Mechanisms of Global Teleconnections Associated with the Asian Summer Monsoon: An Intermediate Model Analysis*

2013 ◽  
Vol 26 (5) ◽  
pp. 1791-1806 ◽  
Author(s):  
Fei Liu ◽  
Bin Wang
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Summer Monsoon ◽  
Rossby Wave ◽  
North Pacific ◽  
Asian Summer Monsoon ◽  
Wave Train ◽  
Westerly Jet ◽  
Asian Summer ◽  
Upper Level

Abstract The Indian summer monsoon (ISM) and western North Pacific summer monsoon (WNPSM) are two subsystems of the Asian summer monsoon, and they exhibit different global teleconnection patterns. The enhanced ISM strengthens the South Asian high and Mascarene high, and the WNPSM excites a meridional tripolar wave train in the Northern Hemisphere and affects the Australian high in the Southern Hemisphere. To understand the dynamics behind these global teleconnections, especially the processes responsible for the cross-equatorial teleconnection, an intermediate model, describing a two-level troposphere and a steady planetary boundary layer (PBL), is linearized from the background horizontal wind field. The model results indicate that the ISM heating, located under the strong easterly vertical shear (VS) and close to the westerly jet in the Northern Hemisphere, can excite a barotropic Rossby wave that emanates northwestward and then propagates downstream along the westerly jet. Since the WNPSM heating is far away from the westerly jet over the North Pacific, it only excites a weak Rossby wave train, which cannot explain the meridional tripolar teleconnection associated with the WNPSM. It is found that both the ISM and WNPSM heating excite strong teleconnections in the Southern Hemisphere via an advection mechanism; that is, the background upper-level northerly winds can transport energy across the equator from the Northern Hemisphere summer monsoon to the Southern Hemisphere westerly jet. In addition, the PBL enhances monsoon teleconnections by trapping more energy in the upper troposphere. The elevated maximum monsoon heating also reinforces upper-level perturbations and enhances the teleconnection pattern.

Nonlinear, Intraseasonal Phases of the East Asian Summer Monsoon: Extraction and Analysis Using Self-Organizing Maps

2012 ◽  
Vol 25 (20) ◽  
pp. 6975-6988 ◽  
Author(s):  
Jung-Eun Chu ◽  
Saji N. Hameed ◽  
Kyung-Ja Ha
Keyword(s):  
Time Scales ◽  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Self Organizing Maps ◽  
Dry Spell ◽  
Asian Summer ◽  
Upper Level ◽  
Self Organizing

Abstract The hypothesis that regional characteristics of the East Asian summer monsoon (EASM) result from the presence of nonlinear coupled features that modulate the seasonal circulation and rainfall at the intraseasonal time scale is advanced in this study. To examine this hypothesis, the authors undertake the analysis of daily EASM variability using a nonlinear multivariate data classifying algorithm known as self-organizing mapping (SOM). On the basis of various SOM node analyses, four major intraseasonal phases of the EASM are identified. The first node describes a circulation state corresponding to weak tropical and subtropical pressure systems, strong upper-level jets, weakened monsoonal winds, and cyclonic upper-level vorticity. This mode, related to large rainfall anomalies in southeast China and southern Japan, is identified as the mei-yu–baiu phase. The second node represents a distinct circulation state corresponding to a strengthened subtropical high, monsoonal winds, and anticyclonic upper-level vorticity in southeast Korea, which is identified as the changma phase. The third node is related to copious rain over Korea following changma, which we name the postchangma phase. The fourth node is situated diagonally opposite the changma mode. Because Korea experiences a dry spell associated with this SOM node, it is referred to as the dry-spell phase. The authors also demonstrate that a strong modulation of the changma and dry-spell phases on interannual time scales occurs during El Niño and La Niña years. Results imply that the key to predictability of the EASM on interannual time scales may lie with analysis and exploitation of its nonlinear characteristics.

scholarly journals Understanding the Interdecadal Variability of East Asian Summer Monsoon Precipitation: Joint Influence of Three Oceanic Signals

2018 ◽  
Vol 31 (14) ◽  
pp. 5485-5506 ◽  
Author(s):  
Zhiqi Zhang ◽  
Xuguang Sun ◽  
Xiu-Qun Yang
Keyword(s):  
Summer Monsoon ◽  
North Atlantic ◽  
Asian Summer Monsoon ◽  
Wave Train ◽  
Eastern China ◽  
Monsoon Precipitation ◽  
The North ◽  
Joint Influence ◽  
Asian Summer ◽  
Precipitation Anomalies

Abstract East Asian summer monsoon precipitation (EASMP) features complicated interdecadal variability with multiple time periods and spatial patterns. Using century-long datasets of HadISST, CRU precipitation, and the ECMWF twentieth-century reanalysis (ERA-20C), this study examines the joint influence of three oceanic interdecadal signals [i.e., Pacific decadal oscillation (PDO), Atlantic multidecadal oscillation (AMO), and Indian Ocean Basin mode (IOBM)] on the EASMP, which, however, is found not to be simply a linear combination of their individual effects. When PDO and AMO are out of phase, the same-sign SST anomalies occur in the North Pacific and North Atlantic, and a zonally orientated teleconnection wave train appears across the Eurasian mid-to-high latitudes, propagating from the North Atlantic to northern East Asia along the Asian westerly jet waveguide. Correspondingly, the interdecadal precipitation anomalies are characterized by a meridional tripole mode over eastern China. When PDO and AMO are in phase, with opposite sign SST anomalies in the North Pacific and North Atlantic, the sandwich pattern of anomalous stationary Rossby wavenumber tends to reduce the effect of the waveguide in the eastern Mediterranean region, and the teleconnection wave train from the North Atlantic travels only to western central Asia along a great circle route, causing Indian summer monsoon precipitation (ISMP) anomalies. The ISMP anomalies, in turn, interact with the teleconnection wave train induced by the PDO and AMO, leading to a meridional dipole mode of interdecadal precipitation anomalies over eastern China. Through the impact on the ISMP, the IOBM exerts significantly linear modulation on the combined impacts of PDO and AMO, especially over northern East Asia.

The leading mode and factors for coherent variations among the sub-systems of tropical Asian summer monsoon onset

2021 ◽  
pp. 1-63
Keyword(s):  
Summer Monsoon ◽  
Rossby Wave ◽  
Asian Summer Monsoon ◽  
Monsoon Onset ◽  
Positive Phase ◽  
Low Level ◽  
Leading Mode ◽  
Rossby Wave Response ◽  
Asian Summer ◽  
The Mean

Abstract Previous studies on the Asian summer monsoon (ASM) onset mainly focused on each monsoon sub-system. Mainly based on the monthly mean rainfall and low-level winds in May, this study investigated the dominant onset mode from the perspective of the entire tropical ASM region, which reveals the coherent features among the regional-scale onsets. The results of multivariate empirical orthogonal function (MV-EOF) analysis indicate that the MV-EOF1 presents reduced rainfall and anomalous low-level easterly winds at 850 hPa over the tropical ASM region in May during its positive phase. The corresponding principal component (PC1) is highly correlated with the local monsoon onset dates over Arabian Sea, Bay of Bengal, Indo-China Peninsula, and South China Sea, where the mean monsoon onsets occur in May. The only exception is India subcontinent, where the mean monsoon onsets occur in June. The results indicate that the leading mode captures the synchronized variation of monsoon onset over most of Asian monsoon sub-systems, which exhibits remarkably interannual and interdecadal changes. The factors that modulate the coherent variation of the tropical ASM onset are further examined. The simultaneously delayed ASM onset tends to occur during the easterly phase of the 30- to 80-day oscillation, the decaying phase of El Niño, and the positive phase of Pacific Decadal Oscillation (PDO). The 30- to 80-day oscillation serves as a background condition for the synchronized delayed or advanced ASM onset. El Niño-related sea surface temperature anomalies modulate the tropical ASM onset mode by modulating the tropical Walker Circulation and inducing an atmospheric Rossby wave response. The PDO affects the tropical ASM onset mode mainly via the equatorial Rossby wave response and the extratropical Rossby wave train.

scholarly journals Distinct responses of Asian summer monsoon to black carbon aerosols and greenhouse gases

2020 ◽  
Author(s):  
Xiaoning Xie ◽  
Gunnar Myhre ◽  
Xiaodong Liu ◽  
Xinzhou Li ◽  
Zhengguo Shi ◽  
...  
Keyword(s):  
Greenhouse Gases ◽  
Black Carbon ◽  
Summer Monsoon ◽  
Radiative Forcing ◽  
Asian Summer Monsoon ◽  
Atmospheric Temperature ◽  
Monsoon Circulation ◽  
Low Level ◽  
Asian Summer ◽  
Upper Level

Abstract. Black carbon (BC) aerosols emitted from natural and anthropogenic sources induce positive radiative forcing and global warming, which in turn significantly affect the Asian summer monsoon (ASM). However, many aspects of the BC effect on ASM remain elusive and largely inconsistent among previous studies, which is strongly dependent on different low-level thermal feedbacks over the Asian continent and the surrounding ocean. This study examines the response of ASM to BC forcing in comparison with the effect of doubled greenhouse gases (GHGs) by analyzing the Precipitation Driver Response Model Intercomparison Project (PDRMIP) simulations under an extreme high BC level (10 times modern global BC emissions or concentrations, labeled by BC × 10) from nine global climate models (GCMs). The results show that although BC and GHGs both enhance the ASM precipitation minus evaporation (P–E) (a 13.6 % increase for BC forcing and 12.1 % for GHGs from the nine-model ensemble, respectively), there exists a much larger uncertainty in changes in ASM P–E induced by BC than by GHGs. The summer P–E is increased by 7.7 % to 15.3 % due to these two forcings over three sub-regions including East Asian, South Asian, and western North Pacific monsoon regions. Further analysis of moisture budget reveals distinct mechanisms controlling the increases in ASM P–E induced by BC and GHGs. The change in ASM P–E by BC is dominated by the dynamic effect due to the enhanced large-scale monsoon circulation, whereas the GHG-induced change is dominated by the thermodynamic effect through increasing atmospheric water vapor. Radiative forcing of BC significantly increases the upper-level atmospheric temperature over the Asian region to enhance the upper-level meridional land-sea thermal gradient (MLOTG), resulting in a northward shift of the upper-level subtropical westerly jet and an enhancement of the low-level monsoon circulation; whereas radiative forcing of GHGs significantly increases the tropical upper-level temperature, which reduces the upper-level MLOTG and suppresses the low-level monsoonal circulation. Hence, our results indicate a different mechanism of BC climate effects under the extreme high BC level, that BC forcing significantly enhances the upper-level atmospheric temperature over the Asian region, determining ASM changes, instead of low-level thermal feedbacks as indicated by previous studies.

scholarly journals Global Extratropical Response to Diabatic Heating Variability of the Asian Summer Monsoon

2009 ◽  
Vol 66 (9) ◽  
pp. 2697-2713 ◽  
Author(s):  
Hai Lin
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Asian Summer Monsoon ◽  
Convective Activity ◽  
Mean Flow ◽  
Asian Summer ◽  
Circulation Anomalies

Abstract Global teleconnections associated with the Asian summer monsoon convective activities are investigated based on monthly data of 29 Northern Hemisphere summers defined as June–September (JJAS). Two distinct teleconnection patterns are identified that are associated respectively with variabilities of the Indian summer monsoon and the western North Pacific summer monsoon. The Indian summer monsoon convective activity is associated with a global pattern that has a far-reaching connection in both hemispheres, whereas the western North Pacific summer monsoon convective activity is connected to a Southern Hemisphere wave train that influences the high-latitude South Pacific and South America. A global primitive equation model is utilized to assess the cause of the global circulation anomalies. The model responses to anomalous heatings of both monsoon systems match the general features of the observed circulation anomalies well, and they are mainly controlled by linear processes. The response patterns are largely determined by the summertime large-scale background mean flow and the location of the heating anomaly relative to the upper easterly jet in the monsoon region.

scholarly journals Impacts of the Pacific–Japan and Circumglobal Teleconnection Patterns on the Interdecadal Variability of the East Asian Summer Monsoon

2016 ◽  
Vol 29 (9) ◽  
pp. 3253-3271 ◽  
Author(s):  
Bo Wu ◽  
Tianjun Zhou ◽  
Tim Li
Keyword(s):  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Wave Train ◽  
East Asian ◽  
Interdecadal Variability ◽  
Convective Heating ◽  
Indian Ocean Basin Mode ◽  
Circumglobal Teleconnection ◽  
Asian Summer

Abstract Based on the Twentieth Century Reanalysis (20CR) dataset, the dominant modes of interdecadal variability of the East Asian summer monsoon (EASM) are investigated through a multivariate empirical orthogonal function analysis (MV-EOF). The first mode (EA1) is characterized by an anomalous cyclone centered over Taiwan and an anomalous anticyclone centered over the Bohai Sea. These phenomena are part of the meridional wave–like teleconnection pattern propagating poleward from the southern tropical western North Pacific (WNP), referred to as the interdecadal Pacific–Japan (PJ) pattern. The interdecadal PJ pattern is driven by negative anomalous convective heating over the southern tropical WNP, which is associated with the interdecadal Pacific oscillation (IPO) and the interdecadal Indian Ocean basin mode (IOBM). The amplitude of the EA1 and its contribution to the total variance of the EASM decrease remarkably after the 1960s. The second MV-EOF mode (EA2) is characterized by cyclone anomalies extending from northeastern China to Japan, which are part of a circumglobal wave train. Given the spatial scale of the wave train in the zonal direction (wavenumber 5), as well as the fact that it possesses barotropic structures and propagates along the Northern Hemispheric jet stream, it is referred to herein as the interdecadal circumglobal teleconnection (CGT) pattern. The interdecadal CGT pattern is associated with the forcing from the Atlantic multidecadal oscillation (AMO). Though the interdecadal PJ and CGT patterns are derived from the 20CR dataset, they are carefully verified through comparisons with various observational and reanalysis datasets from different perspectives.

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