Summer Monsoon Circulation Research Articles

Relative role of sea surface temperature and snow on Indian summer monsoon seasonal simulation using a GCM

Indian summer monsoon is a global scale phenomenon controlled by different land, ocean, and atmospheric parameters. Sea surface temperature (SST) and snow are two of the major parameters, which may alter the spatial and temporal patterns of circulation and rainfall during Indian summer monsoon. In the current paper, we study the monsoon variability using long integrations (20 years) of the Indian Institute of Technology Delhi (IITD) Spectral model at T80L18 resolution with observed and climatological SST and snow. Study shows response of IITD GCM in simulating the Indian summer monsoon rainfall and circulation relative to the snow and SST as boundary conditions. The model’s response to SST and snow is examined by conducting four types of experiments by varying observed and climatological values of snow and SST. This paper discusses the seasonal total rainfall for country as a whole and 850 and 200 hPa wind for the period of 20 years starting from 1985 to 2004. The model has been integrated in the ensemble mode with five different initial conditions from the last week of April and first week of May. The model is able to capture the climatological patterns of seasonal total rainfall and averaged wind at lower and upper levels. Observed snow in the presence of climatological SST as a boundary condition shows much impact on rainfall and circulation than observed SST in the presence of climatological snow. Model performance is good in simulating the normal and excess monsoon conditions; it shows poor skill in capturing deficit monsoon years.

Possible ENSO Influences on the Northwestern Tibetan Plateau Revealed by Annually Resolved Ice Core Records

AbstractTwo annually resolved ice core records, one drilled on Mutztagata (7,000 m above sea level) on the western slope (dated 1952–2002) and the other drilled on Kuokuosele (5,600 m above sea level) on the southwestern slope (dated 1900–2010) of the Pamir Plateau of the northwestern Tibetan Plateau (TP), were selected to study possible El Niño–Southern Oscillation (ENSO) influences on the northwestern TP. δ18O at KKSL was more enriched, though both records varied in phase. Eight of the 10 noticeably strong El Niño events since 1955 corresponded to δ18O depletions in both ice core records, which were followed by δ18O enrichment. Atmospheric circulation indices, including water vapor flux and divergence, had a coincidence of a positive Indian Ocean Dipole mode with El Niño events, which contributed to the northward transport of southerly flows from the western Indian Ocean; its convergence with midlatitude wind flows at high levels depleted δ18O levels. The meridional shift in the Asian‐Pacific subtropical high induced by latent heat release due to precipitation in the northwestern Pacific was found to play an important role in initiating convergence. A statistical analysis confirmed the significant correlations in δ18O with the ENSO index and tropical and subtropical summer monsoon circulations. We noted that the dominant circulation pattern over the northwestern TP was characterized by a midlatitude flow regime that had a teleconnection with tropical sea surface temperatures. Therefore, ENSO is one of a variety of influences on ice core δ18O on the TP.

Variations in the Iron Mineralogy of a Loess Section in Tajikistan During the Mid‐Pleistocene and Late Pleistocene: Implications for the Climatic Evolution in Central Asia

AbstractThe loess sequences in Tajikistan are an important archive of information about the development of climate and atmospheric circulation in central Asia during the Pleistocene. Here we present the results of an iron mineralogical study of a loess sequence in Tajikistan to reconstruct paleoclimate evolution during the mid‐Pleistocene and late Pleistocene. The record indicates that interglacial intervals were relatively humid and glacials were dry. We propose a shift in the character of the interglacial climate of the region to more humid after beginning of MIS 9; however, temperature was relatively stable. The location and intensity of Westerlies have a close link with Asian Summer Monsoon (ASM) circulations. From the beginning of MIS 9, there was a southward movement of the Westerlies circulation, which corresponded to a retreat of the Indian Summer Monsoon (ISM). A similar relationship also existed between the East Asian Summer Monsoon (EASM) circulation and the Westerlies, which is evidenced by the formation of the most weakly developed soil unit in the EASM‐dominated regions during MIS 9, in contrast with the formation of the most strongly developed soil unit in the Westerlies‐dominated regions. As conditions in the areas of loess deposition became more humid, the sedimentary basins which are the dust source areas became progressively more arid. The aridification of the source areas may be the result of increased Northern Hemisphere ice volume and accelerated high mountains and/or plateaus uplift in the surrounding regions.

Impact of Tropospheric Ozone on Summer Climate in China

The spatial distribution, radiative forcing, and climatic effects of tropospheric ozone in China during summer were investigated by using the regional climate model RegCM4. The results revealed that the tropospheric ozone column concentration was high in East China, Central China, North China, and the Sichuan basin during summer. The increase in tropospheric ozone levels since the industrialization era produced clear-sky shortwave and clear-sky longwave radiative forcing of 0.18 and 0.71 W m–2, respectively, which increased the average surface air temperature by 0.06 K and the average precipitation by 0.22 mm day–1 over eastern China during summer. In addition, tropospheric ozone increased the land–sea thermal contrast, leading to an enhancement of East Asian summer monsoon circulation over southern China and a weakening over northern China. The notable increase in surface air temperature in northwestern China, East China, and North China could be attributed to the absorption of longwave radiation by ozone, negative cloud amount anomaly, and corresponding positive shortwave radiation anomaly. There was a substantial increase in precipitation in the middle and lower reaches of the Yangtze River. It was related to the enhanced upward motion and the increased water vapor brought by strengthened southerly winds in the lower troposphere.

Reduced connection between the East Asian Summer Monsoon and Southern Hemisphere Circulation on interannual timescales under intense global warming

Previous studies show a close relationship between the East Asian Summer Monsoon (EASM) and Southern Hemisphere (SH) circulation on interannual timescales. In this study, we investigate whether this close relationship will change under intensive greenhouse-gas effect by analyzing simulations under two different climate background states: preindustrial era and Representative Concentration Pathway (RCP) 8.5 stabilization from the Community Climate System Model Version 4 (CCSM4). Results show a significantly reduced relationship under stabilized RCP8.5 climate state, such a less correlated EASM with the sea level pressure in the southern Indian Ocean and the SH branch of local Hadley Cell. Further analysis suggests that the collapse of the Atlantic Meridional Overturning Circulation (AMOC) due to this warming leads to a less vigorous northward meridional heat transport, a decreased intertropical temperature contrast in boreal summer, which produces a weaker cross-equatorial Hadley Cell in the monsoonal region and a reduced Interhemispheric Mass Exchange (IME). Since the monsoonal IME acts as a bridge connecting EASM and SH circulation, the reduced IME weakens this connection. By performing freshwater hosing experiment using the Flexible Global Ocean—Atmosphere—Land System model, Grid-point Version 2 (FGOALS-g2), we show a weakened relationship between the EASM and SH circulation as in CCSM4 when AMOC collapses. Our results suggest that a substantially weakened AMOC is the main driver leading to the EASM, which is less affected by SH circulation in the future warmer climate.

Directional Absorption of Parameterized Mountain Waves and Its Influence on the Wave Momentum Transport in the Northern Hemisphere

AbstractThe directional absorption of mountain waves in the Northern Hemisphere is assessed by examination of horizontal wind rotation using the 2.5° × 2.5° European Centre for Medium‐Range Weather Forecasts ERA‐Interim reanalysis between 2011 and 2016. In the deep layer of troposphere and stratosphere, the horizontal wind rotates by more than 120° all over the Northern Hemisphere primary mountainous areas, with the rotation mainly occurring in the troposphere (stratosphere) of lower (middle to high) latitudes. The rotation of tropospheric wind increases markedly in summer over the Tibetan Plateau and Iranian Plateau, due to the influence of Asian summer monsoonal circulation. The influence of directional absorption of mountain waves on the mountain wave momentum transport is also studied using a new parameterization scheme of orographic gravity wave drag (OGWD) which accounts for the effect of directional wind shear. Owing to the directional absorption, the wave momentum flux is attenuated by more than 50% in the troposphere of lower latitudes, producing considerable orographic gravity wave lift which is normal to the mean wind. Compared with the OGWD produced in traditional schemes assuming a unidirectional wind profile, the OGWD in the new scheme is suppressed in the lower stratosphere but enhanced in the upper stratosphere and lower mesosphere. This is because the directional absorption of mountain waves in the troposphere reduces the wave amplitude in the stratosphere. Consequently, mountain waves are prone to break at higher altitudes, which favors the production of stronger OGWD given the decrease of air density with height.

On the Linkage Between the Asian Summer Monsoon and Tropopause Folds

AbstractThis study uses a set of idealized aquaplanet model experiments to investigate the linkage between the Asian summer monsoon circulation and tropopause fold activity. It is found that folds tend to occur on the northwestern side of the upper‐level anticyclone associated with the monsoon circulation and are generated due to intensified monsoon circulation and resulting intensified subsidence. In addition, the impact of tropopause folds on extreme rainfall events is also examined. It is found that while the likelihood of extreme rainfall is largely decreased at and upstream of the occurrence of folds, the likelihood is significantly increased downstream. This pattern of suppression of extreme rainfall upstream and promotion downstream also persists for about 1–2 days, which likely suggests a positive feedback between extreme rainfall downstream and tropopause folds. Finally, changes in tropopause folds with monsoon intensity are also discussed.

Exploring the relationship between the cloud-top and tropopause height in boreal summer over the Tibetan Plateau and its adjacent region

AbstractThe distribution characteristics of cloud-top and tropopause height in the tropics and subtropics in boreal summer are analyzed based on CALIPSO data for the period 2008–2012. The maximum values of cloud-top vertical cumulative frequency above the tropopause (CTAT) are concentrated in three tropical regions: the Asian summer monsoon region, Central America, and western Africa. The contributions to the area-weighted CTAT frequency in the three regions from the Northern Hemisphere are 49.0%, 13.5%, and 12.4%, respectively. Moreover, the contribution of troposphere-to-stratosphere transport (TST) in the Asian monsoon region to global TST can be far greater than 50%, according to analysis of the continuous equation, velocity potential, and divergent wind from ERA-Interim data. Furthermore, the Asian summer monsoon circulation system controls the distribution of the cloud top. On the south side of the Tibetan Plateau, the maximum frequency of the cloud top, more than 10% per 500 m vertically, is most l...

The role of monsoon low‐level jet in modulating heavy rainfall events

ABSTRACTMonsoon low‐level jet (MLLJ) is an important component of Asian summer monsoon circulation, which is responsible for large‐scale distribution and variability of rainfall over the Indian subcontinent. The evolution of MLLJ characteristics prior to heavy rainfall days and its changes which lead to instances of heavy rainfall over the south‐western coast of India are studied. The European Centre for Medium Range Weather Forecasts (ECMWF) re‐analysis data and India Meteorological Department (IMD) rainfall data during 1979–2007 were used for this study. It is found that the MLLJ core speed, westerly wind depth, zonal water vapour flux, horizontal wind shear and cyclonic vorticity show a steady increase towards the day of heavy rainfall and gradually decrease thereafter. The intensification of these parameters not only brings in abundant moisture but also triggers convection, thereby resulting in the formation of heavy rainfall during monsoon season. The large‐scale advection of moisture brought about by strengthening of MLLJ is shown to be a prerequisite for heavy rainfall over the Indian subcontinent. An interesting result of this study is that heavy rainfall days may have some predictability by continuous monitoring of the progression of MLLJ.

Intensified East Asian summer monsoon and associated precipitation mode shift under the 1.5 °C global warming target

In this study, the East Asian summer climate changes under the 1.5 °C global warming (1.5 GW) target in 30 simulations derived from 15 coupled models within the Coupled Model Intercomparison Program phase 5 (CMIP5) are examined. Compared with the current summer climate (1975–2005), both surface air temperature and precipitation increase significantly over the East Asian continent during the 1.5 GW period (average period 2021–2051). In northeastern China this is particularly pronounced with regional averaged precipitation increases of more than 7.2%, which is greater than that for the whole East Asian continent (approximately 4.2%). Due to stronger enhancement of precipitation north of 40°N, the leading empirical orthogonal function (EOF) mode of summer precipitation over the East Asian continent changes from tripolar-like mode to dipole mode. As there is stronger surface warming over the East Asian continent than that over surrounding ocean, the land–sea thermal contrast is enhanced during the 1.5 GW period. As a result, the monsoon circulation in the lower troposphere is significantly strengthened, which causes the increased summer precipitation over the East Asian continent. In addition, larger interannual variabilities of East Asian summer monsoon circulation and associated precipitation are also suggested for the 1.5 GW period.

Synoptic characteristics, atmospheric controls, and long-term changes of heat waves over the Indochina Peninsula

The characteristics of heat wave (HW) events over the Indochina Peninsula are studied using the Climate Forecast System Reanalysis data for 1979–2010. HWs in the dry and wet seasons of Indochina are considered separately, and their typical synoptic behavior is examined in detail. Our results show that HWs in both seasons are accompanied by suppressed precipitation, and the region lies under an anomalously dry, hot, and subsiding atmospheric column. Further diagnoses reveal that HWs in the dry and wet seasons are linked to the weakening of the East Asian winter monsoon (EAWM) and the South Asian summer monsoon (SASM) circulations, respectively. On the one hand, HWs in the dry season are coincident with high-temperature anomalies over East Asia and accompanied by an anomalous cyclone over eastern China. The anomalous southwesterly flow over East Asia indicates a weakening of the climatological northeasterly circulation associated with the EAWM. On the other hand, HWs in the wet season are coincident with hot and dry anomalies in South Asia (i.e., Indian subcontinent). The anomalous easterly flow in that region opposes the climatological westerly regime of the SASM. Moreover, we found that the statistics for the frequency, duration, and amplitude of HWs for both seasons exhibit prominent intensifying trends, and the intensifying trends in the wet season are mostly about two to three times stronger than the dry season. These intensifying HWs activities are likely attributable to the weakening trend of monsoon circulations in recent decades.

Indian Summer Monsoon Sub-seasonal Low-Level Circulation Predictability and its Association with Rainfall in a Coupled Model

This study investigates predictability of the sub-seasonal Indian summer monsoon (ISM) circulation and its relation with rainfall variations in the coupled model National Centers for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2). Hindcasts based on CFSv2 for the period of 1982–2009 are used for detailed analysis. Though the model is capable of predicting the seasonal ISM rainfall at long lead months, the predication skill of the model for sub-seasonal rainfall in general is poor for short and long lead except for September. Rainfall over the ISM region/Indian Subcontinent is highly correlated with the low-level jet (LLJ) or Somali jet both in the observations and the model. The model displays improved skill in predicting LLJ as compared to precipitation in seasonal mean and September, whereas the model skill is poor for June and August. Detailed analysis reveals that the model LLJ variations throughout the season are overdependent on the El Nino-Southern Oscillation (ENSO) unlike in the observations. This is mainly responsible for the model’s low skill in predicting LLJ especially in July and August, which is the primary cause for the poor rainfall skill. Though LLJ is weak in September, the model skill is reasonably good because of its ENSO dependency both in model and the observations and which is contributed to the seasonal mean skill. Thus, to improve the skill of seasonal mean monsoon forecast, it is essential to improve the skill of individual months/sub-seasonal circulation and rainfall skill.

Response of the tropical Indian Ocean SST to decay phase of La Niña and associated processes

Delayed impact of El Niño on Tropical Indian Ocean (TIO) Sea Surface Temperature (SST) variations and associated physical mechanisms are well documented by several studies. However, TIO SST evolution during the decay phase of La Niña and related processes are not adequately addressed before. Strong cooling associated with La Niña decay over the TIO could influence climate over the Indian Oceanic rim including Indian summer monsoon circulation and remotely northwest Pacific circulation. Thus understanding the TIO basin-wide cooling and related physical mechanisms during decaying La Niña years is important. Composite analyses revealed that negative SST anomalies allied to La Niña gradually dissipate from its mature phase (winter) till subsequent summer in central and eastern Pacific. In contrast, magnitude of negative SST anomalies in TIO, induced by La Niña, starts increasing from winter and attains their peak values in early summer. It is found that variations in heat flux play an important role in SST cooling over the central and eastern equatorial Indian Ocean, Bay of Bengal and part of Arabian Sea from late winter to early summer during the decay phase of La Niña. Ocean dynamical processes are mainly responsible for the evolution of southern TIO SST cooling. Strong signals of westward propagating upwelling Rossby waves between 10°S to 20°S are noted throughout (the decaying phase of La Niña) spring and summer. Anomalous cyclonic wind stress curl to the south of the equator is responsible for triggering upwelling Rossby waves over the southeastern TIO. Further, upwelling Rossby waves are also apparent in the Arabian Sea from spring to summer and partly contributing to the SST cooling. Heat budget analysis reveals that negative SST/MLT (mixed layer temperature) anomalies over the Arabian Sea are mostly controlled by heat flux from winter to spring and vertical advection plays an important role during early summer. Vertical and horizontal advection terms primarily contribute to the SST cooling anomalies over southern TIO and the Bay of Bengal cooling is primarily dominated by heat flux. Further we have discussed influence of TIO cooling on local rainfall variations.

Multidecadal Weakening of Indian Summer Monsoon Circulation Induces an Increasing Northern Indian Ocean Sea Level

AbstractNorth Indian Ocean sea level has shown significant increase during last three to four decades. Analyses of long‐term climate data sets and ocean model sensitivity experiments identify a mechanism for multidecadal sea level variability relative to global mean. Our results indicate that North Indian Ocean sea level rise is accompanied by a weakening summer monsoon circulation. Given that Indian Ocean meridional heat transport is primarily regulated by the annual cycle of monsoon winds, weakening of summer monsoon circulation has resulted in reduced upwelling off Arabia and Somalia and decreased southward heat transport, and corresponding increase of heat storage in the North Indian Ocean. These changes in turn lead to increased retention of heat and increased thermosteric sea level rise in the North Indian Ocean, especially in the Arabian Sea. These findings imply that rising North Indian Ocean sea level due to weakening of monsoon circulation demands adaptive strategies to enable a resilient South Asian population.

Change in the relationship between the Australian summer monsoon circulation and boreal summer precipitation over Central China in the late 1990s

Recent study revealed a close connection between the Australian summer monsoon (ASM) and boreal summer precipitation over Central China (SPCC). This study further revealed a strengthening of the ASM–SPCC relationship around the late 1990s. It is found that the relationship between the ASM and the SPCC during 1979–1997 (1998–2014) relationship is statistically insignificant (significant). Further analysis indicated that during 1998–2014, the weakened ASM is concurrent with significant positive sea surface temperature (SST) in the Indian Ocean and South China Sea, which could persist into the following boreal summer and further lead to intensified East Asian summer monsoon, strengthened western North Pacific subtropical high, and anomalous ascending motion over Central China. Consequently, more moisture is transported from the western Pacific northward to Central China where significant anomalous convergence appears. Therefore, the ASM could potentially influence the SPCC during 1998–2014. By contrast, the ASM-related SST and atmospheric circulation anomalies in boreal winter are statistically insignificant during 1979–1997. Such an interdecadal change might be attributed to the interdecadal warming that occurred in the Indian Ocean and South China Sea around the late 1990s. This study might be useful for the prediction of the SPCC.

Changes in urban-related precipitation in the summer over three city clusters in China

The impacts of urban surface expansion on the summer precipitations over three city clusters [Beijing-Tianjin-Hebei (BTH), the Yangtze River Delta (YRD), and the Pearl River Delta (PRD)] in eastern China under different monsoonal circulation backgrounds were explored using the nested fifth-generation Penn State/NCAR Mesoscale Model version 3.7 (MM5 V3.7), including the urban-related thermal and dynamical parameters. Ten-year integrations were performed using satellite image data from 2000 and 2010 to represent the urban surface distributions and expansions in China. Changes in the precipitation revealed obvious subregional characteristics, which could be explained by the influences of the vertical wind velocity and moisture flux. With urban-related warming, vertical wind motion generally intensified over urban surface-expanded areas. Meanwhile, the increase in impervious surface areas induced rapid rainwater runoff into drains, and the Bowen ratio increased over urban areas, which further contributed to changes in the local moisture fluxes in these regions. The intensities of the changes in precipitation were inconsistent over the three city clusters, although the changes in vertical motion and local evaporation were similar, which indicates that the changes in precipitation cannot be solely explained by the changes in the local evaporation-related moisture flux. The changes in precipitation were also influenced by the changes in the East Asian summer monsoon (EASM) circulation and the corresponding moisture flux, which are expressed in marked subregional characteristics. Therefore, the influence of urban-related precipitation over the three city clusters in China, for which changes in moisture flux from both the impacted local evaporation and EASM circulation should be considered, varied based on the precipitation changes of only a single city.

Influence of Latent Heating over the Asian and Western Pacific Monsoon Region on Sahel Summer Rainfall

There has been an interdecadal shift towards a less humid state in Sahel summer rainfall since the 1960s. The decreased Sahel summer rainfall was associated with enhanced summer latent heating over the South Asian and western Pacific summer monsoon region and anomalous zonal-vertical cell of the Asian summer monsoon circulation, indicating that the latent heating plays a significant role in the change in Sahel rainfall. The effects of the latent heating over different monsoon domains on the Sahel rainfall are investigated through several model experiments. Results show that the remote monsoon heating mainly affects Sahel rainfall by generating changes in the zonal-vertical atmospheric circulation.

Assessment of two versions of regional climate model in simulating the Indian Summer Monsoon over South Asia CORDEX domain

This study assess the performance of two versions of Regional Climate Model (RegCM) in simulating the Indian summer monsoon over South Asia for the period 1998 to 2003 with an aim of conducting future climate change simulations. Two sets of experiments were carried out with two different versions of RegCM (viz. RegCM4.2 and RegCM4.3) with the lateral boundary forcings provided from European Center for Medium Range Weather Forecast Reanalysis (ERA-interim) at 50 km horizontal resolution. The major updates in RegCM4.3 in comparison to the older version RegCM4.2 are the inclusion of measured solar irradiance in place of hardcoded solar constant and additional layers in the stratosphere. The analysis shows that the Indian summer monsoon rainfall, moisture flux and surface net downward shortwave flux are better represented in RegCM4.3 than that in the RegCM4.2 simulations. Excessive moisture flux in the RegCM4.2 simulation over the northern Arabian Sea and Peninsular India resulted in an overestimation of rainfall over the Western Ghats, Peninsular region as a result of which the all India rainfall has been overestimated. RegCM4.3 has performed well over India as a whole as well as its four rainfall homogenous zones in reproducing the mean monsoon rainfall and inter-annual variation of rainfall. Further, the monsoon onset, low-level Somali Jet and the upper level tropical easterly jet are better represented in the RegCM4.3 than RegCM4.2. Thus, RegCM4.3 has performed better in simulating the mean summer monsoon circulation over the South Asia. Hence, RegCM4.3 may be used to study the future climate change over the South Asia.

Lagged response of summer precipitation to insolation forcing on the northeastern Tibetan Plateau during the Holocene

The precipitation changes on the northeastern Tibetan Plateau during the Holocene remain unclear due to discrepancies among different proxy records. We compared proxy records with the results from a transient simulation performed using the Kiel Climate Model forced by orbital variations, to analyse summer precipitation changes in this area during the Holocene (9.5–0 ka BP). The model results suggested increasing amounts of summer precipitation from 9.5 to ~6.2 ka BP and a persistent decline thereafter, which matched well with pollen records but was inconsistent with ostracod δ18O records. The Holocene climatic optimum lagged the Northern Hemisphere summer insolation maximum by ~3.5 ka, caused by the interplay between the East Asian summer monsoon (EASM) circulation and the mid-latitude westerlies. The ostracod δ18O values reflected the strength of the EASM circulation. A strong EASM circulation increased the transport of water vapour towards the northeastern Tibetan Plateau from the northwestern Pacific. Weakened mid-latitude westerlies increased the incursion of cold air masses into the northeastern Tibetan Plateau. During the early Holocene, relatively strong mid-latitude westerlies, resulting from an enhanced Arctic Oscillation, reduced summer precipitation on the northeastern Tibetan Plateau, in spite of a strong insolation-driven EASM circulation. The weakening EASM circulation and the strengthening westerlies together induced the decreasing trend of summer precipitation from the middle to late Holocene. In addition, summer precipitation variations were further modulated by sea-surface temperatures in the northwestern Pacific, through weakening the strength of the EASM.

Midlatitude Rossby wave modulation of the Indian summer monsoon

The dominant mode of July–August seasonal variability of Indian summer monsoon rainfall obtained by performing an empirical orthogonal function analysis over India, excluding northeast India, for the period 1979–2014 is highly correlated to the quasi‐stationary midlatitude Eurasian Rossby wave train, known as the ‘Silk Road’ pattern. A new hypothesis has been proposed and tested using observed Indian rainfall and the ERA‐Interim dataset, by which the positive feedback between the midlatitude Rossby wave and the Indian summer monsoon circulation has been established. A Rossby wave train features successive upper‐tropospheric negative and positive geopotential height anomalies over the northeast of the Mediterranean and northwest of India, respectively. The negative height anomaly decreases the sum of the vertical integral of potential and internal energy, while this increases in the region of positive geopotential height anomalies. This is associated with middle to lower tropospheric midlatitude descent and ascent anomalies at 40°E and 50°E, which cause negative surface temperature anomalies over Syria, Iraq, Jordan and Saudi Arabia, and a positive surface temperature anomaly over Iran, respectively. The negative and positive surface temperature anomalies are associated with positive and negative surface pressure anomalies over Saudi Arabia and Iran, respectively, which generate anomalous northwesterly winds over eastern Saudi Arabia and the Persian Gulf. Further downstream this anomalous northwesterly wind combines with the climatological background cross‐equatorial southwesterly flow in the Arabian Sea. The flow further converges towards central and northwest India. The flow also acts as a source of moisture supply from the warm Arabian Sea and Persian Gulf for the deep convection over the Western Ghats, northwest and central India and hence reinforces active Indian summer monsoon conditions.