Monsoon Regime Research Articles

Comparative analysis of cloud properties over drought- and flood-prone regions of western India using machine learning techniques

ABSTRACT Cloud properties are pivotal in analyzing rainfall patterns in monsoon-dependent countries such as India. The impact of climate change becomes more important in regions susceptible to hydrometeorological events due to different monsoon regimes. To examine regional heterogeneity of cloud properties, this study investigates long-term trends and predictive capabilities for cloud properties in drought- and flood-prone regions of western India, utilizing satellite data and employing machine learning (ML) models to comprehend intricate data patterns and enhance predictive accuracy. The results show higher mean and variability in cloud parameters over the flood-prone area due to favorable rain conditions, reflecting higher cloud microphysical and optical properties. These parameters negatively correlate with some cloud macrophysical properties and aerosol property in the drought-prone area. A moderate correlation exists between certain cloud characteristics of one region and another. Employing ML for regression analysis and comparing them for cloud effective radius across regions shows promising results, with random forest demonstrating high coefficient of determination (0.86, 0.93) and low root mean squared error (0.76, 1.15) due to its robustness and high accuracy. This research enhances the understanding of regional heterogeneity in India and shows that ML can help in predicting future cloud dynamics and climate by suitable model.

Mid-Holocene climate at mid-latitudes: assessing the impact of Saharan greening

Abstract. During the first half of the Holocene (11 000 to 5000 years ago), the Northern Hemisphere experienced a strengthening of the monsoonal regime, with climate reconstructions robustly suggesting a greening of the Sahara region. Palaeoclimate archives also show that this so-called African humid period (AHP) was accompanied by changes in climate conditions at middle to high latitudes. However, inconsistencies still exist in reconstructions of the mid-Holocene (MH) climate at mid-latitudes, and model simulations provide limited support in reducing these discrepancies. In this paper, a set of simulations performed using a climate model are used to investigate the hitherto unexplored impact of Saharan greening on mid-latitude atmospheric circulation during the MH. Numerical simulations show Saharan greening has a year-round impact on the main circulation features in the Northern Hemisphere, especially during boreal summer (when the African monsoon develops). Key findings include a westward shift in the global Walker Circulation, leading to modifications in the North Atlantic jet stream in summer and the North Pacific jet stream in winter. Furthermore, Saharan greening modifies atmospheric synoptic circulation over the North Atlantic, enhancing the effect of orbital forcing on the transition of the North Atlantic Oscillation phase from predominantly positive to negative in winter and summer. Although the prescription of vegetation in the Sahara does not improve the proxy–model agreement, this study provides the first constraint on the influence of Saharan greening on northern mid-latitudes, opening new opportunities for understanding MH climate anomalies in regions such as North America and Eurasia.

Bioaccumulation of Cadmium in Muscle and Liver Tissues of Juvenile Yellowfin Tuna (Thunnus albacares) from the Indian Ocean.

The present study evaluated the cadmium (Cd) levels and temporal variation of Cd in dark muscle, white muscle, and liver of juvenile Thunnus albacares. 72 individuals (Standard length: 50-67 cm; weight: 0.8-2.5 kg) were collected from Indian Oceanic water around Sri Lanka during the period between April 2021 to May 2022. Total Cd levels were analyzed using an Inductively Coupled Plasma Mass Spectrophotometer. The mean Cd levels (mean ± SD mg kg-1 dry weight) in different tissues varied with significantly higher levels in the liver (13.62 ± 0.98, p < 0.05), compared to dark muscle (0.52 ± 0.05), and white muscle (0.42 ± 0.04). Cd levels in liver tissues were positively correlated (p < 0.05) with the fish weight. The Cd levels reported in dark muscles, white muscles, and liver tissues were significantly higher (p < 0.05) during 2nd inter-monsoon than in the other monsoonal regimes and exceeded the maximum permissible level (0.1 mg kg-1 wet weight) set by the European Union (EU). However, the measured Cd levels in white and dark muscles were below the maximum permissible level (0.2 mg kg-1 wet weight) set by FAO/WHO. The Cd levels in all the liver tissues were above the levels set by the EU and FAO/WHO. Accordingly, people should avoid the consumption of liver tissues of T. albacares from the Indian Ocean. A human with a body weight of 60 kg can consume white muscles up to 4.667 kg per week without exceeding the Provisional Tolerable Weekly Intake.

Orographic effects on droughts in a monsoon climate with the world's highest rainfall

AbstractDrought, a recurring natural phenomenon in South Asia's monsoon climate, presents challenges in delineating its spatiotemporal patterns within complex topographies. This study investigated the impact of the orographic barrier in the rice‐dominated agricultural region of northeastern India and Bangladesh on drought characteristics during 1951–2020, employing the relative Standardized Precipitation Index (rSPI) and relative Standardized Precipitation‐Evapotranspiration Index (rSPEI) across 3‐, 6‐ and 12‐month scales. The results indicate that even in the rainiest region of the world, droughts extend beyond the limits of the dry season inherent in the monsoon regime. These mostly regional droughts exhibit weak correlations with the core of the Indian subcontinent and other parts of Bangladesh. The region's orographic barrier has a greater influence on drought intensity than on frequency. The rSPI index, which depends solely on rainfall, may overestimate drought intensity and frequency in regions with high seasonal/annual rainfall and substantial intermonthly variability. In contrast, the rSPEI index, which depends on both rainfall and potential evapotranspiration (PET), better reflects the spatial variation of drought in complex terrain, identifying the leeward hinterland of the orographic barrier as the most drought‐prone area. The two indices give similar results for drought characteristics away from the barrier. Furthermore, the orographic barrier exerts a negligible influence on the trends in rSPI and rSPEI. Principal component analysis (PCA) highlights the influences of the rainfall coefficient of variation and elevation on rSPI, while the PET coefficient of variation strongly influences rSPEI. Strategies to minimize the adverse effects of drought in complex topography and year‐round cropping should be local and season‐specific. These include using shorter‐growing, drought‐resistant rice varieties and adjusting planting schedules in rain shadow areas during the summer monsoon. These efforts should be complemented by integrating indigenous irrigation methods with modern practices such as roof water harvesting and tube wells in winter.

Drought, temperature, and moisture availability: understanding the drivers of isotopic decoupling in native pine species of the Nepalese Himalaya.

The Himalayas experienced long-term climate changes and recent extreme weather events that affected plant growth and the physiology of tree species at high-elevation sites. This study presents the first statistically robust δ18OTR chronologies for two native pine species, Pinus roxburghii, and Pinus wallichiana, in the lower Nepalese Himalaya. The isotope chronologies exhibited 0.88‰ differences in overall mean isotope values attributed to varying elevations (460-2000m asl). Comparative analysis of climate response using data sets from different sources and resolutions revealed the superiority of the APHRODITE (Asian Precipitation - Highly-Resolved Observational Data Integration Towards Evaluation) data set calibrated for the South Asian Summer Monsoon (SASM)-dominated region. Both species exhibited negative correlations with monsoon precipitation and positive correlations with temperature. However, during the peak monsoon season (July-August), daily resolved climate data disentangled statistically insignificant relationships, and revealed that δ18OTR is influenced by atmospheric moisture. Both congeneric species showed a decoupling between the chronologies after 1995. However, no significant change in air moisture origin and monsoon regime between the study sites was observed, indicating a consistent dominant moisture source during different monsoon seasons. Besides, we also observed the decreased inter-series correlation of both δ18OTR chronologies after 1995, with P. wallichiana experiencing a steeper decrease than P. roxburghii. The weakening correlations between and within the chronologies coincided with a regional drought during 1993-1995 in both sites, highlighting the strong regulation of local climate on the impact of regional extreme climate events. Our findings emphasise the importance of employing climate data with optimal spatial and temporal resolution for improved δ18OTR-climate relationships at the intra-annual scale while considering the influence of site-specific local environmental conditions. Assessing climate data sets with station data is vital for accurately interpreting climate change's impact on forest response and long-term climate reconstructions.

Evolution of ocean circulation and water masses in the Guaymas Basin (Gulf of California) during the last 31,000 years revealed by radiolarians and silicoflagellates in IODP expedition 385 sediment cores

The high-resolution analysis of radiolarians and silicoflagellates in sediments from Holes U1545A and U1549A drilled during IODP Expedition 385 in the Guaymas Basin, in the Gulf of California provides detailed insights into the evolution of ocean circulation and water masses, and its relation to Eastern Tropical Pacific Ocean climate conditions, over the past 31,000 cal years BP (based on AMS radiocarbon dates). In the pre-Last Glacial Maximum, the Guaymas Basin experienced alternating circulation patterns of California Current Water (CCW) and Gulf of California Water (GCW), with an extended presence of the Pacific Intermediate Water (PIW) owing to: amplified jet streams; southern movement of the California Current System (CCS) and the incursion of CCW into the gulf; and increased North Pacific Intermediate Water (NPIW) formation. The Last Glacial Maximum witnessed the incursion of CCW due to the stronger CCS. The dominance of the PIW indicates the expansion and formation of NPIW. The Heinrich-I event as manifested in the core record, displays two distinct patterns, one suggesting GCW-like dominance and the other, the occurrence of CCW. The Bølling-Ållerød interstadial featured the entry of Tropical Surface Water (TSW), GCW, and CCW, linked with the northward migration of the Intertropical Convergence Zone. In the Younger Dryas, CCW dominated, transitioning to GCW as colder climatic conditions and more intense CCS. The Holocene displayed alternating periods of TSW and GCW, with a modern monsoon regime from 7,600 to 1,000 cal years BP. From 1,000 cal years BP to the present the ITCZ shifted to the south.

A Fresh View of the Asian‐Australian Monsoon Complexity: The Intertropical Convective Cell (ITCC) Framework

AbstractThe monsoon holds great significance in Asian‐Australian civilization. Recent studies realized the link between the monsoon onset and the seasonal migration of the Intertropical Convergence Zone (ITCZ). However, no clear ITCZ band is observed in the Asian‐Australian sector due to the strong influence of topography. Instead, there exists a large‐scale (∼1,500 km) tropical convective cell––a perennial system that we hereafter coin as the “intertropical convective cell (ITCC).” Using ERA5 reanalysis and satellite‐based outgoing longwave radiation products, here we show by objective detection and tracking that the ITCC exhibits eight phases during its seasonal migration along the Asian‐Maritime land bridge. Particularly, its sudden northward jump in boreal spring coincides well with the earliest (abrupt) onset of the Asian rainy season, while its equatorward retreat heralds the overall (gradual) monsoon withdrawal. These findings demonstrate the close link of the ITCC behavior to the spring‐fall asymmetry of the monsoon. Dynamically, the off‐equatorial ITCC features a monsoon regime with a cross‐equatorial overturning circulation, differing markedly from its equatorial regime with two weak overturning cells on each side. Further budget analyses prove our hypothesis that the north‐south charging gradient of the moist static energy determines the ITCC's spring‐fall asymmetric propagation, illuminating the physical origin of the spring‐fall asymmetry in the monsoon. Our results demonstrate the usefulness of the ITCC framework in understanding the Asian‐Australian monsoon complexity in a fresh and holistic manner. The framework will facilitate monsoon diagnosis, modeling and subseasonal‐to‐seasonal forecasting in the Asian‐Australian sector.

Optically stimulated luminescence dating of Paleolithic sites reveals population shifts in North China during the last glacial period

The Greater Khingan and Yanshan mountain ranges in northern China not only constitute a significant physical obstacle to the northward movement of monsoon circulation, but also represent a natural barrier for human migration and cultural interactions between in-migrating Paleolithic populations and those indigenous to East Asia during the Late Pleistocene. We dated two Paleolithic sites, Yangzhuangxishan and Taiziling, located in the southern piedmont of the Yanshan Mountains with artifacts typified by simple core and flake technology associated with foraging populations, to ∼39–29 ka and ∼ 52–47 ka respectively, using the optically stimulated luminescence dating method. Our results indicate that northern China as far south as the Yanshan Mountains was occupied mainly by autochthonous East Asian Paleolithic populations using a core and flake lithic technology, although during this period Initial Upper Paleolithic (IUP) modern humans and Mousterian populations dispersed into East Asia. By synthesizing and integrating the ages of Northeast Asian Paleolithic sequences during the last glacial period (ca. 70–10 ka), we analyzed spatio-temporal variations in Late Pleistocene human populations during relatively cold stadial events (MIS 4 & 2) and warmer interstadials (e.g., MIS 3), revealing an “ebb and flow” pattern for migrations of Western IUP/Mousterian populations and indigenous core and flake technology populations in East Asia corresponding to the advance and retreat of the East Asian monsoon regime. The subsequent extremely cold climate phase engendered a major population shift during the Last Glacial Maximum (ca. 26.5–19 ka) which drove the reduction of both these Paleolithic populations, but afterward facilitated the emergence and rapid dispersal of microlithic technologies in East Asia. The peoples associated with microlithic technologies achieved their maximum geographical extent after the Bølling-Allerød Late Glacial interstadial event (ca. 14.7–12.9 ka) and then gradually decreased, perhaps due to the development of agriculture after ∼13 ka with concomitant increasing settlement stability.

Palaeoenvironmental reconstruction of a lower to middle Permian terrestrial composite succession from the Catalan Pyrenees: Implications for the evolution of tetrapod ecosystems in equatorial Pangaea

Tetrapod diversity in Permian terrestrial ecosystems of southwestern Europe is poorly recorded by bone specimens, but it is better represented by an important tetrapod ichnological record that is relevant to our understanding of vertebrate communities in equatorial Pangaea. Herein, two tetrapod ichnoassociations from three new ichnosites, within Cisuralian and Guadalupian volcanosedimentary terrestrial successions (the Lower Red Unit and the Upper Red Unit deposits) of the Castellar de n'Hug sub-basin (Catalan Pyrenees, NE Iberian Peninsula) are presented. Tetrapod ichnology in combination with stratigraphic and facies analyses permit a characterisation of these ecosystems. The sedimentary deposits show an evolution from fluvial meandering systems to playa-lake floodplains, denoting increased aridification and seasonality under a monsoonal regime. The ichnofossil record shows how tetrapod assemblages shifted from a prevalence of non-amniotes and eureptiles to a dominance of therapsids, eureptiles and parareptiles. The reported ichnotaxa are distributed in two ichnoassociations. The first preserves Batrachichnus, Dromopus, Hyloidichnus, Characichnos and an indeterminate tetrapod morphotype, whereas the second is defined by the presence of Dromopus, Hyloidichnus, Brontopus antecursor and Pachypes. The stratigraphically older ichnoassociation, preserved in volcaniclastic and fluvial deposits, presents features of the early Erpetopus biochron, whereas the stratigraphically younger one, preserved in playa-lake deposits, is constrained to the Brontopus sub-biochron. Biostratigraphic and magnetostratigraphic data suggest a late Cisuralian to middle Guadalupian age for the whole succession. The ichnoassemblage highlights a palaeobiogeographical connection between the Pyrenean Basin and other peri-Tethyan basins, which allows us to expand our knowledge about the palaeoecology and palaeobiodiversity of the Cisuralian to Guadalupian terrestrial ecosystems.

Stalagmite-based long-term and multi-centennial hydroclimatic variations in southwestern China during the Holocene and relations to global climate change

Knowing the behavior of the Asian summer monsoon (ASM) and its global correlation help understand roles of the ASM in global climate change. Here we synthesize a stalagmite δ18O record, based on a new record and an available nearby record, both covering the nearly entire Holocene. The synthesized δ18O record correlates with meridional migration of the Intertropical Convergence Zone (ITCZ), and with change in inter-subtropical insolation contrast throughout the Holocene. However, its correlation with the Atlantic meridional overturning circulation (AMOC) broken down during the period of the strongest ASM, when the AMOC weakened. This scenario points to a persistent influence of the ITCZ and subtropical insolation contrast on the change in ASM throughout the Holocene. Our record also correlates with a change in atmospheric CO2 concentration on the multi-millennial scale. These correlations of our cave record with variations in the ITCZ, subtropical insolation contrast, and CO2 level indicate that changes in low-latitude climates, including the ASM, were involved in the evolution of the Holocene CO2 concentration. These changes in the low-latitude climates were likely connected with variation in the Holocene southern westerly wind, which modulated upwelling of carbon-enriched deep ocean water around Antarctica. On the multi-centennial scale, seven weak ASM events are identified, with the magnitudes of the Younger Dryas and the events at 9.8 ka and 8.2 ka event broadly three and two times larger than the other ones. These events have a quasi-period of approximately 1.463 ka. This period in the monsoon regime probably arose from solar activity, but involving the feedback of ENSO. In summary, our study provides insights into the connection of the Holocene ASM with tropical climate, and into the involvement of the ASM in the change of the Holocene CO2 concentration.

Holocene climate change in southern Oman deciphered by speleothem records and climate model simulations

Qunf Cave oxygen isotope (δ18Oc) record from southern Oman is one of the most significant of few Holocene Indian summer monsoon cave records. However, the interpretation of the Qunf δ18Oc remains in dispute. Here we provide a multi-proxy record from Qunf Cave and climate model simulations to reconstruct the Holocene local and regional hydroclimate changes. The results indicate that besides the Indian summer monsoon, the North African summer monsoon also contributes water vapor to southern Oman during the early to middle Holocene. In principle, Qunf δ18Oc values reflect integrated oxygen-isotope fractionations over a broad moisture transport swath from moisture sources to the cave site, rather than local precipitation amount alone, and thus the Qunf δ18Oc record characterizes primary changes in the Afro-Asian monsoon regime across the Holocene. In contrast, local climate proxies appear to suggest an overall slightly increased or unchanged wetness over the Holocene at the cave site.

An emerging Asian aerosol dipole pattern reshapes the Asian summer monsoon and exacerbates northern hemisphere warming

Since the early 2010s, anthropogenic aerosols have started decreasing in East Asia (EA) while have continued to increase in South Asia (SA). Yet the climate impacts of this Asian aerosol dipole (AAD) pattern remain largely unknown. Using a state-of-the-art climate model, we demonstrate that the climate response is distinctly different between the SA aerosol increases and EA aerosol decreases. The SA aerosol increases lead to ~2.7 times stronger land summer precipitation change within the forced regions than the EA aerosol decreases. Contrastingly, the SA aerosol increases, within the tropical monsoon regime, produce weak and tropically confined responses, while the EA aerosol decreases yield a pronounced northern hemisphere warming aided by extratropical mean westerly and positive air-sea feedbacks over the western North Pacific. By scaling the observed instantaneous shortwave radiative forcing, we reveal that the recent AAD induces a pronounced northern hemisphere extratropical (beyond 30°N) warming (0.024 ± 0.010 °C decade−1), particularly over Europe (0.049 ± 0.009 °C decade−1). These findings highlight the importance of the pattern effect of forcings in driving global climate and have important implications for decadal prediction.

Plumbing systems and associated seafloor fluid seepages in deep-water Nigeria: Factors controlling their architecture and cyclic evolution

A range of plumbing systems has been identified in deep-water Nigeria by interpreting multi-scale seismic data sets (reprocessed 3D exploration seismic reflection data and 2D very high-resolution near-bottom seismic reflection data) as well as sedimentological and geochemical data obtained from a long sediment core recovered by the seafloor drill rig MARUM-MeBo70. The plumbing systems are characterized by diverse fault networks and lie above tectonic features including thrust/fold structures and strike-slip faults linked to gravity-driven deformation caused by underlying over-pressured shales. The plumbing systems are associated with fluid seeping structures at the seafloor such as pockmarks, mud volcanoes and seafloor zonations colonized by living benthic macrofauna typical of active fluid flow. The comparison of seismic stratigraphic sequences with climate and environmental proxies determined for sediments including lithology, element ratios such as Ca/Fe and Zr/Rb, sedimentation rates, and planktonic foraminifera δ18O records shows a control of short-term (0.1–0.4 Myr) and long-term (around 1 Myr) sedimentary cycles. During short-term fluctuations, the recurrence of fluid seeping structures is controlled by the lithology (coarse-grained versus fine-grained sediments) linked to glacial-interglacial fluctuations and a monsoon regime. Conditions favorable for fluid flow are related to the deposition of coarse-grained layers, glacial periods, sea-level lowstands, and low sedimentation rates. We hypothesize that cyclic gravity-driven sediment deformations controlled by glacial-interglacial and long-term variations in accommodation and sedimentation, have led to the cyclic evolution of the plumbing systems and associated seeping structures since the Plio-Pleistocene.

Climatology of the global summer monsoon rainy seasons: Revisited from a high-resolution satellite climate data record

Reliable information on the monsoon rainfall at finer spatiotemporal scales has always been crucial for applications in hydrometeorology, water resource management, disaster prevention, and assessment of numerical model outputs. Here, the spatial-temporal characteristics of the summer monsoon rainy seasons worldwide are revisited using a global, high-resolution, bias-corrected satellite rainfall climate data record. The Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks–Climate Data Record (PERSIANN-CDR) provides 0.25° rainfall estimates for the latitude band 60°S–60°N from 1983 to the near present. The global monsoon regimes are defined based on the annual rainfall range and the summer rainfall ratio. The onset, peak, and withdrawal of the rainy season are then determined using a concise yet pertinent rainfall parameter with universal objective criteria.Overall, six major summer monsoon regimes of the globe, the Asian Monsoon, Indonesian–Australian monsoon, North African monsoon, South African monsoon, North American and South American monsoon, are all reasonably represented by PERSIANN-CDR. The progression patterns of climatological onset, peak, and withdrawal phases of these monsoons are consistent with those reported by previous global and regional monsoon studies. Furthermore, compared with other coarser resolution satellite rainfall estimates such as the Climate Prediction Center Merged Analysis of Precipitation (CMAP), the present result is clearly in better agreement with that obtained from ground-based observations since it allows the determination of more detailed information associated with local-scale factors such as the sharp land-sea contrast, local surface heating, and topography effects. However, some “spots”, particularly over complex topography lacking ground truth validations, are revealed to have rainy season characteristics that differ substantially from those over the surrounding areas and have not been fully described by published literature. These distinct features need to be confirmed by further regional monsoon studies.

Climate change impacts the distribution of Quercus section Cyclobalanopsis (Fagaceae), a keystone lineage in East Asian evergreen broadleaved forests

East Asian evergreen broadleaved forests (EBFLs) harbor high species richness, but these ecosystems are severely impacted by global climate change and deforestation. Conserving and managing EBLFs requires understanding dominant tree distribution dynamics. In this study, we used 29 species in Quercus section Cyclobalanopsis—a keystone lineage in East Asian EBLFs—as proxies to predict EBLF distribution dynamics using species distribution models (SDMs). We examined climatic niche overlap, similarity, and equivalency among seven biogeographical regions’ species using ‘ecospat’. We also estimated the effectiveness of protected areas in the predicted range to elucidate priority conservation regions. Our results showed that the climatic niches of most geographical groups differ. The western species under the Indian summer monsoon regime were mainly impacted by temperature factors, whereas precipitation impacted the eastern species under the East Asian summer monsoon regime. Our simulation predicted a northward range expansion of section Cyclobalanopsis between 2081 and 2100, except for the ranges of the three Himalayan species analyzed, which might shrink significantly. The greatest shift of highly suitable areas was predicted for the species in the South Pacific, with a centroid shift of over 300 km. Remarkably, only 7.56% of suitable habitat is currently inside protected areas, and the percentage is predicted to continue declining in the future. To better conserve Asian EBLFs, establishing nature reserves in their northern distribution ranges, and transplanting the populations with predicted decreasing numbers and degraded habitats to their future highly suitable areas, should be high-priority objectives.

Aerosol-heavy precipitation relationship within monsoonal regimes in the Western Himalayas

Studies reported increased heavy precipitation and aerosol loading in Western Himalayas (WH) due to changes in large-scale dynamics and anthropogenic emissions. In this study, we investigate the long-term relationship between aerosols and heavy precipitation from 2001 to 2020 by incorporating the changes in dynamics and eliminating the influence of meteorological covariates. We analyzed composites of aerosol optical depth (AOD) from MERRA2 reanalysis and precipitation from GPM IMERG products within monsoonal regimes – M1 (westerly), M2 (westerly + easterly) and M3 (easterly) with distinct large-scale dynamics. A significant positive correlation is found between aerosols and heavy precipitation in M1 (0.27) and M2 (0.15) but not M3. We eliminated the influence of three covariates, specifically the moisture flux convergence (MFC), Webster Yang Index (WYI), and relative humidity (RH) at 850 hPa, on the aerosol-heavy precipitation relationship. We found MFC to be the strongest influencer using partial correlation analysis, whereas WYI and RH only weakly affected this relationship. The overall partial correlation coefficient between aerosols and heavy precipitation is 0.17 in both M1 and M2 but insignificant in M3. Further, we studied the evolution of cloud properties during heavy precipitation under distinct dynamics. We found smaller cloud droplets with a narrow size distribution in M1, but larger droplets and broad distribution for M3. We did not find a significant correlation between AOD and cloud properties in the ice phase in any of the regimes. Our findings imply that dynamical changes result in distinct aerosol-heavy precipitation relations and microphysical processes causing heavy precipitation.

The northern boundary of the Asian summer monsoon and division of westerlies and monsoon regimes over the Tibetan Plateau in present-day

The northern boundary of the Asian summer monsoon and division of westerlies and monsoon regimes over the Tibetan Plateau in present-day

Eddy Characteristics and Vertical Structure in the Bay of Bengal during Different Monsoon Regimes

The evolution of mesoscale eddies in the Bay of Bengal (BoB) and their characteristics (number of eddies, radius, amplitude, and eddy kinetic energy) are addressed during all strong, normal, and weak monsoon regimes from 1993 to 2019. Their impacts on the 3–7-day synoptic oscillations of atmospheric precipitation and upper ocean heat content are also assessed. In the western Bay, eddies are located in the meandering East India Coastal Current (EICC). The propagation of coastally trapped Kelvin waves into the Andaman Sea varies with monsoon intensity. Eddies with smaller radii, weaker amplitudes, increased vertical mixing, and deeper vertical extents were found during weak monsoons. Eddy kinetic energy (EKE) of EICC anticyclonic eddies is high (1200–2000 cm2 s−2) in May and November-December during weak and normal monsoon regimes, and EKE attains a maximum off the Sri Lanka coast during the strong monsoon regime. Throughout the Bay, density anomalies at ~100 m depth are influenced by subsurface temperature anomalies, while those at the surface more closely follow salinity anomalies. Wavelet coherence analysis for all three monsoon regimes reveals stronger coherence between eddy amplitude, atmospheric precipitation, and ocean heat content than the number of eddies for both anticyclonic and cyclonic eddies.

Will Warming Climate Affect the Characteristics of Summer Monsoon Rainfall and Associated Extremes Over the Gangetic Plains in India?

AbstractThe Indo‐Gangetic Plain (IGP) bears great agricultural importance and contributes to a major share of national GDP of India. In present study, a location‐specific comprehensive analysis of rainfall extremes over IGP, using second generation CORDEX‐CORE simulations in the present and future scenarios (under high emission RCP8.5 scenario) have been performed. Here, the high‐resolution CORDEX‐CORE simulations with International Centre for Theoretical Physics's regional climate model (RegCM4.7) have been considered for the detailed rainfall characteristics assessment. Twelve thresholds‐based climate indices have been analyzed to investigate the characteristics of rainfall extremes during three‐time slices: 1986–2005 (historical), 2041–2060 (near future) and 2080–2099 (far future). The RegCM4 projections suggested a substantial decline in mean Indian Summer monsoon rainfall (ISMR) and wet days (rainfall ≥ 1 mm; 7%–14%) over IGP under high‐emission RCP8.5 scenario. The contribution of 90th and 99th percentile days and total rainfall on wet days, seems to be get enhanced in future by 14%–35%, which implies the increase and intensification in rainfall extremes over IGP by the end of the 21st century. Further, the decline in ISMR and negligible changes in annual rainfall over IGP suggest the possible shift of monsoon regime during the later months of the year in warming climate. Thus, findings of present study may play a crucial role in predicting the ISMR and rainfall extremes over the IGP. Therefore, it can be useful for scientists and policymakers to plan and implement mitigation strategies.

A new biologic paleoaltimetry indicating Late Miocene rapid uplift of northern Tibet Plateau

The uplift of the Tibet Plateau (TP) during the Miocene is crucial to understanding the evolution of Asian monsoon regimes and alpine biodiversity. However, the northern Tibet Plateau (NTP) remains poorly investigated. We use pollen records of montane conifers (Tsuga, Podocarpus, Abies, and Picea) as a new paleoaltimetry to construct two parallel midrange paleoelevation sequences in the NTP at 1332 ± 189 m and 433 ± 189 m, respectively, during the Middle Miocene [~15 million years ago (Ma)]. Both midranges increased rapidly to 3685 ± 87 m in the Late Miocene (~11 Ma) in the east, and to 3589 ± 62 m at ~7 Ma in the west. Our estimated rises in the east and west parts of the NTP during 15 to 7 Ma, together with data from other TP regions, indicate that during the Late Miocene the entire plateau may have reached a high elevation close to that of today, with consequent impacts on atmospheric precipitation and alpine biodiversity.