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.

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

2014 ◽  
Vol 14 (3) ◽  
pp. 3269-3300 ◽  
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 NASA/GEOS-4 assimilated meteorological fields to quantify the impacts of the East Asian summer monsoon (EASM) on interannual variations of summertime surface-layer O3 concentrations over China. With anthropogenic emissions fixed at year 2005 levels, model simulation for years 1986–2006 shows that the changes in meteorological parameters alone lead to interannual variations in 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 South China, as the interannual variations are relative to the average O3 concentrations over the 21 yr. Over 1986–2006, O3 concentration averaged over the whole 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 whole China with a nation mean lower O3 concentration by 2.0 ppbv (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 changes in the EASM strength are as important as the changes in anthropogenic emissions over 1986–2006 in influencing JJA surface-layer O3 concentrations in China.

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 Modeling a strong East Asian summer monsoon in a globally cool Earth, the MIS-13 case

2007 ◽  
Vol 3 (6) ◽  
pp. 1261-1282 ◽  
Author(s):  
Q. Z. Yin ◽  
A. Berger ◽  
E. Driesschaert ◽  
H. Goosse ◽  
M. F. Loutre ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Southern China ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Ice Sheet ◽  
The Tibetan Plateau ◽  
Three Dimension ◽  
Asian Summer

Abstract. Deep-sea and ice-core records show a significant reduced amplitude of the ice volume, temperature and greenhouse gases variations before Marine Isotope Stage (MIS) 11, about 400 000 years ago, with less warm (more glaciated) interglacials and less cold glacials. At the same time, the loess in northern China, the sedimentary core in the eastern Tibetan Plateau and the palaeosols in southern China all record an unusually warm and wet climate during MIS-13 (about 500 000 years ago), indicating an extremely strong East Asian summer monsoon. To understand this seeming paradox of a strong East Asian summer monsoon occurring during the cool MIS-13, a three-dimension Earth system Model of Intermediate complexity is used. Modeling results show that this very strong MIS-13 East Asian summer monsoon, identified from the precipitation, horizontal and vertical (omega) wind, and pressure (geopotential) fields, results from the astronomical and ice sheet forcings. North Hemisphere summer at perihelion both at 529 and 506 ka BP leads to an East Asian summer monsoon stronger than during the Pre-Industrial time. In addition, the ice sheets reinforce the East Asian summer monsoon through the propagation of a perturbation wave which is induced mainly by the Eurasian ice sheet and is influenced by the Tibetan Plateau.

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