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Based on the National Oceanic and Atmospheric Administration (NOAA) daily satellite dataset
of global outgoing longwave radiation (OLR) for the period of 1974--2004 and the NCEP-NCAR reanalysis
for 1971--2004, the linkage between persistent heavy rainfall (PHR) events in the vicinity of the Yangtze
River valley and global OLR leading up to those events (with 1- to 30-day lag) was investigated. The
results reveal that there is a significant connection between the initiation of PHR events over the
study area and anomalous convective activity over the tropical Indian Ocean, maritime continent, and
tropical western Pacific Ocean. During the 30-day period prior to the onset of PHR events, the major
significantly anomalous convective centers have an apparent dipole structure, always with enhanced
convection in the west and suppressed convection in the east. This dipole structure continuously shifts
eastward with time during the 30-day lead period. The influence of the anomalous convective activity
over the tropical oceans on the initiation of PHR events over the study area is achieved via an interaction
between tropical and extratropical latitudes. More specifically, anomalous convective activity weakens
the Walker circulation cell over the tropical Indian Ocean first. This is followed by a weakening of
the Indian summer monsoon background state and the excitation and dispersion of Rossby wave activity
over Eurasia. Finally, a major modulation of the large scale background circulation occurs. As a result,
the condition of a phase-lock among major large scale circulation features favoring PHR events is
established over the study area. 相似文献
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中国东部月降水量分布的统计特征 总被引:4,自引:0,他引:4
本文利用中国东部(105°E以东)110个站的30年(1953—1982用降水量资料,分析了月降水量分布的统计特征,经计算,月降水量的变差系数大多在0.5—1.0之间。大部分站点月降水量的频数分布呈较明显的正偏形式,但偏斜程度因时间、地点的不同而异。假设检验的结果表明:在统计意义下(α=0.05),各地都有一些站点的月降水记录遵从正态分布。这些站点的时空分布反映了我国东部干湿季明显的季风气候特点。各地遵从正态分布站点数较高的月份大体上与该地变差系数较小的月份相对应,而这些月份均位于各地的多雨时段。对于其它一些无法用正态分布拟合的月降水的频数分布,绝大部分可用三种偏斜分布模式较好地拟合。 相似文献
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江南地区持续性暴雨过程的月内环流异常和形成机制分析 总被引:1,自引:1,他引:1
利用1951—2009年NCAR/NCEP再分析资料,使用多种统计分析方法识别出对江南地区持续性暴雨过程发生、发展有重要影响的月内环流异常特征,并结合天气分析方法对其影响机制进行初步分析。结果表明,过程发生前3—1周,环流异常特征在中纬度的欧亚地区、北太平洋和南半球印度洋集中分布,其中欧亚和南半球环流异常特征反映的是沿高空急流东传的Rossby波列。正是上述环流异常特征传播和生消所对应的环流异常调整,使得副热带高压(副高)、阻塞高压、梅雨槽等关键环流系统分阶段逐步发展到位,形成有利于过程发生的大尺度环流背景“锁相”特征。 相似文献
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