Variability of boreal spring Hadley circulation over the Asian monsoon domain and its relationship with tropical SST

2020 ◽  
Author(s):  
Yaqi Wang ◽  
Juan Feng ◽  
Jianping Li ◽  
Ran An ◽  
Lanning Wang
Keyword(s):  
Indian Ocean ◽  
Asian Monsoon ◽  
Southern Oscillation ◽  
Critical Role ◽  
Hadley Circulation ◽  
Tropical Indian Ocean ◽  
Dominant Mode ◽  
Main Body ◽  
Boreal Spring ◽  
Sst Anomalies

<p>The variability of boreal spring Hadley circulation (HC) over the Asian monsoon domain over the last four decades is explored. The climatological distribution of the regional HC is symmetric of the equator, with the ascending branch around the equator and sinking branch around the subtropics in each hemisphere. The first dominant mode (EOF1) of the regional HC is equatorial asymmetric, with the main body in the Southern Hemisphere (SH) and the ascending branch to the north of the equator. This mode is mainly characterized by interannual variation and is related to El Niño-Southern Oscillation (ENSO). Significant negative sea surface temperature (SST) anomalies are observed over the tropical Indian Ocean (TIO) along with the development of La Niña events; however, the magnitude of SST anomalies in the southern Indian Ocean is greater than that in the northern counterpart, contributing to EOF1 formation. The spatial distribution of the second dominant mode (EOF2) is with the main body lying in the Northern Hemisphere (NH) and the ascending branch located to the south of the equator. The temporal variation of this mode is connected to the warming of the TIO. The warming rate of the southern TIO SST is faster than that in the northern counterpart, resulting in the southward migration of the rising branch. The above result indicates the critical role of the meridional distribution of SST on the variability of the regional HC.</p>

Structure and Seasonal Variation of the Indian Ocean Tropical Gyre Based on Surface Drifters

2021 ◽  
Author(s):  
Wei Wu ◽  
Yan Du ◽  
Yu-Kun Qian ◽  
Xuhua Cheng ◽  
Tianyu Wang ◽  
...  
Keyword(s):  
Seasonal Variation ◽  
Indian Ocean ◽  
Water Mass ◽  
Southern Oscillation ◽  
Tropical Indian Ocean ◽  
Western Boundary ◽  
Boundary Current ◽  
Boreal Spring ◽  
The Indian Ocean ◽  
Surface Drifters

<p>Using the Gauss–Markov decomposition method, this study investigates the mean structure and seasonal variation of the tropical gyre in the Indian Ocean based on the observations of surface drifters. In the climatological mean, the clockwise tropical gyre consists of the equatorial Wyrtki Jets (WJs), the South Equatorial Current (SEC), and the eastern and western boundary currents. This gyre system redistributes the water mass over the entire tropical Indian Ocean basin. Its variations are associated with the monsoon transitions, featuring a typical clockwise pattern in the boreal spring and fall seasons. The relative importance of the geostrophic and Ekman components of the surface currents as well as the role of eddy activity were further examined. It was found that the geostrophic component dominates the overall features of the tropical gyre, including the SEC meandering, the broad eastern boundary current, and the axes of the WJs in boreal spring and fall, whereas the Ekman component strengthens the intensity of the WJs and SEC. Eddies are active over the southeastern tropical Indian Ocean and transport a warm and fresh water mass westward, with direct impact on the southern branch of the tropical gyre. In particular, the trajectories of drifters reveal that during strong Indian Ocean Dipole or El Niño-Southern Oscillation events, long-lived eddies were able to reach the southwestern Indian Ocean with a moving speed close to that of the first baroclinic Rossby waves.</p>

scholarly journals Possible Role of the Indian Ocean in the In-Phase Transition of the Indian-to-Australian Summer Monsoon

2008 ◽  
Vol 21 (21) ◽  
pp. 5727-5741 ◽  
Author(s):  
Renguang Wu
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Southern Oscillation ◽  
Tropical Indian Ocean ◽  
Australian Summer Monsoon ◽  
The Indian Ocean ◽  
Numerical Model Experiments ◽  
Sst Anomalies ◽  
Australian Summer

Abstract Analysis of observations shows that in-phase transitions from the Indian summer monsoon (ISM) to the Australian summer monsoon (ASM) have occurred both in El Niño–Southern Oscillation (ENSO) and non-ENSO years. The present study investigates possible roles of the Indian Ocean in the in-phase ISM-to-ASM transitions. It is shown that an anomalous ISM leads to sea surface temperature (SST) anomalies in the tropical Indian Ocean through wind–evaporation effects. The resultant Indian Ocean SST anomalies induce an anomalous ASM of the same sign as the ISM through an anomalous east–west circulation over the eastern Indian Ocean and the Maritime Continent–northern Australia. The results indicate that the in-phase ISM-to-ASM transitions in non-ENSO years can be accomplished through monsoon–Indian Ocean interactions. The results of observational analysis are confirmed with numerical model experiments.

Decadal Modulation of the ENSO-Indian Ocean Basin Warming relationship during the decaying summer by the Interdecadal Pacific Oscillation

2021 ◽  
pp. 1-50
Author(s):  
Fangyu Liu ◽  
Wenjun Zhang ◽  
Fei-Fei Jin ◽  
Suqiong Hu
Keyword(s):  
Indian Ocean ◽  
Southern Oscillation ◽  
Equatorial Indian Ocean ◽  
Tropical Indian Ocean ◽  
Seasonal Prediction ◽  
Ocean Basin ◽  
Interdecadal Pacific Oscillation ◽  
Enso Events ◽  
Decadal Modulation ◽  
Sst Anomalies

AbstractMany previous studies have shown that an Indian Ocean basin warming (IOBW) occurs usually during El Niño-Southern Oscillation (ENSO) decaying spring to summer seasons through modifying the equatorial zonal circulation. Decadal modulation associated with the Interdecadal Pacific Oscillation (IPO) is further investigated here to understand the nonstationary ENSO-IOBW relationship during ENSO decaying summer (July-August-September, JAS). During the positive IPO phase, significant warm sea surface temperature (SST) anomalies are observed over the tropical Indian Ocean in El Niño decaying summers and vice versa for La Niña events, while these patterns are not well detected in the negative IPO phase. Different decaying speeds of ENSO associated with the IPO phase, largely controlled by both zonal advective and thermocline feedbacks, are suggested to be mainly responsible for these different ENSO-IOBW relationships. In contrast to ENSO events in the negative IPO phase, the ones in the positive IPO phase display a slower decaying speed and delay their transitions both from a warm to a cold state and a cold to a warm state. The slower decay of El Niño and La Niña thereby helps to sustain the teleconnection forcing over the equatorial Indian Ocean and corresponding SST anomalies there can persist into summer. This IPO modulation of the ENSO-IOBW relationship carries important implications for the seasonal prediction of the Indian Ocean SST anomalies and associated summer climate anomalies.

scholarly journals Origins of Biases in CMIP5 Models Simulating Northwest Pacific Summertime Atmospheric Circulation Anomalies during the Decaying Phase of ENSO

2018 ◽  
Vol 31 (14) ◽  
pp. 5707-5729 ◽  
Author(s):  
Weichen Tao ◽  
Gang Huang ◽  
Renguang Wu ◽  
Kaiming Hu ◽  
Pengfei Wang ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
Southern Oscillation ◽  
Coupled Model ◽  
Tropical Indian Ocean ◽  
Shortwave Radiation ◽  
Cmip5 Models ◽  
Northwest Pacific ◽  
Circulation Anomalies ◽  
Atmospheric Circulation Anomalies ◽  
Sst Anomalies

Abstract The present study documents the biases of summertime northwest Pacific (NWP) atmospheric circulation anomalies during the decaying phase of ENSO and investigates their plausible reasons in 32 models from phase 5 of the Coupled Model Intercomparison Project. Based on an intermodel empirical orthogonal function (EOF) analysis of El Niño–Southern Oscillation (ENSO)-related 850-hPa wind anomalies, the dominant modes of biases are extracted. The first EOF mode, explaining 21.3% of total intermodel variance, is characterized by a cyclone over the NWP, indicating a weaker NWP anticyclone. The cyclone appears to be a Rossby wave response to unrealistic equatorial western Pacific (WP) sea surface temperature (SST) anomalies related to excessive equatorial Pacific cold tongue in the models. On one hand, the cold SST biases increase the mean zonal SST gradient, which further intensifies warm zonal advection, favoring the development and persistence of equatorial WP SST anomalies. On the other hand, they reduce the anomalous convection caused by ENSO-related warming, and the resultant increase in downward shortwave radiation contributes to the SST anomalies there. The second EOF mode, explaining 18.6% of total intermodel variance, features an anticyclone over the NWP with location shifted northward. The related SST anomalies in the Indo-Pacific sector show a tripole structure, with warming in the tropical Indian Ocean and equatorial central and eastern Pacific and cooling in the NWP. The Indo-Pacific SST anomalies are highly controlled by ENSO amplitude, which is determined by the intensity of subtropical cells via the adjustment of meridional and vertical advection in the models.

An Enhanced Influence of Tropical Indian Ocean on the South Asia High after the Late 1970s

2012 ◽  
Vol 25 (20) ◽  
pp. 6930-6941 ◽  
Author(s):  
Xia Qu ◽  
Gang Huang
Keyword(s):  
Indian Ocean ◽  
South Asia ◽  
Tropical Indian Ocean ◽  
Tropospheric Temperature ◽  
Decadal Change ◽  
The South ◽  
South Asia High ◽  
The Impact ◽  
Change In Mean ◽  
Sst Anomalies

Abstract The tropical Indian Ocean (TIO)’s influence on the South Asia high (SAH)’s intensity experiences a decadal change in the late 1970s; after (before) the decadal shift, the influence is significant (insignificant). The present study investigates the role of tropospheric temperature in relaying the impact of sea surface temperature (SST) to the SAH and the change in the TIO’s influence. During the two epochs, the local tropospheric temperature responses to the TIO warming are distinct—more significant during the second epoch. It is inferred that this change may be responsible for the strengthening of the TIO’s influence on the SAH. Encouragingly, the ensemble simulations accurately capture the time of the decadal change, indicating that the enhanced influence is attributed to the SST forcing. There are two possible reasons for the change in the TIO–SAH relationship. The first reason is the change in the locations of the SST anomalies in the TIO. During the second epoch, positive SST anomalies lie in the Indian Ocean warm pool. Through the background vigorous convection and moist adjustment, the SST anomalies affect largely the tropospheric temperature and thus the SAH. The second reason is the decadal change in mean SST and the SST variability. During the recent decades, both the background SST and the variability of the TIO SST increase, which enhance the influence of the SST anomalies on the atmosphere. The influence of the remote oceanic forcing on the enhanced TIO–SAH relationship and its comparison with the contribution of the TIO SST are also discussed.

scholarly journals Indo-Western Pacific Climate Variability: ENSO Forcing and Internal Dynamics in a Tropical Pacific Pacemaker Simulation

2018 ◽  
Vol 31 (24) ◽  
pp. 10123-10139 ◽  
Author(s):  
Chuan-Yang Wang ◽  
Shang-Ping Xie ◽  
Yu Kosaka
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
Internal Variability ◽  
Tropical Pacific ◽  
Western Pacific ◽  
Ocean Atmosphere ◽  
Sst Anomalies

El Niño–Southern Oscillation (ENSO) peaks in boreal winter but its impact on Indo-western Pacific climate persists for another two seasons. Key ocean–atmosphere interaction processes for the ENSO effect are investigated using the Pacific Ocean–Global Atmosphere (POGA) experiment with a coupled general circulation model, where tropical Pacific sea surface temperature (SST) anomalies are restored to follow observations while the atmosphere and oceans are fully coupled elsewhere. The POGA shows skills in simulating the ENSO-forced warming of the tropical Indian Ocean and an anomalous anticyclonic circulation pattern over the northwestern tropical Pacific in the post–El Niño spring and summer. The 10-member POGA ensemble allows decomposing Indo-western Pacific variability into the ENSO forced and ENSO-unrelated (internal) components. Internal variability is comparable to the ENSO forcing in magnitude and independent of ENSO amplitude and phase. Random internal variability causes apparent decadal modulations of ENSO correlations over the Indo-western Pacific, which are high during epochs of high ENSO variance. This is broadly consistent with instrumental observations over the past 130 years as documented in recent studies. Internal variability features a sea level pressure pattern that extends into the north Indian Ocean and is associated with coherent SST anomalies from the Arabian Sea to the western Pacific, suggestive of ocean–atmosphere coupling.

scholarly journals Isolated Effects of Indian Ocean Basin-Wide and El Niño–Southern Oscillation on Austral Winter Rainfall over South America

Atmosphere ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1605
Author(s):  
Mary T. Kayano ◽  
Wilmar L. Cerón ◽  
Rita V. Andreoli ◽  
Rodrigo A. F. Souza ◽  
Itamara P. Souza
Keyword(s):  
Indian Ocean ◽  
South America ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Tropical Indian Ocean ◽  
Ocean Basin ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Partial Correlations

Contrasting effects of the tropical Indian and Pacific Oceans on the atmospheric circulation and rainfall interannual variations over South America during southern winter are assessed considering the effects of the warm Indian Ocean basin-wide (IOBW) and El Niño (EN) events, and of the cold IOBW and La Niña events, which are represented by sea surface temperature-based indices. Analyses are undertaken using total and partial correlations. When the effects of the two warm events are isolated from each other, the contrasts between the associated rainfall anomalies in most of South America become accentuated. In particular, EN relates to anomalous wet conditions, and the warm IOBW event to opposite conditions in extensive areas of the 5° S–25° S band. These effects in the 5° S–15° S sector are due to the anomalous regional Hadley cells, with rising motions in this band for the EN and sinking motions for the warm IOBW event. Meanwhile, in subtropical South America, the opposite effects of the EN and warm IOBW seem to be due to the presence of anomalous anticyclone and cyclone and associated moisture transport, respectively. These opposite effects of the warm IOBW and EN events on the rainfall in part of central South America might explain the weak rainfall relation in this region to the El Niño–Southern Oscillation (ENSO). Our results emphasize the important role of the tropical Indian Ocean in the South American climate and environment during southern winter.

scholarly journals El Niño-Southern Oscillation and Indian Ocean Dipole Modes: Their Effects on South American Rainfall during Austral Spring

Atmosphere ◽  
2021 ◽  
Vol 12 (11) ◽  
pp. 1437
Author(s):  
Mary T. Kayano ◽  
Wilmar L. Cerón ◽  
Rita V. Andreoli ◽  
Rodrigo A. F. Souza ◽  
Itamara P. Souza ◽  
...  
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
Indian Ocean Dipole ◽  
El Nino ◽  
Southern Oscillation ◽  
Tropical Indian Ocean ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Austral Spring ◽  
Precipitation Anomalies

This paper examines the effects of the tropical Pacific Ocean (TPO) and Indian Ocean Dipole (IOD) modes in the interannual variations of austral spring rainfall over South America (SA). The TPO mode refers to the El Niño-Southern Oscillation (ENSO). The isolated effects between IOD and TPO were estimated, events were chosen from the residual TPO (R-TPO) or residual IOD (R-IOD), and the IOD (TPO) effects for the R-TPO (R-IOD) composites were removed from the variables. One relevant result was the nonlinear precipitation response to R-TPO and R-IOD. This feature was accentuated for the R-IOD composites. The positive R-IOD composite showed significant negative precipitation anomalies along equatorial SA east of 55° W and in subtropical western SA, and showed positive anomalies in northwestern SA and central Brazil. The negative R-IOD composite indicated significant positive precipitation anomalies in northwestern Amazon, central–eastern Brazil north of 20° S, and western subtropical SA, and negative anomalies were found in western SA south of 30° S. This nonlinearity was likely due to the distinct atmospheric circulation responses to the anomalous heating sources located in longitudinally distinct regions: the western tropical Indian Ocean and areas neighboring Indonesia. The results obtained in this study might be relevant for climate monitoring and modeling studies.

scholarly journals Dominant Interannual Covariations of the East Asian–Australian Land Precipitation during Boreal Winter

2019 ◽  
Vol 32 (11) ◽  
pp. 3279-3296 ◽  
Author(s):  
Lin Liu ◽  
Jianping Guo ◽  
Wen Chen ◽  
Renguang Wu ◽  
Lin Wang ◽  
...  
Keyword(s):  
Indian Ocean ◽  
General Circulation ◽  
Southern Oscillation ◽  
East Asian ◽  
Circulation Model ◽  
Boreal Winter ◽  
Dipole Structure ◽  
Second Mode ◽  
Precipitation Anomalies ◽  
Sst Anomalies

AbstractThe present study applies the empirical orthogonal function (EOF) method to investigate the interannual covariations of East Asian–Australian land precipitation (EAALP) during boreal winter based on observational and reanalysis datasets. The first mode of EAALP variations is characterized by opposite-sign anomalies between East Asia (EA) and Australia (AUS). The second mode features an anomaly pattern over EA similar to the first mode, but with a southwest–northeast dipole structure over AUS. El Niño–Southern Oscillation (ENSO) is found to be a primary factor in modulating the interannual variations of land precipitation over EA and western AUS. By comparison, the Indian Ocean subtropical dipole mode (IOSD) plays an important role in the formation of precipitation anomalies over northeastern AUS, mainly through a zonal vertical circulation spanning from the southern Indian Ocean (SIO) to northern AUS. In addition, the ENSO-independent cold sea surface temperature (SST) anomalies in the western North Pacific (WNP) impact the formation of the second mode. Using the atmospheric general circulation model ECHAM5, three 40-yr numerical simulation experiments differing in specified SST forcings verify the impacts of the IOSD and WNP SST anomalies. Further composite analyses indicate that the dominant patterns of EAALP variability are largely determined by the out-of-phase and in-phase combinations of ENSO and IOSD. These results suggest that in addition to ENSO, IOSD should be considered as another crucial factor influencing the EAALP variability during the boreal winter, which has large implications for improved prediction of EAALP land precipitation on the interannual time scale.

scholarly journals Possible Impact of the Indian Ocean SST on the Northern Hemisphere Circulation during El Niño*

2007 ◽  
Vol 20 (13) ◽  
pp. 3164-3189 ◽  
Author(s):  
H. Annamalai ◽  
H. Okajima ◽  
M. Watanabe
Keyword(s):  
Indian Ocean ◽  
Northern Hemisphere ◽  
El Niño ◽  
El Nino ◽  
Tropical Indian Ocean ◽  
Tropical Pacific ◽  
The Indian Ocean ◽  
Precipitation Anomalies ◽  
Sst Anomalies ◽  
The Tropical Pacific

Abstract Two atmospheric general circulation models (AGCMs), differing in numerics and physical parameterizations, are employed to test the hypothesis that El Niño–induced sea surface temperature (SST) anomalies in the tropical Indian Ocean impact considerably the Northern Hemisphere extratropical circulation anomalies during boreal winter [January–March +1 (JFM +1)] of El Niño years. The hypothesis grew out of recent findings that ocean dynamics influence SST variations over the southwest Indian Ocean (SWIO), and these in turn impact local precipitation. A set of ensemble simulations with the AGCMs was carried out to assess the combined and individual effects of tropical Pacific and Indian Ocean SST anomalies on the extratropical circulation. To elucidate the dynamics responsible for the teleconnection, solutions were sought from a linear version of one of the AGCMs. Both AGCMs demonstrate that the observed precipitation anomalies over the SWIO are determined by local SST anomalies. Analysis of the circulation response shows that over the Pacific–North American (PNA) region, the 500-hPa height anomalies, forced by Indian Ocean SST anomalies, oppose and destructively interfere with those forced by tropical Pacific SST anomalies. The model results validated with reanalysis data show that compared to the runs where only the tropical Pacific SST anomalies are specified, the root-mean-square error of the height anomalies over the PNA region is significantly reduced in runs in which the SST anomalies in the Indian Ocean are prescribed in addition to those in the tropical Pacific. Among the ensemble members, both precipitation anomalies over the SWIO and the 500-hPa height over the PNA region show high potential predictability. The solutions from the linear model indicate that the Rossby wave packets involved in setting up the teleconnection between the SWIO and the PNA region have a propagation path that is quite different from the classical El Niño–PNA linkage. The results of idealized experiments indicate that the Northern Hemisphere extratropical response to Indian Ocean SST anomalies is significant and the effect of this response needs to be considered in understanding the PNA pattern during El Niño years. The results presented herein suggest that the tropical Indian Ocean plays an active role in climate variability and that accurate observation of SST there is of urgent need.

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