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A new circulation index (ISW) that can realistically describe winter temperature variations over Southwest China is defined based on analysis of the NCEP/NCAR reanalysis data (version 1) and the observations at 585 stations in China. The study period is from January 1961 to February 2011. The relationship between ISW and general circulation patterns in East Asia is also analyzed. Results show that ISW successfully captures the variations in winter temperature over Southwest China. High ISW values correspond to the intensified Mongolian high, the weakened Aleutian low, increases in the strength of the Middle East westerly jet stream over the south of the Tibetan Plateau (TP), and decreases in the strength of the subtropical westerly jet over the north of the TP. Meanwhile, the East Asian trough deepens and extends southwestward, making it easier for the cold air mass from the north to intrude Southwest China along the trough. These circulation patterns lead to a decrease in winter temperature over Southwest China (and vice versa). In addition to the East Asian winter monsoon, the two westerly jets that dominate the upper level circulation over East Asia also exert important influences on winter temperature in Southwest China, especially the Middle East westerly jet to the south of the TP.

Here we use harmonic analyses to examine seasonal variations of China land rainfall, low-level winds, and atmospheric heating over East Asia during spring to summer and the associated subtropical summer monsoon activities. Our results indicate that the South China spring rainfall (SCSR) in March is the prophase of East Asian sub-tropical summer monsoon (EASSM), and the onset of EASSM and China summer rainy season starts in early April, characterized by the enhanced rainfall in South China and the seasonal reverse of zonal land-sea thermal contrast in sub-tropical East Asia. The EASSM onset is earlier than that of South China Sea summer monsoon, and it is active in east of 100°E and north of 20°N. Our analyses suggest that the subsequent heating appears over India-China Peninsula in March and South China in April and causes the low-level atmospheric warming and the zonal land-sea thermal contrast seasonal reverse in East Asian subtropics. The atmospheric heating over South China is the main force to drive the southwesterly winds, updrafts and strengthen the summer precipitation in South China.

Using a monthly precipitation dataset of 160 stations over China and a daily and monthly National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis dataset from 1961 to 2006, we here define an East Asian land-sea atmospheric heat source difference index ILSQD and investigate its relationship to summer rainfall in China and East Asian general circulation. The results show that ILSQD more closely reflects the anomalous variations in summer monsoon phenomena; in the high-index (HI) cases, the strong low-level southerlies over East China and the strong high-level westerlies over middle latitudes indicate an active summer monsoon, and vice versa in the low-index (LI) cases. This index also reflects summer rainfall anomalies over East China; in the HI (LI) cases rainfall increases (decreases) over North China and at the same time decreases (increases) over the mid-lower Yangtze River valley and the southern Yangtze River. Hence, ILSQD can be utilized as a summer monsoon index. There is also remarkable correlation between ILSQD in March and the following summer rainfall over the mid-lower Yangtze River valley. Finally, the Community Atmospheric Model Version 3.1 (CAM3.1) of NCAR is used to run numerical experiments, which verify that the anomalous summer precipitation in simulations is similar to that of diagnosis analysis based on the anomalous summer atmospheric heating forcing. Similarly, the atmospheric heating rate in March can force summer rainfall anomalies in the simulations just as observed in the data.

There exist thermal differences between the Tibetan Plateau (TP) and the plain east of the TP, and between land and sea in East Asia. The influence of the land-sea thermal contrast on the precipitation in East China has been widely investigated; however, a few studies have paid attention to the role of the TP-plain thermal difference. Thus, using the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data and the observation data of China from 1951 to 2007, the area-mean temperature difference between the TP (27.5°–40°N, 80°–100°E) and the plain (27.5°–40°N,110°–120°E) at 500 hPa is defined as an index (dexT-C) of the TP-plain thermal difference in East Asia. The relationship between the dexT-C and East Asian general circulation and the rainfall in China in the summer has been explored. Diagnostic analysis and numerical simulation show that the TP-plain thermal difference is closely related to the rainfall over West China (90°–110°E) in the summer. High values of the dexT-C correspond to the large thermal difference between the TP and the plain, strengthening the heat low over the TP, southward of the northwestern Pacific subtropical high, southern flood and northern drought in West China (90°–110°E), and vice versa. From 1951 to 2007, the variation in dexT-C exhibits a remarkable oscillation and ascending trend, and the abnormal rainfall pattern over West China (90°–110°E) also changes from “northern flood and southern drought” to “southern flood and northern drought”. The above research is favorable to knowing how the two-stage thermal differences influence summer rainfall in China.

We here report our recent research results on the climatic features of Tibetan thermodynamic functions and their impacts on the regional climates of the Northern Hemisphere. The results show that the thermodynamic processes over the Tibetan Plateau not only strongly influence the Asian monsoon and precipitation, but also modulate the atmospheric circulation and climate over North America and Europe through stimulating the large-scale teleconnections such as the Asian-Pacific oscillation and affect the atmospheric circulation over the southern Indian Ocean. The Tibetan climate may be affected by sea surface temperatures over the tropical Pacific. On the other hand, the Tibetan climate also affects the atmosphere-ocean interactions in the tropics and mid-latitudes of the Pacific by the atmospheric circulation over the North Pacific. In spring and summer, the thermodynamic anomalies on the plateau affect the subtropical high pressure, the Hadley circulation, and the intertropical convergence zone over the Pacific, and then modulate the development of the El Nino/Southern Oscillation (ENSO). It is necessary to study the forecasting methods for the development of ENSO from the Tibetan climate anomaly. This result also embodies the essence of interactions among land, atmosphere, and ocean over the Northern Hemisphere. Since the previous studies focused on impacts of the plateau on climates in the Asian monsoon regions, it is essential to pay more attention to studying the roles of the plateau in the Northern Hemispheric and even global climates.

On the basis of NCEP/NCAR version I daily reanalysis data from 1971 to 2000 and by the methods of inverse calculation, correlation analysis and comparative analysis, the influences of atmospheric heat source (AHS) over the Tibetan Plateau on the large-scale AHS and the general circulation in summer are studied in this paper. The results show that AHS over the plateau in summer may trigger a heat source wavetrain propagating northeastward along the coast from the East Asian continent and West Pacific to Bering Strait-Arctic or even North America. In addition, if AHS over the eastern plateau is intense, South Asian High moves to southeast and West Pacific subtropical high moves to southwest; on the contrary, if AHS over the eastern plateau is weak, South Asian High moves to northwest and West Pacific subtropical high moves to northeast. Therefore, South Asian High and West Pacific subtropical high move in the horizontally-opposite directions in terms of interannual variation, for which AHS over the eastern plateau seems to be thermodynamically responsible.

Through analyzing the yearly average data obtained from 123 regular meteorological observatories located in the Tibetan Plateau (T-P), this article studies the characteristics of climate change in T-P in the last 40 years. From the distribution of the linear trend, it can be concluded that the southeastern part of T-P becomes warmer and wetter, with an obvious increase of rainfall. The same characteristics are found in the southwestern part of T-P, but the shift is smaller. In the middle of T-P, temperature and humidity obviously increase with the center of the increase in Bangoin-Amdo. The south of the Tarim Basin also exhibits the same tendency. The reason for this area being humid is that it gets less sunshine and milder wind. The northeastern part of T-P turns warmer and drier. Qaidam Basin and its western and southern areas are the center of this shift, in which the living environment is deteriorating. Analyzing the characteristics of the regional average time series, it can be found that in the mid-1970s, a significant sudden change occurred to annual rainfall, yearly average snow-accumulation days and surface pressure in the eastern part of T-P. In the mid-1980s, another evident climatic jump happened to yearly average temperature, total cloud amount, surface pressure, relative humidity, and sunshine duration in the same area. That is, in the mid 1980s, the plateau experienced a climatic jump that is featured by the increase of temperature, snow-accumulation days, relative humidity, surface pressure, and by the decrease of sunshine duration and total cloud amount. The sudden climatic change of temperature in T-P is later than that of the global-mean temperature. From this paper it can be seen that in the middle of the 1980s, a climatic jump from warm-dry to warm-wet occurred in T-P.

Using the dataset of 1998 TIPEX, the data of 6 automatic heat balance observational stations (AWS) from May to August 1998, a dataset of 52 surface observational stations over the Tibetan Plateau (TP) and its adjacent region, the daily rainfall amounts from about 300 stations in China, the outgoing longwave radiation (OLR) data received by the National Satellite Meteorological Center(NSMC) of China, and TBB data from GMS remote sensing of Japan, the characteristics of the seasonal variation of the surface total heating over TP and its surrounding area in summer 1998 and its relationship with the convection over the subtropical area of the western Pacific is studied in this paper. The results show that the surface total heating over TP had a close relationship with the onset of the rainy season, and after the onset of the rainy season, the regional mean surface total heating over TP decreased distinctly. Furthermore, the regional mean surface total heating over TP had very good negative correlation with TBB over the subtropical area of the western Pacific along 20–30°N, which shows that the surface total heating over TP was able to affect the convection over the subtropical area of the western Pacific.

Using the 1961–1995 monthly averaged meteorological data from 148 surface stations in the Qinghai-Xizang Plateau (QXP) and its surrounding areas, calculation of the 35-year atmospheric heat source/sink ( ) and an analysis on its climatic features and relation to rainfall in China have been made. It is found that on the average, the atmospheric heat source over the QXP is the strongest in June (78 W / m2) and cold source is the strongest in December (−72 W/m2). The sensible heat of the surface increases remarkably over the southwest of the QXP, causing the obvious increase of there in February and March, which makes a center of the atmospheric heat source appear over the north slope of the Himalayas. Afterwards, this center continues to intensify and experiences noticeable migration westwards twice, separately occurring in April and June. The time when the atmosphere over the east of the QXP becomes heat source and reaches strongest is one month later than that over the southwest of the QXP. In summer, the latent heat of condensation becomes a heating factor as important as the sensible heat and is also a main factor that makes the atmospheric heat source over the east of the QXP continue growing. On the interdecadal time scale, (Q1) of the QXP shows an abrupt change in 1977 and a remarkable increase after 1977. The atmospheric heat source of the spring over the QXP is a good indicator for the subsequent summer rainfall over the valleys of the Changjiang and Huaihe rivers and South China and North China. There is remarkable positive correlation between the QXP heat source of summer and the summer rainfall in the valleys of the Changjiang River.

Using 1961–1995 monthly atmospheric apparent heat source/sink/〈Q 1〉 over the Qinghai-Xizang Plateau (QXP) and reanalysis data of NCEP/NCAR, and 1961–1994 monthly SST of UK/GISST2, the statistical study is undertaken on the QXP heat source/sink in relation to both atmospheric circulation in Asia and El Nino/La Nina events. It is discovered that there exists noticeable interaction in a quasi-4-year period among the 〈Q 1〉 of the QXP, low-level meridional winds east of the QXP, low-level zonal winds in the equatorial Pacific, SST in the equatorial eastern Pacific, and the circulation at mid and high latitudes north of the QXP. They have difference in phase. The cold source intensity of the QXP in winter favours a low-level meridional wind anomaly to prevail in the mainland of China and its coast east of the QXP and to last until the subsequent autumn. The wind anomaly can induce a low-level zonal wind anomaly of the tropic Pacific that finally affects an El Nino/La Nina event in the autumn and subsequent winter. The event in autumn/winter has effect on the deep trough position and cold air track of East Asia in next winter that influences the intensity of the QXP winter cold source.

A preliminary study is given on the bulk transfer coefficients and surface fluxes over the Tibetan Plateau, on the basis of data from four sets of AWS in Tibet from July 1993 to March 1999 according to P.R. China-Japan Cooperation Research Project on Asian Monsoon Mechanism. The surface roughness lengths are decided by the logarithmic wind law under neutral conditions using the least square method, the value at each station is scattered and seasonal mean is obtained. The bulk transfer coefficients for momentum and heat are estimated using the flux-profile relationships, means of the bulk transfer coefficients for momentum and heat are 4.44×10-3∼4.75×10-3 and 6.02×10-3∼6.40×10-3, respectively. The surface fluxes of momentum, sensible heat and latent heat are computed by bulk transfer formulations, sum of sensible and latent heat at each station is about 100 W/m2. In addition, diurnal and seasonal variations of the bulk transfer coefficients and surface fluxes as well as the relations among bulk transfer coefficients, bulk Richardson number and surface wind speed are discussed in detail using a composite method. A possible relationship between surface fluxes and monsoon over the Tibetan Plateau is suggested, i.e., the surface heat transfer on the Eastern Tibetan Plateau is dominated by the sensible heat flux and latent heat flux jointly in the pre-monsoon and latent heat flux mainly during the monsoon.

Vsmg an indirect method, aerosol optical depths (AODs) are calculated based on atmospheric visibility and water vapor pressure measured at 94 key climate stations in western China (west of 100Έ) over 1961–2005. Inferred AODs are compared with the MODIS satellite measurements for year of 2004. Results show that AODs averaged over 1961–2005 exhibit large values in southern Xinjiang basin and south of Tianshan mountains, and there is another high AODs in the eastern TP. Inferred AODs in western China show over southern Xinjiang basin and south of Tianshan mountains the strength of AODs increase during the period from 1960s to 1980s and decrease after 1990s. As far as AODs over the eastern TP are concerned, the strength decreases since 1960s and reach the minimum value during the turn of 21 century. Statistical analysis shows that variations in AODs correlate with the changes in precipitation and air temperature in western China from 1961 to 2005. The results show that the increases in AOD are coincident with the increases in rainfall and air temperature in the northern Xinjiang, drought in rainfall and the cooling in surface air temperature in the eastern TP.

[i] Eastern China experienced a series of severe floods during the summer of 1998. These floods are shown to be consistent with the propagation and activity of the 30 - 60 day intraseasonal oscillation (ISO) over the western North Pacific (WNP), where the monsoon trough and the subtropical anti-cyclone appear as an anti-clockwise propagation with the enhanced and suppressed convective anomalies in a 30-60 day period. The Meiyu circulation pattern in the lower atmosphere successively dominates the WNP, which results in southern China and the Yangtze River valley suffering much more rainfall and floods than normal. There are remarkable signals of 30-60-day ISO in convective anomalies over the Bay of Bengal and east of Philippine Sea. During the cycle ofthe 30-60 day ISO, these convective anomalies move towards the South China Sea (SCS), where they affect the convective activity of the SCS summer monsoon, therefore maintaining the cycle of 30-60 day ISO over the WNP.

Estimates of the time and space variability of the atmospheric heat source over Tibet are presented for the summer of 1979. These estimates rely on new data from the People's Republic of China allowing a better assessment of the surface heat fluxes, and on new satellite data from Nimbus-7 giving the radiation balance at the top of the atmosphere. The estimates of the atmospheric heat source turned out to be considerably smaller than those provided earlier in the literature, mainly because of different assumptions of the drag coefficient. The atmospheric heat source over Tibet is mainly modulated by the release of latent heat. Over the southeastern and southwestern plateau regions the heat source appears to be in phase with the precipitation yield of the Indian summer monsoon, whereas central Tibet reveals an out-of-phase behavior. Over western Tibet there appears to be hardly any net import of moisture from outside the region, whereas the maintenance of the hydrological cycle over eastern Tibet requires moisture flux convergence from outside the region of up to 40 percent of the mean rainfall, in agreement with what is known about the surface hydrology of Tibet.

The atmospheric heat source strength over western Tibet has been computed for the period beginning with the last ten days in May, 1979 and extending through August, 1979. Our results show a significantly smaller heat source than that obtained by other authors. The discrepancy is mainly due to adjustments in the drag coefficient suggested by observations and numerical modeling experiments. We subdivided western Tibet into northern and southern parts. In the north sensible heating,SH, provides the dominant input into the atmospheric heat source, whereas in the southern part latent heat,LP, offers a significant contribution after the start of the rainy season.

For better understanding the mechanism of monsoon formation and designing the numerical simulation of the general atmospheric circulation, a new approach of calculating atmospheric radiation is proposed to investigate the distribution of the atmospheric heat source, and the budget of heat component is recalculated. The results show that there is a tremendous atmospheric heat source region over central India, northeast of the Bay of Bengal, east of the South China Sea and about 10 °N at the west Pacific, among which the heating center with a maximum heating rate of 8 °C/day is located over the Bay of Bengal and the average rate in the Plateau is about 1 °C/day.