ENSO Forcing Research Articles

Increased Frequency of Consecutive Positive IOD Events Under Global Warming

AbstractConsecutive positive Indian Ocean Dipole (pIOD) induces more severe climate impacts than a single pIOD because of multi‐year accumulation of precipitation anomalies. Using CMIP6 outputs and reanalysis data, we show that the observed increasing trend of consecutive pIOD frequency will continue in future. The simulated frequency of consecutive pIOD increases by 131.3% over 1950–2100. More than 65% pIOD will manifest as consecutive pIOD events in the second half of this century. The increase in consecutive pIOD is dominated by the rise in mixed consecutive pIOD that contains both ENSO‐pIOD and independent pIOD. Mixed consecutive pIOD that start with ENSO‐pIOD increases fastest among all types of consecutive pIOD events. The increase is contributed by three factors: higher ENSO‐pIOD frequency, weaker biennial component of ENSO forcing, and more active pIOD triggers that are independent from ENSO. Climate extremes associated with consecutive pIOD are therefore expected to occur more frequently under global warming.

ENSO Forcing of Rainfall Erosivity in the Wuding River Basin

Rainfall erosivity (RE) is an important indicator of the ability of rainfall to cause soil erosion and is linked to ENSO through the transport of rainfall. Accurate assessment of RE and improved understanding of RE are essential for soil erosion prediction, optimization of soil and water conservation measures, and ecological management and restoration. Therefore, the Wuding River Basin, a typical ecologically fragile area, is selected as the research area. The erosivity model based on daily rainfall was first used to calculate RE, and the temporal and periodic characteristics of RE are studied. Then the effects of the Southern Oscillation Index (SOI), the Surface Temperature of the Central East Equatorial Pacific Ocean (SST), and the Multivariate ENSO Index (MEI) on RE are explored by using cross wavelet technique. Results indicated that: (1) the concentration of rainfall leads to the largest RE values in summer compared with other seasons, accumulating about 69% of the annual RE; (2) The overall trend of increasing RE in the Wuding River basin is not significant, but shows an abrupt change in 2015; (3) the influence of the SOI and SST indices of ENSO events on RE is significant, which is shown to be a statistically significant correlation (95% confidence level), indicating that ENSO has a strong influence on the changing pattern of RE. These findings are helpful in predicting soil erosion and are significant for developing further erosion control measures.

The Internal and ENSO-Forced Modes of the Indian Ocean Sea Surface Temperature

Abstract The internal and ENSO-forced modes of the Indian Ocean sea surface temperature (SST) are investigated using a high-resolution regional coupled model. Five different model simulations were performed by controlling atmospheric and oceanic boundary conditions (BCs), which are lateral walls of the model domain. In the internal run performed by prescribing the climatological mean oceanic and atmospheric BCs, the first and second empirical orthogonal functions (EOF1 and EOF2) of internal mode are similar to the observed Indian Ocean basin (IOB) and dipole (IOD) modes with relatively weak amplitudes, respectively. In the control run with observed BCs, those EOFs are much amplified with their power spectrums significantly changed, and their spatial patterns are modified, particularly for the EOF2. Three ENSO runs with combinations of ENSO-related and climatological mean BCs show that the modification of spatial pattern of EOFs is mainly due to ENSO forcing. Furthermore, ENSO forcing determines the major 4-yr period of IOB mainly through the atmosphere, whereas the major 3-yr period of IOD is determined by both ENSO atmosphere and ocean forcings. It is also found that IOB and IOD exhibit a significant seasonally dependent relationship in both internal and ENSO-forced simulations. Most importantly, by applying the empirical singular vector method to both observed and modeled data, it is found that the IOD–IOB relationship is associated with an unstable mode of Indian Ocean SST anomalies, evolving from boreal fall to the next spring. This unstable mode is intrinsic within the Indian Ocean but is substantially amplified by the ENSO.

Seasonal extreme rainfall over Indian monsoon region: a moisture budget analysis to distinguish the role of ENSO and non-ENSO forcing

Seasonal extreme rainfall over Indian monsoon region: a moisture budget analysis to distinguish the role of ENSO and non-ENSO forcing

The summer Asia–North America teleconnection and its modulation by ENSO in Community Atmosphere Model, version 5 (CAM5)

Seasonal forecasts of summer continental United States (CONUS) rainfall have relatively low skill, partly due to a lack of consensus about its sources of predictability. The East Asian monsoon (EAM) can excite a cross-Pacific Rossby wave train, also known as the Asia–North America (ANA) teleconnection. In this study, we analyze the ANA teleconnection in observations and model simulations from the Community Atmospheric Model, version 5 (CAM5), comparing experiments with prescribed climatological SSTs and prescribed observed SSTs. Observations indicate a statistically significant relationship between a strong EAM and increased probability of positive precipitation anomalies over the US west coast and the Plains-Midwest. The ANA teleconnection and CONUS rainfall patterns are improved in the CAM5 experiment with prescribed observed SSTs, suggesting that SST variability is necessary to simulate this teleconnection over CONUS. We find distinct ANA patterns between ENSO phases, with the La Niña-related patterns in CAM5 disagreeing with observations. Using linear steady-state quasi-geostrophic theory, we conclude that incorrect EAM forcing location greatly contributed to CAM5 biases, and jet stream disparities explained the ENSO-related biases. Finally, we compared EAM forcing experiments with different mean states using a simple dry nonlinear atmospheric general circulation model. Overall, the ANA pattern over CONUS and its modulation by ENSO forcing are well described by dry dynamics on seasonal-to-interannual timescales, including the constructive (destructive) interference between El Niño (La Niña) modulation and the ANA patterns over CONUS.

气候变暖背景下云南西北部大果红杉径向生长衰退及其气候驱动因子分析

PDF HTML阅读 XML下载 导出引用 引用提醒 气候变暖背景下云南西北部大果红杉径向生长衰退及其气候驱动因子分析 DOI: 10.5846/stxb202011303065 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（32061123008）；云南省教育厅科学研究基金项目（2021Y013） The decline in radial growth of Larix potaninii in Northwestern Yunnan and its driving factors under the background of climate warming Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:气候变化背景下森林生态系统的内部结构和功能发生转变，并减弱了其固碳能力，评估与预测森林生态系统对气候变化响应势在必行。基于采自云南西北部的大果红杉树木年轮样本，建立树轮宽度标准化年表，运用相关分析、空间相关、波谱分析等方法，探讨了滇西北大果红杉径向生长的主控因子及其对气候变化的响应。结果表明：（1）温度是限制滇西北大果红杉树轮径向生长的主要因素，季节性高低温变化交替影响大果红杉树轮径向生长。（2）相对湿度变化与滇西北大果红杉树轮的径向生长紧密关联，对滇西北大果红杉树轮的径向生长起促进作用。（3）波谱分析结果显示滇西北大果红杉径向生长呈周期性变化，受ENSO等外强迫影响显著。（4）气候变暖背景下，滇西北大果红杉的径向生长出现衰退趋势。研究结果为加强云南西北部天然林保护和构建西南绿色生态屏障提供了基础性资料。 Abstract:Due to the change of carbon sequestration capacity and internal structure and function of forest ecosystems under global warming, it is imperative to assess and predict the response of forest ecosystems to climate change. Based on tree-ring samples collected from Northwestern Yunnan, some tree-ring width chronologies were developed. The main limiting factors of radial growth and the temporal stability of the tree growth response to climate change were analyzed by correlation analysis, spatial correlation, and spectral analysis. The results showed that (1) Temperature was the main factor limiting the radial growth of Larix potaninii in Northwestern Yunnan, and seasonal high and low temperatures alternately affected the radial growth of the Larix potaninii. (2) The relative humidity was closely positively related to the radial growth of Larix potaninii in Northwestern Yunnan. (3) The results of spectral analysis showed that the radial growth of Larix potaninii in Northwestern Yunnan periodically changed and was significantly affected by ENSO and other external forcing. (4) Under the background of climate warming, the growth of Larix potaninii in Northwestern Yunnan presented a decline trend. It provides a scientific decision basis for us to strengthen the protection of natural forest and construct green ecological barrier in Northwestern Yunnan. 参考文献 相似文献 引证文献

The Phase‐Locking of Tropical North Atlantic and the Contribution of ENSO

AbstractThe Tropical North Atlantic (TNA) is characterized by significant interannual variability in sea surface temperature (SST), which is phase‐locked to the boreal spring. In this study, the phase‐locking of TNA is investigated by adopting a linear stochastic‐dynamical model (SDM) using seasonally modulated TNA feedbacks together with the seasonal modulation of ENSO forcing. In the observations, the role of local TNA feedbacks and ENSO forcing in TNA phase‐locking are equivalently important with both preferring the peak of TNA variability to appear in the boreal spring. Besides, the seasonal modulation of TNA feedbacks and ENSO forcing strength are both mainly controlled by thermodynamic processes. In most climate models, the contribution of ENSO on TNA phase‐locking is weaker than that in observations. The strength of ENSO‐related TNA phase‐locking is highly correlated with the relationship between ENSO and TNA, which is mainly determined by the amplitude of ENSO and its teleconnection patterns.

Revisiting the strong and weak ENSO teleconnection impacts using a high-resolution atmospheric model

To evaluate the performance of a high-resolution atmospheric model (HiRAM) and to improve our understanding of the climatic impacts of ENSO forcing and associated teleconnections, we analyzed AMIP-style HiRAM simulations conducted effectively at 25 km grid spacing. To better assess HiRAM response to ENSO climate variability; we categorized it into strong and weak El Niño/La Niña episodes. The HiRAM model reproduced the impacts of strong ENSO over global scale very well, however, it underestimated ENSO teleconnection patterns and associated changes over regional scale (e.g., MENA and South Asia), especially following weak ENSO that could be attributed to model weak response to circulation changes such as Pacific North American (PNA) and North Atlantic Oscillation (NAO). Moreover, our results emphasize that ENSO impacts are relatively stronger over the Inter-Tropical Convergence Zone (ITCZ) compared to extra-tropics and high-latitude regions. The positive phase of ENSO causes weakening in rainfall over the African tropical rain-belt, parts of South and Southeast Asia. Both the reanalysis and HiRAM results reveal that ENSO-induced negative (positive) NAO-like response and associated changes over Southern Europe and North Africa vary significantly following the increased intensity of El Niño (La Niña). We further found that the ENSO magnitude significantly impacts Hadley and Walker circulations. The El Niño phase of ENSO overall strengthens the Hadley Cell, and the reverse is true for the La Niña phase. This ENSO-induced strengthening and weakening of Hadley Cell induce significant impact over South Asian and African convective regions through modification of the ITCZ circulation system.

Interannual to Decadal Variability of Tropical Indian Ocean Sea Surface Temperature: Pacific Influence versus Local Internal Variability

AbstractThe Indian Ocean has received increasing attention for its large impacts on regional and global climate. However, sea surface temperature (SST) variability arising from Indian Ocean internal processes has not been well understood particularly on decadal and longer time scales, and the external influence from the tropical Pacific has not been quantified. This paper analyzes the interannual-to-decadal SST variability in the tropical Indian Ocean in observations and explores the external influence from the Pacific versus internal processes within the Indian Ocean using a linear inverse model (LIM). Coupling between Indian Ocean and tropical Pacific SST anomalies (SSTAs) is assessed both within the LIM dynamical operator and the unpredictable stochastic noise that forces the system. Results show that the observed Indian Ocean basin (IOB)-wide SSTA pattern is largely a response to the Pacific ENSO forcing, although it in turn has a damping effect on ENSO especially on annual and decadal time scales. On the other hand, the Indian Ocean dipole (IOD) is an Indian Ocean internal mode that can actively affect ENSO; ENSO also has a returning effect on the IOD, which is rather weak on decadal time scale. The third mode is partly associated with the subtropical Indian Ocean dipole (SIOD), and it is primarily generated by Indian Ocean internal processes, although a small component of it is coupled with ENSO. Overall, the amplitude of Indian Ocean internally generated SST variability is comparable to that forced by ENSO, and the Indian Ocean tends to actively influence the tropical Pacific. These results suggest that the Indian–Pacific Ocean interaction is a two-way process.

Contributions to the Interannual Summer Rainfall Variability in the Mountainous Area of Central China and Their Decadal Changes

Using a high-resolution precipitation dataset, the present study detected that the mountainous area of central China (MACA) is a hotspot of ENSO’s impact on the summer rainfall variability. Further analysis suggests that both ENSO and atmospheric forcing make contributions to the summer rainfall variability in MACA. The dominant rainfall-related SST mode features as a seasonal transition from an El Nino-like warming in the preceding winter to a La Nina-like cooling in the following autumn, and it explains about 29% of the total variance of the rainfall during 1951–2018. It indicates that ENSO with a rapid phase transition is responsible for inducing summer rainfall anomalies in MACA. Besides, an upper-level circumglobal wave mode in the Northern Hemisphere during summer also explains about 29% of the summer rainfall variance. Contributions of both the SST and the atmospheric modes have experienced interdecadal changes. The influence of the SST mode gradually increases and plays a dominant role in the recent decades, suggesting that ENSO with a rapid phase transition becomes more important for rainfall prediction in MACA.

Taiwanese rainfall variability associated with large-scale climate phenomena

Examining the physical mechanisms through which large scale climate indicators, e.g., El Niño-Southern Oscillation and Indian Ocean Dipole, affect hydroclimatic variables in the tropics and extratropics is a scientific challenge. In this study, climatic relationships between large-scale climate indices (CIs) and Taiwan rainfall variability were examined. Not only leading patterns of observed monthly total and extreme rainfall were estimated through an empirical orthogonal teleconnection method (EOT), but also correlation and regression analyses were performed for the leading rainfall patterns and various CIs based on atmospheric-ocean circulation dataset. From the spatial structure of the leading EOT patterns for total and extreme rainfall, the north-coast mode in the cold seasons and the middle-inland mode for the warm seasons were detected. The temporal cycle of the leading EOT patterns indicates decreasing trends in the cold seasons and oscillations mainly on decadal timescales in the warm seasons. The leading EOT patterns of total rainfall showed more widespread coherent patterns than those of extreme rainfall with more variance in rainfall variability. The findings from this study illustrate that tropical ENSO forcing has a coherent association with March and October–November rainfall patterns, while the Indian Ocean Dipole is identified as a driver for rainfall variability during spring and fall. The western North Pacific monsoon activity has a negative (positive) correlation with March (October and December) rainfall variabilities and tropical cyclone indices also exhibit significant positive correlation with October rainfalls. The leading patterns of the October and following-year March rainfall time series are predictable at up to nine-month lead time from the tropical Pacific sea surface temperatures (SSTs).

The variability of South Korean temperature associated with climate indicators

Examining the physical mechanisms through which large-scale climate indicators, e.g., El Nino–Southern Oscillation and Indian Ocean Dipole, affect hydroclimatic variables in the tropics and extratropics is a forefront scientific challenge. We examined climatic teleconnections between large-scale climate indices and temperature variability over South Korea. To do this, we calculated not only leading patterns of observed monthly mean and extreme temperature through an empirical orthogonal teleconnection (EOT) decomposition technique but also statistical correlations on a monthly basis using cross-correlation and lag regression analyses for the leading modes and global atmospheric circulation dataset. As a result, the spatial pattern of the leading EOT modes for mean (extreme high) temperature represents an eastern (southern) coastal mode for boreal summer and a northern (middle) inland mode in boreal winter, while extreme low EOTs exhibit a northern inland mode in summer and a western coastal mode in winter. The temporal evolution of the leading EOT modes exhibits a mostly increasing trend and an interdecadal oscillation. The leading EOT modes of mean temperature explain more variance than those of extreme temperature during warm and cold seasons. The findings from this study illustrate that tropical ENSO forcing has a coherent association with August and December temperature patterns, while the Indian Ocean Dipole is identified as a driver for temperature variability during fall season. The monsoon circulation over the western North Pacific also exhibits a significant negative correlation with the December temperature EOTs. The leading EOTs for October temperature exhibit the positive correlation with the tropical cyclone variability, while the leading EOTs for mean and extreme high temperature exhibit significant negative correlations with the snow depth over northeastern Eurasia in November. The leading patterns of the August and December mean temperature time series are predictable at up to 5-month lead time from the tropical Pacific sea surface temperatures (SSTs), while a predictable response from Indian Ocean SSTs was detected at up to 4-month lead time.

Nonlinearity in the North Pacific Atmospheric Response to a Linear ENSO Forcing

AbstractEl Niño Southern Oscillation (ENSO) exerts a remote impact on the North Pacific and North American winter climate. Both observational and model studies have suggested nonlinearities in this teleconnection. However, it remains unclear if possible nonlinearities arise from the forcing strength or the forcing location in the tropical Pacific, or from factors external to the tropical Pacific. To separate these factors, an idealized model is forced with seasonally varying sea surface temperature with linearly varying strength at a fixed location. Whereas for moderate events the North Pacific response is more linear, strong events exhibit significant nonlinearity both in terms of the strength and location of the impact. The nonlinearity can be traced back to the relationship between sea surface temperature and tropical convection. Nonlinearity in the North Pacific response can have important impacts for long‐range prediction and for potential changes in the diversity of ENSO with climate change.

Joint forcing of climate warming and ENSO on a dual-cropping system

Challenges for achieving food security with an increasing world population are stimulating many stakeholders to consider the impact of climate change on global-regional crop production. One major concern is how the covariations of climate warming and extremes (e.g., ENSO) affect agricultural systems and production. Here, a dual-cropping system in the Huaihe Plain was used as a testbed to address this issue. We found that climate warming during 1982–2013 has produced remarkable influences on the dual-cropping agricultural system. For the spring season crop (i.e., winter wheat), a significant negative effect was found with a production loss of ˜6.9 × 106 tons due to an elevated Tmean (˜2.21 °C) (r=-0.508, p < 0.01), which was associated with water stress. For the summer/autumn crops (i.e., rice and maize), a significant positive effect was found, but with a less substantial production gain (˜1.4 × 106 tons), supposedly due to the relaxed temperature constraints (an increased Tmax of ˜1.28 °C) for high heat resistant crops (r = 0.495, p < 0.01). The phenophase of the crop growing period was shortened by ˜7 days for the spring crop and by ˜4.4 days for the summer/autumn crops with enhanced thermal conditions. Precipitation anomalies, especially those associated with ENSO turning from El Niño to La Niña, imposed an additional serious impact on the dual-cropping system through decreased precipitation in the spring and increased precipitation in the summer/autumn. Potential impacts for the future could be derived from intensification of water and heat stresses, as well as the climate extremes (e.g., ENSO and AAO).

Indian Summer Monsoon as simulated by the regional earth system model RegCM-ES: the role of local air–sea interaction

In this study the regional earth system model RegCM-ES is applied over the South Asia CORDEX domain to improve the simulation of the variability of the Indian Summer Monsoon. RegCM-ES has been integrated for 30 years, from 1979 to 2008, with a spatial resolution of 50 km in the atmospheric component, 18 km in the ocean and 50 or 12 km in the two hydrological models used for this study. A new hydrological component, the Cetemps Hydrological Model (CHyM), is included in the coupled system composed by the regional climate model RegCM4 and the ocean model MITgcm. In our analysis we show how the two way air–sea feedback simulated by the coupled system largely improves the representation of intraseasonal (ISV) and interannual (IAV) modes of variability of the Indian Summer Monsoon Rainfall (ISMR). The comparison with the Hydrological Discharge (HD) model shows large improvements in simulating the correct amount of freshwater river discharge over the Bay of Bengal (BoB), one of the fundamental factor responsible for the formation of the shallow barrier layer (BL) over the BoB. However, the improvements in river discharge do not have a clear effect on the BL due to excessive mixing in the ocean model. The improvements in the simulation of IAV are primarily due to the ability of RegCM-ES to reproduce the Intraseasonal Oscillation modes and to the complex mechanism related to the delayed response of the ISMR to the ENSO forcing. Our results highlight the very important role of fine scale air–sea feedbacks in modulating the ISMR and the internal dynamics of this phenomenon.

Variability, teleconnection, and predictability of Korean precipitation in relation to large scale climate indices

Spatiotemporal variability, teleconnection, and predictability of the Korean precipitation related to large scale climate indices were examined based on leading patterns of observed monthly Rx5day and total precipitation through an empirical orthogonal teleconnection (EOT). Cross-correlation and lag regression analyses for the leading modes and global atmospheric circulation dataset were employed on a monthly basis. The spatial pattern of the leading EOT modes for Rx5day and total precipitation represents a northern inland mode for boreal summer and a southern coastal mode in boreal winter. The temporal evolution of the leading EOT modes exhibits increasing trends during summer season and decadal variability for winter season. The leading EOT patterns of Rx5day precipitation show more widespread coherent patterns than those of total precipitation during warm and cold seasons, while the former explains less variance in precipitation variability than the latter. The tropical ENSO forcing has a coherent teleconnection with September and November-December precipitation patterns, while the Indian Ocean dipole is identified as a driver for precipitation variability in September and November. The monsoon circulation over the western North Pacific also exhibits a significant negative correlation with winter precipitation EOTs, while tropical cyclone indices are positively correlated with the fall precipitation EOTs. The leading patterns of the September and December Rx5day precipitation time series are predictable at up to six month lead time from the tropical Pacific sea surface temperatures (SSTs), while a somewhat weak predictable response from Indian Ocean SSTs was only detected at longer lead times. In addition, predictability from the Pacific SSTs for above normal precipitation is greater than that for below normal precipitation.

Global climate teleconnection with rainfall erosivity in South Korea

Rainfall Erosivity Index (REI) defined as the product of rainfall kinetic energy and rainfall intensity is a well-known hydrologic indicator of the potential risk of soil erosion. Global and regional scale climatic teleconnections with REI variability over South Korea are examined. We calculate leading patterns of observed monthly REIs using the Empirical Orthogonal Teleconnection (EOT) and Function (EOF) decomposition techniques. Also we used monthly statistical analyses using cross-correlation and lag regression for the leading modes and global atmospheric circulation measurement in the Pacific and Indian Ocean. As a result, the northern inland mode is applicable during summer season and the southern coastal mode applies to fall-winter season. The temporal evolution of REI exhibits mostly increasing and depends on interdecadal oscillation patterns. The leading EOT modes explain more variance in REI than the EOF modes during warm and cold seasons. The findings from this study illustrate that the tropical ENSO forcing has the coherent association with fall and winter REI patterns, and the Indian Ocean dipole is identified as a driver for REI variability in November. The monsoon circulations over western North Pacific also exhibit significant negative correlation with the December modes. The September leading modes also show a positive correlation with the tropical cyclone activity. Leading patterns in September and November have predictability up to five month lead time from the tropical Pacific Sea Surface Temperatures (SSTs). In addition, predictability from the Pacific SSTs for above normal extreme value of REI is greater than that for below normal value in winter. In conclusion, South Korea experiences climatic teleconnection between the large scale climate indices and mid-latitude hydrologic variables.

RMetS National Meeting – Seasonal forecasting for the UK and Europe

RMetS National Meeting – Seasonal forecasting for the UK and Europe

Strong sub-seasonal wintertime cooling over East Asia and Northern Europe associated with super El Ni\xf1o events

East Asia experienced a record-breaking cold event during the 2015/16 boreal winter, with pronounced impacts on livelihood in the region. We find that this large-scale cold spell can be attributed to the concurrent super El Niño event in the tropical Pacific. Our analysis reveals that all super El Niño winters (1982/83, 1997/98, and 2015/16) were accompanied by a rapid sub-seasonal North Atlantic Oscillation (NAO)/Arctic Oscillation (AO) phase reversal from a positive to a negative state during early January, which was largely caused by the interaction of these super El Niño events with the subtropical jet annual cycle. The NAO/AO phase transition leads to a rapidly strengthened Siberian High, which favors southward intrusions of cold air to East Asia and thus causes severe local cooling. Similar cold spells can also be detected over Northern Europe associated with the fast sub-seasonal NAO/AO phase reversal. Due to the weaker amplitude of the ENSO forcing, these sub-seasonal atmospheric responses cannot be detected for moderate El Niño events. The super El Niño associated sub-seasonal signal of the East Asian and Northern Europe wintertime temperature responses carries important implications for future predictability of regional extreme events.

Understanding the Variations of the Length and the Seasonal Rainfall Anomalies of the Indian Summer Monsoon

AbstractThe canonical relationship between the length and the total seasonal rainfall anomalies of the Indian summer monsoon (ISM) is the association of the longer (shorter) season with wetter (drier) seasonal rainfall anomalies. This study shows that such canonical behavior is clearly associated with relatively strong ENSO SST anomalies in the eastern equatorial Pacific Ocean that appear in the boreal summer and fall seasons. The noncanonical relationship is caused by a longer (shorter) season associated with drier (wetter) ISM seasonal rainfall anomalies. A majority of these noncanonical seasons, with anomalously short season length but anomalously high seasonal mean rain, tend to occur under relatively weak La Niña forcing during the boreal summer season. Although the onset of such seasons occurs through canonical ENSO forcing of a large-scale meridional temperature gradient, the demise is dictated by the depletion of moist static energy from the underlying cooling of the upper ocean in the northern Indian Ocean. This is due to stronger meridional Ekman ocean heat transport forced by the stronger low-level atmospheric southwesterlies than those in the corresponding canonical wet ISM season.