Simulation of Synoptic- and Subsynoptic-Scale Phenomena Associated with the East Asian Summer Monsoon Using a High-Resolution GCM

2009 ◽  
Vol 137 (1) ◽  
pp. 137-160 ◽  
Author(s):  
Ngar-Cheung Lau ◽  
Jeffrey J. Ploshay
Keyword(s):  
Summer Monsoon ◽  
Bay Of Bengal ◽  
General Circulation ◽  
Asian Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Western Pacific ◽  
Low Level ◽  
Continental Scale ◽  
Asian Summer

Abstract A 20-yr simulation using a global atmospheric general circulation model with a resolution of 0.5° latitude × 0.625° longitude is compared with observational findings. The primary goal of this survey is to assess the model performance in reproducing various summertime phenomena related to the continental-scale Asian monsoon in general, and the regional-scale East Asian monsoon in particular. In both model and observed atmospheres, the seasonal march of the precipitation centers associated with the Asian summer monsoon is characterized by onsets occurring earliest over the southeastern Bay of Bengal, followed by rapid northeastward advances over Indochina, the South China Sea–Philippine Sea and the western Pacific, northward evolution in the East Asian sector, as well as northwestward development over the Bay of Bengal, the Indian subcontinent, and the Arabian Sea. This onset sequence is accompanied by southwesterly low-level flows over the rainy regions, as well as northwestward migration of the 200-mb Tibetan anticyclone. Analysis of the heat sources and sinks in various regions illustrates the prominent role of condensational heating in the local energy budget during the mature phases of monsoon development. In accord with observations, the simulated monsoon rains in the East Asian sector are organized about zonally elongated “mei-yu–baiu” (plum rain) systems. These precipitation features advance to higher latitudes during the June–July period, in conjunction with displacements of the axis of the low-level anticyclone over the subtropical western Pacific. A detailed case study is performed on a prominent rainy episode in the simulation. The model is capable of reproducing the observed intense gradients in temperature, humidity, and moist static stability in the vicinity of the mei-yu–baiu front, as well as the spatial relationships between the rainband and the three-dimensional flow field. The axis of the mei-yu–baiu rainband in this event is aligned with the trajectory of a succession of mesoscale cyclonic vortices, which originate from southwestern China and travel northeastward over the Yangtze River basin.

scholarly journals The Variability of the Indian–East Asian Summer Monsoon Interface in Relation to the Spring Seesaw Mode between the Indian Ocean and the Central-Western Pacific

2016 ◽  
Vol 29 (13) ◽  
pp. 5027-5040 ◽  
Author(s):  
Jie Cao ◽  
Shu Gui ◽  
Qin Su ◽  
Yali Yang
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
General Circulation ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Western Pacific ◽  
Observational Analysis ◽  
Westerly Winds ◽  
Asian Summer

Abstract The interannual zonal movement of the interface between the Indian summer monsoon and the East Asian summer monsoon (IIE), associated with the spring sea surface temperature (SST) seesaw mode (SSTSM) over the tropical Indian Ocean (TIO) and the tropical central-western Pacific (TCWP), is studied for the period 1979–2008. The observational analysis is based on Twentieth Century Reanalysis data (version 2) of atmospheric circulations, Extended Reconstructed SST data (version 3), and the Climate Prediction Center Merged Analysis of Precipitation. The results indicate that the IIE’s zonal movement is significantly and persistently correlated with the TIO–TCWP SSTSM, from spring to summer. The results of two case studies resemble those obtained by regression analysis. Experiments using an atmospheric general circulation model (ECHAM6) substantiate the key physical processes revealed in the observational analysis. When warmer (colder) SSTs appear in the TIO and colder (warmer) SSTs occur in the TCWP, the positive (negative) SSTSM forces anomalous easterly (westerly) winds over the Bay of Bengal (BOB), South China Sea (SCS), and western North Pacific (WNP). The anomalous easterly (westerly) winds further result in a weakened (strengthened) southwest summer monsoon over the BOB and a strengthened (weakened) southeast summer monsoon over the SCS and WNP. This causes the IIE to shift farther eastward (westward) than normal.

scholarly journals Three exceptionally strong East-Asian summer monsoon events during glacial conditions in the past 470 kyr

2008 ◽  
Vol 4 (6) ◽  
pp. 1289-1317 ◽  
Author(s):  
D.-D. Rousseau ◽  
N. Wu ◽  
Y. Pei ◽  
F. Li
Keyword(s):  
Summer Monsoon ◽  
Asian Monsoon ◽  
East Asian Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Precipitation Regime ◽  
The Past ◽  
Ecological Requirements ◽  
Asian Summer ◽  
The Tropics

Abstract. Chinese loess sequences are interpreted as a reliable record of the past variation of the East Asian monsoon regime through the alternation of loess and paleosols units, dominated by the winter and summer monsoon, respectively. Different proxies have been used to describe this system, mostly geophysical, geochemical or sedimentological. Terrestrial mollusks are also a reliable proxy of past environmental conditions and are often preserved in large numbers in loess deposits. The analysis of the mollusk remains in the Luochuan sequence, comprising L5 loess to S0 soil, i.e. the last 500 ka, shows that for almost all identified species, the abundance is higher at the base of the interval (L5 to L4) than in the younger deposits. Using the present ecological requirements of the identified mollusk species in the Luochuan sequence allows the definition of two main mollusk groups varying during the last 500 kyr. The cold-aridiphilous individuals indicate the so-called Asian winter monsoon regime and predominantly occur during glacials, when dust is deposited. The thermal-humidiphilous mollusks are prevalent during interglacial or interstadial conditions of the Asian summer monsoon, when soil formation takes place. In the sequence, three events with exceptionally high abundance of the Asian summer monsoon indicators are recorded during the L5, L4 and L2 glacial intervals, i.e., at about 470, 360 and 170 kyr, respectively. The L5 and L4 events appear to be the strongest (high counts). Similar variations have also been identified in the Xifeng sequence, distant enough from Luochuan, but also in Lake Baikal further North, to suggest that this phenomenon is regional rather than local. The indicators of the summer monsoon within the glacial intervals imply a strengthened East-Asian monsoon interpreted as corresponding to marine isotope stages 6, 10 and 12, respectively. The L5 and L2 summer monsoons are coeval with Mediterranean sapropels S12 and S6, which characterize a strong African summer monsoon with relatively low surface water salinity in the Indian Ocean. Changes in the precipitation regime could correspond to a response to a particular astronomical configuration (low obliquity, low precession, summer solstice at perihelion) leading to an increased summer insolation gradient between the tropics and the high latitudes and resulting in enhanced atmospheric water transport from the tropics to the African and Asian continents. However, other climate drivers such as reorganization of marine and atmospheric circulations, tectonic, and the extent of the Northern Hemisphere ice sheet are also discussed.

scholarly journals Juxtaposition of Western Pacific Subtropical High on Asian Summer Monsoon Shapes Subtropical East Asian Precipitation

2020 ◽  
Vol 47 (3) ◽  
Author(s):  
Hai Xu ◽  
Yonaton Goldsmith ◽  
Jianghu Lan ◽  
Liangcheng Tan ◽  
Xulong Wang ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Western Pacific Subtropical High ◽  
Western Pacific ◽  
Subtropical High ◽  
Asian Summer

Sensitivity of East Asian summer monsoon precipitation to the location of the Tibetan Plateau

2021 ◽  
pp. 1-36
Author(s):  
Soo-Hyun Seok ◽  
Kyong-Hwan Seo
Keyword(s):  
Tibetan Plateau ◽  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
General Circulation ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Circulation Model ◽  
Dynamical Response ◽  
The Tibetan Plateau ◽  
Asian Summer

AbstractRecent studies have highlighted that a primary mechanism of the East Asian summer monsoon (EASM) is the fluid dynamical response to the Tibetan Plateau (TP), that is, orographically forced Rossby waves. With this mechanism in mind, this study explores how changes in the location of the TP affect the EASM precipitation. Specifically, the TP is moved in the four cardinal directions using idealized general circulation model experiments. The results show that the monsoon aspects are entirely determined by the location of the TP. Interestingly, the strongest EASM precipitation occurs when the TP is situated near its current location, a situation in which downstream southerlies are well developed from the surface to aloft. However, southerlies into the EASM region weaken as the TP moves, which in turn reduces the precipitation. Nevertheless, as long as it moves in the east–west direction, the TP is likely to force the stationary waves that induce precipitation over the mid-latitudes (not necessarily over East Asia). In contrast, moving the TP well north of its original location does not induce strong monsoon flows over the EASM region, resulting in the driest case. Meanwhile, although the southward movement of the TP triggers downstream southerlies to some extent, it does not lead to an increase in the precipitation. Overall, these results show that the location of the TP is crucial in determining the EASM precipitation, and the latter is much more sensitive to the displacement of the TP in the meridional direction than in the zonal direction.

scholarly journals Orographic Effects of the Tibetan Plateau on the East Asian Summer Monsoon: An Energetic Perspective

2014 ◽  
Vol 27 (8) ◽  
pp. 3052-3072 ◽  
Author(s):  
Jinqiang Chen ◽  
Simona Bordoni
Keyword(s):  
Tibetan Plateau ◽  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Thermal Gradient ◽  
General Circulation ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Eastern China ◽  
The Tibetan Plateau ◽  
Asian Summer

Abstract This paper investigates the dynamical processes through which the Tibetan Plateau (TP) influences the East Asian summer monsoon (EASM) within the framework of the moist static energy (MSE) budget, using both observations and atmospheric general circulation model (AGCM) simulations. The focus is on the most prominent feature of the EASM, the so-called meiyu–baiu (MB), which is characterized by a well-defined, southwest–northeast elongated quasi-stationary rainfall band, spanning from eastern China to Japan and into the northwestern Pacific Ocean between mid-June and mid-July. Observational analyses of the MSE budget of the MB front indicate that horizontal advection of moist enthalpy, and primarily of dry enthalpy, sustains the front in a region of otherwise negative net energy input into the atmospheric column. A decomposition of the horizontal dry enthalpy advection into mean, transient, and stationary eddy fluxes identifies the longitudinal thermal gradient due to zonal asymmetries and the meridional stationary eddy velocity as the most influential factors determining the pattern of horizontal moist enthalpy advection. Numerical simulations in which the TP is either retained or removed show that the TP influences the stationary enthalpy flux, and hence the MB front, primarily by changing the meridional stationary eddy velocity, with reinforced southerly wind over the MB region and northerly wind to its north. Changes in the longitudinal thermal gradient are mainly confined to the near downstream of the TP, with the resulting changes in zonal warm air advection having a lesser impact on the rainfall in the extended MB region.

scholarly journals Origins of East Asian Summer Monsoon Seasonality

2020 ◽  
Vol 33 (18) ◽  
pp. 7945-7965 ◽  
Author(s):  
J. C. H. Chiang ◽  
W. Kong ◽  
C. H. Wu ◽  
D. S. Battisti
Keyword(s):  
Tibetan Plateau ◽  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
General Circulation ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Circulation Model ◽  
Northeastern China ◽  
The Tibetan Plateau ◽  
Asian Summer

AbstractThe East Asian summer monsoon is unique among summer monsoon systems in its complex seasonality, exhibiting distinct intraseasonal stages. Previous studies have alluded to the downstream influence of the westerlies flowing around the Tibetan Plateau as key to its existence. We explore this hypothesis using an atmospheric general circulation model that simulates the intraseasonal stages with fidelity. Without a Tibetan Plateau, East Asia exhibits only one primary convective stage typical of other monsoons. As the plateau is introduced, the distinct rainfall stages—spring, pre-mei-yu, mei-yu, and midsummer—emerge, and rainfall becomes more intense overall. This emergence coincides with a pronounced modulation of the westerlies around the plateau and extratropical northerlies penetrating northeastern China. The northerlies meridionally constrain the moist southerly flow originating from the tropics, leading to a band of lower-tropospheric convergence and humidity front that produces the rainband. The northward migration of the westerlies away from the northern edge of the plateau leads to a weakening of the extratropical northerlies, which, coupled with stronger monsoonal southerlies, leads to the northward migration of the rainband. When the peak westerlies migrate north of the plateau during the midsummer stage, the extratropical northerlies disappear, leaving only the monsoon low-level circulation that penetrates northeastern China; the rainband disappears, leaving isolated convective rainfall over northeastern China. In short, East Asian rainfall seasonality results from the interaction of two seasonally evolving circulations—the monsoonal southerlies that strengthen and extend northward, and the midlatitude northerlies that weaken and eventually disappear—as summer progresses.

scholarly journals The East Asian Monsoon During MIS 2 Expressed in a Speleothem δ18O Record From Jintanwan Cave, Hunan, China

2010 ◽  
Vol 73 (3) ◽  
pp. 541-549 ◽  
Author(s):  
Jason Cosford ◽  
Hairuo Qing ◽  
Yin Lin ◽  
Bruce Eglington ◽  
Dave Mattey ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Asian Monsoon ◽  
East Asian Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Climatic Changes ◽  
Decadal Scale ◽  
Socotra Island ◽  
Asian Summer

Stalagmite J1 from Jintanwan Cave, Hunan, China, provides a precisely dated, decadally resolved δ18O proxy record of paleoclimatic changes associated with the East Asian monsoon from ∽29.5 to 14.7 ka and from ∽12.9 to 11.0 ka. At the time of the last glacial maximum (LGM), the East Asian summer monsoon weakened and then strengthened in response to changes in Northern Hemisphere insolation. As the ice sheets retreated the East Asian summer monsoon weakened, especially during Heinrich event H1, when atmospheric and oceanic teleconnections transferred the climatic changes around the North Atlantic to the monsoonal regions of Eastern Asia. A depositional hiatus between ∽14.7 and 12.9 ka leaves the deglacial record incomplete, but an abrupt shift in δ18O values at ∽11.5 ka marks the end of the Younger Dryas and the transition into the Holocene. Comparisons of the J1 record to other Chinese speleothem records indicate synchronous climatic changes throughout monsoonal China. Further comparisons to a speleothem record from western Asia (Socotra Island) and to Greenland ice cores support hemispherical-scale paleoclimatic change. Spectral and wavelet analyses reveal centennial- and decadal-scale periodicities that correspond to solar frequencies and to oscillations in atmospheric and oceanic circulation.

scholarly journals Recent Intensification of the Western Pacific Subtropical High Associated with the East Asian Summer Monsoon

2015 ◽  
Vol 28 (7) ◽  
pp. 2873-2883 ◽  
Author(s):  
Shinji Matsumura ◽  
Shiori Sugimoto ◽  
Tomonori Sato
Keyword(s):  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Western Pacific Subtropical High ◽  
Western Pacific ◽  
Subtropical High ◽  
The Past ◽  
The North ◽  
Asian Summer

Abstract The summer western Pacific subtropical high (WPSH) has intensified during the past three decades. However, the underlying mechanism is not yet well understood. Here, it is shown that baiu rainband activity in midsummer, which is part of the East Asian summer monsoon, plays an important role in recent intensification in the WPSH along the baiu rainband. In contrast with the WPSH, the summer Okhotsk high, which is located to the north of the baiu rainband, has weakened during the past three decades. The north–south contrasting changes between the two highs reflect a response to northward-moved and enhanced baiu heating, which intensifies the upper-tropospheric ridge, resulting in the baroclinic intensification of the WPSH. Regional climate model experiments also support the observational analysis. Therefore, baiu convective activity in midsummer can act as a major driver for the WPSH intensification. The results here suggest that the mechanism intensifying the summer North Pacific subtropical high clearly differs between the western and eastern Pacific.

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