Over the past century, East Asian land monsoon rainfall (EALMR) has exhibited significant decadal variations, primarily linking to sea surface temperature anomalies (SSTAs) in the tropical and North Pacific (TNP). However, how will the decadal variability of EALMR change and the role of TNP SSTAs in a warming world remain uncertain. Projections from the Coupled Model Intercomparison Project Phase 6 (CMIP6) indicate that the leading mode of decadal EALMR will retain its near-uniform spatial pattern, but no significant change in the intensity of decadal EALMR compared to the historical period, which may attribute to the insignificant change in intensity of TNP SSTAs and its relationship with the decadal EALMR. It hints that TNP SSTAs may continue to serve as a key predictability source for decadal EALMR. Comparisons with different external forcings and pre-industrial control experiments indicate that the unchanged property and the role of TNP SSTAs are primarily influenced by the internal variability, which possibly results in the insignificant intensity changes of decadal EALMR under various future scenarios.

In recent years, glacier shrinkage and frozen soil degradation have accelerated in the central and western Tibetan Plateau (CWTP), yet it remains unclear how soil moisture (SM) anomalies induced by freeze-thaw affect thermal conditions. Using ERA5-Land dataset, this study analyzes the influence of spring SM anomalies on thermal conditions in the subsequent summer. Results show that March SM anomalies in CWTP exhibit a north–south dipole pattern and are significantly correlated with land surface temperature (LST) in June. When spring SM in CWTP exhibits a “dry in the north and wet in the south” pattern, a geopotential height anomaly wave train from eastern Europe through the Iranian Plateau to the northeastern Tibetan Plateau (TP) emerges in the mid-and-upper-troposphere, increasing the southerly wind over the Pamir Plateau. Water vapor on the southwestern slope of TP flows clockwise from the Bay of Bengal to the Arabian Sea, then converges across the Pamir Plateau. Consequently, water vapor does not ascend onto the TP, resulting in divergence and reduced precipitation over the southwestern TP. Meanwhile, fewer low clouds increase net solar radiation reaching the surface, enhancing the sensible heat flux and evaporation, which is not conducive to SM retention. As a result, soil in the southwestern TP changes from wet to dry, triggering positive feedback between SM and LST that contributes to warming the entire TP. Whereas it is opposite when the spring SM in CWTP displays a “wet north and dry south” pattern. These conclusions are also found in the CMIP6 model simulations.

In this study, the impacts of different types of La Nina development on the precipitation in the Maritime Continent are examined via observational and modelling analyses. The development processes of La Nina events primarily manifest in two types. One is El-To-La, originating from the transition of El Nino in the preceding winter, and the other is Non-El-To-La, evolving from a non-El Nino state in the previous winter. During La Nina developing summer, both types show a similar intensity of negative sea surface temperature (SST) anomalies over the central and eastern tropical Pacific (CETP), and the Maritime Continent (MC) exhibits positive precipitation anomalies. However, a notable difference occurs in the spatial pattern of MC precipitation response between these two types.For the El-To-La type, the local SST anomalies are positive in the entire MC region, which sets up a strong SST gradient between the warm MC and the cold CETP. The anomalous zonal Walker circulation associated with the zonal SST gradient causes uniform ascending anomalies over the MC region, promoting widespread positive precipitation. The local uniform warm SST anomalies contribute to positive specific humidity, further enhancing the precipitation anomaly. Therefore, positive precipitation anomalies span the entire MC region for the El-To-La type. Contrastingly, for the Non-El-To-La type, SST anomalies are only positive in the far eastern MC and negative in the western MC. Despite the establishment of large-scale Walker circulation between the MC and the CETP, the ascending branch of Walker circulation is positioned more to the east, resulting in increased precipitation over the eastern MC region. The local cold SST anomalies over the western MC hinder the moisture supply and are not favourable for precipitation enhancement. Therefore, the positive precipitation anomalies are only confined to the southeastern MC region for the Non-El-To-La type. [Traduit par la redaction] Dans le cadre de cette etude, les consequences des differents types de developpement de La Nina sur les precipitations dans le continent maritime sont examinees au moyen d'analyses d'observation et de modelisation. Les processus de developpement des evenements La Nina se manifestent principalement sous deux formes. L'un est El-To-La, provenant de la transition d'El Nino au cours de l'hiver precedent, et l'autre est Non-El-To-La, evoluant a partir d'un etat non-El Nino au cours de l'hiver precedent. Pendant l'ete ou se developpe La Nina, les deux types presentent une intensite similaire d'anomalies negatives de la temperature de la surface de la mer (TSM) sur le centre et l'est du Pacifique tropical (CEPT), et le continent maritime (CM) presente des anomalies positives de precipitations. Cependant, une difference notable apparait dans la configuration spatiale de la reponse des precipitations du CM entre ces deux types.Pour le type El-To-La, les anomalies locales de TSM sont positives dans toute la region du CM, ce qui cree un fort gradient de TSM entre le CM chaud et le CEPT froid. La circulation zonale anormale de Walker associee au gradient zonal de TSM provoque des anomalies ascendantes uniformes sur la region du CM, favorisant des precipitations positives generalisees. Les anomalies locales de TSM chaudes et uniformes contribuent a une humidite specifique positive, ce qui renforce encore l'anomalie de precipitations. Par consequent, les anomalies de precipitations positives s'etendent a toute la region du CM pour le type El-To-La. En revanche, pour le type Non-El-To-La, les anomalies de TSM ne sont positives que dans l'extreme est du CM et negatives dans l'ouest du CM. Malgre l'etablissement d'une circulation de Walker a grande echelle entre le CM et le CEPT, la branche ascendante de la circulation de Walker est positionnee plus a l'est, ce qui entraine une hausse des precipitations sur la region est du CM. Les anomalies locales et froides de la TSM sur l'ouest de la region du CM entravent l'apport d'humidite et ne sont pas favorables a l'augmentation des precipitations. Par consequent, les anomalies de precipitations positives ne se limitent qu'a la region sud-est du CM pour le type Non-El-To-La.

Due to the scarcity of meteorological stations on the Tibetan Plateau (TP), owing to the high altitude and harsh climate, studies often resort to satellite, reanalysis, and merged multi-source precipitation data. This necessitates an evaluation of TP precipitation data applicability. Here, we assess the following three high-resolution gridded precipitation datasets: the China Meteorological Forcing Dataset (CMFD), the European Center for Medium-Range Weather Forecasts Reanalysis V5-Land (ERA5-Land), and Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG) during TP summers. Using observations from the original 133 China Meteorological Administration stations on the TP as a reference, the evaluation yielded the following conclusions: (1) In summer, from 2000 to 2018, discrepancies among the datasets were largest in the western TP. The CMFD showed the smallest deviation from the observations, and the annual summer precipitation was only overestimated by 12.3 mm. ERA5-Land had the closest trend (0.41 mm/y) to the annual mean summer precipitation, whereas it overestimated the highest precipitation (>150 mm). (2) The reliability of the three datasets at annual and monthly scales was in the following order: CMFD, ERA5-Land, and IMERG. The daily scales exhibited a lower accuracy than the monthly scales (correlation coefficient CC of 0.51, 0.38, and 0.26, respectively). (3) The CMFD assessments, referencing the 114 new stations post-2016, had a notably lower accuracy and precipitation capture capability at the daily scale (CC and critical success index (CSI) decreased by 0.18 and 0.1, respectively). These results can aid in selecting appropriate datasets for refined climate predictions on the TP.

对2020年7月22日山东半岛一次极端暴雨天气过程开展观测分析,并利用中尺度模式WRF对此次局地降水过程进行了高分辨率数值模拟,对暴雨过程进行了天气背景和中尺度降雨的诊断.WRF模式较好地再现了此次极端暴雨过程,结果表明:此次极端暴雨过程短时降水强度大且局地性强,在时空上具有明显中尺度特征.降水发生在北抬副热带高压与华北低涡底部之间的西南气流中,强低涡与低空急流是影响此次降水的重要天气系统.西南急流为本次暴雨过程极端水汽的主要输送载体;在弱高空辐散场下,从地表延伸至500 hPa高空的深厚低涡是造成本次暴雨的主要影响因子,其时空演变特征与中尺度云团变化一致,与暴雨的发生直接相关.低涡、低空急流和副高之间的相互作用使低涡加强发展,低涡南部有暖湿气流入流,北部有干冷气流流入,比湿梯度基本呈现为自南向北递减分布,是典型的伴有低空急流的中尺度低涡流场分布;低涡辐合及其与副热带高压边缘强风速带的共同作用,导致强垂直运动发展并维持,是造成本次山东半岛极端暴雨的重要原因.

This article investigates the climatic characteristics of Meiyu over the Yangtze-Huaihe River Basin and the primary impact system based on Meiyu onset data from 1954 to 2020, precipitation during the Meiyu Period, NCEP/NCAR reanalysis data, sea surface temperature (SST) data of NOAA, and western Pacific subtropical high (sub-high) data provided by the National Climate Center. The main analytical method used is synthetic analysis. The results indicate that the Meiyu onset date has enormous interannual variation. The date of the earliest Meiyu emergence is 27 days prior to the latest. There is a strong relationship between the duration of Meiyu and rainfall. The start of Meiyu correlates with the northward motion of the South Asia High, the northward jump of the westerly jet, the northward jump of the subtropical high, and the northward motion of the low-level jet. In the early Meiyu years featured in this study, the northward jump of the aforementioned systems occurred earlier and the position of the westerly jet shifted from 34–35°N to 38–40°N, which is much further north than its position under typical climatic circumstances. From late May to early June, the subtropical high was extraordinarily powerful, the ridgeline reached 20°N, and its position was further to the north. In years with a late Meiyu onset, the position of the westerly jet and the ridgeline were further south than the climatological average from early to late June; the jump to the north was not evident until late June. In addition, SST anomalies of the Indian Ocean and Pacific Ocean are significant external forcing variables that influence the Meiyu start date. The high SST of the equatorial Indian Ocean and the equatorial tropical eastern Pacific in the autumn of the preceding year and the high SST of the equatorial Indian Ocean in the spring of that year are prophase indicators of an early Meiyu start in the Yangtze-Huaihe River Basin.

International science and technology cooperation is an important part of the internationalization of higher education and an important way for universities to achieve the strategic goal of "double first-class" construction. At present, international science and technology cooperation has shown a trend of accelerated development. However, due to the lack of top-level design and planning, unsound investment mechanism, the lack of new mechanism of alliance, the imperfect incentive mechanism and other reasons, the international science and technology cooperation in Chinese universities still has the problem of insufficient effectiveness. Facing the new development requirements, universities should focus on improving the level of international science and technology cooperation from the aspects of organization and management, resource investment, platform building and talent construction.

Based on the daily precipitation from China Meteorological Administration and the daily atmospheric circulation data from the Japanese 55-year Reanalysis (JRA-55) from 1979 to 2018, this paper analyzes the evolution of 10-30-day intra-seasonal oscillation (ISO) of the precipitation in the Yangtze-Huaihe River Basin (YHRB) and the modulation of the atmospheric heat source over the Tibetan Plateau (TP) with different intensity on the peak and trough values of the precipitation in the YHRB. When the atmospheric heating is strong on the southern flank of TP (STP), the lower-level anomalous low strengthens on the STP, which leads to convergence of airflow in the lower troposphere, ascent and divergence in the upper troposphere. Thus, the intense pumping action on the STP results in the convergence of water vapour from the Bay of Bengal to the STP. Due to the high altitude of TP, the water vapour turns eastward and increases the convergence and ascent of water vapour in the YHRB, which is conductive to enhancement of the peak values or weakening of trough values of the ISO of precipitation in the YHRB. When the STP heating is weak, the lower-level anomalous low decreases on the STP, leading to divergence in the lower troposphere, descent and convergence in the upper troposphere. Then the convergence of water vapour from the Bay of Bengal to the STP is suppressed and the transport of water vapour to the YHRB is interrupted, thus the peak values of precipitation are weakened or the trough are enhanced.

Typhoons are among the most dangerous weather systems on earth and can cause devastating disasters. Although great improvements have been made in the prediction of typhoon tracks during the past decades, typhoon frequency remains a major challenge in operational forecasting and climate prediction. Typhoon genesis frequency focuses on the frequency of formation of a single typhoon. However, the accumulation of single typhoons cannot effectively represent the anomalous characteristics of the corresponding circulation because of considerable differences among the typhoons, such as life history, track, and intensity. The occurrence of multiple typhoons or a single typhoon lasting for a long time over a particular region is usually closely related to the atmospheric circulation over that region. Therefore, in this study, the frequency of typhoons during a certain period and region is used to measure typhoon activity in the western North Pacific (WNP). It is found that the variation of typhoon existence frequency is different from that of typhoon genesis frequency. Typhoon existence frequency greatly improves the connection between typhoon activity and large-scale air-sea interactions (such as the El Nino-Southern Oscillation) and can better indicate the difference in weather and climate corresponding to typhoon activity anomalies. Further investigation reveals that typhoon existence frequency in the WNP during typhoon season is closely related to the North Pacific tripole pattern of sea surface temperature (SST) anomaly (NPSST) and the SST anomaly along the eastern coast of Australia in the South Pacific (SPSST) in the spring (April). A regression model using the NPSST and SPSST indices in April as predictors proved to have good skill in predicting the existence frequency of typhoons in the WNP during typhoon season.

Based on the daily Japanese 55-year Reanalysis (JRA-55) from 1979 to 2015, this study shows that atmospheric heat sources over the Tibetan Plateau (TP) and its surrounding areas (TPSR) in summer have a significant 10- to 30-day intraseasonal oscillation (ISO). The linkage of the ISO with the amplified precipitation to the south of the middle and lower reaches of the Yangtze River (MLYR) is also investigated. The results show that when anomalous positive heat sources over the TPSR strengthen, an anomalous thermal low pressure develops, leading to anomalous positive vorticity over the TPSR. Meanwhile, a mid-high latitude wavetrain with alternating positive and negative vorticity anomaly centres over the Eurasian continent propagates eastward across the TP. The anomalous positive vorticity over the northeastern TP is enhanced when combined with a deep positive vorticity anomaly over the TPSR. The wave-activity flux in the eastern TPSR turns southward or southeastward, with a positive vorticity anomaly propagating to the southeast of China. As a result, positive vorticity advection to the south of the MLYR increases with height and is conducive to convergence, upward motion, and increased precipitation. The situation is the reverse when negative anomalous heat sources develop over the TPSR. Therefore, the 10- to 30-day ISO of the atmospheric heat source over the TPSR in summer could contribute to the amplification of the intraseasonal precipitation anomalies to the south of the MLYR by regulating the range and intensity of the anomalous vorticity of the Eurasian wavetrain.

Based on the daily Japanese 55-year Reanalysis data, the characteristics of the summer (June-July-August) quasi-biweekly oscillation (QBWO) of atmospheric apparent heat sources over the Tibetan Plateau (TP) and its surrounding areas (TPSR) are investigated. The first three leading modes of the atmospheric intraseasonal heat source over the TPSR reflect two independent propagation features of the QBWO. The first, which propagates from east to west, is associated with the mid- to upper tropospheric circulation, with large-scale anomalous cyclones and anticyclones propagating from northeast China, across the TP, and finally arriving in West Asia. The intensity of this QBWO rapidly increases when approaching the TP and significantly weakens during its westward journey upon leaving the TP. The second, which moves from west to east, is closely correlated with the mid-latitude Rossby wave train emanating from southern Europe that travels over the TP to the East Asian coast. Remarkable differences can be observed between the intensity of the wave train over the east and west sides of the TP. To the west of 90 degrees E, the QBWO strengthens when proceeding to the TP and reaches its maximum over the TP. To the east of 90 degrees E, the circulation anomalies are maintained for about half a cycle. For both propagation pathways, the QBWO of the heat source over the TPSR greatly modulates the circulation and precipitation anomalies over the TP, the Indian Peninsula, and the Indochina Peninsula.

采用1979-2017年NCEP/NCAR逐日再分析资料估算大气热源,研究夏季青藏高原大气热源准双周振荡(Quasi-BiWeekly Oscillation,QBWO)的特征及传播途径.结果 表明:青藏高原及其周边的大气热源QBWO的前两个主模态,即荷载中心在高原东南部的全区一致型和高原东南-西北反位相变化的偶极型,呈现了高原夏季大气热源QBWO自东向西传播过程中所处的两种不同状态.这主要是由于在中纬度地区对流层中上层,低频大气环流的活动表现为大的异常气旋和反气旋环流从我国东北经青藏高原至西亚的自东向西的传播,当移近高原时迅速增强,当西移离开高原时明显减弱.在此过程中,青藏高原及其周边、孟加拉湾以及印度半岛等地区的降水都发生了异常变化.

The interannual relationship between the spring sea surface temperature over the western tropical Indian Ocean (WTIO SST) and summer water vapor content over Tibetan Plateau (TPWVC) enhances significantly after 1992/1993. The regressed atmospheric circulation against WTIO SST index (WTIO SSTI) for two periods is explored to explain the interdecadal variation. During ID1 (1979–1991), the center of the anomalous anticyclone is generally located eastward and the weak easterly anomalies on its southern flank transport moisture from the western Pacific to Southeast China with no effects on TPWVC. In ID2 (1994–2017), the Northwest Pacific anticyclone, the anomalous easterlies, and the subtropical high at 500 hPa all move westward and enhance significantly; thus, it forms a westward moisture transport pathway delivering the water vapor from the western Pacific into Tibetan Plateau. A possible mechanism is raised. On the one hand, the SST anomalies (SSTA) related to WTIO SSTI extend eastward from spring to summer in ID2. With the increased mean SST in the Indo-western Pacific Ocean under the global warming and the stronger mean summer SST in the eastern Indian Ocean, the positive SSTA induce the enhanced Kelvin waves and Northwest Pacific anticyclone with strong easterly anomalies during ID2. But in ID1, the SSTA related to WTIO SST confined in the western-central Indian Ocean from spring to summer excite the decreased Kelvin waves with less significant easterly anomalies due to the weaker mean SST. On the other hand, the eastward shift of tropical summer SSTA generates the increased convection and rising motion over the Southeast Indian Ocean in ID2. They enhance the easterly anomalies on the southern flank of the Northwest Pacific anticyclone and induce anticyclonic shear through the meridional circulation. As a result, the easterly anomalies shift westward to transport more moisture into Tibetan Plateau. However, in ID1, the easterly anomalies of the anticyclone cannot be strengthened with no westward shift. Therefore, the above reasons lead to the interdecadal enhancement of relationship between the spring WTIO SST and summer TPWVC.

大气热源是高原气象学的理论要点,研究其计算方法及其适用性,对加深高原气象学的认识,开拓"高原气象学"课程学生的视野,都具有重要意义.然而,精确计算大气热源仍是个挑战.本文详细介绍了大气热源两种计算方法,即正算法和倒算法,并基于站点观测、卫星辐射资料(ISCCP和SRB)及4套再分析资料(NCEP/NCAR、NCEP/DOE、ERA-Interim和JRA55),比较了不同资料计算所得夏季高原热源多尺度变率的差异.结果显示利用正算法时,辐射资料的选择需慎重;而在利用倒算法时,再分析资料的选择则需根据热源的研究尺度而定,不同再分析资料差异颇大.就长期趋势变化而言,再分析结果<Q1>-JRA55最接近观测;而在年际尺度上,<Q1>-ERAI与<Q1>-JRA55两套结果能近似重复观测计算所得热源变率;在季节内尺度上,多套再分析资料差异性缩小,均可细致刻画高原夏季热源变化周期,在高原地区均有较好的适用性.

采用英国哈德来(Hadley)中心的HadGHCND逐日近地面最高气温,定义并统计了中国冬季暖日频次(冬季高温持续6天以上的天数),分析了其变化规律及可能成因.中国冬季暖日频次有两个主模态:一个是全国一致变化型,其最大荷载区主要位于长江以北至华北地区.当中国冬季暖日频次一致增多,在东半球中—高纬为正负偶极型高度异常分布.另一个是南北反位相不对称型,其最大荷载区在青藏高原东南部坡度较大区域.当暖日频次北少南多,大气环流场呈现从极地向南排列的“+-+”高度异常分布.这种分布类似北极涛动(Arctic Oscillation,AO)型(负位相)和北太平洋西部南北反位相的西太平洋(Western Pacific,WP)型的组合.中国邻海异常暖SSTA和黑潮延伸区异常暖舌的分布与上述两个主模态有密切联系,对冬季暖日频次的季节预测具有先兆意义.此外,青藏高原地形以及冬季冷源的热力作用对于高原附近暖日频次变化有重要影响.

This study investigates the typhoon genesis frequency (TGF) in the dominant season (July to October) in Western North Pacific (WNP) using observed data in 1965–2015. Of particular interest is the predictability of the TGF and associated preseason sea surface temperature (SST) in the Pacific. It is found that, the TGF is positively related to a tri-polar pattern of April SST anomalies in North Pacific (\({\text{NP}}{{\text{T}}_{{\text{Apr}}}}\)), while it is negatively related to SST anomalies over the Coral Sea (\({\text{CSS}}{{\text{T}}_{{\text{Apr}}}}\)) off east coast of Australia. The \({\text{NP}}{{\text{T}}_{{\text{Apr}}}}\) leads to large anomalous cyclonic circulation over North Pacific. The anomalous southwesterly weakens the northeast trade wind, decreases evaporation, and induces warm water in central tropical North Pacific. As such, the warming effect amplifies the temperature gradient in central tropical North Pacific, which in turn maintains the cyclonic wind anomaly in the west tropical Pacific, which favors the typhoon genesis in WNP. In the South Pacific, the \({\text{CSS}}{{\text{T}}_{{\text{Apr}}}}\) supports the typhoon formation over the WNP by (a) strengthening the cross-equatorial flows and enhancing the Inter-tropical Convergence Zone; (b) weakening southeast and northeast trade wind, and keeping continuous warming in the center of tropical Pacific. The influence of both \({\text{NP}}{{\text{T}}_{{\text{Apr}}}}\) and \({\text{CSS}}{{\text{T}}_{{\text{Apr}}}}\) can persistently affect the zonal wind in the tropical Pacific and induce conditions favorable for the typhoon genesis in the typhoon season. A Poisson regression model using \({\text{NP}}{{\text{T}}_{{\text{Apr}}}}\)and \({\text{CSS}}{{\text{T}}_{{\text{Apr}}}}\)is developed to predict the TGF and a promising skill is achieved.

利用1971-2010年内蒙古锡林郭勒盟15个地面气象观测站基本资料和常规观测资料,综合分析出了大雪天气的主要特征.结果表明:(1)40a大雪、暴雪日数由东南向西北逐渐减少.(2)10a大雪、暴雪平均日数呈波动变化的特点,纯雪的大雪、暴雪日数20世纪80年代和21世纪10年代整体偏少于20世纪70和90年代,且近20a出现降雪集中出现和不出现大雪的年份;含雨夹雪的大雪日数则是20世纪70年代和21世纪10年代整体多于20世纪八九十年代,暴雪日数则随年代逐渐减少.(3)大雪、暴雪(纯雪)出现在9月至次年5月,3月最多,全年在3月和10月存在两个峰值.而含雨夹雪的大雪、暴雪10月份出现最多,其次是4月.(4)综合分析2000年以来的24次大雪、暴雪(纯雪)过程,可把锡盟的降雪天气系统分为5类.

通过多变量联合经验正交函数分解(MV-EOF)方法揭示了近30年(1979-2010年)春季和夏季东亚大气环流所发生的年代际转折及其与中国南方降水年代际季节反相变化的内在联系,探讨了局地性大气热源年代际变化影响东亚大气环流年代际转折的可能机理.结果表明:(1)东亚大气环流春季第1模态和夏季第2模态在20世纪90年代中期都发生了明显的年代际转折；(2)与春季大气环流第1模态和夏季大气环流第2模态年代际转折相对应的是中国南方降水明显的年代际季节反相变化,即春季降水年代际减少,夏季降水年代际增多；(3)春季青藏高原和夏季贝加尔湖地区大气热源年代际变化对东亚大气环流年代际转折有一定贡献,是造成中国南方降水年代际季节反相变化的直接原因；(4)春季青藏高原大气热源的年代际减弱,使高原东南侧的西南风减弱,导致中国南方上空水汽输送不足,春季降水减少.夏季贝加尔湖大气热源偶极型分布由“南负北正”转变为“南正北负”,由此在贝加尔湖上空激发高压异常,使夏季雨带北进受阻而停滞于南方,造成中国南方夏季降水增多.

Because of a lack of sufficient observations over the Tibetan Plateau (TP), the measurement of the strength of the thermal effects of the TP is a challenging issue, yet of crucial importance for climate research. In this study, two sets of daily reanalysis data (1979-2001) from the National Centers for Environmental Prediction reanalysis version 1 (NCEP-I) and the European Centre for Medium-Range Weather Forecasts 40-year Reanalysis data (ERA-40) are used to calculate the atmospheric diabatic heating effects of the TP and the adjacent regions with an inverse algorithm. The observational data obtained from the recent atmospheric experiments over the TP are applied to verify and evaluate the results from NCEP-I and ERA-40 reanalysis data, respectively. It is found that the ERA-40 results are closer to the observations in terms of the structure and seasonal variation of the vertical profile of the diabatic heating over the TP. The horizontal distributions of the apparent heat source are quite reasonable over Asia for both the NCEP-I and ERA-40 results.

Northern China has been subject to increased heatwave frequency (HWF) in recent decades, which deteriorates the local droughts and desertification. More than half a billion people face drinking water shortages and worsening ecological environment. In this study, the variability in the western Tibetan Plateau snow cover (TPSC) is observed to have an intimate linkage with the first empirical orthogonal function mode of the summer HWF across China. This distinct leading mode is dominated by the decadal to inter-decadal variability and features a mono-sign pattern with the extreme value center prevailing over northern China and high pressure anomalies at mid- and upper troposphere over Mongolia and the adjacent regions. A simplified general circulation model is utilized to examine the possible physical mechanism. A reduced TPSC anomaly can induce a positive geopotential height anomaly at the mid- and upper troposphere and subsequently enhance the climatological high pressure ridge over Mongolia and the adjacent regions. The subsidence associated with the high pressure anomalies tends to suppress the local cloud formation, which increases the net radiation budget, heats the surface, and favors more heatwaves. On the other hand, the surface heating can excite high pressure anomalies at mid- and upper troposphere. The latter further strengthens the upper troposphere high pressure anomalies over Mongolia and the adjacent regions. Through such positive feedback effect, the TPSC is tied to the interdecadal variations of the northern China HWF.