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AS1.18

EDI
Monsoon systems in a changing climate: past, present and future

The regional monsoons and the global monsoon circulation to which they belong have profound impacts on water, energy, and food security. Monsoons cause severe floods and droughts as well as undergoing variability on subseasonal, interannual and decadal-to-multi-decadal time scales. In addition to profound local effects, monsoon variability is also associated with global-scale impacts via teleconnections.

Monsoons are among the most complex phenomena involving coupled atmosphere-ocean-land interactions and remain notoriously difficult to forecast at leads times ranging from numerical weather prediction (NWP) to long-term climate projections. A better understanding of monsoon physics and dynamics, with more accurate simulation, prediction and projection of monsoon systems is therefore of great importance.

This session invites presentations on all aspects of monsoon research in present-day, future and palaeoclimate periods, involving observations, modelling, attribution, prediction and climate projection. Topics ranging from theoretical works based on idealized planets and ITCZ frameworks to the latest field campaign results are also invited, as is work on impacts, extremes, NWP modelling, S2S and decadal forecasting, and the latest CMIP6 findings.

Co-organized by CL5.3
Convener: Andrew Turner | Co-conveners: Jianping Li, Roberta D AgostinoECSECS, Kyung-Ja Ha
Presentations
| Tue, 24 May, 08:30–11:44 (CEST), 13:20–14:37 (CEST)
 
Room M2

Tue, 24 May, 08:30–10:00

Chairpersons: Andrew Turner, Roberta D Agostino

08:30–08:40
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EGU22-5015
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solicited
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Highlight
Salvatore Pascale and William Boos

The core of the North American monsoon (NAM) is characterized by a band of intense rainfall along the western coast of Mexico. This rainfall band is commonly understood to be caused by thermal forcing from both the elevated terrain of that region (Sierra Madre) and land. This fits into the general paradigm of monsoons as thermally direct circulations driven by heat sources. In this talk, instead, we show that the NAM rainfall is generated by the interaction of the extratropical jet stream with mountain ranges. We reach this conclusion using observations, a high-resolution global climate model, and stationary wave solutions to show that the NAM core rainfall band arises when Mexico’s Sierra Madre mountains mechanically force an adiabatic stationary wave through the equatorward diversion of extratropical westerly winds; westerly, upslope flow associated with that stationary wave then lifts warm and moist air to cause convective rainfall. Heat fluxes at the surface precondition the atmosphere for convection, especially in summer afternoons, but they alone are insufficient to produce the observed rainfall maximum.

 

These results, together with dynamical structures in observations and models, indicate that the core monsoon should be understood as convectively enhanced orographic rainfall in a mechanically forced stationary wave, not as a classic, thermally forced tropical monsoon. This has implications for the response of the NAM to past and future global climate change, making trends in jet stream interactions with orography of central importance.

How to cite: Pascale, S. and Boos, W.: Mechanical forcing of the North American monsoon by orography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5015, https://doi.org/10.5194/egusphere-egu22-5015, 2022.

08:40–08:47
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EGU22-6986
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ECS
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Ruolan Xiang et al.

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.

08:47–08:54
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EGU22-12069
Andrew Turner et al.

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.

08:54–09:01
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EGU22-8832
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ECS
Rajat Masiwal et al.

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.

09:01–09:08
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EGU22-6769
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ECS
Deepika Rai and Shira Raveh-Rubin

Daily-to-weekly variations between active and break monsoon phases critically control Indian summer monsoon (ISM) rainfall and directly influence society. This variability depends on the complex air flows from different origins; for example, dry intrusions (DIs) reaching the Indian region from western Asia limit ISM rainfall. This study documents DIs that originate in the southern hemisphere winter, cross the equator and reach the Arabian Sea during the ISM season. Being a global hot spot of such cross-equatorial intrusions, they have great potential to modify the moisture availability and hence the ISM rainfall.
Using 6-hourly ERA-Interim reanalysis data with a Lagrangian approach, we show that more than 95% of cross-equatorial DIs reach below 850 hPa in the Arabian Sea within five days of their initiation in the southern hemisphere. Though rare (<1% frequency in time), their presence in the marine boundary layer triggers intense ocean evaporation and enhances the low-level Somali jet intensity. The result is compensation for their initial dryness and overall increasing the moisture transport towards India. Analysis based on 130 DI events during the ISM season from 1979-2018, shows that more than 64% of the DI events are associated with more rainfall, with a mean 12% enhancement in the rain compared to climatology. These DI events favor the central Indian Ocean as the major source of moisture during the ISM season, different from mean conditions. Indeed, 52% of known active spells are preceded by DI events. In summary, cross-equatorial DIs reaching the marine boundary layer over the tropical Indian ocean during ISM season is responsible for the development of anomalously moist air, which enhances the rainfall over the Indian region downstream, and are thus crucial for ISM rainfall predictability.

How to cite: Rai, D. and Raveh-Rubin, S.: Contribution of cross-equatorial dry intrusions to Indian summer monsoon rainfall, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6769, https://doi.org/10.5194/egusphere-egu22-6769, 2022.

09:08–09:15
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EGU22-1759
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ECS
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Luisa E. Aviles Podgurski et al.

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.

09:15–09:22
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EGU22-12004
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ECS
Maxime Colin et al.

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.

09:22–09:29
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EGU22-3137
Michela Biasutti and Aiko Voigt

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.

09:29–09:36
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EGU22-5658
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ECS
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Priyanshi Singhai et al.

The extremes of Indian summer monsoon rainfall (ISMR) are largely driven by the modulation of vertically integrated moisture flux over the Arabian sea (70oE) and the Bay of Bengal (90oE). 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 70oE. 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 (90oE) 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.

09:36–09:43
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EGU22-11673
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ECS
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Popat Salunke and Saroj Kanta Mishra

The performance of climate models and their multi-model mean (MMM) in CMIP6 and CMIP5 precipitation simulations is compared using the India Meteorological Department (IMD) observations over the Indian summer monsoon (ISM) season (June-September) from 1975-2005. It is found that CMIP6 MMM better simulates the spatial distribution of seasonal mean precipitation than CMIP5 MMM and has shown improvements in biases over central India, northeast India, and also in capturing orography related precipitation over western Ghats and the northeast Himalayas. CMIP6 MMM performed better than CMIP5 MMM in capturing precipitation trends but failed to capture the overall declining trend. In consequence, in terms of precipitation simulation, the CMIP6 models (pattern correlation 0.4-0.8) outperformed the CMIP5 models (pattern correlation 0.2-0.7). MMMs well capture the observed phase of the annual cycle of the precipitation but underestimate the amplitude during summer monsoon months. In contrast, most of the CMIP6 models and their MMM have improved skill scores (SS) (SS 0.66) in reproducing the climatological summer precipitation compared to CMIP5 models and their MMM (SS 0.57). Furthermore, the results show that the Somali jet strength is well associated with ISM rainfall and has risen by about 2 m s-1 in CMIP6 MMM compared to CMIP5 MMM. 

Key Word: Indian Summer Monson, MMM, CMIP6, CMIP5, Precipitation

 

How to cite: Salunke, P. and Mishra, S. K.: Evaluation of Indian Summer Monsoon Precipitation using CMIP5 and CMIP6 models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11673, https://doi.org/10.5194/egusphere-egu22-11673, 2022.

09:43–09:50
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EGU22-735
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ECS
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Marcellin Guilbert et al.

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.

09:50–09:57
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EGU22-7470
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ECS
Matthias Fischer et al.

Forecasting the West African monsoon (WAM) on weather and climate timescales suffers from large uncertainties. Particularly the precipitation associated with the WAM has a great socioeconomic impact through effects on agriculture, energy production, water resources and health.  Aside from errors stemming from initial condition uncertainty, forecasts are generally affected by model uncertainties associated with parameter choices in the representation of sub-gridscale processes. To quantify the combined effect of the latter, a comprehensive sensitivity study is conducted by feeding output of a highly-resolved atmospheric model into so-called surrogate models. This technique allows a comprehensive but resource-friendly statistical investigation of the sensitivity of key WAM characteristics to uncertain model parameters.

The ICON (Icosahedral Nonhydrostatic) model, which is operationally used by the German Weather Service (DWD), is used to simulate the WAM in limited-area mode at 13km grid spacing, using ERA-5 re-analyses as boundary data. To separate model parameter related sensitivities from weather noise and to reduce the influence of initial conditions, a sufficiently long simulation time (in this study 4 WAM seasons with 41 days each starting on July 21st) is required. To avoid the immense computational costs of conducting a large matrix of month-long numerical simulations, surrogate models are used to statistically describe the relationship between uncertain model parameters and quantities of interest (QoIs) derived from the simulation output. For this study, we selected the QoIs total precipitation, latitudinal position of the WAM rain belt, location and strength of the Tropical Easterly Jet (TEJ) and the African Easterly Jet (AEJ), location and extent of the Saharan heat low (SHL) as well as location of the Intertropical Discontinuity (ITD).

For each of the chosen six uncertain model parameters probability density functions are assigned based on measurements and previous studies. Maximin Latin hypercube sampling is applied in order to define 60 parameter combinations. Universal kriging as a general case of Gaussian process regression is used to build surrogate models for the QoIs. These then serve to carry out global sensitivity studies in order to identify the parameters that have the greatest influence on the QoIs. The results indicate for which parameters (and thus processes) uncertainties need to be reduced to lower the spread in simulated QoIs. Furthermore, the surrogate model can serve as a basis for parameter identification studies, e. g. by means of maximum likelihood estimation where simulations are compared to observations.

Among the investigated model parameters, the entrainment rate in the convection scheme and the terminal fall velocity of cloud ice show the greatest effects on the QoIs. The former mainly affects the AEJ, the SHL and the ITD, whereas the latter mainly influences the TEJ. Simple isolated relationships between individual model parameters and WAM QoIs, however, rarely exist. Consistent with the complex nature of the WAM system, individual QoIs instead are affected by multiple parameters. On the other hand, individual parameters affect multiple QoIs simultaneously, reflecting the physical relationships between them. This highlights the usefulness of incorporating surrogate models in the analysis of model uncertainty.

How to cite: Fischer, M., Knippertz, P., van der Linden, R., Lemburg, A., Pante, G., and Proppe, C.: Using surrogate models to quantify uncertainty in simulations of the West African Monsoon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7470, https://doi.org/10.5194/egusphere-egu22-7470, 2022.

Tue, 24 May, 10:20–11:50

Chairpersons: Roberta D Agostino, Andrew Turner

10:20–10:27
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EGU22-7261
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ECS
Felix Strnad and Bedartha Goswami

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.

10:27–10:34
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EGU22-191
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ECS
smrutishree lenka et al.

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.

10:34–10:41
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EGU22-10671
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Highlight
Alice M Grimm and Lais G Fernandes

The changes in the Madden-Julian Oscillation (MJO) and its impacts on the South American monsoon season during different El Niño-Southern Oscillation (ENSO) states (El Niño – EN, La Niña – LN, neutral – NT) are analyzed in the global context of the MJO propagating anomalies of convection and circulation. The background ENSO-related anomalies influence several aspects of MJO (relative occurrence of phases, propagation, convection and teleconnections), and therefore modify the MJO impacts on South America (SA), such as precipitation anomalies and frequency of extreme events, as well as their temporal distribution throughout the MJO cycle. Changes include: (1) a delay in the peak of the teleconnections between central-eastern Pacific and SA, from MJOphase8 in LN to MJOphase1 in EN; (2) enhanced MJO convection in the central-east subtropical South Pacific in MJOLNphases7+8 and a little further east in MJOENphases8+1, in a region efficient in generating tropics-extratropics teleconnections via Rossby wave to SA, producing rainfall anomalies over Central-East SA (CESA), especially the South Atlantic Convergence Zone (SACZ), strongest one phase earlier in LN (MJOLNphase8) than in EN (MJOENphase1), and a little shifted east in the latter than in the former; (3) enhancement of the extratropical teleconnection via Rossby wave and its impacts over subtropical CESA in both EN and LN (with regard to NT), suggesting that both ENSO states generate forcing in the source region that more efficiently triggers stronger Rossby waves than forcing in NT ENSO years, indicating nonlinear ENSO effects on MJO anomalies over SA; (4) predominant increase (or reduction) in the frequency of extreme events over densely populated SA regions where both ENSO and MJO contribute in the same direction, with the greatest increase over CESA (including SACZ) during EN, in MJOENphase1, and over Southeast SA (SESA), in MJOENphase3; (4) enhanced amplitude in both states, EN and LN, of the first continental intraseasonal dipole-like mode of precipitation variability between CESA and SESA, with maximum opposite anomalies in CESA, the center with largest amplitude, in phases 1 and 4 for EN, and phases 8 and 5 for LN. Significant effects can also be observed in other regions, such as northeast and northwest SA.

How to cite: Grimm, A. M. and Fernandes, L. G.: ENSO modulation of MJO and its impacts on South America: enhancement of extreme events, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10671, https://doi.org/10.5194/egusphere-egu22-10671, 2022.

10:41–10:48
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EGU22-6741
June-Yi Lee and Tamas Bodai

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.

10:48–10:55
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EGU22-432
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ECS
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Hanna Heidemann et al.

We analyse the decadal variability in the relationship between Australian monsoon rainfall (AUMR) and the El Niño Southern Oscillation (ENSO). A composite analysis is conducted to examine monsoon season (December to March) rainfall anomalies over northern Australia during central and eastern Pacific ENSO events between 1920 to 2020. These composites are evaluated separately for positive and negative phases of the Interdecadal Pacific Oscillation (IPO) and reveal differences in AUMR anomalies with respect to ENSO event diversity. During central Pacific (CP) El Niño events, the key month is February, in which the AUMR is above average in positive IPO phases and below average during negative IPO phases. This is due to low-level circulation anomalies northwest of Australia, which are cyclonic in the positive IPO phases and anticyclonic in negative IPO phases, in addition to moisture fluxes directed towards the central Pacific, away from northern Australia. During CP La Niña events, there are insignificant rainfall anomalies over northern Australia in December during positive IPO phases. In contrast, during negative IPO phases, strong and significant positive rainfall anomalies cover much of northern and eastern Australia, which relate to large-scale convergence of moisture and an intensification of the Walker Circulation. In summary, AUMR anomalies during CP ENSO events differ between positive and negative phases of the IPO due to variability in the large-scale atmospheric circulation.

How to cite: Heidemann, H., Ribbe, J., Cowan, T., and Henley, B. J.: The decadal modulation of the ENSO-Australian monsoon rainfall teleconnection , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-432, https://doi.org/10.5194/egusphere-egu22-432, 2022.

10:55–11:02
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EGU22-12204
Arindam Chakraborty

In a continuing warming climate, it is necessary to understand how the Indian summer monsoon (ISM) will respond to El Nino Southern Oscillation (ENSO) and other dominant Non-ENSO climate patterns. Using several coupled climate models participated in the CMIP6 simulations, we show that the frequency of droughts and floods is similar in these models either in the historical or future scenarios (ssp126, ssp245, ssp370, ssp585). This symmetry is unlike the observation where droughts are more frequent and vigorous than floods. We show that while the number of ENSO years is projected to increase with raised CO2 forcings, the fraction of ENSO and Non-ENSO years experiencing extremes of ISM remain relatively constant. However, the future scenarios indicate more frequent La Nina-related floods than the historical period. We show that most models do not capture the observed spatial maps of vertically integrated moisture flux during Non-ENSO ISM extreme years. While in the observation, a stronger role is played by the climate of the Arabian Sea and West Asia, most models are driven by the climate of the western North Pacific Ocean during non-ENSO ISM extremes. Our results indicate changes in the future teleconnection pattern during Non-ENSO related ISM extremes. These results call for special attention for model diagnosis and development for a better seasonal prediction.

How to cite: Chakraborty, A.: On the present and future teleconnection to the Indian summer monsoon in CMIP6 models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12204, https://doi.org/10.5194/egusphere-egu22-12204, 2022.

11:02–11:09
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EGU22-8983
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ECS
Yazhou Zhang and Jianping Li

The impact of the South China Sea summer monsoon (SCSSM) on the Indian Ocean dipole (IOD) has been systematically investigated in observations. This study focuses on the ability of climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5) to reproduce the observed relationship between the SCSSM and IOD, and the relevant physical mechanisms. All 23 models reproduce significant correlations between the SCSSM and IOD during boreal summer (June–July–August, JJA), whereas the influence of the SCSSM on the IOD varies considerably across the CMIP5 models. To explore the causes, all models are divided into two groups. Models that successfully simulated both the correlations between the SCSSM and JJA IOD and of the SCSSM and JJA IOD with precipitation over the western North Pacific and Maritime Continent are classified as Type-I, and these produce stronger low-level wind anomalies over the tropical southeastern Indian Ocean. The stronger low-level wind anomalies enhance local sea surface temperature (SST) anomalies via positive wind–evaporation–SST (WES) and wind–thermocline–SST (Bjerknes) feedbacks. This corresponds to a strengthening of IOD events due to the increased zonal gradient of SST anomalies over the tropical Indian Ocean. In contrast, Type-II models perform poorly in representing the relationship between the SCSSM and JJA IOD or relevant atmospheric bridges, corresponding to weaker WES and Bjerknes feedbacks, and produce weaker IOD events. These results demonstrate that the better the model simulation of the atmospheric bridge, the larger contribution of the SCSSM to the IOD.

How to cite: Zhang, Y. and Li, J.: Impact of the South China Sea summer monsoon on the Indian Ocean dipole in CMIP5 models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8983, https://doi.org/10.5194/egusphere-egu22-8983, 2022.

11:09–11:16
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EGU22-13381
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Highlight
Ben Webber et al.

Indian Summer Monsoon (ISM) precipitation is known to be influenced by both the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). El Niño events often coincide with droughts in the ISM region, yet there is considerable variability in the ISM response, partially due to coincident IOD events. However, it is unclear how SST patterns associated with different El Niño types combine with IOD-related SST anomalies to produce the ISM response. Here we use an atmospheric general circulation model forced by combinations of regional SST anomalies in both Pacific and Indian Oceans during the developing phase of El Niño (i.e., the ISM season prior to peak ENSO SST anomalies) to identify interactions in the teleconnection pathways. We find that the responses combine in a strongly non-linear manner. Consistent with previous studies, we find that IOD events largely counteract the influence of ENSO events, but also that this interaction depends on the pattern and magnitude of SST anomalies in the Indian Ocean. The impact on the ISM depends substantially on the details of the SST gradients, especially in the vicinity of the Maritime Continent where relatively minor differences in the pattern of cold SSTs and associated gradients generate regional circulation patterns that interfere with the large-scale teleconnection pathways. When combined with cold IOD SST anomalies, the influence of Eastern Pacific El Niño events on the ISM is smaller than the influence of Central Pacific El Niño events. Small differences in SST patterns and associated gradients can have substantial impacts on ISM precipitation anomalies, which may contribute to the observed variability in the ISM response to ENSO events, and as such are worthy of further research.

How to cite: Webber, B., Uppara, U., Joshi, M., and Turner, A.: The influence of cold SST anomalies surrounding the Maritime Continent on the El Niño-Indian monsoon teleconnection , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13381, https://doi.org/10.5194/egusphere-egu22-13381, 2022.

11:16–11:23
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EGU22-9522
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ECS
Zhaolu Hou et al.

Numerical seasonal forecasts in Earth science always contain forecast errors that cannot be eliminated by improving the ability of the numerical model. Therefore, correction of model forecast results is required. Analog correction is an effective way to reduce model forecast errors, but the key question is how to locate analogs. In this paper, we updated the local dynamical analog (LDA) algorithm to find analogs and depicted the process of model error correction as the LDA correction scheme. The LDA correction scheme was first applied to correct the operational seasonal forecasts of sea surface temperature (SST) over the period 1982–2018 from the state-of-the-art coupled climate model named NCEP Climate Forecast System, version 2. The results demonstrated that the LDA correction scheme improves forecast skill inmany regions as measured by the correlation coefficient and root-mean-square error, especially over the extratropical eastern Pacific and tropical Pacific, where the model has high simulation ability. El Niño–Southern Oscillation (ENSO) as the focused physics process is also improved. The seasonal predictability barrier of ENSO is in remission, and the forecast skill of central Pacific ENSO also increases due to the LDA correction method. The intensity of the ENSOmature phases is improved.Meanwhile, the ensemble forecast results are corrected, which proves the positive influence from this LDA correction scheme on the probability forecast of cold and warm events. Overall, the LDA correction scheme, combining statistical and model dynamical information, is demonstrated to be readily integrable with other advanced operational models and has the capability to improve forecast results.

How to cite: Hou, Z., Li, J., and Zuo, B.: Correction of Monthly SST Forecasts in CFSv2 Using the Local Dynamical Analog Method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9522, https://doi.org/10.5194/egusphere-egu22-9522, 2022.

11:23–11:30
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EGU22-2120
Jianping Li et al.

In this paper, we investigate the influence of the winter NAO on the multidecadal variability of winter East Asian surface air temperature (EASAT) and its decadal prediction. The observational analysis shows that the winter EASAT and East Asian minimum SAT (EAmSAT) display strong in-phase fluctuations and a significant 60–80-year multidecadal variability, apart from a long-term warming trend. The winter EASAT experienced a decreasing trend in the last two decades, which is conducive to the occurrence of winter extremely cold events in East Asia in recent years. The winter NAO leads the detrended winter EASAT by 12–18 years with a maximumly significant positive correlation at the leading time of 15 years. Further analysis shows that ENSO may affect winter EASAT interannual variability, but does not affect the robust leading relationship between the winter NAO and EASAT. We present the coupled oceanic-atmospheric bridge (COAB) mechanism of the NAO influences on winter EASAT multidecadal variability through its accumulated delayed effect of ~15 years on the Atlantic Multidecadal Oscillation (AMO) and Africa–Asia multidecadal teleconnection (AAMT) pattern. Based on the COAB mechanism an NAO-based linear model for predicting winter decadal EASAT is constructed, with good hindcast performance. The winter EASAT for 2020–2034 is predicted to keep on fluctuating downward until ~2025, implying a high probability of occurrence of extremely cold events in coming winters in East Asia, and then turn towards sharp warming. The predicted 2020/21 winter EASAT is almost the same as the 2019/20 winter.

Keywords: winter East Asian surface air temperature (EASAT), North Atlantic Oscillation (NAO), Atlantic Multidecadal Oscillation (AMO), Africa-Asia multidecadal teleconnection (AAMT) pattern, coupled oceanic-atmospheric bridge (COAB), multidecadal variability.

How to cite: Li, J., Xie, T., Tang, X., Wang, H., Sun, C., Feng, J., Zheng, F., and Ding, R.: Influence of the NAO on wintertime surface air temperature over the East Asia: multidecadal variability and decadal prediction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2120, https://doi.org/10.5194/egusphere-egu22-2120, 2022.

11:30–11:37
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EGU22-7125
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ECS
Cassien Diabe Ndiaye et al.

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.

11:37–11:44
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EGU22-8335
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ECS
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Aissatou Badji et al.

The intraseasonal characteristics of rainfall are crucial in monsoon regions, in particular for
agriculture. Crop yields indeed depend on the rainfall seasonal amount, but also on other
intraseasonal characteristics such as the onset of the rainy season or the distribution of rainy days.
In the Sahel region, while the average amount of seasonal rainfall has been shown to be marked by
strong decadal variability over the 20 th century, the modulations of intraseasonal rainfall
characteristics has received less attention in the literature so far. In this study, we show that the
frequency and intensity of intraseasonal rainfall events in Senegal exhibit a marked decadal
variability over the 1918-2000 period, similar to that of mean seasonal rainfall in the Sahel during
the 20 th century, and in phase with the Atlantic Multidecadal Variability (AMV). The representation
of the decadal modulation of these rainfall indices is further investigated using the atmospheric
component of the IPSL-CM6 model forced by the historically observed SST. Preliminary results
show that the model represents fairly well the observed decadal modulation of these extreme events.
Thus, the model simulations allow an in-depth understanding of the associated mechanism.

How to cite: Badji, A., Mignot, J., Mohino, E., Diakhaté, M., and Gaye, A. T.: Decadal variability of rainfall extreme events in Senegal over the 20th century:observations and modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8335, https://doi.org/10.5194/egusphere-egu22-8335, 2022.

Tue, 24 May, 13:20–14:50

Chairpersons: Andrew Turner, Roberta D Agostino

13:20–13:27
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EGU22-997
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ECS
Devanil Choudhury et al.

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.

13:27–13:34
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EGU22-1120
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ECS
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Anupama K Xavier et al.

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.

13:34–13:41
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EGU22-2891
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Highlight
Roberto Ingrosso and Francesco Rocco Salvatore Pausata

The Great GreenWall (GGW) is a multibillion-dollar African initiative to combat desertification and drought in the Sahel.  In Western Africa, the most important climate feature is the West African Monsoon (WAM), which brings rainfall over the Sahel during the Northern Hemisphere summer. Changes in WAM strength and length could impact climate both regionally and far afield, such as the tropical Atlantic, equatorial Pacific or the Arctic, Potential climatic system response to a greener Sahel are investigated, by means of an atmospheric climate model, looking at changes in the regional atmospheric circulation and climate indices aimed at providing information about changes in extreme events. The analysis shows significant changes in temperature, precipitation and atmopsheric circulation and in the climate indices considered related to the presence of the GGW for the end of this century. 

How to cite: Ingrosso, R. and Pausata, F. R. S.: On the potential impact of the Great Green Wall on the West African Monsoon , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2891, https://doi.org/10.5194/egusphere-egu22-2891, 2022.

13:41–13:48
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EGU22-12436
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ECS
Lucy Recchia and Valerio Lucarini

The Indian summer monsoon is a key meteorological event in the Indian calendar, bringing approximately 80% of India’s annual rainfall over the months of June—September. How the monsoon system will react to a changing future climate is of crucial importance for India’s agriculture, industry and economy.

 

Uncertainty remains in the future climate projections of the Indian monsoon,  primarily due to uncertainties in the amount and composition of aerosols over the Asian region. A further complication is that greenhouse gases, expected to increase over the next 50 years and dominate over aerosol forcing, have a directly competing effect on the monsoon. Generally, greenhouse gases act to heat the Earth’s surface, enabling greater moisture uptake and enhancing monsoonal precipitation. In contrast, aerosols have a cooling effect at the surface. The presence of aerosols is analogous to anomalous heating in the mid-troposphere, increasing the static stability of the atmosphere, which is associated with a weakening of the large-scale circulation and thus a weakening of the monsoon. 

 

We use the Planet Simulator (PlaSim), an intermediate complexity climate model, to investigate the interplay between varying aerosol and greenhouse gas forcing, in relation to the Indian summer monsoon. The model is modified to include anomalous heating in the mid-troposphere, which represents the presence of aerosols and effectively cools the surface. Varying the intensity and location of aerosol forcing, as well doubling the amount of carbon dioxide, alters the spatial pattern of precipitation over the Asian region. Increasing the anomalous heating to 150 Watts and applying over the regions of India, East China and Southeast Asia, significantly weakens the large-scale circulation and reduces the summer precipitation to 10-20% of a normal year; essentially a breakdown of the monsoon system. Through modelling sensitivity studies, we define a safe operating space of future climate conditions, where the Indian and East Asian monsoons retain their current regimes. We can also show early warning signals in the precipitation intensity, indicating a phase change of the Indian or the East Asian monsoon.

How to cite: Recchia, L. and Lucarini, V.: Effect of varying aerosol forcing on the Indian summer monsoon in an intermediate complexity climate model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12436, https://doi.org/10.5194/egusphere-egu22-12436, 2022.

13:48–13:55
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EGU22-221
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ECS
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Jeet Majumder et al.

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.

13:55–14:02
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EGU22-2652
Ori Adam et al.

The tropical rain belt is composed of rain bands that lie along the rising branches of the tropical atmospheric overturning circulation. The properties of these rain bands determine the zonal-mean tropical precipitation distribution, which varies between uni- and bimodality. Here we define tropical modality as an index that varies continuously between 1 and 2 for purely uni- and bimodal distributions. We examine the relation of tropical modality to the seasonal cycle of the tropical rain belt across a wide range of climate models from phases 5 and 6 of the climate model intercomparison project, simulations of Earth's climate over geological timescales (~300Ma to present), and observations. Our analysis shows that modality is an essential characteristic of tropical climate, which binds together fundamental properties of the tropical rain belt and its associated tropical overturning circulation. Specifically, tropical modality is found to efficiently parse differences across models and climates, especially in regions where variance is greatest. Increased tropical modality (i.e., tendency toward bimodality) is strongly related to increased width of the tropical rain belt, wider and weaker Hadley circulation, colder equatorial cold tongues, and more severe double-intertropical convergence zone bias in modern climate models. As tropical modality increases, considering shifts of hemispheric precipitation peaks becomes crucial. In particular, counter to general wisdom, for large tropical modality (i.e., ~2), seasonal migrations of the tropical rain belt do not follow the Hadley circulation paradigm, to the extent that hemispheric rain bands might not follow the Sun.

How to cite: Adam, O., Farnsworth, A., and Lunt, D.: Modality and seasonal variation of the tropical rain belt across climates and models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2652, https://doi.org/10.5194/egusphere-egu22-2652, 2022.

14:02–14:09
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EGU22-6833
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ECS
Suyeon Moon and Kyung-Ja Ha

Future change in summertime rainfall under a warmer climate will impact the lives of more than two-thirds of the world’s population. However, the future changes in the duration of the rainy season affected by regional characteristics are not yet entirely understood. We try to understand changes in the length of the rainy season as well as the amounts of the future summertime precipitation, and the related processes over regional monsoon domains using phase six of the Coupled Model Intercomparison Project archive. Projections reveal extensions of the rainy season over the most of monsoon domains, except over the American monsoon. Enhancing the precipitation in the future climate has various increasing rates depending on the subregional monsoon, and it is mainly affected by changes in thermodynamic factors. This study promotes awareness for the risk of unforeseen future situations by showing regional changes in precipitation according to future scenarios.

 

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.

14:09–14:16
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EGU22-11378
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ECS
Rohtash Saini et al.

The South Asian monsoon is a lifeline of over two billion inhabitants of the Indian subcontinent. Hence, a reliable monsoon prediction system is essential for the operation of weather and climate over the region. The state-of-art General Circulation Models (GCMs) are powerful tools for monsoon prediction and assessing the effects of climate change on precipitation and temperature in rising extreme events such as floods, storms, heatwaves, and drought. However, selecting appropriate GCMs is a grand challenge for assessing climate change projections due to their significant uncertainties. The present study will evaluate the relative performance of GCMs of phases 5 and 6 of the Coupled Model Intercomparison Project dataset based on their multi-model mean (MMM) ability to project rainfall and temperature during the summer season (JJAS) over central India. In addition to the spatial patterns under the Shared Socioeconomic Pathways (SSPs), the study will also examine the model's ability to simulate interannual variability. The present research aims to determine the most reliable CMIP6 and CMIP5 datasets model and their comparison in simulation and projection of seasonal temperature and precipitation. The seasonal climatological mean of GCMs simulated rainfall and temperature shows variability at different scales over central India. CMIP6 multi-model mean demonstrate a reasonably well performance than CMIP5 in the seasonal mean cycle simulation with a better representation of the rainfall. The present study will also investigate the changes in sources of projection uncertainty and future precipitation indices. Finally, the current research will discuss the highlights of comparing the CMIP6 and CMIP5 datasets and their representations of better simulation performances based on the skill score metrics of precipitation and temperature indices.

KEYWORDS. CMIP6, CMIP5, MMM precipitation and temperature, Projection

How to cite: Saini, R., Attada, R., and Pathaikara, A.: Comparison of CMIP6 and CMIP5 Models in Projections of Precipitation and Temperature over Central India, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11378, https://doi.org/10.5194/egusphere-egu22-11378, 2022.

14:16–14:23
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EGU22-1006
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ECS
Tresa Mary Thomas et al.

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.

14:23–14:30
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EGU22-3471
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ECS
Guillaume Chagnaud et al.

Regional projections of rainfall changes are required for adaptation planning, especially in regions where unprecedented climatic evolution are underway, such as the West African Sahel. The potential of models to draw a realistic picture of future regional changes remains to be assessed through the lens of past evolution. Here we make sense of several rainfall regime indicators, a widespread raingauge dataset and a set of the most recent climate model simulations to identify features that deserve confidence and others that require care. We show that, at the sahelian scale, the mean intensity and occurrence of rainy days are well reproduced, yielding a good depiction of the recent rainfall intensification. However, unlike wet extremes, changes in dry extremes are not captured, pointing to model deficiencies in reproducing realistic changes in intraseasonal rainfall variability. We also show that the regional rainfall evolution of the last 35 years is very unlikely due to neither internal variability nor to natural forcing factors alone; based on a qualitative attribution analysis, aerosols turn out to account for the largest share of the recent increasing signal. The greenhouse-gases (GHG) influence makes less consensus among models, especially regarding extreme rainfall trends. This is a major concern for projections of future hydro-climatic trajectories in the region since GHG is to become the predominant climate forcing factor for the coming decades.

How to cite: Chagnaud, G., Panthou, G., Vischel, T., and Lebel, T.: What do CMIP6 models tell us about rainfall intensification in the West African Sahel?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3471, https://doi.org/10.5194/egusphere-egu22-3471, 2022.

14:30–14:37
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EGU22-5558
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ECS
Renaud Falga and Chien Wang

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.