利用格点化降水观测数据集(CN05.1)以及ECMWF再分析资料(ERA5),分析1961—2020年夏季西南地区东部(Eastern Southwest China,ESWC)的降水、水汽含量及降水转化率特征,并利用天气学分析方法初步探究地形分布对降水转化率空间分布差异的影...利用格点化降水观测数据集(CN05.1)以及ECMWF再分析资料(ERA5),分析1961—2020年夏季西南地区东部(Eastern Southwest China,ESWC)的降水、水汽含量及降水转化率特征,并利用天气学分析方法初步探究地形分布对降水转化率空间分布差异的影响,最后利用中尺度数值模式WRF4.0(Weather Research and Forecasting Model)设计地形敏感性试验验证地形对西南地区东部夏季降水的作用。结果表明:(1)1961—2020年夏季西南地区东部的降水呈现东多西少的分布特征,但水汽含量却在其东南部和西北部存在两个大值区,水汽大值区降水转化率偏低,强降水区与水汽含量大值区分布存在明显差异,通过分析强降水区与水平风场及垂直速度场的形势配合发现地形是导致此差异的重要因素。(2)WRF模式能较好地模拟出西南地区东部夏季降水的空间分布特征,通过地形敏感性试验发现,区域内大娄山、方斗山及大巴山组成的西南-东北向山地地形分布对降水强度有显著影响,地形高度的降低将导致区域东南部降水量显著减少。(3)敏感性试验中将区域地形高度分别降低一半和去除地形后,区域东南部的降水在月时间尺度中将分别减少9.89%和19.90%。地形高度的改变也会引起区域垂直速度、水平风场、水汽输送及水汽辐合量发生改变,当地形高度降低后,上升运动及西南风明显减弱,水汽输送强度降低,水汽辐合量减少,不利于降水形成。展开更多
利用1961—2010年NCEP/NCAR再分析资料和全国753站月平均降水资料,研究了我国西南地区东部秋季干旱的环流特征及其成因。结果表明,西南地区东部秋季降水存在明显的年际和年代际变化。其中,年代际变化主要表现为,在20世纪80年代中后期,...利用1961—2010年NCEP/NCAR再分析资料和全国753站月平均降水资料,研究了我国西南地区东部秋季干旱的环流特征及其成因。结果表明,西南地区东部秋季降水存在明显的年际和年代际变化。其中,年代际变化主要表现为,在20世纪80年代中后期,降水存在由多转少的突变;降水量年际变化则与苏门答腊—西太平洋和热带东太平洋的海温分布存在很好的关系。当苏门答腊—西太平洋和东太平洋海温呈现"+-"异常分布时,引起大气热源的异常,加强哈德莱环流,同时,在南海及孟加拉湾附近激发出异常气旋性环流,而西南地区东部则处于南海气旋性环流外围异常偏北气流控制,削弱了孟加拉湾的水汽输送,从而造成西南地区东部的干旱。通过大气环流模式NCAR CAM3.0(Community Atmosphere Model 3.0)的海温异常试验,验证了上述观测结论。展开更多
Using the NCAR/NCEP（National Center for Atmospheric Research/National Centers for Environmental Prediction）reanalysis and the NOAA Climate Prediction Center’s merged analysis of precipitation（CMAP） during 1981–2...Using the NCAR/NCEP（National Center for Atmospheric Research/National Centers for Environmental Prediction）reanalysis and the NOAA Climate Prediction Center’s merged analysis of precipitation（CMAP） during 1981–2000,we investigated the seasonal evolution of the southwesterly wind and associated precipitation over the eastern China–subtropical western North Pacific area and its relationship with the tropical monsoon and rainfall,and analyzed the reasons responsible for the onset and development of the wind.It was found that the persistent southwesterly wind appears over southern China and the subtropical western Pacific the earliest in early spring,and then expands southwards to the tropics and advances northward to the midlatitudes.From winter to summer,the seasonal variation of surface heating over western China and the subtropical western Pacific may result in an earlier reversal of the westward tropospheric temperature gradient over the subtropics relative to the tropics,which may contribute to the earliest beginning of the sub-tropical southwesterly wind.Additionally,the strengthening and eastward expanding of the trough near the eastern Tibetan Plateau as well as the strengthening and westward moving of the western Pacific subtropical high also exert positive influences on the beginning and development of the subtropical southwesterly wind. In early summer,the northward expansion of the southwesterly wind over southern China is associated with a northward shift of the subtropical high,while the southward stretch of the southwesterly wind is associated with a southward stretch of the trough in the eastern side of the plateau.With the beginning and northward expansion of the subtropical southwesterly wind（namely southwest monsoon）,convergences of the low-level air and water vapor and associated upward motion in front of the strongest southwesterly wind core also strengthen and move northward,leading to an increase in rainfall intensity and a northward shift of the rain belt.Accordingly,the subtropical rainy season occurs the earliest over southern China in spring,moves northward to the Yangtze-Huaihe River valley in early summer,and arrives in North China in mid summer. Compared with the subtropical rainy season,the tropical rainy season begins later and stays mainly over the tropics,not pronouncedly moving into the subtropics.Clearly,the Meiyu rainfall over the Yangtze-Huaihe River valley in early summer results from a northward shift of the spring rain belt over southern China, instead of a northward shift of the tropical monsoon rain belt.Before the onset of the tropical monsoon, water vapor over the subtropical monsoon region comes mainly from the coasts of the northern Indo-China Peninsula and southern China.After the onset,one branch of the water vapor flow comes from the Bay of Bengal,entering into eastern China and the subtropical western Pacific via southwestern China and the South China Sea,and another branch comes from the tropical western North Pacific,moving northwestward along the west edge of the western Pacific subtropical high and entering into the subtropics.展开更多
Strong correlations between species diversity and climate have been widely observed,but the mechanism underlying this relationship is unclear.Here,we explored the causes of the richness-climate relationships among pas...Strong correlations between species diversity and climate have been widely observed,but the mechanism underlying this relationship is unclear.Here,we explored the causes of the richness-climate relationships among passerine birds in China by integrating tropical conservatism and diversification rate hypotheses using path models.We found that assemblages with higher species richness southwest of the Salween-Mekong-Pearl River Divide are phylogenetically overdispersed and have shorter mean root distances(MRDs),while species-rich regions northeast of this divide(e.g.,north Hengduan Mountains-south Qinling Mountains)are phylogenetically clustered and have longer MRDs.The results of the path analyses showed that the direct effect of climatic factors on species richness was stronger than their indirect effects on species richness via phylogenetic relatedness,indicating that neither tropical conservatism nor diversification rate hypotheses can well explain the richness-climate relationship among passerines in China.However,when path analyses were conducted within subregions separately,we found that the tropical conservatism hypothesis was well supported in the southwestern Salween-Mekong-Pearl River Divide,while the diversification rate hypothesis could explain the richness-climate relationship well in the northeastern divide.We conclude that the diversity patterns of passerines in different subregions of the Eastern Himalayas-Mountains of Southwest China may be shaped by different evolutionary processes related to geological and climatic histories,which explains why the tropical conservatism or diversification rate hypothesis alone cannot fully explain the richness-climate relationships.展开更多
文摘利用格点化降水观测数据集(CN05.1)以及ECMWF再分析资料(ERA5),分析1961—2020年夏季西南地区东部(Eastern Southwest China,ESWC)的降水、水汽含量及降水转化率特征,并利用天气学分析方法初步探究地形分布对降水转化率空间分布差异的影响,最后利用中尺度数值模式WRF4.0(Weather Research and Forecasting Model)设计地形敏感性试验验证地形对西南地区东部夏季降水的作用。结果表明:(1)1961—2020年夏季西南地区东部的降水呈现东多西少的分布特征,但水汽含量却在其东南部和西北部存在两个大值区,水汽大值区降水转化率偏低,强降水区与水汽含量大值区分布存在明显差异,通过分析强降水区与水平风场及垂直速度场的形势配合发现地形是导致此差异的重要因素。(2)WRF模式能较好地模拟出西南地区东部夏季降水的空间分布特征,通过地形敏感性试验发现,区域内大娄山、方斗山及大巴山组成的西南-东北向山地地形分布对降水强度有显著影响,地形高度的降低将导致区域东南部降水量显著减少。(3)敏感性试验中将区域地形高度分别降低一半和去除地形后,区域东南部的降水在月时间尺度中将分别减少9.89%和19.90%。地形高度的改变也会引起区域垂直速度、水平风场、水汽输送及水汽辐合量发生改变,当地形高度降低后,上升运动及西南风明显减弱,水汽输送强度降低,水汽辐合量减少,不利于降水形成。
文摘利用1961—2010年NCEP/NCAR再分析资料和全国753站月平均降水资料,研究了我国西南地区东部秋季干旱的环流特征及其成因。结果表明,西南地区东部秋季降水存在明显的年际和年代际变化。其中,年代际变化主要表现为,在20世纪80年代中后期,降水存在由多转少的突变;降水量年际变化则与苏门答腊—西太平洋和热带东太平洋的海温分布存在很好的关系。当苏门答腊—西太平洋和东太平洋海温呈现"+-"异常分布时,引起大气热源的异常,加强哈德莱环流,同时,在南海及孟加拉湾附近激发出异常气旋性环流,而西南地区东部则处于南海气旋性环流外围异常偏北气流控制,削弱了孟加拉湾的水汽输送,从而造成西南地区东部的干旱。通过大气环流模式NCAR CAM3.0(Community Atmosphere Model 3.0)的海温异常试验,验证了上述观测结论。
基金the basic research project for the State Key Laboratory of Severe Weather of Chinese Academy of Meteorological Sciences(2008LASWZI01)the National Natural Science Foundation of China(40921003)the Chinese COPES project(GYHY200706005)
文摘Using the NCAR/NCEP（National Center for Atmospheric Research/National Centers for Environmental Prediction）reanalysis and the NOAA Climate Prediction Center’s merged analysis of precipitation（CMAP） during 1981–2000,we investigated the seasonal evolution of the southwesterly wind and associated precipitation over the eastern China–subtropical western North Pacific area and its relationship with the tropical monsoon and rainfall,and analyzed the reasons responsible for the onset and development of the wind.It was found that the persistent southwesterly wind appears over southern China and the subtropical western Pacific the earliest in early spring,and then expands southwards to the tropics and advances northward to the midlatitudes.From winter to summer,the seasonal variation of surface heating over western China and the subtropical western Pacific may result in an earlier reversal of the westward tropospheric temperature gradient over the subtropics relative to the tropics,which may contribute to the earliest beginning of the sub-tropical southwesterly wind.Additionally,the strengthening and eastward expanding of the trough near the eastern Tibetan Plateau as well as the strengthening and westward moving of the western Pacific subtropical high also exert positive influences on the beginning and development of the subtropical southwesterly wind. In early summer,the northward expansion of the southwesterly wind over southern China is associated with a northward shift of the subtropical high,while the southward stretch of the southwesterly wind is associated with a southward stretch of the trough in the eastern side of the plateau.With the beginning and northward expansion of the subtropical southwesterly wind（namely southwest monsoon）,convergences of the low-level air and water vapor and associated upward motion in front of the strongest southwesterly wind core also strengthen and move northward,leading to an increase in rainfall intensity and a northward shift of the rain belt.Accordingly,the subtropical rainy season occurs the earliest over southern China in spring,moves northward to the Yangtze-Huaihe River valley in early summer,and arrives in North China in mid summer. Compared with the subtropical rainy season,the tropical rainy season begins later and stays mainly over the tropics,not pronouncedly moving into the subtropics.Clearly,the Meiyu rainfall over the Yangtze-Huaihe River valley in early summer results from a northward shift of the spring rain belt over southern China, instead of a northward shift of the tropical monsoon rain belt.Before the onset of the tropical monsoon, water vapor over the subtropical monsoon region comes mainly from the coasts of the northern Indo-China Peninsula and southern China.After the onset,one branch of the water vapor flow comes from the Bay of Bengal,entering into eastern China and the subtropical western Pacific via southwestern China and the South China Sea,and another branch comes from the tropical western North Pacific,moving northwestward along the west edge of the western Pacific subtropical high and entering into the subtropics.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences[XDA19050202]the National Natural Science Foundation of China[31630069]+1 种基金the Second Tibetan Plateau Scientific Expedition and Research(STEP)programme[2019QZKK05010112 and 2019QZKK0304]other programs[KGFZD-135-19-05].
文摘Strong correlations between species diversity and climate have been widely observed,but the mechanism underlying this relationship is unclear.Here,we explored the causes of the richness-climate relationships among passerine birds in China by integrating tropical conservatism and diversification rate hypotheses using path models.We found that assemblages with higher species richness southwest of the Salween-Mekong-Pearl River Divide are phylogenetically overdispersed and have shorter mean root distances(MRDs),while species-rich regions northeast of this divide(e.g.,north Hengduan Mountains-south Qinling Mountains)are phylogenetically clustered and have longer MRDs.The results of the path analyses showed that the direct effect of climatic factors on species richness was stronger than their indirect effects on species richness via phylogenetic relatedness,indicating that neither tropical conservatism nor diversification rate hypotheses can well explain the richness-climate relationship among passerines in China.However,when path analyses were conducted within subregions separately,we found that the tropical conservatism hypothesis was well supported in the southwestern Salween-Mekong-Pearl River Divide,while the diversification rate hypothesis could explain the richness-climate relationship well in the northeastern divide.We conclude that the diversity patterns of passerines in different subregions of the Eastern Himalayas-Mountains of Southwest China may be shaped by different evolutionary processes related to geological and climatic histories,which explains why the tropical conservatism or diversification rate hypothesis alone cannot fully explain the richness-climate relationships.
