Contrasting Regional Responses of Indian Summer Monsoon Rainfall to Exhausted Spring and Concurrently Emerging Summer El Nino Events

The inverse relationship between the warm phase of the El Nino Southern Oscillation(ENSO)and the Indian Summer Monsoon Rainfall(ISMR)is well established.Yet,some El Nino events that occur in the early months of the year(boreal spring)transform into a neutral phase before the start of summer,whereas others begin in the boreal summer and persist in a positive phase throughout the summer monsoon season.This study investigates the distinct influences of an exhausted spring El Nino(springtime)and emerging summer El Nino(summertime)on the regional variability of ISMR.The two ENSO categories were formulated based on the time of occurrence of positive SST anomalies over the Nino-3.4 region in the Pacific.The ISMR’s dynamical and thermodynamical responses to such events were investigated using standard metrics such as the Walker and Hadley circulations,vertically integrated moisture flux convergence(VIMFC),wind shear,and upper atmospheric circulation.The monsoon circulation features are remarkably different in response to the exhausted spring El Nino and emerging summer El Nino phases,which distinctly dictate regional rainfall variability.The dynamic and thermodynamic responses reveal that exhausted spring El Nino events favor excess monsoon rainfall over eastern peninsular India and deficit rainfall over the core monsoon regions of central India.In contrast,emerging summer El Nino events negatively impact the seasonal rainfall over the country,except for a few regions along the west coast and northeast India.

Weakening of Indian Summer Monsoon in Recent Decades

The analysis of 43 years of NCEP-NCAR reanalysis data and station observations reveals the connections between tropospheric temperature variations and the weakening of the Indian summer monsoon circulation. The Indian summer monsoon variation is strongly linked to tropospheric temperature over East Asia, showing significant positive correlations of mean tropospheric temperature with all-Indian summer rainfall and the monsoon circulation

The cold pool of the Bay of Bengal and its association with the break phase of the Indian summer monsoon

During the summer monsoon season, strong coastal upwelling occurs along the southwest coast of India and at the southern tip of India, which cools the surface temperature of the waters around these regions. The summer monsoon current carries the upwelled cold waters into the Bay of Bengal and forms the ‘cold pool of the Bay of Bengal', with its core south of Sri Lanka and over the southcentral Bay of Bengal. The present study focuses on the intrusion of these cold waters into the south of the Bay of Bengal, its interannual variability, and its association with the surface wind during the break phase of the summer monsoon, when strong westerly surface winds flow south of 10°N.The authors hypothesize that the enhanced cooling in the cold pool region during monsoon spells is associated with the strong westerly wind stress there during the break spells of the monsoon.Seven cases of long break monsoon spells that occurred during the nine years from 2001 to 2009 are analyzed, and the results confirm our hypothesis.

Indian summer monsoon rainfall (ISMR) forecasting using time series data: A fuzzy-entropy-neuro based expert system

This study presents a model to forecast the Indian summer monsoon rainfall（ISMR）（June-September）based on monthly and seasonal time scales. The ISMR time series data sets are classified into two parts for modeling purposes, viz.,（1） training data set（1871-1960）, and（2） testing data set（1961-2014）.Statistical analyzes reflect the dynamic nature of the ISMR, which couldn＇t be predicted efficiently by statistical and mathematical based models. Therefore, this study suggests the usage of three techniques,viz., fuzzy set, entropy and artificial neural network（ANN）. Based on these techniques, a novel ISMR time series forecasting model is designed to deal with the dynamic nature of the ISMR. This model is verified and validated with training and testing data sets. Various statistical analyzes and comparison studies demonstrate the effectiveness of the proposed model.

Global Annual Mean Surface Air Temperature Anomalies and Their Link with Indian Summer Monsoon Failures

Analysis of the global mean annual temperature anomalies based on land and marine data for the last 88 years (1901-1988) of this century has been carried out with a view to find any relationship with failures in Indian summer monsoon rainfall. On the climatological scale (i.e. 30 years) it has been noticed that there is an abnormal increase in the frequency of drought years during epochs of global warming and cooling, while it is considerably less when global temperatures are near normal. Results are unchanged even when the data are filtered out for ENSO (El-Nino Southern Oscillation) effect.It has also been noticed that during warm and cold epochs in global temperatures the amount of summer monsoon rainfall decreases as compared to the rainfall during a normal temperature epoch.

Variation of Zonal Winds in the Upper Troposphere and Lower Stratosphere in Association with Deficient and Excess Indian Summer Monsoon Scenario

The Indian summer monsoon is one of the most dominant tropical circulation systems in the general circulation of the atmosphere. The country receives more than 80% of the annual rainfall during a short span of four months (June to September) of the southwest monsoon season. Variability in the quantum of rainfall during the monsoon season has profound impacts on water resources, power generation, agriculture, economics and ecosystems in the country. The inter annual variability of Indian Summer Monsoon Rainfall (ISMR) depends on atmospheric and oceanic conditions prevailed during the season. In this study we have made an attempt to understand the variation of the of zonal winds in the tropical Upper Troposphere and Lower Stratosphere (UT/LS) region during deficient and Excess rainfall years of Indian summer monsoon and its relation to Indian Summer Monsoon Rainfall (ISMR). It is found that in the equatorial Upper Troposphere zonal winds have westerly anomalies during deficient rainfall year’s and easterly anomaly during excess rainfall years of Indian summer monsoon and opposite zonal wind anomaly is noted in the equatorial Lower Stratosphere during the deficient and excess rainfall years of Indian summer monsoon. It is also found that the June to September upper troposphere zonal winds averaged between 15°N and 15°S latitudes have a long-term trend during 1960 to 1998. Over this period the tropical easterlies and the tropical jet stream have weakened with time.

Intraseasonal Oscillation of Tropospheric Ozone over the Indian Summer Monsoon Region

Boreal summer intraseasonal oscillation(BSISO) of lower tropospheric ozone is observed in the Indian summer monsoon(ISM) region on the basis of ERA-Interim reanalysis data and ozonesonde data from the World Ozone and Ultraviolet Radiation Data Centre. The 30–60-day intraseasonal variation of lower-tropospheric ozone shows a northwest–southeast pattern with northeastward propagation in the ISM region. The most significant ozone variations are observed in the Maritime Continent and western North Pacific. In the tropics, ozone anomalies extend from the surface to 300 hPa; however, in extratropical areas, it is mainly observed under 500 hPa. Precipitation caused by BSISO plays a dominant role in modulating the BSISO of lower-tropospheric ozone in the tropics, causing negative/positive ozone anomalies in phases 1–3/5–6. As the BSISO propagates northeastward to the western North Pacific, horizontal transport becomes relatively more important, increasing/reducing tropospheric ozone via anticyclonic/cyclonic anomalies over the western North Pacific in phases 3–4/7–8.As two extreme conditions of the ISM, most of its active/break events occur in BSISO phases 4–7/1–8 when suppressed/enhanced convection appears over the equatorial eastern Indian Ocean and enhanced/suppressed convection appears over India, the Bay of Bengal, and the South China Sea. As a result, the BSISO of tropospheric ozone shows significant positive/negative anomalies over the Maritime Continent, as well as negative/positive anomalies over India, the Bay of Bengal,and the South China Sea in active/break spells of the ISM. This BSISO of tropospheric ozone is more remarkable in break spells than in active spells of the ISM, due to the stronger amplitude of BSISO in the former.

Effects of Large-Scale Climatic Oscillations on the Variability of the Indian Summer Monsoon Rainfall

In India,large-scale climatic oscillations have strong influences on the Indian summer monsoon rainfall(ISMR),which plays a crucial role in India’s agricultural production and economic growth.However,there are limited studies in India that explore the influences of decadal and multidecadal oscillations on the ISMR and associated El Niño–Southern Oscillation(ENSO).Therefore,in this study we carried out a comprehensive and detailed investigation to understand the influences of ENSO,Pacific decadal oscillation(PDO),and Atlantic multidecadal oscillation(AMO)on ISMR across different regions in India.The statistical significance of ISMR associated with different phases(positive/warm and negative/cold)of ENSO,PDO,and AMO(individual analysis),and combined ENSO–AMO,and ENSO–PDO(coupled analysis)were analysed by using the nonparametric Wilcoxon Rank Sum(WRS)test.The individual analysis results indicate that in addition to the ENSO teleconnection,AMO and PDO significantly affect the spatial patterns of ISMR.Coupled analysis was performed to understand how the phase shift of PDO and AMO has modulated the rainfall during El Niño and La Niña phases.The results indicate that the La Niña associated with a positive PDO phase caused excessive precipitation of about 21%–150%in the peninsular,west–central,and hilly regions compared to the individual effect of ENSO/PDO/AMO on ISMR;similarly,the west–central,coastal,and northwest regions received 15%–56%of excessive rainfall.Moreover,during the El Niño combined with PDO positive(AMO positive),above-normal precipitation was observed in hilly,northeast,and coastal(hilly,northeast,west–central,and coastal)regions,opposite to the results obtained from the individual ENSO analysis.This study emphasizes the importance of accounting the decadal and multidecadal forcing when examining variations in the ISMR during different phases of ENSO events.

Characteristics and triggering mechanisms of early negative Indian Ocean Dipole

Negative Indian Ocean Dipole(nIOD)can exert great impacts on global climate and can also strongly influence the climate in China.Early nIOD is a major type of nIOD,which can induce more pronounced climate anomalies in summer than La Niña-related nIOD.However,the characteristics and triggering mechanisms of early nIOD are unclear.Our results based on reanalysis datasets indicate that the early nIOD and La Niña-related nIOD are the two major types of nIOD,and the former accounts for over one third of all the nIOD events in the past six decades.These two types of nIODs are similar in their intensities,but are different in their spatial patterns and seasonal cycles.The early nIOD,which develops in spring and peaks in summer,is one season earlier than the La Niña-related nIOD.The spatial pattern of the wind anomaly associated with early nIOD exhibits a winter monsoon-like pattern,with strong westerly anomalies in the equatorial Indian Ocean and eastly anomalies in the northern Indian Ocean.Opposite to the triggering mechanism of early positve IOD,the early nIOD is induced by delayed Indian summer monsoon onset.The results of this study are helpful for improving the prediction skill of IOD and its climate impacts.

Relationship between Indian and East Asian Summer Rainfall Variations

The Indian and East Asian summer monsoons are two components of the whole Asian summer monsoon system. Previous studies have indicated in-phase and out-of-phase variations between Indian and East Asian summer rainfall. The present study reviews the current understanding of the connection between Indian and East Asian summer rainfall. The review covers the relationship of northern China, southern Japan, and South Korean summer rainfall with Indian summer rainfall; the atmospheric circulation anomalies connecting Indian and East Asian summer rainfall variations; the long-term change in the connection between Indian and northern China rainfall and the plausible reasons for the change; and the influence of ENSO on the relationship between Indian and East Asian summer rainfall and its change. While much progress has been made about the relationship between Indian and East Asian summer rainfall variations, there are several remaining issues that need investigation. These include the processes involved in the connection between Indian and East Asian summer rainfall, the non-stationarity of the connection and the plausible reasons, the influences of ENSO on the relationship, the performance of climate models in simulating the relationship between Indian and East Asian summer rainfall, and the relationship between Indian and East Asian rainfall intraseasonal fluctuations.

Differences in Atmospheric Heat Source between the Tibetan Plateau–South Asia Region and the Southern Indian Ocean and Their Impacts on the Indian Summer Monsoon Outbreak

In this paper, the NCEP-NCAR daily reanalysis data are used to investigate the characteristics of the atmospheric heat source/sink （AHSS） over South Asia （SA） and southern Indian Ocean （SIO）. The thermal differences between these two regions and their influence on the outbreak of the Indian summer monsoon （ISM） are explored. Composite analysis and correlation analysis are applied. The results indicate that the intraseasonal variability of AHSS is signi- ficant in SA but insignificant in the SIO. Large inland areas in the Northern Hemisphere still behave as a heat sink in March, similar to the situation in winter. Significant differences are found in the distribution of AHSS between the ocean and land, with distinct land-ocean thermal contrast in April, and the pattern presents in the transitional period right before the ISM onset. In May, strong heat centers appear over the areas from the Indochina Peninsula to the Bay of Bengal and south of the Tibetan Plateau （TP）, which is a typical pattern of AHSS distribution during the monsoon season. The timing of SA-SIO thermal difference turning positive is about 15 pentads in advance of the onset of the ISM. Then, after the thermal differences have turned positive, a pre-monsoon meridional circulation cell develops due to the near-surface heat center and the negative thermal contrast center, after which the meridional circulation of the ISM gradually establishes. In years of early （late） conversion of the SASIO thermal difference turning from neg- ative to positive, the AHSS at all levels over the TP and SIO converts later （earlier） than normal and the establish- ment of the ascending and descending branches of the ISM＇s meridional circulation is later （earlier） too. Meanwhile, the establishment of the South Asian high over the TP is later （earlier） than normal and the conversion of the Mas- carene high from winter to summer mode occurs anomalously late （early）. As a result, the onset of the ISM is later （earlier） than normal. However, the difference in vorticity between early and late conversion only shows in the changes of strong vorticity centers＇ location in the upper and lower troposphere.

Analysis and Numerical Simulations of the Teleconnection Between Indian Summer Monsoon and Precipitation in North China

In the early 1980s, Chinese meteorologists discovered the positive correlation in summer rainfall between India and North China and the correlation was later confirmed by some researches in and outside China. Based on a variety of meteorological data from 1951 to 2005 and numerical simulations, the present study investigates such a correlation between Indian summer monsoon （ISM） and precipitation in North China. Furthermore, we discuss the intrinsic relations of the positive （Northwest India）-negative （the Tibetan Plateau）-positive （North China） precipitation anomaly teleconnection pattern from two aspects of thermal and dynamical factors, which not only confirms the precipitation teleconnection previously discovered again, but also reveals the influence mechanism of the ISM on the rainfall in North China. The results show that： （1） When the ISM is strong （weak）, the precipitation in North China tends to be more （less） than normal; however, when the rainfall in North China is more （less） than normal, the probability of the strengthening （weakening） of the ISM is relatively lower. This implies that the ISM anomaly has more impact on the rainfall in North China. （2） The Indian low usually dominantly impacts the intensity of the ISM. When the Indian low deepens, the low troughs in mid-high latitudes are frequently strengthened, and the ridge of the western Pacific subtropical high （WPSH） extends westward. The southwesterly water vapor transport originated from low-latitudes and the southeasterly water vapor transport along the southwestern flank of the WPSH converge in North China, which is favorable for more rainfall there than normal, and vice versa. （3） The simulations from the regional climate model developed by National Climate Center （ReGCM_NCC） capture the salient feature of the precipitation teleconnection between India and North China. The simulated anomalous atmospheric existence of such a teleconnection from another circulations are close to observations, which confirms the angle.

THE INDIAN SUMMER MONSOON AND SUMMER RALNFALL IN NORTH CHINA

The analyses have been made of the summer precipitation data over Indian and North China during 1891—1983.The statistic results show that the climatic characteristics of the Indian summer monsoon rainfall are similar to summer rainfall in North China,and a steady and significant positive correlation exists be- tween them. The circulation systems associated with the Indian monsoon and the rainfall in North China in summer have also been discussed.It is found that there are same predictors in April to be used for the forecast of North China rainfall and Indian monsoon.

Correlation Between the Arabian Sea Surface Temperature and the Onset Period of South Asian Summer Monsoon with Trend Analysis on the Intensity

The long-term trend of the Arabian Sea surface temperature(ASST)during the formation of the South Asian summer monsoon(SASM)is discussed in this manuscript.From April to June,ASST changed from a meridional gradual distribution to a spatially uniform distribution and then to a zonal gradual distribution.The South Asian summer monsoon intensity(SASMI)and South Asian summer monsoon direction(SASMD)indicate that the variation of the ASST is highly related to the formation of the SASM during the summer monsoon period and can contribute to the spread of the SASM from the Southwest Arabian Sea throughout all of South Asia.Results of the correlation between the ASST and SASMI for the same month and its adjacent months were the same,and the areas of the positive correlation between the ASST and SASMI significantly increased from May–June as compared to April–May.The maximum correlation coefficient was 0.86.The results of the ASST and SASMD for the same month and its adjacent months were substantially different.However,the ASST and SASMD for May and April also showed a high positive correlation with a maximum correlation coefficient of 0.61 in the southwestern Arabian Sea.Existence of the ASST had a spatially consistent and significant upward trend with a mean increase of 0.6℃during the summer monsoon period from 1980 to 2020(between April and September),whereas the SASMI had a strengthening trend along the western and southwestern regions of the Arabian Sea and the southeastern region of the Arabian Peninsula.Meanwhile,the rest of the study regions showed a declining trend.Overall,the entire study region showed a slight downward trend,and the average value decreased by 0.02ms^(−1).

Teleconnection between the Indian summer monsoon onset and the Meiyu over the Yangtze River Valley

Based on the Indian and Chinese precipitation data and the NCEP-NCAR reanalysis circulation data, the relationship between the Indian summer monsoon (ISM) onset and the Meiyu over the Yangtze River Valley has been discussed by the methods of correlation analysis and composite analysis. The results show that the date of ISM onset over Kerala in the southwestern coast of the Indian Peninsula is about two weeks earlier than the beginning of the Meiyu over the Yangtze River Valley. After the outbreak of ISM, the teleconnection mode sets up from the western coast of India via the Bay of Bengal (BOB) to the Yangtze River Valley and southern Japan. It is different both in time and space from the telecon- nection mode which is from the northwest of India via the Tibetan Plateau to northern China. The for- mer mode is defined as the "south" teleconnection of the Asian summer monsoon, forming in the pe- riod of ISM onset; while the latter mode is called the "north" teleconnection, mainly occurring in the Asian monsoon culminant period. During the process of the "south" teleconnection’s formation, the Asian monsoon circulation has experienced a series of important changes: ISM onset, the northward movement of the south Asia high (SAH), the onset vortex occurrence, the eastward extension of the stronger tropical westerly belt, and the northeastward jump of the western Pacific subtropical high (WPSH), etc. Consequently, since ISM sets up over Kerala, the whole Asian continent is covered by the upper SAH after about two weeks, while in the mid- and lower troposphere, a strong wind belt forms from the Arabian Sea via the southern India, BOB and the South China Sea (SCS), then along the western flank of WPSH, to the Yangtze River Valley and southern Japan. With the northward moving of the subtropical jet streams, the upper westerly jet stream and the low level jet have been coupled ver- tically over east Asia, while the Yangtze River Valley happens to locate in the ascending motion area between the upper jet stream and the low level jet, i.e. right of the entrance of the upper jet stream and left of the low level jet. Such a structure of the vertical circulation can trigger the Meiyu onset over the Yangtze River Valley.

Impacts of intraseasonal oscillation on the onset and interannual variation of the Indian summer monsoon

The role of the intraseasonal oscillation (ISO) on the seasonal and interannual variations of the Indian summer monsoon is investigated based on the analysis of observational data. It is shown that the ISO significantly contributes to the establishment of low-level westerlies during the monsoon onset and developing periods. The effect of the ISO on the annual cycle of the monsoon is through nonlinear eddy momentum transport. On the interannual timescale, the Indian summer monsoon rainfall exhibits a significant out-of-phase relationship with the ISO intensity over the Indian monsoon region. In strong ISO years it appears the weak monsoon when there is an abnormal high over the India subcontinent in the lower troposphere. In weak ISO years there exists an abnormal low and the strong monsoon ap-pears.

The Summer Monsoon Onset over the Tropical Eastern Indian Ocean: The Earliest Onset Process of the Asian Summer Monsoon

The onset process of the tropical eastern Indian Ocean （TEIO） summer monsoon （TEIOSM） and its relationship with the cross-equatorial flows are investigated via climatological analysis. Climatologically, results indicate that the earliest onset process of the Asian summer monsoon occurs over the TEIO at pentad 22 （April 15-20）. Unlike the abrupt onset of the South China Sea （SCS） summer monsoon, the TEIOSM onset process displays a stepwise advance. Moreover, a close relationship between the TEIOSM development and the northward push of the cross-equatorial flows over 80^-90~E is revealed. A difference vorticity center, together with the counterpart over the southern Indian Ocean, constitutes a pair of difference cyclonic vortices, which strengthens the southwesterly wind over the TEIO and the northerly wind to the west of the Indian Peninsula from the end of March to late May. Therefore, the occurrence of the southwesterly wind over the TEIO is earlier than its counterpart over the tropical western Indian Ocean, and the cross-equatorial flows emerge firstly over the TEIO rather than over the Somali area. The former increases in intensity during its northward propagation, which provides a precondition for the TEIOSM onset and its northward advance.

Roles of forced and inertially unstable convection development in the onset process of Indian summer monsoon

The NCEP/NCAR R1 reanalysis data are employed to investigate the impact of forced and inertial instability in the lower troposphere over the Arabian Sea on the onset process of Indian summer monsoon(ISM),and to reveal the important role of zonal advection of zonal geostrophic momentum played in the forced unstable convection.Results show that during the ISM onset the zero absolute vorticity contour(??=0)shifts northward due to the strong cross-equatorial pressure gradient in the lower troposphere over southern Arabian Sea.Thus a region with negative absolute vorticity is generated near the equator in the northern hemisphere,manifesting the evident free inertial instability.When a southerly passes through this region,under the influence of friction a lower convergence that facilitates the convection flourishing at the lower latitudes appears to the north of zero absolute vorticity contour.However,owing to such a traditional inertial instability,the convection is confined near the equator which does not have direct influence on the ISM onset.On the contrary in the region to the north of the zero absolute vorticity contour and to the south of the low pressure center near the surface,although the atmosphere there is inertially stable,the lower westerly jet can develop and bring on the apparent zonal advection of zonal geostrophic momentum.Both theoretical study and diagnosing analysis present that such a zonal advection of geostrophic momentum is closely associated with the zonal asymmetric distribution of meridional land-sea thermal contrast,which induces a convergence center near and further north of the westerly jet in the lower troposphere over the southwestern coast of the Indian Peninsula,providing a favorable lower circulation for the ISM onset.It illustrates that the development of convection over the Arabian Sea in late spring and early summer is not only due to the frictional inertial instability but also strongly affected by the zonal asymmetric distribution of land-sea thermal contrast.Moreover,before the ISM onset due to the eastward development of the South Asian High(SAH)in the upper troposphere,high potential vorticity is transported to the region over the Arabian Sea.Then a local trumpet-shaped stream field is generated to cause the evident upper divergence-pumping effect which favors the ISM onset.When the upper divergence is vertically coupled with the lower convergence resulted from the aforementioned forced unstable convection development near the southwestern coast of Indian Peninsula,the atmospheric baroclinic unstable development is stimulated and the ISM onset is triggered.

The Interannual Variations of Summer Precipitation in the Northern Indian Ocean Associated with ENSO

Using rainfall data from the Global Precipitation Climatology Project(GPCP),NOAA extended reconstruction sea surface temperature(ERSST),and NCEP/NCAR reanalysis,this study investigates the interannual variation of summer rainfall southwest of the Indian Peninsula and the northeastern Bay of Bengal associated with ENSO.The composite study indicates a decreased summer rainfall southwest of the Indian Peninsula and an increase in the northeastern Bay of Bengal during the developing phase,but vice versa during the decay phase of El Ni o.Further regression analysis demonstrates that abnormal rainfall in the above two regions is controlled by different mechanisms.Southwest of the Indian Peninsula,the precipitation anomaly is related to local convection and water vapor flux in the decay phase of El Ni o.The anomalous cyclone circulation at the lower troposphere helps strengthen rainfall.In the northeastern Bay of Bengal,the anomalous rainfall depends on the strength of the Indian southwest summer monsoon(ISSM).A strong/weak ISSM in the developing/decay phase of El Ni o can bring more/less water vapor to strengthen/weaken the local summer precipitation.

Recent Changes of Northern Indian Ocean Summer Rainfall Based on CMIP5 Multi-Model

This study evaluates the simulation of summer rainfall changes in the Northern Indian Ocean (NIO) based on the fifth phase of Coupled Model Intercomparison Project (CMIP5). The historical runs of 20 CMIP5 coupled General Circulation Models (GCMs) are analyzed. The Multi-Model ensemble (MME) of the CMIP5 models well reproduces the general feature of NIO summer rainfall. For a short period 1979?2005, 14 out of 20 models show an increased trend in the mean rainfall and a similar spatial distri-bution to the Global Precipitation Climatology Project (GPCP) observations in MME. The increasing of the convergence in the equatorial IO results in the increase of rainfall significantly. The equatorial rainfall trend patterns seem modulated by the SST warm-ing in the tropical Indian Ocean, which confirm the mechanism of 'warmer-get-wetter' theory. For a long period 1950?2005, the trend of monsoon rainfall over India shows a decrease over the most parts of the India except an increase over the south corn er of the Indian Peninsula, due to a weakened summer monsoon circulation. The pattern is well simulated in half of the CMIP5 models. The rainfall over the north India is different for a short period, in which rainfall increases in 1979?2005, implying possible decadal varia-tion in the NIO summer climate.