scholarly journals Effects of Suppressed Transient Eddies by the Tibetan Plateau on the East Asian Summer Monsoon

2021 ◽  
pp. 1-59
Author(s):  
QIAOLING REN ◽  
XINGWEN JIANG ◽  
YANG ZHANG ◽  
ZHENNING LI ◽  
SONG YANG
Keyword(s):  
Tibetan Plateau ◽  
East Asia ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Jet Stream ◽  
The Tibetan Plateau ◽  
Rain Belt ◽  
Westerly Jet ◽  
Asian Summer ◽  
East Asian Westerly Jet

AbstractIt is known that the Tibetan Plateau (TP) can weaken the transient eddies (TEs) transported along the westerly jet stream. This study investigates the effects of the persistently suppressed TEs by the TP on the East Asian summer monsoon and the associated mechanisms using the NCAR Community Earth System Model. A nudging method is used to modify the suppression of the TEs without changing the steady dynamic and thermodynamic effects of the TP.The suppressed TEs by the TP weaken the East Asian westerly jet stream through the weakened poleward TE vorticity flux. On the one hand, the weakened jet stream leads to less (more) rainfall in northern (southern) East Asia by inducing anomalous moisture convergence, mid-tropospheric warm advection, and upper-level divergence, particularly in early summer when the eastward propagation of TE suppression by the TP is strong. On the other hand, the precipitation anomalies can shift the East Asian westerly jet stream southward and promote the moisture convergence in southern East Asia through latent heat release. Therefore, the persistent suppression of the TEs leads to a southward shift of the East Asian rain belt by a convective feedback, as previously found that the steady thermodynamic and dynamic forcings of the TP favored a northward shift of the rain belt. This study suggests that the anomalously weak TEs can lead to the south-more-north-less rainfall change over East Asia.

Effects of the Tibetan Plateau on East Asian Summer Monsoon via Weakened Transient Eddies

2020 ◽  
Author(s):  
Qiaoling Ren ◽  
Song Yang ◽  
Xinwen Jiang ◽  
Yang Zhang ◽  
Zhenning Li
Keyword(s):  
East Asia ◽  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Early Summer ◽  
The Tibetan Plateau ◽  
Rain Belt ◽  
Westerly Jet ◽  
Asian Summer

<p>Previous studies have revealed that the Tibetan Plateau (TP) can weaken the high-frequency and low-frequency transient eddies (TE) transported along the westerly jet. Here the effects of TP on East Asian summer monsoon via weakened TE are investigated based on the simulations by the NCAR Community Earth System Model, in which a nudging method is used to amplify the TP’s inhibition of TE without changing the steady dynamic and thermodynamic effects of TP. Results reveal that the weakened TE by TP weaken the East Asian westerly jet (EAWJ) and shift the jet southward via transient vorticity flux. The southward EAWJ accompanied with reduced poleward transport of moisture by TE results in less rainfall in northern East Asia but more rainfall in southern East Asia, particularly in early summer when the EAWJ is stably located over the TP and the meridional gradient of water vapor is large. Furthermore, the anomalous precipitation can move the EAWJ further southward through the anomalous diabatic heating in early summer, forming a positive feedback. Therefore, the TP’s inhibition of TE can shift the East Asian rain belt southward, different from the TP’s steady forcing which favors a poleward shift of the rain belt. It is also demonstrated that the atmospheric internal variability can lead to the south-flood-north-drought pattern of summer rainfall change over East Asia, indicating the important role of TE in East Asian summer monsoon.</p>

scholarly journals Relationship between the Tibetan Snow in Spring and the East Asian Summer Monsoon in 2003: A Global and Regional Modeling Study

2009 ◽  
Vol 22 (8) ◽  
pp. 2095-2110 ◽  
Author(s):  
Kyung-Hee Seol ◽  
Song-You Hong
Keyword(s):  
Tibetan Plateau ◽  
East Asia ◽  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Central China ◽  
The Tibetan Plateau ◽  
Asian Summer ◽  
Circulation Anomalies

Abstract In 2003, a climate extreme accompanying a wet and cool summer over East Asia was recorded over the East Asian countries including central China, Korea, and Japan. A possible relation of this record-breaking summer in East Asia to above-normal snowfall over the Tibetan Plateau in spring has been investigated using the National Centers for Environmental Prediction (NCEP) global and regional models. The changes in the simulated East Asian summer monsoon circulations in response to snow anomalies over Tibet are highlighted. The results from both global and regional model experiments suggest that above-normal snowfall over the Tibetan Plateau in May induces a weakening of the Tibetan high, which leads to the formation of favorable upper-level circulations accompanying cyclonic circulation anomalies covering the East Asian region in summer. These circulation anomalies in response to the snow anomalies over the plateau are more robust and closer to what was observed in the regional than in the global model results. The sensitivity experiments also show that the precipitation and lower-level circulation anomalies in summer, caused by the snow anomalies in spring, influence the above-normal precipitation in the lower reaches of the Yangtze River basin, as revealed in previous observational studies. However, the experiments do not fully explain the observed signals in Korea and Japan since the spring snow anomaly over Tibet plays a role in weakening the western Pacific subtropical high in the simulated summer, whereas in reality the intensity of the high was stronger than normal in 2003.

scholarly journals East Asian Summer Monsoon Precipitation Response to Variations in Upstream Westerly Wind

2021 ◽  
Author(s):  
Jun-Hyeok Son ◽  
Kyong-Hwan Seo
Keyword(s):  
Wind Speed ◽  
Tibetan Plateau ◽  
Interannual Variability ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
The Tibetan Plateau ◽  
Westerly Wind ◽  
Dynamical Mechanism ◽  
Asian Summer

Abstract From spring to summer, the East Asian summer monsoon (EASM) rainband migrates northwestward. During summer, East Asian countries experience extensive precipitation due to the EASM rainband, but the springtime monsoon rainband lies over the Pacific. The seasonal evolution of the EASM rainband is influenced by the mechanical effect of the Tibetan Plateau, and seasonal changes in the westerly wind speeds impinging on the Tibetan Plateau are a key driver of this process. In this study, using interannual variability of the upstream zonal wind speed, the dynamical mechanism for the interannual variations of the EASM precipitation is revealed based on the topographically forced stationary Rossby wave theory. The dynamical mechanism regulating interannual variability in the EASM rainband is essentially the same mechanism that drives the seasonal evolution of the climatological EASM rainband. If the westerly winds impinging on the Tibetan Plateau are stronger (weaker) than average, then the EASM rainband shifts eastward (westward). Large variations in the upstream westerly wind during May induced considerable interannual variation in the zonal location of the rainband (up to a 20–30º shift). The westerly wind speed exhibited less variations in June and July, resulting in a smaller zonal shift of approximately 10º.

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 Impacts of the East Asian summer monsoon on interannual variations of summertime surface-layer ozone concentrations over China

2014 ◽  
Vol 14 (13) ◽  
pp. 6867-6879 ◽  
Author(s):  
Y. Yang ◽  
H. Liao ◽  
J. Li
Keyword(s):  
Surface Layer ◽  
Tibetan Plateau ◽  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Anthropogenic Emissions ◽  
The Tibetan Plateau ◽  
Interannual Variations ◽  
Asian Summer

Abstract. We apply a global three-dimensional Goddard Earth Observing System (GEOS) chemical transport model (GEOS-Chem) driven by the NASA/GEOS-4 assimilated meteorological fields to quantify the impacts of the East Asian summer monsoon (EASM) on interannual variations of June-July-August (JJA) surface-layer O3 concentrations over China. With anthropogenic emissions fixed at year 2005 levels, the model simulation for years 1986–2006 shows that the changes in meteorological parameters alone lead to interannual variations in JJA surface-layer O3 concentrations by 2–5% over central eastern China, 1–3% in northwestern China, and 5–10% over the Tibetan Plateau as well as the border and coastal areas of southern China, as the interannual variations are relative to the average O3 concentrations over the 21 yr period. Over the years 1986–2006, the O3 concentration averaged over all of China is found to correlate positively with the EASM index with a large correlation coefficient of +0.75, indicating that JJA O3 concentrations are lower (or higher) in weaker (or stronger) EASM years. Relative to JJA surface-layer O3 concentrations in the strongest EASM years (1990, 1994, 1997, 2002, and 2006), O3 levels in the weakest EASM years (1988, 1989, 1996, 1998, and 2003) are lower over almost all of China with a national mean lower O3 concentration by 2.0 ppbv (parts per billion by volume; or 4%). Regionally, the largest percentage differences in O3 concentration between the weakest and strongest EASM years are found to exceed 6% in northeastern China, southwestern China, and over the Tibetan Plateau. Sensitivity studies show that the difference in transboundary transport of O3 is the most dominant factor that leads to lower-O3 concentrations in the weakest EASM years than in the strongest EASM years, which, together with the enhanced vertical convections in the weakest EASM years, explain about 80% of the differences in surface-layer O3 concentrations between the weakest and strongest EASM years. We also find that the impacts the EASM strength on JJA surface-layer O3 can be particularly strong (comparable in magnitude to the impacts on O3 by changes in anthropogenic emissions over years 1986–2006) for certain years. The largest increases in O3 by anthropogenic emissions are simulated over southeastern China, whereas the largest impacts of the EASM on O3 are found over central and western China.

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