.5194/egusphere-egu22-3137, 2022.

The extremes of Indian summer monsoon rainfall (ISMR) are largely driven by the modulation of vertically integrated moisture flux over the Arabian sea (70^oE) and the Bay of Bengal (90^oE). The droughts and floods are resulted due to strong divergence and convergence of the moisture-laden winds over India associated with various external forcings. Therefore, identifying the association of the zonal moisture flux with ISMR in the observation and Climate Forecast System version 2 (CFSv2) model is essential to improve the prediction of the ISMR extremes. We find that, unlike observation, ISMR extremes in CFSv2 are all ENSO-related and mainly driven by the moisture flux over the Bay of Bengal and remain unresponsive to eastward boundary flux at 70^oE. Further decomposition of the fluxes into dynamical (winds) and thermodynamical (moisture) components shows that both moisture and winds terms over the Arabian sea are necessary for determining extremes. However, in CFSv2, only the winds component of the eastern boundary (90^oE) flux plays a significant role in driving the ISMR extremes. It is due to the presence of strong heating over the Western Pacific which results in strong eastward moisture flux over the Bay of Bengal through a Gill-type response.    

How to cite: Singhai, P., Chakraborty, A., Rajendran, K., and Surendran, S.: Are winds and moisture necessary to cause Indian summer monsoon extremes?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5658, https://doi.org/10.5194/egusphere-egu22-5658, 2022.

Robust projections of the Indian Summer Monsoon Rainfall (ISMR) are critical as it provides 80 % of the annual precipitation to more than one billion people who are very vulnerable to changes. However, even over the historical period, CMIP (Coupled Model Intercomparison Project) coupled models have difficulties to reproduce the observed ISMR trends and are affected by a large inter-model spread, which question the reliability of the ISMR projections. When studying climate response, three main sources of uncertainties exist : scenario uncertainties, internal variability and models bias. We study the impact of the latter on the historical response of ISMR of 34 models from CMIP6. First we show that model local biases over India do not impact significantly how they simulate the response of ISMR over the recent period. However, when we enlarge the analysis to the whole tropics and study the impact of regional and remote rainfall and SST biases on ISMR historical response by using a Maximum Covariance Analysis (MCA), we do find statistical significant relationships, which may provide observational constraints on future ISMR projections. Our results highlight the key-role of the temperature gradient errors between the arid regions surrounding India and the Arabian Sea on one hand, and of Pacific rainfall and SST biases on the other hand, as an important source of inter-model spread in the ISMR response. The physical mechanisms underlying these statistical relationships between ISMR response and the inter-model spread are finally explored.

How to cite: Guilbert, M., Mignot, J., and Terray, P.: Is there a relationship between the intermodel spread of biases and historical simulation of Indian Summer Monsoon Rainfall in CMIP6 coupled models ?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-735, https://doi.org/10.5194/egusphere-egu22-735, 2022.

Climate networks have recently helped to unravel spatial patterns of extreme rainfall events (EREs). However, EREs remain challenging to analyse due to their inherent stochasticty involved in their local distribution and intensity. Here, we present a principled approach to identify regions of similar ERE dynamics with the idea that this will help developing ERE prediction schemes in a later study.
We use a probabilistic approach to quantify community structures and estimating the structural uncertainties involved in the community detection process. First, we use time-delayed event synchronization to construct a network of ERE teleconnections. Using a Bayesian hierarchical community detection algorithm based on the Stochastic Block Model (SBM) enables us to estimate the likelihood that spatial locations belong to the same community via a point-wise spatial density analysis.
We apply our method to the South Asian Monsoon system and reveal a latitudinal band-like structure of synchronous EREs, whose occurrence is consistent with the onset and withdrawal of the monsoon season. Moreover, we demonstrate that exceptionally strong synchronization is observed when a fast developing low pressure system over the South China Sea occurs, as demonstrated by climatologies of days with maximum synchronization. 

How to cite: Strnad, F. and Goswami, B.: Spatio-temporal communities in networks of extreme rainfall events of the South Asian Monsoon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7261, https://doi.org/10.5194/egusphere-egu22-7261, 2022.

Madden–Julian oscillation (MJO) is an important oceanic and atmospheric phenomenon in the tropical belt around the globe which influences the global weather & climate system. The process mainly results east ward propagating band of rain clouds and its circulation pattern has a remarkable effect on the global annual rainfall. Monsoon onset is important as the rainfall transition and its progress has direct impact on the sectors like agriculture, water, health and economy etc. over the continent of India. As there are different phases in the MJO so it clearly affects the intra-seasonal and inter seasonal variability of rainfall, like for few phases it gives monsoon break type rainfall distribution whereas for some other phases it gives active rainfall distribution. It is also possible that the MJO phases have direct impact on the dynamics and physics during the onset as well as the progress of south west monsoon in India. In this study the association of different MJO phases and the resultant rainfall dynamics during onset period are analyzed using the multi-source weather observations for 68 years (1951-2018). The link of both active and weak phase of MJO and rainfall (duration and intensity) during the onset phases and thereafter during the progress of monsoon are quantified and presented. Also the spatial relation of the MJO location and the regional rainfall along with other oceanic parameters like Sea Surface Temperature, heat flux etc. are evaluated using the observed and reanalysis product. It is observed that mostly the active (weak) phase leads to early (late) onset over Kerala coast in India. Finally the tele-connection of progress of monsoon in continental India and the MJO phases are discussed. This association study will certainly help the researchers in better understanding of the MJO and regional rainfall dynamics and this information can be integrated with numerical weather prediction models for better and accurate prediction of the monsoon onset as well as the rainfall in the sub continent.

How to cite: lenka, S., Gouda, K. C., and Joseph, C. M.: Understanding the Dynamical Relation of MJO with Indian Summer Monsoon Onset and Progress, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-191, https://doi.org/10.5194/egusphere-egu22-191, 2022.

Coupled ocean-atmosphere teleconnections are characteristics of internal variability which have a forced response just like mean states. It is not trivial how to correctly and optimally estimate the forced response and changes of the El Niño-Southern Oscillation (ENSO)-Indian summer monsoon (ISM) teleconnection under greenhouse forcing. Here we use two different approaches to address it. The first approach, based on the conventional temporal method applied to 30 model simulations in Coupled Model Intercomparison Project Phase 6, suggests no model consensus on changes in the teleconnection on interannual timescale under global warming. The second approach is based on a converged infinite single model initial condition large ensemble (SMILE) and defines the relationship in an instantaneous climatological sense. In view of several characteristics of the teleconnection, a robust long-term strengthening of the teleconnection is found in the MPI-GE but not in the CESM1-LE. We discuss appropriateness and limitations of the two methods. 

How to cite: Lee, J.-Y. and Bodai, T.: Future Changes of the ENSO-Indian Summer Monsoon Teleconnection: The temporal vs ensemble-wise approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6741, https://doi.org/10.5194/egusphere-egu22-6741, 2022.

During the 20th Century, Sahel rainfall has experienced strong variability at decadal timescales, partly attributed to the internal variability of the climate system, mediated by changes in oceanic sea surface temperature (SST). However, a stronger emphasis has been more recently given to the role of external forcing. Thus, the attribution of past decadal modulations of Sahel rainfall is still under debate.

In this study, we propose a diagnostic of the contribution of external forcing to observed Sahel rainfall decadal modulations based on a correlation analysis. We apply it to six models of the sixth coupled model intercomparison project (CMIP6) in the whole 20th Century. Our results show that external forcings induce a weak amplitude of Sahel rainfall modulations in the models and these modulations are in general insignificantly correlated with the observed modulations. There are two notable exceptions: IPSL-CM6A-LR and INM-CM5-0 models.

With the IPSL-CM6-LR model, our results show that this correlation primarily arises from the role of anthropogenic aerosols. This effect is partly explained via the ocean mediated mechanism in particular the North Atlantic ocean and Mediterranean sea. In CanESM5 and CNRM-CM6-1 models, the Sahel rainfall decadal forced modulations are also dominantly due to anthropogenic aerosols, although not significantly correlated with the observations. In addition, the greenhouse gases (GHG) contribute significantly to the forced response of these models, which could explain partly the insignificant correlation of these CMIP6 models. 

How to cite: Ndiaye, C. D., Mignot, J., and Mohino, E.: Forced modulations of Sahel rainfall at decadal timescales over the20th Century using CMIP6 models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7125, https://doi.org/10.5194/egusphere-egu22-7125, 2022.

The NCAR CESM low-warming simulations (1.5⁰C, 2.0⁰C), RCP4.5 and RCP8.5 scenarios are used to assess the near term (2021–2050) changes of the Indian Summer Monsoon (ISM) variability. It is demonstrated that with the increase in warming and radiative forcing likely to cause an enhanced monsoon precipitation over east Asia. In 1.5⁰C forced climate, a weak ISM circulation is projected, while for 2.0⁰C warming monsoon circulation is likely to strengthen over the north Indian Ocean and intense easterlies from the equatorial Pacific are projected. Projection from the RCP4.5 scenario is associated with strong southwesterly monsoon wind over the entire Indian Ocean to the South China Sea and an intense easterly wind from the North Pacific to east Asia. The monsoon circulation over the north Indian Ocean is likely to weaken in the RCP8.5 forced climate. In all the scenarios, SLP variability over the far North Pacific is likely to play a dominant role as an internal variability to be able to influence the ISM circulation. It is found that an increasing standard deviation of internal Variability in SLP over the far North Pacific with increasing warming. Therefore, the importance of internal climate variability in SLP over the far North Pacific is clearly seen to influence the ISM projection pattern in the warming climate. Although model systematic biases in simulation still cause great concern for climate modelers, it is recognized that climate projections are inherently uncertain because a model can never fully describe the system that it attempts to specify. It is anticipated that this analysis based on the CESM ensemble will inspire probabilistic thinking and inform planning for the summer monsoon community and related stakeholders.

How to cite: Choudhury, D., Nath, D., and Chen, W.: Near-term Projection of the Indian Summer Monsoon Circulation Using CESM 1.5C, 2.0C, RCP4.5 and RCP8.5 Scenarios, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-997, https://doi.org/10.5194/egusphere-egu22-997, 2022.

Indian summer monsoon provides rainfall over a large area during 01 June to 30 September and it plays vital role for the water needs of the population of India. It is intense because strong differential heating prevails over the region due to geographical features of India. Further, it can be viewed as a synoptic scale ocean - atmosphere interactive system. In this study, we investigated the possible relation between the Indian summer monsoon and the combination of the different phases of Pacific Decadal Oscillation (PDO) and El Niño Southern Oscillation (ENSO) before and after the climate shift in 1976. This study is carried out using IMD’s precipitation dataset, HadISST v1.1 dataset and twentieth century reanalysis dataset by comparing anomalies of the respective parameters from 1901 to 2020. It is found that when positive (negative) phases of PDO and El Niño (La Niña) co-occur, deficit (surplus) rainfall are likely to occur over entire India. SST signatures of both phenomena are evident in this context. However, when negative (positive) PDO and El Niño (La Niña) co-occur, the signal is mixed and it is unlikely that either surplus or deficit rainfall conditions will occur over entire India. SST signatures are disrupted and minimized. In other words, when ENSO and PDO are in (out of) phase they enhance (counteract) the conventional monsoon-ENSO relation. Further, the study periods were divided into pre and post climate shift periods based on Niño 3.4 index and PDO index and analysed their impact on the Indian summer monsoon rainfall. In the pre-shift period, in-phase conditions exhibit similar qualities to those described above. Rainfall patterns are more indicative of ENSO than PDO. In the post-shift situation, the positive anomaly of SST in the PDO and Niño region is significantly stronger than that of the pre-shift phase. When compared to the pre-shift, positive rainfall anomalies are amplified during positive PDO and El Niño,  while negative PDO and La Niña show a weakening of positive rainfall anomalies. The out of phase condition has a balancing effect due to the counteracting impact, but with an increased positive anomaly of SST. In that combination, rainfall patterns with PDO characteristics rather than ENSO characteristics emerge. Significant warming of the Indian Ocean basin was also evident in the above combinations after the climate shift in 1976. Low level wind anomalies and other circulation features are consistent with the above result.

How to cite: K Xavier, A., Varikoden, H., and Chethalan Anthony, B.: Influence of PDO and ENSO on Indian summer monsoon rainfall and its changing relationship before and after climate shift, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1120, https://doi.org/10.5194/egusphere-egu22-1120, 2022.

Multiproxy records of benthic foraminifera, pteropods, and total organic carbon (TOC) of sediment samples from Core SK291/GC17 (water depth 182 meter), eastern Arabian Sea, indicate changes in monsoonal conditions and associated oceanographic variabilities during ~13000 to 3400 calibrated years before present (cal yr BP). During ~8000 cal yr BP, decreased abundance of pteropod Limacina trochiformis as well as the lower value of TOC, might be a proxy for a dry phase of monsoon. The interval from ~7800 to 6400 cal yr BP can be characterized by favorable bottom water conditions, as suggested by higher value of number of species (S), Information Function (H) and alpha index (α) of the benthic foraminiferal assemblage. The middle Holocene (~6200 to 4200 cal yr BP) interval is marked by a significant increase in the number of epipelagic pteropods caused by higher surface productivity and decreasing abundance of mesopelagic pteropods caused by the shoaling and intensification of the OMZ. The oxic group of benthic foraminifera decreased drastically while dysoxic group of benthic foraminifera increased during this interval, due to the intensified OMZ. After ~4200 cal yr BP, the oxic assemblage of benthic foraminifera and pteropods, coincide with a pronounced arid phase (4.2 ka event) in the Indian subcontinent. The oxic assemblage of benthic foraminifera shows high frequency cycles centered at 692, 440 and 358 yr driven by solar variability; while Uvigerina peregrina, a benthic foraminifer sensitive to OMZ variability, shows high frequency cycles of 403 and 745 yr.

How to cite: Majumder, J., Gupta, A., and Panigrahi, M.: A multi-proxy approach to understand the monsoon driven changes in the eastern Arabian Sea during the Holocene, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-221, https://doi.org/10.5194/egusphere-egu22-221, 2022.

How to cite: Moon, S. and Ha, K.-J.: Future changes in monsoon duration and precipitation using CMIP6, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6833, https://doi.org/10.5194/egusphere-egu22-6833, 2022.

The synoptic-scale tropical cyclonic disturbances that form over the monsoon trough region over the Indian subcontinent called monsoon low pressure systems (LPS) are the major rain bearers for the country. They are also known to cause extreme precipitation events leading to multiple catastrophic floods almost every year. Understanding the change in their characteristics under a warming climate is necessary for better preparedness and mitigation of their adverse effect. In this study, we use the Climate Earth System Model (CESM1.2.2) to investigate the impact of climate change on LPS characteristics over India. The model is run at 0.9°×1.25° horizontal resolution, and output is saved at 6-hourly intervals for LPS track analysis. Two experiments are performed: a present-day control simulation (CTRL) and an RCP8.5 simulation (indicating warmer climate) towards the end of the current century. LPS are tracked in the experiments using an Automated Tracking Algorithm using Geopotential Criteria (ATAGC) for a 37-year period in the control simulation and during 2070-2100 in the RCP8.5 scenario. As expected, an increase in mean monsoon precipitation and a decrease in monsoon circulation are simulated over the Indian subcontinent in RCP8.5 compared to CTRL. But the change in the number of LPS is insignificant under a warming climate. A shift is found in the number of LPS genesis over land and ocean, with a larger number of genesis over the land in the RCP8.5 scenario. The trend in precipitation is consistent with mean monsoon precipitation, i.e., an increase in the magnitude of mean and extreme precipitation associated with LPS occurs under a warmer climate. Results from the investigations on the likely causes of the model results will be presented at the meeting.

How to cite: Thomas, T. M., Bala, G., and Srinivas, V. V.: Change in characteristics of Monsoon low pressure systems under a warming climate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1006, https://doi.org/10.5194/egusphere-egu22-1006, 2022.

The trends of extreme precipitation events during the Indian summer monsoon measured by two different indicators have been analyzed for the period 1901-2020, covering the entire India in 9 regions segregated by a clustering analysis based on rainfall characteristics using the Indian Meteorological Department high-resolution gridded data. The important climatological parameters correlating to such increasing trends have also been identified by performing for the first time a multivariate analysis using a nonlinear machine learning regression with 17 input variables. It is found that man-made long-term shifting of land-use and land-cover patterns, and most significantly the urbanization, play a crucial role in the prediction of the long-term trends of extreme precipitation events, particularly of the intensity of extremes. To further study this urbanization impact, a regional cloud-resolving model has been used to examine causal relation between drastic long-lasting change brought by urbanization and extreme precipitation events. The preliminary results will be presented.

How to cite: Falga, R. and Wang, C.: On the rise of Indian summer monsoon precipitation extremes and its correlations with long-term changes of certain anthropogenic factors and climate variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5558, https://doi.org/10.5194/egusphere-egu22-5558, 2022.