华西秋雨起止与秋冬季节大气环流转换

根据1961—2010年平均的逐候NCEP/NCAR再分析资料、1979—2008年平均的逐候CMAP降水资料以及1961—2010年逐候平均的中国553个台站降水资料,讨论了华西秋雨起止日期与秋冬季大气环流转换特征的关系。结果表明,华西地区降水年变化表现为明显的夏、秋双峰特征,8月4—8日(第44候)为双峰间的低谷,10月8—12日(第57候)以后降水降至年平均以下。由此,将华西秋雨建立和结束日期分别确定为8月9—13日(第45候)和10月8—12日(第57候)。华西秋雨的建立对应于东亚夏季风开始向冬季风转变,其标志性环流调整特征是江南地区的西南风转为东南风。东亚经向海平面气压梯度在8月9—13日(第45候)由南高北低转为南低北高,造成850 hPa江南地区的西南风转为东南风,该东南风与来自孟加拉湾的热带西南季风交汇于华西地区,形成风向和水汽的辐合,使得华西地区的降水在夏峰之后再次增强,华西秋雨由此建立。华西秋雨的结束则对应于孟加拉湾热带西南季风结束和东亚冬季风完全建立,其标志性环流调整特征是孟加拉湾地区的西南风转为东北风。随着东亚纬向海平面气压梯度由北向南依次发生东高西低向东低西高的转变,东亚冬季风也逐步向南推进,9月8—12日(第51候)东北冬季风到达江南地区,10月8—12日(第57候)进一步推进到南海地区,此时来自孟加拉湾的热带西南季风消失,造成华西地区完全受大陆冷高压控制,东亚季风经圈环流也转为冬季型哈得来环流,东亚冬季风完全建立,华西秋雨也随之结束。因此,华西秋雨起止可能与东亚夏季风、南亚夏季风向冬季风的转变时间不同步有关,东亚季风与南亚季风的共同作用使得华西秋雨成为亚洲夏季风在中国大陆上的最后一个雨季。     

夏季亚洲-太平洋遥相关季节演变与大气环流和降水

利用1981-2007年逐日大气再分析资料和降水资料以及统计分析方法,研究了夏季(5-9月)亚洲与太平洋区域的大气遥相关,并分析了其季节演变与夏季亚洲-太平洋大气环流和亚洲季风区降水的联系.结果表明:在5-9月逐日对流层上层扰动温度场上,亚洲与北太平洋中纬度存在着类似于亚洲太平洋涛动的遥相关现象,即在季节尺度上,当亚洲大陆中纬度对流层上层偏暖时,北太平洋中纬度对流层上层偏冷,反之亦然;亚洲与太平洋对流层上层温度的反位相变化特征也出现在对流层中下层和平流层低层.亚洲-太平洋涛动指数不仅可以指示夏季亚洲与太平洋中纬度纬向热力差异的变化特征,也可以较好地指示亚洲与热带印度洋经向热力差异的变化特征.亚洲-太平洋涛动指数最大值常出现在7月中旬到8月初,并且从1981年到2007年该最大值出现时间有偏早趋势.当夏季亚洲太平洋涛动指数偏高(低)时,亚洲大陆上空的南亚高压和其下方的亚洲大陆低压系统偏强(弱),太平洋副热带高压偏强(弱)并偏北(南),亚洲-非洲上空的热带东风急流和低层的西南风偏强(弱),从印度到中国华南的广大地区、中国华北以及东北亚等地降水偏多(少).     

欧亚大陆夏季地表温度的气候特征及与大气环流的联系

采用1960—2010年NCEP/NCAR逐月再分析资料,利用经验正交函数(EOF)展开方法等,分析了欧亚大陆夏季地表温度变化特征及其与大气环流的关系。结果表明:欧亚大陆夏季地表温度的均方差在高纬度地区大于在低纬度地区。欧亚大陆夏季地表温度最主要的特征是全区一致变化,除了青藏高原东侧为降温趋势外,其他地区为变暖趋势,其中40~65°N增温明显;其次,高纬度地区表现出"-+-"变化特征。西风环流指数的变化与地表温度的增温密切相关,而EU指数与中高纬度地区地表温度异常的分布类型密切相关。根据欧亚大陆夏季地表温度的气候特征和时空变化特征,确定了5个关键区。各关键区指数都有增温趋势,但是变化特征不同。不同关键区指数的异常所对应的环流形势异常均不相同,与不同关键区地表温度密切联系的环流因子也不相同。     

春季中国南方雨带年际变动与大气环流异常

利用1960—2008年中国693个站逐日降水资料和NCEP/NCAR日平均再分析资料,采用统计分析方法,分析了中国南方春季降水强度和位置的年际变率及其与大气环流的关系。结果表明:在年代际尺度上,江南春季降水在20世纪60年代中、后期偏少,70年代中期到80年代初偏多,90年代初开始减少;在年际尺度上,当春季西太平洋副热带高压和青藏高原东侧的低层低压系统加强,并且异常中心分别位于20°N以南和30°N以南时,异常西南风主要位于长江以南地区,在异常西南风逐渐减弱区出现明显的辐合,伴随着该地区低层空气质量辐合、对流层上升运动和水汽辐合加强,造成江南地区降水偏多,此时来自西太平洋的异常水汽到达南海后,没有在南海聚集,而是转向北输送到江南;当春季西太平洋副热带高压以及青藏高原东侧低压系统加强且异常中心位于30°N以北时,异常西南风盛行在中国东部大部分地区,此时低层异常空气质量辐合、对流层异常上升运动以及异常水汽通量辐合区都向北移到江淮地区,使江淮地区降水增加,而华南地区为异常空气质量辐散、异常下沉运动以及异常水汽通量辐散,伴随着降水减少,这时异常水汽主要来自西太平洋副热带地区。由于上述观测结果与通过改变东亚和周边海域海-陆热力差异的数值试验结果有很好的一致性,因此,这里观测到的降水和大气环流异常可以被东亚区域热力差异异常激发出来。     

重庆秋季降水特征及大气环流异常分析

利用重庆1960-2006年秋季降水量计算了重庆地区秋季区域降水指数,采用相关与合成分析、线性趋势估计、Mann-Kendall突变检测方法和小波分析等统计诊断方法分析了重庆秋季降水变化特征及其与同期和前期大气环流的关系.结果表明:重庆秋季降水偏多、偏少年同期及前期中高纬度地区高度场距平都有明显的差异.前期冬季北太平洋中纬度地区对流层高度距平为正,加拿大西部对流层高度距平为负时,秋季重庆降水异常偏多,具有一定的预测意义.在此基础上定义了影响重庆地区秋季降水的前期因子.     

Seasonal stability of snow cover in Poland in relation to the atmospheric circulation

The seasonal stability of snow cover (ISS) was defined as a percentage ratio of the real and the potential snow cover duration in a winter season. Main results of the study are as follows: (1) alternately occurring periods of high and low values of the index of snow cover stability did not appeared simultaneously in mountainous and non-mountainous areas; (2) in the majority of Poland area both zonal and meridional components of the atmospheric circulation influence the ISS; however, in south the meridional air flow reveals the stronger impact, mostly due to the intensification of the southern advection by the foehn effect; and (3) changes of two or three indices describing atmospheric circulation explain up to 50 % of the ISS in Poland. The diminishing stability of snow cover in Poland corresponds with an increasing intensity of the advection from the western sector in winter in the second half of the twentieth century in Europe.     

Influence of the surface water temperature and heat flux in the North Atlantic on the atmospheric circulation

Correlation of water temperature and latent heat fluxes in winter in the North Atlantic with the atmospheric circulation in the subsequent months are analyzed based on the NCEP/NCAR reanalysis data. Monthly and daily indices of the North Atlantic Oscillation are used as characteristics of the atmosphere circulation. It is shown that conditions of the heat exchange between ocean and atmosphere in the western North Atlantic in February can influence the atmospheric circulation and air temperature in Europe in March.     

Impacts of the leading modes of tropical Indian Ocean sea surface temperature anomaly on sub-seasonal evolution of the circulation and rainfall over East Asia during boreal spring and summer

The two leading modes of the interannual variability of the tropical Indian Ocean (TIO) sea surface temperature (SST) anomaly are the Indian Ocean basin mode (IOBM) and the Indian Ocean dipole mode (IODM) from March to August. In this paper, the relationship between the TIO SST anomaly and the sub-seasonal evolution of the circulation and rainfall over East Asia during boreal spring and summer is investigated by using correlation analysis and composite analysis based on multi-source observation data from 1979 to 2013, together with numerical simulations from an atmospheric general circulation model. The results indicate that the impacts of the IOBM on the circulation and rainfall over East Asia vary remarkably from spring to summer. The anomalous anticyclone over the tropical Northwest Pacific induced by the warm IOBM is closely linked with the Pacific–Japan or East Asia–Pacific teleconnection pattern, which persists from March to August. In the upper troposphere over East Asia, the warm phase of the IOBM generates a significant anticyclonic response from March to May. In June and July, however, the circulation response is characterized by enhanced subtropical westerly flow. A distinct anomalous cyclone is found in August. Overall, the IOBM can exert significant influence on the western North Pacific subtropical high, the South Asian high, and the East Asian jet, which collectively modulate the precipitation anomaly over East Asia. In contrast, the effects of the IODM on the climate anomaly over East Asia are relatively weak in boreal spring and summer. Therefore, studying the impacts of the TIO SST anomaly on the climate anomaly in East Asia should take full account of the different sub-seasonal response during boreal spring and summer.     

长江三角洲梅汛期降水与大气环流季节内演变的关系及延伸期预报

基于1981—2020年长江三角洲(简称长三角)地区62个国家基本气象站的逐日降水量资料及NCEP/NCAR全球大气逐日再分析资料,分析了长三角地区梅汛期降水与前期大气环流季节内协同演变的关系,在此基础上利用改进的时空投影方法(STPM)构建了针对该地区梅汛期降水的延伸期预报模型.结果表明:(1)长三角地区梅汛期降水存...     

Reconstructions of spring/summer precipitation for the Eastern Mediterranean from tree-ring widths and its connection to large-scale atmospheric circulation

This study represents the first large-scale systematic dendroclimatic sampling focused on developing chronologies from different species in the eastern Mediterranean region. Six reconstructions were developed from chronologies ranging in length from 115 years to 600 years. The first reconstruction (1885–2000) was derived from principal components (PCs) of 36 combined chronologies. The remaining five, 1800–2000, 1700–2000, 1600–2000, 1500–2000 and 1400–2000 were developed from PCs of 32, 18, 14, 9, and 7 chronologies, respectively. Calibration and verification statistics for the period 1931–2000 show good levels of skill for all reconstructions. The longest period of consecutive dry years, defined as those with less than 90% of the mean of the observed May–August precipitation, was 5 years (1591–1595) and occurred only once during the last 600 years. The longest reconstructed wet period was 5 years (1601–1605 and 1751–1755). No long term trends were found in May–August precipitation during the last few centuries. Regression maps are used to identify the influence of large-scale atmospheric circulation on regional precipitation. In general, tree-ring indices are influenced by May–August precipitation, which is driven by anomalous below (above) normal pressure at all atmospheric levels and by convection (subsidence) and small pressure gradients at sea level. These atmospheric conditions also control the anomaly surface air temperature distribution which indicates below (above) normal values in the southern regions and warmer (cooler) conditions north of around 40°N. A compositing technique is used to extract information on large-scale climate signals from extreme wet and dry summers for the second half of the twentieth century and an independent reconstruction over the last 237 years. Similar main modes of atmospheric patterns and surface air temperature distribution related to extreme dry and wet summers were identified both for the most recent 50 years and the last 237 years. Except for the last few decades, running correlation analyses between the major European-scale circulation patterns and eastern Mediteranean spring/summer precipitation over the last 237 years are non-stationary and insignificant, suggesting that local and/or sub-regional geographic factors and processes are important influences on tree-ring variability over the last few centuries.     

双鸭山市春夏秋季旱涝预报方法研究

<正>1旱涝分级与指标的划定(1)用双鸭山各县气象站(台)1956～2009年降水资料作为划定春、夏、秋季的旱涝依据。(2)采用5级分类,即旱、偏旱、正常、偏涝、涝。(3)旱涝分级的降水量指标以降水量距平值、降水量百分比、直接用降水量指标3种方法来确定。在确定旱涝等级时,     

浙江秋季连阴雨气候统计特征及其异常环流背景

利用1971—2016年浙江常规气象站观测资料和多种再分析资料,分析了浙江省秋季连阴雨的气候特征及其异常环流背景。结果表明:(1)浙江每年每站平均出现1.8次秋季连阴雨天气,过程平均可持续5.5 d,平均雨量77 mm;秋季3个月中9月出现连阴雨的频次最高;大多年份会发生1～2次持续5～7 d的连阴雨,78%过程累计降水量在100 mm以下;发生时多为全省一致变化型,多发区集中在杭州—绍兴一带。(2)连阴雨过程次数、累计持续天数及累计降水量有一致变化性,均反映出浙江秋季连阴雨有明显的年际变化特征,有4个强年和7个弱年。(3)浙江秋季连阴雨强(弱)年对应南亚高压和西太平洋副热带高压"相向(背)而行"。强(弱)年时,西太平洋副热带高压异常偏西(东),南亚高压异常偏东(西),华东地区上空垂直上升运动强(盛行下沉气流),低层异常偏南(北)风提供了充足的水汽(阻碍了暖湿空气北上),有(不)利于浙江连阴雨的发生。(4)连阴雨强弱年大气环流异常与热带海表温度强迫有关。强(弱)年时,赤道太平洋海温呈拉尼娜状态(距平不明显),使东印度洋—南海—海洋性大陆上空对流活跃(偏弱),潜热加热(不足以)激发低层Matsuno-Gill型响应,(不能)在亚洲大陆激发气旋性环流异常,而赤道中东太平洋强(弱)下沉气流则(不能)在西北太平洋激发反气旋性环流异常,此低层气旋—反气旋异常环流配置(弱环流异常)使华东地区有低层偏南(北)风异常,水汽增多(减少),有(不)利于浙江连阴雨的发生。     

Characteristics and evolution of atmospheric circulation patterns during Meiyu over the Jianghuai valley

This study focuses on the evolution of large-scale circulations before and after the beginning of the Meiyu and analyzes the formations of the typical vertical circulation pattern associated with Meiyu and its relationship with the Meiyu rainband. Results show that the typical vertical circulation pattern during the Meiyu season is characterized by the ??two-leg??-type pattern in the vorticity field, a typhoon eye-like structure of the equivalent potential temperature field, as well as the sharp gradient of the equivalent potential temperature zone, i.e., the Meiyu front are typically presented in the Meiyu season. Tracking its evolution process, we find that the typical vertical circulation pattern is built at late March and early April along with the rainband locating at the area south to the Yangtze River. This typical pattern and the rainband both advance northward affecting Jianghuai valley since the beginning of Meiyu. Moreover, the typical vertical circulation pattern derived from Meiyu season has been formed in April and corresponds to the reverse of the land-sea thermal contrast between the Eastern Asia and western Pacific Ocean, demonstrating the close relationship of the movement between the rainband and the march of the East Asian subtropical summer monsoon.     

中国东部夏季季节内降水异常及其伴随的热带和中高纬度大气环流演变特征

利用1981—2020年夏季(5—8月)CPC(Climate Prediction Center)逐日降水资料、NCEP/NCAR逐日再分析资料以及NOAA的向外长波辐射资料,通过经验正交函数(EOF)分解、超前滞后合成等方法,分析了中国东部夏季季节内降水异常的主要模态(即南方型和江淮型降水异常)及其伴随的热带和中高...     

热带太平洋低层环流主模态与东亚大气环流的可能联系

利用1958—2001年NCEP/NCAR再分析资料,探讨了热带太平洋(100°E~60°W,10°S~10°N)10 m风场的时空变化特征及其与东亚大气环流的可能联系。结果表明:1)热带太平洋风场异常存在两种主模态,第一模态对应中西太平洋一致的西(东)风异常,关于赤道呈准对称分布,与ENSO(El Nio-Southern Oscillation)暖(冷)位相时风场的分布对应;第二模态则关于赤道呈反对称分布,西北太平洋存在显著的反气旋(气旋)式环流,中太平洋异常西风不再位于赤道上,而是南移到了10°S左右,对应ENSO暖(冷)位相向相反位相转换时的风场分布特征。2)两模态时间系数的主振荡周期不同,与ENSO循环的位相关系也不同。研究发现,当两模态呈正(负)位相分布时,贝加尔湖南侧(South to Lake Baikal,SLB)容易发生持续的高压(低压)异常环流。3)两模态与SLB异常环流的联系途径不同。第一模态正位相对应热带中东太平洋大范围暖海温引起的二极型Walker环流异常,SLB异常高压不仅能通过东亚沿岸北风和南海低槽的作用促进第一模态的前期发展,还对其后期维持起重要作用。负位相时,情况相反。该环流系统既与热带中东太平洋大范围垂直运动有关,还与邻近的中国东南沿海低层异常辐合有关;第二模态则对应热带西太平洋及东印度洋为主、大西洋为辅的暖海温引起的热带四极型Walker环流异常。此时热带西太平洋到东印度洋局地偏强的经圈Hadley环流可能是SLB异常环流维持的主要原因。     

水城2009—2010年秋冬春季连旱气候分析

利用水城站1957年以来的历史气象资料,对水城2009—2010年秋冬春季连旱的气候特征进行了分析,结果表明:此次干旱属50 a一遇,历史罕见。     

Variability of surface wind directions over Finnmark, Norway, and coupling to the larger-scale atmospheric circulation

This study documents the temporal and spatial variability of surface wind conditions over the Norwegian county of Finnmark and the coupling of local surface winds to the larger-scale atmospheric circulation, represented by the mean sea level pressure field. At locations along the northern coast, thermally driven offshore winds from the south dominate, especially during the cold season. During the warm season, downward mixing of westerly overlying winds becomes more important as the stability of the boundary layer stratification decreases. In the western part, locations are situated in valleys, resulting in two opposing along-channel dominant wind directions. Seasonal changes in atmospheric conditions are reflected in a reversal of the dominant wind direction, with a component towards the coast during the cold season. At all locations, a clear separation between different prevailing surface wind directions in each season can be achieved based exclusively on local mean sea level geostrophic wind direction. This allows statistical downscaling of the prevailing surface wind conditions from lower-resolution simulations of the surface pressure field and may improve local wind forecasts over complex terrain.