Magnetic variations in surface soils in the NE Tibetan Plateau indicating the climatic boundary between the Westerly and East Asian summer monsoon regimes in NW China

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.

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Impacts of Tibetan Plateau Snow Cover on the Interannual Variability of the East Asian Summer Monsoon

Journal of Climate ◽

10.1175/jcli-d-16-0029.1 ◽

2016 ◽

Vol 29 (23) ◽

pp. 8495-8514 ◽

Cited By ~ 51

Author(s):

Zhixiang Xiao ◽

Anmin Duan

Keyword(s):

Tibetan Plateau ◽

Snow Cover ◽

Summer Monsoon ◽

East Asian Summer Monsoon ◽

Asian Summer Monsoon ◽

East Asian ◽

Eastern China ◽

Snow Albedo ◽

Winter Snow ◽

Asian Summer

Abstract The relationship between Tibetan Plateau (TP) snow cover and the East Asian summer monsoon (EASM) has long been discussed, but the underlying mechanism remains controversial. In this paper, the snow–albedo and snow–hydrology feedbacks over the TP are investigated based on multiple sources of snow data for the period 1979–2011. The results indicate that winter snow cover plays an important role in cooling local air temperature through the snow–albedo effect; the TP surface net solar radiation in years with above-normal snow cover is approximately 18 W m−2 less than that in below-normal snow cover years. However, data analysis demonstrates that persistent effects of winter snow cover are limited to the period from winter to spring over most parts of the central and eastern TP. Therefore, the preceding snow cover over the central and eastern TP exerts little influence over either the in situ summer atmospheric heat source or the EASM, because of its limited persistence. In contrast, the effects of winter or spring snow cover anomalies over the western TP and the Himalayas can last until summer, and these anomalies further influence the EASM by modulating moisture transport to eastern China and favoring eastward-propagating synoptic disturbances that are generated over the TP. Generally, above-normal snow cover over the western TP and the Himalayas facilitates abundant summer precipitation between the Yangtze and Yellow River basins, which is confirmed by results from a regional Weather Research and Forecasting model simulation.

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Relationship between the Tibetan Plateau heating and East Asian summer monsoon rainfall

Geophysical Research Letters ◽

10.1029/2003gl017909 ◽

2003 ◽

Vol 30 (20) ◽

Cited By ~ 109

Author(s):

Huang‐Hsiung Hsu ◽

Xin Liu

Keyword(s):

Tibetan Plateau ◽

Summer Monsoon ◽

East Asian Summer Monsoon ◽

Monsoon Rainfall ◽

Asian Summer Monsoon ◽

East Asian ◽

Summer Monsoon Rainfall ◽

The Tibetan Plateau ◽

Asian Summer ◽

Asian Summer Monsoon Rainfall

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

Journal of Climate ◽

10.1175/jcli-d-13-00479.1 ◽

2014 ◽

Vol 27 (8) ◽

pp. 3052-3072 ◽

Cited By ~ 58

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.

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Origins of East Asian Summer Monsoon Seasonality

Journal of Climate ◽

10.1175/jcli-d-19-0888.1 ◽

2020 ◽

Vol 33 (18) ◽

pp. 7945-7965 ◽

Cited By ~ 4

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.

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The East Asian Summer Monsoon at mid-Holocene: results from PMIP3 simulations

Climate of the Past ◽

10.5194/cp-9-453-2013 ◽

2013 ◽

Vol 9 (1) ◽

pp. 453-466 ◽

Cited By ~ 23

Author(s):

W. Zheng ◽

B. Wu ◽

J. He ◽

Y. Yu

Keyword(s):

Tibetan Plateau ◽

Summer Monsoon ◽

East Asian Summer Monsoon ◽

Large Scale ◽

Asian Summer Monsoon ◽

East Asian ◽

Eastern China ◽

Large Scale Circulation ◽

Asian Summer ◽

Yangzi River

Abstract. Ten Coupled General Circulation Models (CGCMs) participated in the third phase of Paleoclimate Modelling Intercomparison Project (PMIP3) are assessed for the East Asian Summer Monsoon (EASM) in both the pre-Industrial (PI, 0 ka) and mid-Holocene (MH, 6 ka) simulations. Results show that the PMIP3 model median captures well the large-scale characteristics of the EASM, including the two distinct features of the Meiyu rainbelt and the stepwise meridional displacement of the monsoonal rainbelt. At mid-Holocene, the PMIP3 model median shows significant warming (cooling) during boreal summer (winter) over Eurasia continent that are dominated by the changes of insolation. However, the PMIP3 models fail to simulate a warmer annual mean and winter surface air temperature (TAS) over eastern China as derived from proxy records. The EASM at MH are featured by the changes of large-scale circulation over Eastern China while the changes of precipitation are not significant over its sub-domains of the Southern China and the lower reaches of Yangzi River. The inter-model differences for the monsoon precipitation can be associated with different configurations of the changes in large-scale circulation and the water vapour content, of which the former determines the sign of precipitation changes. The large model spread for the TAS over Tibetan Plateau has a positive relationship with the precipitation in the lower reaches of Yangzi River, yet this relationship does not apply to those PMIP3 models in which the monsoonal precipitation is more sensitive to the changes of large-scale circulation. Except that the PMIP3 model median captured the warming of annual mean TAS over Tibetan Plateau, no significant improvements can be concluded when compared with the PMIP2 models results.

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-6867-2014 ◽

2014 ◽

Vol 14 (13) ◽

pp. 6867-6879 ◽

Cited By ~ 55

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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