热带海面温度对亚马逊旱季降水年际变率的影响及机制

用偏最小二乘(Partial Least Square,PLS)回归方法分析了 1979～2018年影响亚马逊旱季(6～8月)降水年际变率的热带海面温度模态.第一海面温度模态解释了总方差的64％,主要表现为前期亚马逊雨季(12月至次年2月)至旱季(6～8月)热带东太平洋La Ni?a型海面温度异常演变.12月至次年2月...     

Tanzanian rainfall responses to El Niño and positive Indian Ocean Dipole events during 1951–2015

The relative impacts of Indian and Pacific Ocean processes on Tanzanian rainfall was evaluated using composite and correlation analyses. It was found that the seasonal responses of rainfall to positive Indian Ocean Dipole (pIOD) and El Niño events are substantial from September–October–November (SON) to December–January–February (DJF), whereas the Indian Ocean Dipole (IOD) exerts more control than El Niño–Southern Oscillation (ENSO) in both seasons. The associated relationship with the sea surface temperature (SST) and large-scale atmospheric circulations revealed distinct features. For the pure pIOD years, there is above-normal rainfall over the entire country. A strong rainfall condition is evident over the Lake Victoria basin and coastal and northeastern highland parts of the country during SON, while areas of the central and southern highlands exhibit substantial rains during DJF. For the pure El-Niño events, Tanzania has suffered from insignificant, weak, and non-coherent rainfall conditions during SON. However, a contrasting insignificant rainfall signature is found between the northern and southern parts of the country during the subsequent DJF season. For the co-occurrence of pIOD and El Niño, significant, excessive rainfall conditions are restricted to over the northern coast and northeastern areas of the country during SON, consistent with the rainfall pattern for pIOD. A weak, positive rainfall condition is observed over the entire country in the following season of DJF. Generally, in terms of Tanzanian rainfall, the IOD/ENSO variability and the associated impacts can be explained by the anomalous SST and circulation anomalies.     

热带对流季内振荡强度异常特征及其与海表温度的关系

利用外逸长波辐射 (outgoing longwave radiation, OLR) 资料分析了热带对流季内振荡 (ISO) 强度的季节变化及年际异常特征, 重点研究其与海表温度的关系。结果表明:最强的OLR季内振荡主要位于高海表温度 (SST) 区, 即热带印度洋和热带西太平洋区域, 终年存在, 冬、春季最强, 振荡中心偏于夏半球。OLR季内振荡强度年际异常显著区域是热带中东太平洋区域、西北太平洋区域和西南太平洋区域, 它与SST年际异常存在局地正相关关系, 伴随环流的辐合辐散, 并与ENSO事件关系密切。另外, El Ni?o事件发生之前, 热带印度洋和热带西太平区域OLR季内振荡增强, 其中心随事件的发展逐渐东移, 事件发生后这两个区域ISO减弱, 这与OLR季内振荡强度年际异常显著的区域具有内在连贯性。海表温度是决定OLR季内振荡强度季节变化、年际异常的一个关键因子。     

Does sea surface temperature outside the tropical Pacific contribute to enhanced ENSO predictability?

In this paper we seek to identify inter-annual sea surface temperature anomalies (SSTA) patterns outside the tropical Pacific that may influence El Niño/Southern Oscillation (ENSO) through atmospheric teleconnections. We assume that a linear ENSO hindcast based on tropical Pacific warm water volume and Niño3.4 SSTA indices captures tropical Pacific intrinsic predictability inherent to recharge oscillator dynamics. This simple hindcast model displays statistically significant skill at the 95 % confidence level at leads of up to seven seasons ahead of the ENSO peak. Our results reveal that ENSO-independent equatorial wind stress anomalies only significantly improve the skill of that linear hindcast at the 95 % level in boreal spring and summer before the ENSO peak and in boreal fall, five seasons ahead of the ENSO peak. At those seasons, the robust large-scale SST patterns that provide a statistically significant enhancement of ENSO predictability are related to the Atlantic meridional mode and south Pacific subtropical dipole mode in spring, the Indian Ocean Dipole and the south Atlantic subtropical dipole mode in fall. While the first two regions display significant simultaneous correlations with western equatorial Pacific wind stress in three reanalyses (ERA-I, NCEP and NCEP2), the Indian Ocean Dipole and south Atlantic subtropical dipole mode correlation with Pacific winds is less robust amongst re-analyses. We discuss our results in view of other studies that suggest a remote influence of various regions on ENSO. Although modest, the sensitivity of our results to the dataset and to details of the analysis method illustrates that finding regions that influence ENSO from the statistical analysis of observations is a difficult task.     

热带太平洋海表能量收支平衡特征及其与两类ENSO事件的联系

利用月平均的HadISST海表温度、NCEP再分析资料、OAFlux海表面热通量及相关物理量资料、NCAR/NOAA云量场资料,分析了热带太平洋海表热通量的年际特征,并且进一步分析了传统El Ni?o和El Ni?o Modoki事件中湍流热通量的异常演变特征以及影响因子。在热带太平洋上,净热通量的年际变化最大振幅出现在赤道太平洋上,且主要取决于潜热通量和短波辐射通量的变化。本文还利用两类ENSO事件旺盛期海温指数对不同时期海面热通量场的偏回归分析,考察了热带太平洋海表面热通量与两类ENSO事件中海温的联系。两类海温指数对各时期热带太平洋净热通量的回归均表现为赤道太平洋上存在显著的负异常,在Ni?o3指数偏回归下的负异常范围和强度都较El Ni?o Modoki指数回归的要大,且更偏于赤道东太平洋,而旺盛期海温对同期赤道东太平洋上湍流热通量的影响最大。     

A note on the break‐up of lakes and rivers as indicators of climate change

Abstract

A detailed examination has been made of the relationship between the space and time variations of the Indian summer monsoon rainfall and the equatorial eastern‐Pacific sea surface temperature (SST) anomaly in different seasons for the 108‐year period, 1871–1978. There is a strong inverse relationship between the two. The correlation coefficients between All‐India monsoon rainfall and the sea surface temperature anomaly for the concurrent season; June, July and August (JJA) and for the succeeding seasons; September, October and November (SON) and December, January and February (DJF) are consistently and highly significant. Even a random sample of 50 years gave values significant at the 0.1 percent level. The sliding window correlation analysis of 10‐, 20‐ and 30‐year widths indicates that the relationships between All‐India monsoon rainfall and the sea surface temperature anomaly for the concurrent JJA and the succeeding SON and DJF seasons exhibit stability and consistency in significance. For contiguous meteorological sub‐divisions west of longitude 80°E the relationship is highly significant for JJA and for succeeding SON and DJF seasons.     

Exploring the impacts of the tropical Pacific SST on the precipitation patterns over South America during ENSO periods

Summary Previous studies on precipitation over South America that strongly support the existence of links between precipitation and SST anomalies in the Pacific Ocean have identified specific regions where the ENSO signal is particularly stronger. Northeast of Brazil and some parts of southern South America are examples of these regions. However, the same attention was not taken to identify which regions in the Central and East Pacific ocean are better correlated with the South America precipitation during extreme ENSO events, and also which are the transition regions of the precipitation signal over South America during these events. Coincident periods of ENSO events for both SST over the tropical Pacific ocean and monthly precipitation sums from many observational stations over South America were selected and analyzed. Two statistical methods were used for the data analysis: Singular Value Decomposition (SVD) and Simple Linear Correlation (SLC). The SVD results for warmer events in the Pacific corroborate previous ones and also clearly identified a transition region between the drier conditions in the Northeast of Brazil and the wetter conditions in the Southeast/South of Brazil. Transition regions were also determined over Peru and central Amazon. The SLC results indicated that the SST anomalies in the tropical east Pacific ocean has the strongest influence in the South American precipitation during El Ni?o events. During La Ni?a events the central area of the Pacific, around 180°, has shown a more significant influence. Received August 10, 2000 Revised August 22, 2001     

ENSO induced monthly oscillations of precipitation: the unique case of the south tropical Indian Ocean in austral summer

Seasonal (three-month average) climate forecasts have advanced due in large part to improved modeling of the ENSO phenomenon. Long-range monthly forecasts are more problematic because of internal atmospheric variability. Further, it is often assumed that monthly precipitation anomalies are representative of the overall seasonal anomaly. This is not always the case as, according to the Global Precipitation Climatology Project Version 2.1 data set, up to 20% of areas demonstrating some significant teleconnection to ENSO show El Ni?o minus La Ni?a differences of one sign in the middle month and the opposite sign in the adjacent months. Most interestingly, this maximum percentage occurs in December–January–February (DJF), a time when the ENSO boundary forcing is strongest. These oscillatory DJF seasons also cluster in space—with significant positive–negative-positive differences in the western South Tropical Indian Ocean (STIO) and negative–positive–negative differences in the far eastern STIO. Representative gauges confirm that these precipitation patterns have been associated with ENSO events since 1951, and pentad precipitation data confirm that they are confined to DJF and evolve at the monthly scale. The abrupt end of the Indian Ocean Dipole mode in January, an increase in the importance of local SST anomalies in February, and an ENSO-induced mid-latitude Rossby wave during austral summer combine to generate the cross-basin precipitation gradient around 15°S.     

Climate variability in the south-eastern tropical Pacific and its relation with ENSO: a GCM study

About a third of the El-Niño/Southern Oscillation (ENSO) variability in the HadCM3 coupled general-circulation model is shown to be associated with variability in the south-east tropical Pacific (SETP) area. Sea-surface temperature (SST) anomalies along the east Pacific tend to precede ENSO anomalies. In HadCM3, SST tendencies in the SETP area are controlled mainly by surface latent heat fluxes and short-wave cloud forcing. Interannual SST anomalies in the SETP tend to propagate meridionally. In the winter season (JJA), this is consistent with a wind-evaporation-SST (WES) mode. Coupling with the strato-cumulus cloud (Sc) cover is critical in reducing the evaporative damping of the WES mode, and external forcing is provided by extratropical circulation anomalies. In spring, SETP variability and ENSO are coupled via the low-level circulation, resulting in a mutual reinforcement. Cloud-cover anomalies are not strongly controlled by local SSTs, and appear mainly dependent on atmospheric meridional advection. The apparent association between cold SSTs and Sc cover does not reflect a positive local feedback. These conclusions are not sensitive to the model’s warm SST bias, associated with reduced stratocumulus clouds and weak southerly wind stress, which depends on erroneous near-field orographic forcing of the coastal circulation. Some of our results are supported by similar evidence from observational datasets and other CMIP3 models.     

北太平洋海温Victoria模态与ENSO年际关系的非对称特征

利用美国NOAA海表温度资料,重点分析了北太平洋海温异常EOF第二模态Victoria模态(VM)与ENSO年际关系的非对称特征.研究发现,VM和ENSO在年代际尺度上相关性较弱,而在年际尺度上有很好的相关关系,两者同期为负相关,VM超前1 a为正相关.然而,正负VM事件与ENSO冷暖位相在年际尺度上的联系存在着一定的...     

A New Index About the Walker Circulation

The Walker circulation (WC) has always been an important issue in atmospheric science research due to the association between the WC and tropical Pacific sea surface temperature (SST), and between the WC and ENSO events. In this paper, a new index-Omega index (OMGI) - is constructed for WC characterization based on the NCEP / NCAR reanalysis data of monthly mean vertical velocity in recent 70 years (1948-2017). Results show that the OMGI can accurately depict the variation characteristics of WC on seasonal, annual and decadal time-scales. There is a significant inverse correlation between the OMGI and equatorial eastern and central Pacific SST. Meanwhile, the peak of the OMGI appears ahead of the ENSO peak, and therefore is able to reflect the SST in the equatorial Pacific. Especially, in 35 ENSO events, the peak of the OMGI appears earlier than Ni?o 3.4 index for 19 times with 2.6 months ahead on average. In 16 El Ni?o events, the peak of the OMGI occurs ahead of the El Ni?o for 9 times with 4 months ahead on average. In 19 La Ni?a events, the OMGI peak arises 10 times earlier than the La Ni?a peak, with an average of 1.4 months ahead. OMGI shows obvious leading effect and stability over ENSO events with different strengths and types of single peak and multi peaks: the peak of the OMGI keeps about 2-3 months ahead of the ENSO. Compared with other WC indexes such as UWI and SPLI, OMGI has some advantages in the ability to describe WC changes and present the probability and thetime of prediction of ENSO event peaks.     

ENSO and seasonal sea-level variability – A diagnostic discussion for the U.S.-Affiliated Pacific Islands

Summary The El Ni?o-Southern Oscillation (ENSO) climate cycle is the basis for this paper, aimed at providing a diagnostic outlook on seasonal sea-level variability (i.e. anomalies with respect to the Climatology) for the U.S.-Affiliated Pacific Islands (USAPI). Results revealed that the sea-level variations in the northwestern tropical Pacific islands (e.g. Guam and Marshall Islands) have been found to be sensitive to ENSO-cycle, with low sea-level during El Ni?o and high sea-level during La Ni?a events. The annual cycle (first harmonic) of sea-level variability in these north Pacific islands has also been found to be very strong. The composites of SST and circulation diagnostic show that strong El Ni?o years feature stronger surface westerly winds in the equatorial western/central Pacific, which causes north Pacific islands to experience lower sea-level from July to December, while the sea-level in south Pacific islands (e.g. American Samoa) remains unchanged. As the season advances, the band of westerly winds propagates towards the south central tropical Pacific and moves eastward, which causes American Samoa to experience a lower sea-level from January to June, but with six months time lag as compared to Guam and the Marshalls. U.S.-Affiliated Pacific Islands are among the most vulnerable communities to climate variability and change. This study has identified the year-to-year ENSO climate cycle to have significant impact on the sea-level variability of these islands. Therefore, regular monitoring of the ENSO climate cycle features that affect seasonal sea-level variability would provide substantial opportunities to develop advance planning and decision options regarding hazard management in these islands.     

NUIST地球系统模式模拟ENSO对西北太平洋热带气旋活动的影响

地球系统模式已经逐步成为研究热带气旋（TC）活动气候变化的重要工具之一,之前的研究发现南京信息工程大学地球系统模式（NESM）高分辨率版本可以较好地模拟全球海温分布及TC活动的气候特征。本研究进一步分析了NESM地球系统模式模拟西北太平洋TC活动的年际变化,并与1967～2016年观测的TC活动进行对比。NESM模式高分辨率版本能够较好地模拟西北太平洋平均海温及与ENSO事件联系的海温异常变化特点,对El Ni?o事件发生时西北太平洋TC的生成频数和路径分布的模拟较好,也能模拟El Ni?o年TC生成位置比La Ni?a年偏东的特征,但是未能模拟出TC平均生命周期和Ni?o3.4地区海温的相关性。并且模式模拟的La Ni?a年TC的生成位置偏东,主要原因是模拟La Ni?a年季风槽平均位置偏东。研究结果有助于进一步改进NESM模式和利用NESM模式研究TC活动。     

ENSO variability and atmospheric response in a global coupled atmosphere-ocean GCM

The interannual variability associated with the El Ni?o/Southern Oscillation (ENSO) cycle is investigated using a relatively high-resolution (T42) coupled general circulation model (CGCM) of the atmosphere and ocean. Although the flux correction is restricted to annual means of heat and freshwater, the annual as well as the seasonal climate of the CGCM is in good agreement with that of the atmospheric model component forced with observed sea surface temperatures (SSTs). During a 100-year simulation of the present-day climate, the model is able to capture many features of the observed interannual SST variability in the tropical Pacific. This includes amplitude, lifetime and frequency of occurrence of El Ni?o events and also the phase locking of the SST anomalies to the annual cycle. Although the SST warming during the evolution of El Ni?os is too confined spatially, and the warming along the Peruvian coast is much too weak, the patterns and magnitudes of key atmospheric anomalies such as westerly wind stress and precipitation, and also their eastward migration from the western to the central equatorial Pacific is in accord with observations. There is also a qualitative agreement with the results obtained from the atmospheric model forced with observed SSTs from 1979 through 1994. The large-scale dynamic response during the mature phase of ENSO (December through February) is characterized by an eastward displacement and weakening of the Walker cell in the Pacific while the Hadley cell intensifies and moves equatorward. Similar to the observations, there is a positive correlation between tropical Pacific SST and the winter circulation in the North Pacific. The deepening of the Aleutian low during the ENSO winters is well captured by the model as well as the cooling in the central North Pacific and the warming over Canada and Alaska. However, there are indications that the anomalies of both SST and atmospheric circulation are overemphasized in the North Pacific. Finally, there is evidence of a coherent downstream effect over the North Atlantic as indicated by negative correlations between the PNA index and the NAO index, for example. The weakening of the westerlies across the North Atlantic in ENSO winters which is related to a weakening and southwestward displacement of the Icelandic low, is in broad agreement with the observations, as well as the weak tendency for colder than normal winters in Europe. Received: 31 October 1995 / Accepted: 29 May 1996     

Southern Hemisphere extra-tropical forcing: a new paradigm for El Ni?o-Southern Oscillation

The main goal of this paper is to shed additional light on the reciprocal dynamical linkages between mid-latitude Southern Hemisphere climate and the El Ni?o-Southern Oscillation (ENSO) signal. While our analysis confirms that ENSO is a dominant source of interannual variability in the Southern Hemisphere, it is also suggested here that subtropical dipole variability in both the Southern Indian and Atlantic Oceans triggered by Southern Hemisphere mid-latitude variability may also provide a controlling influence on ENSO in the equatorial Pacific. This subtropical forcing operates through various coupled air?Csea feedbacks involving the propagation of subtropical sea surface temperature (SST) anomalies into the deep tropics of the Atlantic and Indian Oceans from boreal winter to boreal spring and a subsequent dynamical atmospheric response to these SST anomalies linking the three tropical basins at the beginning of the boreal spring. This atmospheric response is characterized by a significant weakening of the equatorial Atlantic and Indian Inter-Tropical Convergence Zone (ITCZ). This weakened ITCZ forces an equatorial ??cold Kelvin wave?? response in the middle to upper troposphere that extends eastward from the heat sink regions into the western Pacific. By modulating the vertical temperature gradient and the stability of the atmosphere over the equatorial western Pacific Ocean, this Kelvin wave response promotes persistent zonal wind and convective anomalies over the western equatorial Pacific, which may trigger El Ni?o onset at the end of the boreal winter. These different processes explain why South Atlantic and Indian subtropical dipole time series indices are highly significant precursors of the Ni?o34 SST index several months in advance before the El Ni?o onset in the equatorial Pacific. This study illustrates that the atmospheric internal variability in the mid-latitudes of the Southern Hemisphere may significantly influence ENSO variability. However, this surprising relationship is observed only during recent decades, after the so-called 1976/1977 climate regime shift, suggesting a possible linkage with global warming or decadal fluctuations of the climate system.     

全球变暖、AMO、IPO对全球陆地降水变化的相对贡献

本文探究了不同海表温度(SST)模态对6—8月和12月—次年2月全球陆地降水的趋势以及年代际变化的相对贡献。首先对热带地区陆地降水和SST进行SVD分析,得到影响陆地降水的趋势和年代际变化主要的海洋模态为：海洋中的全球变暖(Global Warming, GW)、大西洋多年代际振荡(Atlantic Multidecadal Oscillation, AMO)和太平洋多年代际振荡(Interdecadal Pacific Oscillation, IPO)。其次利用多元线性回归模型进一步定量评估了全球变暖、AMO和IPO对不同地区陆地降水的相对贡献大小。结果表明,全球变暖对陆地降水变化的贡献在冬夏季都是最大的,AMO在6—8月的贡献次之。IPO在12月—次年2月的贡献次之。不同纬度带,三者的贡献不同。GW的贡献在6—8月期间对10°N以北地区较大,南半球受GW的贡献相对较小,GW在12月—次年2月对40°N以北降水贡献异常显著;AMO主要在6—8月对10°～40°S和50°～60°S纬度带上的降水变化的贡献比较大;而IPO主要在12月—次年2月对北半球中纬度降水变化的贡献比较大。GW对...     

The Optimal Precursors for ENSO Events Depicted Using the Gradientdefinition-based Method in an Intermediate Coupled Model

The predictability of El Ni?o?Southern Oscillation (ENSO) has been an important area of study for years. Searching for the optimal precursor (OPR) of ENSO occurrence is an effective way to understand its predictability. The CNOP (conditional nonlinear optimal perturbation), one of the most effective ways to depict the predictability of ENSO, is adopted to study the optimal sea surface temperature (SST) precursors (SST-OPRs) of ENSO in the IOCAS ICM (intermediate coupled model developed at the Institute of Oceanology, Chinese Academy of Sciences). To seek the SST-OPRs of ENSO in the ICM, non-ENSO events simulated by the ICM are chosen as the basic state. Then, the gradient-definition-based method (GD method) is employed to solve the CNOP for different initial months of the basic years to obtain the SST-OPRs. The experimental results show that the obtained SST-OPRs present a positive anomaly signal in the western-central equatorial Pacific, and obvious differences exist in the patterns between the different seasonal SST-OPRs along the equatorial western-central Pacific, showing seasonal dependence to some extent. Furthermore, the non-El Ni?o events can eventually evolve into El Ni?o events when the SST-OPRs are superimposed on the corresponding seasons; the peaks of the Ni?o3.4 index occur at the ends of the years, which is consistent with the evolution of the real El Ni?o. These results show that the GD method is an effective way to obtain SST-OPRs for ENSO events in the ICM. Moreover, the OPRs for ENSO depicted using the GD method provide useful information for finding the early signal of ENSO in the ICM.     

Decadal Changes in Interannual Dependence of the Bay of Bengal Summer Monsoon Onset on ENSO Modulated by the Pacific Decadal Oscillation

Interannual variations of the Bay of Bengal summer monsoon (BOBSM) onset in association with El Ni?o?Southern Oscillation (ENSO) are reexamined using NCEP1, JRA-55 and ERA20C atmospheric and Hadley sea surface temperature (SST) reanalysis datasets over the period 1900?2017. Decadal changes exist in the dependence of the BOBSM onset on ENSO, varying with the Pacific Decadal Oscillation (PDO). A higher correlation between the BOBSM onset and ENSO arises during the warm PDO epochs, with distinct late (early) onsets following El Ni?o (La Ni?a) events. In contrast, less significant correlations occur during the cold PDO epochs. The mechanism for the PDO modulating the ENSO?BOBSM onset relationship is through the variations in SST anomaly (SSTA) patterns. During the warm PDO epochs, the superimpositions of the PDO-related and ENSO-related SSTAs lead to the SSTA distribution of an El Ni?o (La Ni?a) event exhibiting significant positive (negative) SSTAs over the tropical central?eastern Pacific and Indian Ocean along with negative (positive) SSTAs, especially over the tropical western Pacific (TWP), forming a strong zonal interoceanic SSTA gradient between the TWP and tropical Indian Ocean. Significant anomalous lower tropospheric easterlies (westerlies) together with upper-tropospheric westerlies (easterlies) are thus induced over the BOB, favoring an abnormally late (early) BOBSM onset. During the cold PDO epochs, however, the superimpositions of PDO-related SSTAs with El Ni?o-related (La Ni?a-related) SSTAs lead to insignificant SSTAs over the TWP and a weak zonal SSTA gradient, without distinct circulation anomalies over the BOB favoring early or late BOBSM onsets.     

Extra-tropical atmospheric response to ENSO in the CMIP5 models

The seasonal mean extra-tropical atmospheric response to El Niño/Southern Oscillation (ENSO) is assessed in the historical and pre-industrial control CMIP5 simulations. This analysis considers two types of El Niño events, characterized by positive sea surface temperature (SST) anomalies in either the central equatorial Pacific (CP) or eastern equatorial Pacific (EP), as well as EP and CP La Niña events, characterized by negative SST anomalies in the same two regions. Seasonal mean geopotential height anomalies in key regions typify the magnitude and structure of the disruption of the Walker circulation cell in the tropical Pacific, upper tropospheric ENSO teleconnections and the polar stratospheric response. In the CMIP5 ensembles, the magnitude of the Walker cell disruption is correlated with the strength of the mid-latitude responses in the upper troposphere i.e., the North Pacific and South Pacific lows strengthen during El Niño events. The simulated responses to El Niño and La Niña have opposite sign. The seasonal mean extra-tropical, upper tropospheric responses to EP and CP events are indistinguishable. The ENSO responses in the MERRA reanalysis lie within the model scatter of the historical simulations. Similar responses are simulated in the pre-industrial and historical CMIP5 simulations. Overall, there is a weak correlation between the strength of the tropical response to ENSO and the strength of the polar stratospheric response. ENSO-related polar stratospheric variability is best simulated in the “high-top” subset of models with a well-resolved stratosphere.     

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

The inverse relationship between the warm phase of the El Ni?o Southern Oscillation(ENSO) and the Indian Summer Monsoon Rainfall(ISMR) is well established. Yet, some El Ni?o 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 Ni?o(springtime)...