Tibetan Plateau Heating Research Articles

The severity of drought and precipitation prediction in the eastern fringe of the Tibetan Plateau

The trend, severity, and duration of drought in the eastern fringe of the Tibetan Plateau (EFTP) have been investigated using the Mann-Kendall (M-K) trend test, standardized precipitation index (SPI), and generalized extreme value (GEV), using data obtained from 438 rainfall stations and reanalysis datasets for the period 1961–2014. A recent drought trend is evident from a decrease in rainfall, with this mainly occurring on the eastern slope of the TP (< 3000-m elevation); this is attributed to downward air flows over the eastern slope of the Tibetan Plateau (TP) induced by TP heating. Recent droughts have also been more severe, with these again mostly occurring on the eastern slopes. The duration of drought illustrates that extreme droughts are becoming more frequent. The study also predicted summer precipitation, due to its crucial role in drought research in the EFTP. Results show that the preceding May–June–July (MJJ) averaged column-integrated meridional water vapor transport (MWVT) from the South China Sea (SCS), Philippine Sea, and tropical western Pacific is a vital predictor of summer precipitation in the EFTP. A partial least squares (PLS) regression prediction model is therefore constructed, using the leading PLS components of preceding MJJ-averaged column-integrated MWVT. Compared to the observed summer rainfall, the PLS prediction model performs an excellent reconstructed skill with a correlation of 0.81 (1961–2006) and exhibits a promising forecast skill with a correlation of 0.67 (2007–2014). Results suggest that southerly moisture transport in early summer would help prevent summer drought in the EFTP.

Interannual variation of the northward movement of the South Asian High towards the Tibetan Plateau and its relation to the Asian Summer Monsoon onset

The interannual variation of the northward movement of the upper-level South Asian High (SAH) towards the Tibetan Plateau (TP) in the early summer and its relation to the Asian summer monsoon (ASM) onset are still unclear. This study shows that when the ASM onset occurs earlier, there is an anomalous westerly/easterly in the lower/upper troposphere, accompanying an anomalous ascending motion over the southern part of Asia. Meanwhile, cyclonic circulation anomalies occur over the Arabian Sea, the Bay of Bengal, and the South China Sea and are conducive to the earlier development and spread of the deep convection and atmospheric heating. Consequently, the warm center in the mid-upper troposphere surrounding the TP generates earlier in May, resulting in an earlier reversal of the meridional temperature gradient over the southern slope of the TP. Based on the thermal wind relationship, the vertical shear of the zonal wind reverses earlier and finally the SAH shifts over the TP earlier. The opposite is true when the ASM onset occurs later. Compared with the evolution of the diabatic heating over South Asia from May to June, there is no significant difference in the diabatic heating over the TP between the earlier and later years, indicating that the ASM heating may play a more important role in the northward movement of the SAH than the TP heating. Therefore, the ASM heating is essential to the interannual variation of the northward shift of the SAH towards the TP in the early summer.

Potential regulation on the climatic effect of Tibetan Plateau heating by tropical air–sea coupling in regional models

Based on the conventional weather research and forecasting (WRF) model and the air–sea coupled mode WRF-OMLM, we investigate the potential regulation on the climatic effect of Tibetan Plateau (TP) heating by the air–sea coupling over the tropical Indian Ocean and western Pacific. Results indicate that the TP heating significantly enhances the southwesterly monsoon circulation over the northern Indian Ocean and the South Asia subcontinent. The intensified southwesterly wind cools the sea surface mainly through the wind-evaporation-SST (sea surface temperature) feedback. Cold SST anomaly then weakens monsoon convective activity, especially that over the Bay of Bengal, and less water vapor is thus transported into the TP along its southern slope from the tropical oceans. As a result, summer precipitation decreases over the TP, which further weakens the TP local heat source. Finally, the changed TP heating continues to influence the summer monsoon precipitation and atmospheric circulation. To a certain extent, the air–sea coupling over the adjacent oceans may weaken the effect of TP heating on the mean climate in summer. It is also implied that considerations of air–sea interaction are necessary in future simulation studies of the TP heating effect.

Quantitative identification of moisture sources over the Tibetan Plateau and the relationship between thermal forcing and moisture transport

Despite the importance of the Tibetan Plateau (TP) to the surrounding water cycle, the moisture sources of the TP remain uncertain. In this study, the moisture sources of the TP are quantitatively identified based on a 33-year simulation with a horizontal resolution of 1.9° × 2.5° using the Community Atmosphere Model version 5.1 (CAM5.1), in which atmospheric water tracer technology is incorporated. Results demonstrate that the major moisture sources differ over the southern TP (STP) and northern TP (NTP). During the winter, Africa, the TP, and India are the dominant source regions, contributing nearly half of the water vapour over the STP. During the summer, the tropical Indian Ocean (TIO) supplies 28.5 ± 3.6% of the water vapour over the STP and becomes the dominant source region. The dominant moisture source regions of the water vapour over the NTP are Africa (19.0 ± 2.8%) during the winter and the TP (25.8 ± 2.4%) during the summer. The overall relative contribution of each source region to the precipitation is similar to the contribution to the water vapour over the TP. Like most models, CAM5.1 generally overestimates the precipitation over the TP, yielding uncertainty in the absolute contributions to the precipitation. Composite analyses exhibit significant variations in the TIO-supplied moisture transport and precipitation over the STP during the summer alongside anomalous TP heating. This relationship between moisture transport from the TIO and the TP heating primarily involves the dynamic change in the TIO-supplied moisture flux, which further controls the variation in the TIO-contributed precipitation over the STP.

The modulation of Tibetan Plateau heating on the multi-scale northernmost margin activity of East Asia summer monsoon in northern China

Abstract The northernmost margin of East Asian summer monsoon (EASM) could well reflect wet/dry climate variability in the EASM marginal zone (northern China). The study shows that EASM occurs in northern China from Meiyu period to midsummer, and it is also the advancing period of the northern margin of EASM (NMEASM) before the 43rd pentad. NMEASM activity exhibits multi-scale variability, at cycles of 2–3-yr, 4–6-yr and 9–12-yr, which respond not only to EASM intensity but also to westerly circulation anomaly, exhibiting the mid-latitude Eurasian waves and the high-latitude Eurasian teleconnection (EU) patterns. The positive anomalies of Silk Road pattern and EU pattern in recent two decades contribute to the enhanced west-ridge and east-trough anomaly around 120°E over northern China, leading to divergence of moisture flux and north wind anomaly, which is helpful for southward western pacific subtropical high (WPSH) and southward NMEASM. Negative Eurasian pattern along subtropical Jet leads to anticyclone anomaly over south of the Yangtze River, deep trough and north wind anomaly along the west coast of the subtropical Pacific, contributing to southward WPSH and NMEASM at the cycle of 4–6-yr. Remote forcing sources of these anomalous Eurasian waves include North Europe, north of Caspian Sea, Central Asia, Tibetan Plateau and the west of Lake Baikal; the south of Lake Baikal is a local forcing region. The Tibetan Plateau heating and snow cover could modulate Eurasian wave pattern at multi-scale, which could be used as prediction reference of multi-scale NMEASM.

Direct radiative effects of dust aerosols emitted from the Tibetan Plateau on the East Asian summer monsoon – a regional climate model simulation

Abstract. While dust aerosols emitted from major Asian sources such as Taklimakan and Gobi deserts have been shown to have strong effect on Asian monsoon and climate, the role of dust emitted from Tibetan Plateau (TP) itself, where aerosols can directly interact with the TP heat pump because of their physical proximity both in location and elevation, has not been examined. This study uses the dust-coupled RegCM4.1 regional climate model (RCM) to simulate the spatiotemporal distribution of dust aerosols originating within the TP and their radiative effects on the East Asian summer monsoon (EASM) during both heavy and light dust years. Two 20-year simulations with and without the dust emission from TP showed that direct radiative cooling in the mid-troposphere induced by the TP locally produced dust aerosols resulted in an overall anticyclonic circulation anomaly in the low troposphere centered over the TP region. The northeasterly anomaly in the EASM region reduces its strength considerably. The simulations found a significant negative correlation between the TP column dust load produced by local emissions and the corresponding anomaly in the EASM index (r = −0.46). The locally generated TP dust can cause surface cooling far downstream in Bohai Gulf and the China–North Korea border area through stationary Rossby wave propagation. Although dust from within TP (mainly Qaidam Basin) is a relatively small portion of total Asian aerosols, its impacts on Asian monsoon and climate seems disproportionately large, likely owning to its higher elevation within TP itself.

Possible effect of the Tibetan Plateau on the \u201cupstream\u201d climate over West Asia, North Africa, South Europe and the North Atlantic

We conduct several experiments using a fully-coupled climate model to understand the role of Tibetan Plateau (TP) surface heating in the climate variations over West Asia, South Europe, North Africa, and the North Atlantic during summer. Emphasis has been placed on the physical processes and responsible mechanisms that involve the shift of the Hadley cell and the important features of rotational and divergent response of the atmosphere to the TP heating. The relative importance of the TP to the Asian continent is also analyzed. A heating of the TP surface leads to local increases in tropospheric temperature and the thickness of the air column due to the so-called air pumping effect. In the upper troposphere, the South Asian high intensifies and extends westward. To the west of TP, especially in West Asia, South Europe, North Africa, and the North Atlantic, distinguished Rossby wave responses to the TP heating occur with anomalous high pressure and uniform warming in the entire troposphere. Correspondingly, descending motions intensify and precipitation decreases. However, the tropical Sahel rainfall increases because of a northward shift of the Atlantic intertropical convergence zone and the anomalous westerlies due to the weakening of the southeastern portion of the Atlantic subtropical high. These effects of the TP heating explain a remarkable portion of the effects by the Asian continent heating. In addition, the impacts of different magnitudes of TP surface heating are also discussed.

Double‐mode adjustment of Tibetan Plateau heating to the summer circumglobal teleconnection in the Northern Hemisphere

ABSTRACTA quasi‐stationary circumglobal teleconnection (CGT) in the Northern Hemisphere in summer is associated with summer droughts and floods and exhibits some vorticity anomalies. The CGT anomaly and its forcing sources were explored based on reanalysis data and the EI Nino 3.4 index. The term ∂v′/∂x was used to describe the multi‐scale variability of vorticity and the CGT anomaly, which had a 7‐wavenumber and a small interannual amplitude of ∂v′/∂x from 1987 to 2000 but a large amplitude from 2000 to 2010. The interannual CGT intensity was enhanced by an EI Nino sea surface temperature pattern in spring via key forcing sources that led to an enduring effect on the summer circulation; it was also a response to anomalies in Tibetan Plateau (TP) heating in spring–summer in two ways. First, increasing TP heating in the mid‐eastern TP caused an eastward shift and northerly extension of the South Asian High (SAH), which exhibited a Tibetan‐mode SAH as well as a 7‐wavenumber CGT anomaly. This enhanced the CGT over Eurasia and extended the wave pattern of the EI Nino contribution over the North Pacific and Eurasia. Second, increased snow cover in the west of the TP could have offset the TP heating effect and adjusted the position and intensity of the Tibetan‐mode SAH. This phenomenon weakened vorticity and wave amplitude and finally led to a weak CGT anomaly. This finding indicates a coupled effect of double‐mode TP heating (i.e. both heating and TP snow cover) on the CGT anomaly, which reveals the linkage of TP heating with weather over Eurasia and North America that could be predicted by TP heating and other factors.

Impacts of the global sea surface temperature anomaly on the evolution of circulation and precipitation in East Asia on a quasi-quadrennial cycle

Based on multi-source observational data from 1979 to 2013, we investigate the evolution of the global sea surface temperature anomaly (SSTA) on a quasi-quadrennial cycle and its impact on the seasonal evolution of circulation and precipitation in East Asia. We do this by using principal oscillation pattern analysis and associated correlation pattern analysis, together with numerical experiments from an atmospheric general circulation model. The results indicate that the global SSTA exerts profound impacts on the East Asian climate anomaly, while distinct responses exist between the SSTA developing and decaying stages. From winter to autumn in the developing year, southern China is typically wetter than normal. In the decaying year, however, the precipitation over most parts of East Asia is above normal from winter to spring, and the main rainfall band meandering from the Yangtze River to South Japan is enhanced in summer. During the developing and decaying years, an upper-level anomalous cyclone moves from Northeast Asia to the Tibetan Plateau, and then retreats back. A low-level anomalous cyclone occurs over Northeast Asia in spring, but weakens in summer and then strengthens gradually from autumn to the following summer. An anomalous Philippine Sea anticyclone occurs in winter and spring, but is replaced by an anomalous cyclone in summer before reappearing and persisting from autumn to the decaying year. The abrupt change in circulation patterns in summer of the developing year might be related to the anomalous weakening of the Tibetan Plateau heating. These anomalies can be attributed to the combined effects of the global large-scale heating, regional-scale oceanic forcing, and thermal feedback of the land.

The link between Tibetan Plateau monsoon and Indian summer precipitation: a linear diagnostic perspective

The thermal forcing of the Tibetan Plateau (TP) is analyzed to investigate the formation and variability of Tibetan Plateau Summer Monsoon (TPSM), which affects the climates of the surrounding regions, in particular the Indian summer monsoon precipitation. Dynamic composites and statistical analyses indicate that the Indian summer monsoon precipitation is less/greater than normal during the strong/weak TPSM. Strong (weak) TPSM is associated with an anomalous near surface cyclone (anticyclone) over the western part of the Tibetan Plateau, enhancing (reducing) the westerly flow along its southern flank, suppressing (favoring) the meridional flow of warm and moist air from the Indian ocean and thus cutting (providing) moisture supply for the northern part of India and its monsoonal rainfall. These results are complemented by a dynamic and thermodynamic analysis: (i) A linear thermal vorticity forcing primarily describes the influence of the asymmetric heating of TP generating an anomalous stationary wave flux. Composite analysis of anomalous stationary wave flux activity (after Plumb in J Atmos Sci 42:217–229, 1985) strongly indicate that non-orographic effects (diabatic heating and/or interaction with transient eddies) of the Tibetan Plateau contribute to the generation of an anomalous cyclone (anti-cyclone) over the western TP. (ii) Anomalous TPSM generation shows that strong TPSM years are related to the positive surface sensible heating anomalies over the eastern TP favoring the strong diabatic heating in summer. While negative TPSM years are associated with the atmospheric circulation anomalies during the preceding spring, enhancing northerly dry-cold air intrusions into TP, which may weaken the condensational heat release in the middle and upper troposphere, leading to a weaker than normal summer monsoon over the TP in summer.

Numerical simulation of Tibetan Plateau heating anomaly influence on westerly jet in spring

The intensity and location of the westerly jet (WJ) in the mid-latitudes of the Northern Hemisphere has been closely related to weather and climate changes in Eurasia. In this paper, we analyzed the seasonal and inter-annual variations in the strength and position of the WJ, using the NCEP-DOE reanalysis II (NCEP) data. Spring is the period that the Tibetan Plateau (TP) transits from a cold to a warm condition, and at the same time the WJ weakens and moves northward. Correlation analysis showed that the westerly wind over the north (south) of the TP has a significant positive (negative) correlation with the TP surface temperature in spring during 1979–2013 (99.9% significance level). In spring, surface sensible heat release dominates thermal conditions of the TP, while the contribution of latent heat becomes important in summer. We conducted three numerical experiments to determine the effects of the TP surface sensible heat flux anomaly in spring on the intensity and location of the WJ using the community atmosphere model 5 (CAM5). Experimental results indicated that changing the TP surface sensible heat flux can produce changes in the TP heat sources. When the TP sensible heat flux is switched off (TPSHL), the TP surface has a lower temperature and no longer heats up the middle and upper troposphere, and leads to a maximum cooling of –1.2∘C at 200 hPa over the TP with a significance level of 95%. In spring, the abnormal low temperature over the TP caused the WJ to strengthen and move southward compared with the control experiment (CTL), and this results in a westerly (easterly) wind anomaly over the south (north) of the TP with a significance level of 95%. We obtained the opposite conclusion from the comparison of the enhanced TP surface sensible heat flux (TPSHH) with CTL test results. In TPSHL, the WJ is still steadily located near 30∘N in May as well as April, i.e., the first northward jump occurs from May to June which is a delay of one month compared to CTL. While in TPSHH, the WJ moves northward approximately 10∘ of latitude from April to May which is 5∘ larger than CTL. Thus, the strength and north–south migration of WJ is closely linked to the TP heat source, especially during the spring–summer seasonal transition period, while TP surface temperature increased significantly and showed early signal compared to the surroundings with the global warming. Therefore, considerable attention must be paid to the location and strength of the WJ with respect to the sensible heat flux over the TP.

Characteristics and Mechanisms of the Subseasonal Eastward Extension of the South Asian High

Abstract This study investigates the features of eastward extension of the South Asian high (SAH) and its connection with diabatic heating and rainfall over eastern Asia on subseasonal time scales. The causes of SAH’s eastward extension are examined by potential vorticity (PV) diagnosis with emphasis on the joint role of diabatic heating feedback and midlatitude wave train. The SAH’s eastward extension features eastward propagation of a wave train across Eurasia. Among the wave train, the migration of weak high from the western flank of the Tibetan Plateau (TP) to the east of TP contributes to the SAH’s eastward extension at the early stage. When the SAH approaches its easternmost position, a strong negative PV (positive geopotential height) center prevails to the east of the TP at 200 hPa. The associated anomalies in diabatic heating and rainfall include the anomalous heating and above-normal rainfall over the South China Sea (SCS) and subtropical western Pacific occurring 12 days before the SAH’s easternmost stretch, and then anomalous cooling and below-normal rainfall over the southern foot of the TP and southern China and heating and above-normal rainfall over the northern TP and northern China a week later. The anomalous heating and ascending motion over the northern TP and northern China act to increase negative PV locally at 200 hPa. The cooling and descending induce positive PV over southern China. The north–south dipolar structure of PV anomaly with the climatological northerly flow is favorable to southward advection of a negative PV anomaly at 200 hPa. The anomalous heating over the SCS–western Pacific helps to develop a below-normal rainfall condition over southern China via inducing a lower-level anomalous cyclone over coastal region. These processes are conducive to the SAH’s eastward extension at its later stage.

Impacts of Abnormal Heating of Tibetan Plateau on Rossby Wave Activity and Hazards Related to Snow and Ice in South China

In January 2008, extreme freezing rain struck South China. At the same time, the Tibetan Plateau (TP) was experiencing pronounced surface heating. The characteristics of this extreme weather and its linkage to the TP surface heating anomaly were analyzed in this paper. The results show that (1) anomalous heating of the TP helps to form and sustain the Siberian blocking high, which is important for persistent southward flow of dry and cold Siberian air; (2) TP heating helps the moisture flux move more north and strengthens the southerly wind above 850 hPa; (3) there are two Rossby wave trains at 500 hPa and the layers above it (at about 20∘N–40∘N). Correlation analysis reveals that TP heating anomalies are closely associated with these Rossby wave trains; (4) the Rossby wave propagates downstream from the TP to South China in the mid and high layers of the atmosphere when the TP changes swiftly from a heat sink to a heat source. This implies that anomalous heating of the TP may stimulate the Rossby wave train to propagate downward in midlatitudes.

The persistent heavy rainfall over southern China in June 2010: Evolution of synoptic systems and the effects of the Tibetan Plateau heating

This study investigates influencing weather systems for and the effect of Tibetan Plateau (TP)’s surface heating on the heavy rainfall over southern China in June 2010, focusing on the four persistent heavy rainfall events during 14–24 June 2010. The major weather systems include the South Asian high, midlatitude trough and ridge, western Pacific subtropical high in the middle troposphere, and shear lines and eastward-moving vortices in the lower troposphere. An ensemble of convection-permitting simulations (CTL) is carried out with the WRF model for these rainfall events, which successfully reproduce the observed evolution of precipitation and weather systems. Another ensemble of simulations (SEN) with the surface albedo over the TP and its southern slope changed artificially to one, i.e., the surface does not absorb any solar heating, otherwise it is identical to CTL, is also performed. Comparison between CTL and SEN suggests that the surface sensible heating of TP in CTL significantly affects the temperature distributions over the plateau and its surroundings, and the thermal wind adjustment consequently changes atmospheric circulations and properties of the synoptic systems, leading to intensified precipitation over southern China. Specifically, at 200 hPa, anticyclonic and cyclonic anomalies form over the western and eastern plateau, respectively, which enhances the southward cold air intrusion along the eastern TP and the divergence over southern China; at 500 hPa, the ridge over the northern plateau and the trough over eastern China are strengthened, the southwesterly flows along the northwestern side of the subtropical high are intensified, and the positive vorticity propagation from the plateau to its downstream is also enhanced significantly; at 850 hPa, the low-pressure vortices strongly develop and move eastward while the southwesterly low-level jet over southern China strengthens in CTL, leading to increased water vapor convergence and upward motion over the precipitation region.

Time-lagged impact of spring sensible heat over the Tibetan Plateau on the summer rainfall anomaly in East China: case studies using the WRF model

This study explores the time-lagged impact of the spring sensible heat (SH) source over the Tibetan Plateau (TP) on the summer rainfall anomaly in East China using the Weather Research and Forecasting model. Numerical experiments for 2003 indicate that a spring SH anomaly over the TP can maintain its impact until summer and lead to a strong atmospheric heat source, characterized both by the enhanced SH over the western TP and enhanced latent heat of condensation to the east. Wave activity diagnosis reveals that the enhanced TP heating forces a Rossby wave train over the downstream regions. A cyclonic response over the northeast TP brings about a low-level northerly anomaly over northern China, while an anticyclonic response over the western Pacific enhances the subtropical high and the low-level southerly on its western flank. As a result, cold and dry airflow from mid-high latitudes, and warm and wet airflow from tropical oceans converge around the Huaihe River basin. In addition, warm advection originating from the TP induces vigorous ascending motion over the convergence belt. Under these favorable circulation conditions the eastward-propagating vortexes initiated over the TP intensify the torrential rainfall processes over the Huaihe River basin. In contrast, additional experiments considering the year 2001 with weak spring SH over the TP and an overall southward retreat of the summer rainfall belt in East China further demonstrate the role of spring SH over the TP in regulating the interannual variability of EASM in terms of wave activity and synoptic disturbances.

Signatures of Tibetan Plateau heating on Indian summer monsoon rainfall variability

Despite recent challenges, conventional wisdom has held that heating over the Tibetan Plateau leads to increased Indian summer monsoon rainfall via enhancement of cross‐equatorial circulation aloft, and a concurrent strengthening of both the Somali Jet and westerly winds that bring moisture to southern India. We show that such heating, quantified by monthly estimates of moist static energy in the atmosphere just above the surface, correlates with summer monsoon rainfall, but only in the early (20 May to 15 June) and late (September 1 to 15 October) monsoon season. Correlations during the main monsoon season (15 June to 31 August) are small and insignificant. The positive correlations with early and late monsoon season, however, allow for heating over Tibet to modulate as much as ~30% of the total rainfall. Furthermore, we demonstrate that heating over Tibet is independent of the El Niño Southern Oscillation, so that together they explain a substantial portion of variability in the early and late season rainfall, providing potential predictability. These links may also explain the wet conditions over India during early Holocene time and provide a quantitative link between a rise of Tibet and stronger Somali Jet.

Response of water resources to climate change and its future trend in the source region of the Yangtze River

In this paper, variations of surface water flow and its climatic causes in China are analyzed using hydrological and meteorological observational data, as well as the impact data set (version 2.0) published by the National Climate Center in November 2009. The results indicate that surface water resources showed an increasing trend in the source region of the Yangtze River over the past 51 years, especially after 2004. The trend was very clearly shown, and there were quasi-periods of 9 years and 22 years, where the Tibetan Plateau heating field enhanced the effect, and the plateau monsoon entered a strong period. Precipitation notably increased, and glacier melt water increased due to climate change, all of which are the main climatic causes for increases in water resources in the source region. Based on global climate model prediction, in the SRESA1B climate change scenarios, water resources are likely to increase in this region for the next 20 years.

Dominant control of the South Asian monsoon by orographic insulation versus plateau heating

The Tibetan plateau, like any landmass, emits energy into the atmosphere in the form of dry heat and water vapour, but its mean surface elevation is more than 5 km above sea level. This elevation is widely held to cause the plateau to serve as a heat source that drives the South Asian summer monsoon, potentially coupling uplift of the plateau to climate changes on geologic timescales. Observations of the present climate, however, do not clearly establish the Tibetan plateau as the dominant thermal forcing in the region: peak upper-tropospheric temperatures during boreal summer are located over continental India, south of the plateau. Here we show that, although Tibetan plateau heating locally enhances rainfall along its southern edge in an atmospheric model, the large-scale South Asian summer monsoon circulation is otherwise unaffected by removal of the plateau, provided that the narrow orography of the Himalayas and adjacent mountain ranges is preserved. Additional observational and model results suggest that these mountains produce a strong monsoon by insulating warm, moist air over continental India from the cold and dry extratropics. These results call for both a reinterpretation of how South Asian climate may have responded to orographic uplift, and a re-evaluation of how this climate may respond to modified land surface and radiative forcings in coming decades.

New evidences on the climatic causes of the formation of the spring persistent rains over southeastern China

The spring persistent rains (SPR) over southeastern China (SEC) are a unique synoptic and climatic phenomenon in East Asia. A former study has found that the southwesterly flow which lies on the southeastern flank of the Tibetan Plateau (TP) is one of the deflected westerly flows of the TP, and it is suggested to be the direct climatic cause of SPR. This study found that the southwesterly flow is also highly correlated with the sensible heating of the southeastern TP in interannual variability, in addition to having a high correlation in seasonal variability. These facts suggest that the thermal forcing of the TP is another important climatic cause of SPR. Numerical sensitivity experiments further prove that the mechanical and thermal forcings of the TP are the climatic causes of the formation of the SPR. On the other hand, the Nanling Mountains and Wuyi Mountains (NWM) over southeastern China not only increase the SPR precipitation amount evidently, but also make the SPR rain belt move to the south by blocking the strong southwesterly flow.

Seasonal cycle of the zonal land-sea thermal contrast and East Asian subtropical monsoon circulation

Based on analysis of the climatic temperature latitudinal deviation on middle troposphere, its seasonal cycle suggests that due to the rapid warming from eastern China continent to the east of Tibetan Plateau and the heating of Tibetan Plateau in spring, seasonal transition of the thermal difference between East Asia continent and West Pacific first takes place in the subtropical region with greatest intensity. On the accompanying low troposphere, the prevailing wind turns from northerly in winter to southerly in summer with the convection precipitation occurring at the same time. This maybe indicates the onset of the East Asian subtropical summer monsoon. Consequently, we advice that the seasonal cycle formed by the zonal thermal contrast between Asian continent and West Pacific may be an independent driving force of East Asian subtropical monsoon.