The recent La-Nina phase of the El Nino Southern Oscillation (ENSO) phenomenon unusually lasted for third consecutive year, has disturbed global weather and linked to Indian monsoon. However, our understanding on the linkages of such changes to regional air quality is poor. We hereby provide a mechanism that beyond just influencing the meteorology, the interactions between the ocean and the atmosphere during the retreating phase of the La-Nin similar to a produced secondary results that significantly influenced the normal distribution of air quality over India through disturbed large-scale wind patterns. The winter of 2022-23 that coincided with retreating phase of the unprecedented triple dip La-Nin similar to a, was marred by a mysterious trend in air quality in different climatological regions of India, not observed in recent decades. The unusually worst air quality over South-Western India, whereas relatively cleaner air over the highly polluted North India, where levels of most toxic pollutant (PM2.5) deviating up to about +/- 30 % from earlier years. The dominance of higher northerly wind in the transport level forces influx and relatively slower winds near the surface, trapping pollutants in peninsular India, thereby notably increasing PM2.5 concentration. In contrast, too feeble western disturbances, and unique wind patterns with the absence of rain and clouds and faster ventilation led to a significant improvement in air quality in the North. The observed findings are validated by the chemical-transport model when forced with the climatology of the previous year. The novelty of present research is that it provides an association of air quality with climate change. We demonstrate that the modulated large-scale wind patterns linked to climatic changes may have far reaching consequences even at a local scale leading to unusual changes in the distribution of air pollutants, suggesting ever -stringent emission control actions.

Robust relationship between Antarctic sea ice and Indian summer monsoon rainfall (ISMR) is demonstrated using microwave satellite data for the period 1983–2015. A direct significant relationship is observed between sea ice over the Western Pacific Ocean (WPO) sector and ISMR, while for the same period, an inverse relationship is observed between sea ice over the Bellingshausen and Amundsen Seas (BAS) sector with that of ISMR. The underlying physical mechanism that relays southern polar variability signal to the Indian summer monsoon region is shown through the Pacific Ocean marked by El Niño Southern Oscillation (ENSO), wherein above normal sea ice over BAS (WPO) sector is associated with concurrently occurring warm sea surface temperature (SST) anomalies over the central (western) equatorial Pacific. Anomalous meridional circulations supplemented by above normal BAS (WPO) sea ice is accompanied by an ascending motion over the central (western) equatorial Pacific, which contemporaneously impacts summer monsoon rainfall over the Indian region adversely (favorably). The connection of ISMR with that of sea ice over BAS and WPO sectors as well as the governing physical mechanism is documented in Prabhu et al. (2021). Physical mechanism for ISMR-sea ice link is speculated through large-scale atmospheric circulations. Antarctic sea ice–ENSO–Walker cell–Hadley cell– ISMR is a new channel proposed in this study. The present study is dedicated at diagnosing regional facets of the relationship between spatial distribution of rainfall over India and sea ice averaged over BAS and WPO sectors during the summer monsoon season and to understand the physical mechanism governing their relation. A two-way interaction between sea ice over Antarctica and SST over the equatorial Pacific is suggested. Further, it is verified that Antarctic sea-ice variability, in conjunction with ENSO, has a significant regionally dependent impact on rainfall variability over different parts of India.

The isotopic values of rainfall in the southern parts of India exhibit strong seasonality. Such a contrast in isotopic values arises mainly due to the seasonal reversal of the monsoon winds. During the summer monsoon season, moisture is primarily transported from the Arabian Sea, while during the winter, it is sourced mainly from the Bay of Bengal. Additionally, atmospheric processes contribute to these differences. We collected precipitation samples from a southern Indian site and two neighboring island locations to study their isotopic characteristics from intra-seasonal to seasonal timescale. Oxygen isotopes in the marine environment seem to respond differently to the surface and tropospheric temperature than their counterparts from the land region. The seasonal isotopic gradient in the marine environment appears to be modulated by the tropospheric temperature anomaly. Oxygen isotopic values showed a strong association with the Webster-Yang monsoon index. Two distinct clusters were formed when the oxygen isotopes were plotted against the above-mentioned monsoon index. The formation of these clusters indicates the precipitation isotopes' response to moisture dynamics, which significantly change during the transition phase of the southwest to the northeast monsoon. Finally, we examine the potential of the precipitation isotopic records in studying the monsoon process, viz, the use of precipitation isotopes in characterizing the thermodynamical properties of the atmosphere and estimating the summer monsoon withdrawal phase.

The summer (June through September) monsoon 2020 has been very erratic with episodes of heavy and devastating rains, landslides and catastrophic winds over South Asia (India, Pakistan, Nepal, Bangladesh), East Asia (China, Korea, and Japan), and Southeast Asia (Singapore, Thailand, Vietnam, Laos, Cambodia, Philippines, Indonesia). The withdrawal of the summer monsoon over India was delayed by 2 weeks. The monsoon season over East Asia has been the longest. China recorded a Dam burst in the twentieth century. Furthermore, the Korean Peninsula has experienced back-to-back severe tropical cyclones. Could the lockdown activities initiate to control the COVID-19 spread a possible cause for these major episodes? The strict enforcement of the lockdown regulations has led to a considerable reduction of air pollutants-dust and aerosols throughout the world. A recent study based on satellites and merged products has documented a statistically significant mean reduction of about 20, 8, and 50% in nitrogen dioxide, Aerosol Optical Depth (AOD) and PM2.5 concentrations, respectively over the megacities across the globe. Our analysis reveals a considerable reduction of about 20% in AOD over South as well as over East Asia, more-over East Asia than over South Asia. The reduced aerosols have impacted the strength of the incoming solar radiation as evidenced by enhanced warming, more-over the land than the oceans. The differential warming over the land and the ocean has resulted in the amplification of the meridional ocean-land thermal contrast and strengthening of the monsoon flow. These intense features have supported the surplus transport of moisture from the oceans towards the main lands. Some similarity between the anomalous rainfall pattern and the anomalous AOD pattern is discernable. In particular, the enhancement of rainfall, the reduction in AOD and the surface temperature warming match very well over two regions one over West-Central India and the other over the Yangzte River Valley. Results further reveal that the heavy rains over the Yangzte River Valley could be associated with the preceding reduced aerosols, while the heavy rains over West-Central India could be associated with reduced aerosols and also due to the surface temperature warming.

Previous studies have shown that the vertical variations of upper-tropospheric temperature over the Mediterranean region significantly influence the convection over the western Tibetan Plateau (WTP) via modulating dynamics and thermodynamics over the WTP. Here we explore the possible connection the other way round, i.e., the impact of the Tibetan Plateau on the Mediterranean region. Results reveal that there exists an increase/decrease in upper-tropospheric temperature at the 100 hPa/250 hPa over the WTP during El Niño years. The upper-tropospheric temperature at 100 hPa/250 hPa is attributed to an anti-cyclonic/cyclonic circulation in the wind shear. The vertical thermal contrast (VTC) formed between the pressure levels (i.e., between 100 and 250 hPa) over the WTP induces a cyclonic circulation in the wind shear around 250 hPa over the Mediterranean region and thereby impacting the convection over the Mediterranean region. To substantiate, we explored the possible pathway for this teleconnection. An analysis of 200 hPa zonal winds (a proxy for the subtropical jet) regressed onto the WTP VTC exhibits westerly winds over the southern part of the Mediterranean region and easterly winds over the northern part implying a cyclonic circulation in support of convection over the Mediterranean region. Thus, ascertaining the role of the subtropical jet in facilitating the teleconnection between the WTP and the Mediterranean region. A dominant causality further corroborated the findings.

The present study reveals significantly out-of-phase changes at 100 and 250 hPa over the western North Pacific (WNP) during ENSO years. We found that the tropospheric temperature exhibits an increase and decrease in the 100 and 250 hPa respectively over the WNP during the La Nina episodes. The tropospheric temperature pattern over the 100 and 250 hPa during La Nina episodes are found to be described by an anti-cyclonic and cyclonic circulation in the wind shear respectively. Concomitant with the tropospheric temperature change an increase/decrease of convection over the WNP is observed during the La Nina/El Nino years. The further finding shows the robust dynamical changes in the subtropical jet over the WNP during ENSO episodes act as pathways leading to moisture transport towards the east side of the Tibetan Plateau and thereby affect the convection pattern over there. To affirm the findings, a novel causal inference technique is used to identify a dominant causality between the WNP vertical thermal contrast (VTC) and the longwave fluxes over the east side of the Tibetan plateau.

This study investigates the rainfall anomaly patterns over Asia associated with interannual variations of early summer (May–June) and peak summer (July–August) Indochina Peninsula (ICP) rainfall during 1979–2016. It is found that the early and peak summer rainfall variation in the ICP displays an out‐of‐phase relation to that in central Asia and central China, respectively. Analysis reveals that the out‐of‐phase early summer rainfall variation between the ICP and central Asia tends to occur in ENSO decaying years and the out‐of‐phase peak summer rainfall variation between the ICP and central China tends to occur in ENSO developing years. The early summer out‐of‐phase rainfall anomaly pattern between the ICP and central Asia forms due to a Rossby wave type response to anomalous heating extending from the ICP to northeast India, which is attributed to a combined influence of same sign sea surface temperature (SST) anomalies in the equatorial eastern Pacific and tropical southwestern Indian Ocean and opposite sign SST anomalies in the tropical western North Pacific. The peak summer out‐of‐phase rainfall variation between the ICP and central China forms due to a meridional atmospheric circulation pattern over East Asia and the western North Pacific, which is resulted from the combined impacts of opposite SST anomalies in the equatorial central Pacific and tropical southeastern Indian Ocean. Further analysis indicates that the out‐of‐phase rainfall variations between the ICP and central Asia in early summer and between the ICP and central China in peak summer may occur without anomalous tropical Indo‐Pacific SST forcing.

Having witnessed one of the most dramatic monsoons on record, the year 2020 established a record as the third highest, after 112% of the long period average (LPA) in 1994 and 110% of LPA in 2019. An analysis of upper tropospheric dynamic and thermodynamic variation was conducted to understand the abnormality in the 2020 monsoon. We found not only a dramatic variation in upper tropospheric temperature during 2020, with one centered over the Tibetan Plateau and another over the western Pacific, but also an interaction of these air temperatures. In tandem to this, induced thermal wind-driven circulation impacting the upper tropospheric relative humidity over the Indian subcontinent was observed. Interestingly, an east-to-west progression of relative humidity was found during 2020, while such emblematic progression was not seen in the LPA. The disparity in monsoon progression during 2020 from the LPA was found to be associated with the interaction of the as yet unexplored large-scale upper tropospheric dynamical features driven by the thermal wind relation. As implied by the thermal wind relation, distinctly different circulation patterns during 2020 over the two regions at 250 hPa, which were characterized by an anticyclonic and cyclonic circulation over the Tibetan Plateau and Western Pacific, provided the dynamical reason behind the moisture transport from the western Pacific towards the Indian subcontinent. A precise progression of east-to-west relative humidity further substantiated the findings: increased moisture flux from the western Pacific towards the Indian subcontinent during 2020.

The Indian summer monsoon (ISM) plays a crucial role in the well-being of billion Indians. This study discusses teleconnection between ISM with two dominant tropical sea surface temperature modes, namely, the El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). Results are analyzed for observation and CMIP5 simulations in both historical and future scenarios. ENSO and IOD exert an offsetting impact on ISM. Due to an overly strong control by ENSO, the majority of CMIP5 models simulate an unrealistic IOD and ISM rainfall correlation, that might contribute to major uncertainties in ISM simulations in both historical as well as in future projections. For ENSO, the further focus was on the East Pacific type or Canonical ENSO and the Central Pacific type or ENSO Modoki, and their regional teleconnection was explored. Regions of Central North East India suggest strong teleconnection in models that matches with observation, though for ENSO Modoki case that completely disappears in the future. In terms of mechanism, tropic and mid-latitude connection, the influence of regional Hadley circulation, and the role of the Sun were addressed. Finally, a hypothesized mechanism was proposed for disruption of ISM–ENSO teleconnection in the latter two decades of the last century.

In this paper, results of diagnostic analysis for the period 1983–2015, demonstrate a robust relationship between Indian Summer Monsoon Rainfall (ISMR) and sea ice area (SIA) over the two sectors of Antarctica namely, Western Pacific Ocean (WPO) and Bellingshausen and Amundsen Seas (BAS). A significant direct (inverse) relationship is observed between ISMR and SIA over the WPO (BAS) sector. Further, plausible physical mechanism governing this relationship is proposed. El Niño Modoki exhibit direct (inverse) relation with SIA over BAS (WPO) sector during summer monsoon season, which has prompted investigation of SIA-El Niño Modoki-ISMR connection. The linkage between southern polar sea ice and the Indian summer monsoon has been demonstrated through the Pacific Ocean, wherein above normal SIA over the BAS (WPO) sector is associated with concurrent warm equatorial central (western) Pacific Sea Surface Temperature (SST) anomalies. Associated meridional circulations supplemented by above normal BAS (WPO) SIA extremes is accompanied by an ascending motion over the equatorial central (western) Pacific. In turn, through large-scale zonal circulation, ascending branch of circulation over the central (western) Pacific Ocean contemporaneously impacts ISMR adversely (favourably). Large-scale atmospheric circulation modulated by equatorial Pacific SST signature is suggested as a possible link between Antarctic sea ice and ISMR.

This study presents some new perspectives on the progression of the Indian summer monsoon (June through September) during two contrasting summer seasons of 2013 and 2014. Monsoon 2013 witnessed above normal rainfall (105% of long period June-September average rainfall); on the other hand, 2014 experienced a severe drought (87% average rainfall). Furthermore, the south to north progression of monsoon 2013 was very rapid, but very slow during monsoon 2014. The disparity of monsoon progressions during the contrasting monsoons is demonstrated through the interaction between the vertical thermal contrast (VTC) of the upper troposphere over the western Tibetan Plateau (TP) and the South China Sea (SCS): a new dynamic perspective. This new perspective suggests interactions of the large-scale circulation anomalies driven by the thermal wind relation, which causes contrasts in the progression of the Indian monsoon. While during 2013 the SCS provided substantial moisture flux towards the Indian subcontinent, the year 2014 witnessed comparatively very few moisture flux incursions towards the Indian subcontinent. This highlights the role of the SCS in driving the differences during the contrasting monsoons. The role of VTC gradient (i.e., the difference in the VTC between the SCS and the western TP) is further demonstrated using a newly developed methodology, which exhibits causal relations of the VTC gradient between the two aforementioned regions with longwave flux (LWF) at the top of the atmosphere.

The Kashmir Valley represents a critical region for understanding isotopic changes in the atmospheric moisture sources since it is located at the intercept between the influences of mid-latitude westerlies and the southwest monsoon circulation. This study presents the variation in isotopic composition (delta O-18 and delta H-2) of daily precipitation samples collected from the Kashmir Valley, North-Western Himalaya, to quantify the effect of meteorological parameters, separately for the Southwest monsoon (SWM) season and the periods of Western Disturbances (WDs). The results suggest that precipitation isotopic composition is strongly modulated by temperature and relative humidity during the periods of WDs. Still, this dependency is weak in the case of the SWM season. Moisture transport pathways calculated from HYSPLIT back trajectory analysis shows a wide spatial variability during the monsoon season. On the other hand, the origin of moisture during the WD season was mostly restricted from the Mediterranean region, providing an explanation of a strong dependency between the precipitation isotopes and the meteorological parameters during the WD period. Such kind of relation may provide additional diagnostic for the WD events and may help in paleo-monsoon investigations.

The role of natural factors, mainly the sun, is explored on major tropospheric modes of variability in a holistic way. It formulates a flow chart, depicting coupling in the ocean-atmosphere system, initiated by solar decadal variability that involves El Niño Southern Oscillation (ENSO). Possible mechanisms for Canonic ENSO, Modoki ENSO and Canonic-Modoki ENSO are proposed considering their relevance to the decadal variation of Hadley, Walker circulation and mid-latitude jets. The upper stratospheric feature of the polar vortex is included too. Teleconnections by the ENSO on Indian Summer Monsoon (ISM) with a special emphasis on the later two decades of the last century is discussed. The disruption of usual ENSO-ISM teleconnection during that period is also attended. Subsequent analyses presented some results of solar signature which could possibly trigger different types of ENSO, agreeing with proposed mechanisms of the flow chart. It addressed the changing pattern of ENSO behaviour since the 1970s. The overall study can benefit the modelling community by an improved representation of ENSO in models and a better representation of ISM teleconnection via regional Hadley cell.

In this study, a comparison in the precipitation extremes as exhibited by the seven reference datasets is made to ascertain whether the inferences based on these datasets agree or they differ. These seven datasets, roughly grouped in three categories i.e. rain-gauge based (APHRODITE, CPC-UNI), satellite-based (TRMM, GPCP1DD) and reanalysis based (ERA-Interim, MERRA, and JRA55), having a common data period 1998–2007 are considered. Focus is to examine precipitation extremes in the summer monsoon rainfall over South Asia, East Asia and Southeast Asia. Measures of extreme precipitation include the percentile thresholds, frequency of extreme precipitation events and other quantities. Results reveal that the differences in displaying extremes among the datasets are small over South Asia and East Asia but large differences among the datasets are displayed over the Southeast Asian region including the maritime continent. Furthermore, precipitation data appear to be more consistent over East Asia among the seven datasets. Decadal trends in extreme precipitation are consistent with known results over South and East Asia. No trends in extreme precipitation events are exhibited over Southeast Asia. Outputs of the Coupled Model Intercomparison Project Phase 5 (CMIP5) simulation data are categorized as high, medium and low-resolution models. The regions displaying maximum intensity of extreme precipitation appear to be dependent on model resolution. High-resolution models simulate maximum intensity of extreme precipitation over the Indian sub-continent, medium-resolution models over northeast India and South China and the low-resolution models over Bangladesh, Myanmar and Thailand. In summary, there are differences in displaying extreme precipitation statistics among the seven datasets considered here and among the 29 CMIP5 model data outputs.

The combined impact of Greenland sea ice, Eurasian snow, and the El Nino-Southern Oscillation (ENSO) on the out-of-phase relationship between the Indian summer monsoon (ISM) and Korean summer monsoon (KSM) were investigated through numerical experiments. The results revealed that Indian and Korean summer rainfalls showed nonlinear responses to ENSO and Greenland sea ice forcing when the events co-occurred. Above-normal Greenland sea ice and a concurrent La Nina showed a distinct in-phase relationship with ISM and out-of-phase relationship with KSM. Below-normal and above-normal Greenland sea ice during boreal autumn surrounded the Greenland region with anomalous low pressure and high pressure, respectively. These were associated with a barotropic +west/-east or -west/+east dipole pattern, respectively, over Eurasia during the subsequent winter and spring seasons. Furthermore, these patterns led to positive and negative snow depth anomalies, respectively, over western Eurasia and the opposite snow tendency over eastern Eurasia during the subsequent spring. This variability in Eurasian snow patterns may play a crucial role in ISM and KSM. The co-occurrence of ENSO variability also generates high- and low-pressure anomaly patterns over the Indian Ocean that may be related to unfavourable or favourable ISM, respectively, while influencing the negative or positive phases of a Pacific Japan (PJ)-like teleconnection pattern that may be related to unfavourable or favourable KSM, respectively. Therefore, coexisting ENSO forcing may play a dominant role in ISM and KSM, but Greenland sea ice forcing and Eurasian snow variation intensify the out-of-phase relationship between ISM and KSM.

This study discusses the role of natural factors and related teleconnections for Indian summer monsoon (ISM) with a special emphasis on later two decades of the last century. The combined influence of the sun and volcanos on ISM is examined using observational data as well as CMIP5 model outputs. Possible mechanisms relating to a disruption of the usual ENSO-ISM teleconnection for those decades are explored. Observation suggested that the regional Hadley circulation, via the NAO in the northern hemisphere and Indian Ocean Dipole in the southern hemisphere, may have a role in the change in ISM behaviour. Such features though captured well in the observation are shown missing in models. Additionally, it indicates that differences among models mainly originate in a regional level, which could be due to inconsistency in representing regional teleconnection features. Interestingly, all models perform reasonably well in terms of global thermodynamic scaling arguments. The overall study underpins important areas, where natural factors influence regional climate, but models miss out and suggest discrepancies among each other. Such knowledge has major implications in regional as well as global scale. The modelling community will also greatly benefit by an improved representation of ENSO and ISM in models.

Variability of Indian summer monsoon droughts is investigated by computing all-India drought indices namely Percent of Normal Precipitation, Standardized Precipitation Index and percentage area of India under moderate and severe drought conditions. Observations for recent decades, post 1960, exhibit declining trend in monsoon rainfall with frequent occurrence and intensification of droughts along with an increase in percentage of area under moderate and severe drought conditions, in association with variations in sea surface temperature (SST). Historical simulations from CMIP5 models suggest that two models, ACCESS1.0 and INMCM4, could well simulate monsoon rainfall variability, particularly the frequent occurrence of droughts and spatial variability of rainfall during drought years in recent historical period (1961–2005). Future projections of all-India drought indices from these two models indicate frequent droughts during near and mid future (2010–2069) with respect to the recent historical period. Intensification of severe droughts for near and mid future are suggested to be more pronounced over north-central India. The reduction in rainfall in the near and mid future is dynamically consistent with a westward shift in large-scale monsoon circulation, particularly the monsoon trough over South Asia. Interestingly, future projections of monsoon teleconnections indicate a weakening (strengthening) of in-phase (out-of-phase) relationship of all-India drought intensity with the equatorial eastern Pacific and the Indian Ocean (western Pacific) SST. Whereas, a strengthening of in-phase relationship between percentage of area under drought conditions and the equatorial eastern Pacific SST is projected for near and mid future with respect to the recent historical period. These drought features are consistent in both the models.

An examination of the contrasting behaviour of the Indian summer monsoon during peak monsoon months of July and August 2002 in relation to the South China Sea (SCS) SST variations on intra-seasonal time scale have been carried out in this study. Monsoon rainfall over India was a deficit during July whereas enhanced rainfall activity was evident during August. Interestingly, SST over the SCS also exhibited similar contrasting behaviour with less variation during July and strong biweekly intra-seasonal (BWI) oscillation with 10–20 day periodicity during August. During August, the BWI oscillation in the SCS SST could induce anomalous cyclonic circulation and enhancement in rainfall over the SCS, suggestive of a strong air–sea interaction process. Moreover, a strong relationship between the Indian monsoon and SCS SST is evident during August, at 3-day lead time of SST. The SCS SST variations could enhance westward propagation of moisture flux from the SCS to the Indian subcontinent and thereby influences the Indian monsoon. The SST variations and air–sea interaction processes over the SCS, also westward propagation of BWI moisture flux were weak during July. Our analysis suggests that SST variations over the SCS could modulate the monsoon circulation as well as the moisture flux from the SCS to the Indian subcontinent and thereby influence the Indian monsoon, particularly on biweekly time scale at least 3 days in advance. The study indicates a potential role of the SCS SST in foreshadowing the biweekly intra-seasonal oscillation during the Indian summer monsoon period.

The overall yearly seasonal performance of Indian southwest monsoon rainfall (ISMR) for the whole Indian land mass is presently expressed by the India Meteorological Department (IMD) by a single number, the total quantum of rainfall. Any particular year is declared as excess/deficit or normal monsoon rainfall year on the basis of this single number. It is well known that monsoon rainfall also has high interannual variability in spatial and temporal scales. To account for these aspects in ISMR, we propose two new spatial and temporal indices. These indices have been calculated using the 115 years of IMD daily 0.25° × 0.25° gridded rainfall data. Both indices seem to go in tandem with the in vogue seasonal quantum index. The anomaly analysis indicates that the indices during excess monsoon years behave randomly, while for deficit monsoon years the phase of all the three indices is the same. Evaluation of these indices is also studied with respect to the existing dynamical indices based on large-scale circulation. It is found that the new temporal indices have better link with circulation indices as compared to the new spatial indices. El Nino and Southern Oscillation (ENSO) especially over the equatorial Pacific Ocean still have the largest influence in both the new indices. However, temporal indices have much better remote influence as compared to that of spatial indices. Linkages over the Indian Ocean regions are very different in both the spatial and temporal indices. Continuous wavelet transform (CWT) analysis indicates that the complete spectrum of oscillation of the QI is shared in the lower oscillation band by the spatial index and in the higher oscillation band by the temporal index. These new indices may give some extra dimension to study Indian summer monsoon variability.

We demonstrate that a large-scale longitudinally symmetric global phenomenon in the Southern Hemisphere sub-polar region can transmit its influence over a remote local region of the Northern Hemisphere traveling more than 100° of latitudes (from ~70°S to ~40°N). This is illustrated by examining the relationship between the Southern Annular Mode (SAM) and the Korean Monsoon Rainfall (KMR) based on the data period 1983-2013. Results reveal that the May-June SAM (MJSAM) has a significant in-phase relationship with the subsequent KMR. A positive MJSAM is favorable for the summer monsoon rainfall over the Korean peninsula. The impact is relayed through the central Pacific Ocean. When a negative phase of MJSAM occurs, it gives rise to an anomalous meridional circulation in a longitudinally locked air-sea coupled system over the central Pacific that propagates from sub-polar to equatorial latitudes and is associated with the central Pacific warming. The ascending motion over the central Pacific descends over the Korean peninsula during peak-boreal summer resulting in weakening of monsoon rainfall. The opposite features prevail during a positive phase of SAM. Thus, the extreme modes of MJSAM could possibly serve as a predictor for ensuing Korean summer monsoon rainfall.