In this study, we unveil atmospheric circulation anomalies associated with the large-scale tropical teleconnections using National Center for Environmental Prediction (NCEP) reanalysis dataset. Composite analyses have...In this study, we unveil atmospheric circulation anomalies associated with the large-scale tropical teleconnections using National Center for Environmental Prediction (NCEP) reanalysis dataset. Composite analyses have been performed to know the impact of large-scale tropical circulations on the Horn of Africa. The composite analysis performed at the geopotential height of 850 Mb and 200 Mb, and precipitation rate (mm/day) during six strong El Niño and La Niña episodes revealed that the large-scale tropical variability induced climate anomalies in space and time. A substantial decrease in upper-level height (200 Mb) has been observed in the study area during El Niño composite years as compared to the La Niña years. During El Niño conditions, the upper-level divergence initiates low-level vertical motion, thereby enhancing convection, however, during La Niña composite years, nearly contrasting situations are noticed in Belg (February to May) season in Ethiopia. However, geopotential height anomalies at 850 Mb are above-normal during the strong El Niño years, suggesting suppressed convection due to vertical shrinking and enhancement of divergence at the lower level. Compared to the Belg (February to May), geopotential anomalies were generally positive during the Kiremt (June to September) season, thereby suppressing the rainfall, particularly in Southern Ethiopia and Northern Part of Kenya. In contrast, an increase in rainfall was observed during the Belg season (February to May).展开更多
利用常规气象观测资料和NCEP2再分析资料,对2016年1月24日广州白云机场出现的一次强冷空气过程的环流背景、主要影响系统以及期间降水多相态转换的天气特征进行了分析。结果表明:本次天气过程来源于一次横槽转竖型寒潮,冷锋、中低空切...利用常规气象观测资料和NCEP2再分析资料,对2016年1月24日广州白云机场出现的一次强冷空气过程的环流背景、主要影响系统以及期间降水多相态转换的天气特征进行了分析。结果表明:本次天气过程来源于一次横槽转竖型寒潮,冷锋、中低空切变线和低空急流给华南地区带来了较长时间的降水天气;白云机场上空存在多条0℃等温线和逆温层,探空廓线多次穿过0℃等温线,使得地面出现了雨和冰粒的相态转换;降水相态变化时暖层温度、0℃层高度、位势厚度、边界层高度、气柱云水量和地表抬升指数等指数均发生较大变化;当降水相态为雨时,暖层温度≥2℃,0℃层高度≤975 h Pa;当降水相态为冰粒时,暖层温度≤0℃,0℃层高度≌1000 h Pa。展开更多
深入理解青藏高原上空大气非绝热加热三维结构,有助于揭示高原热动力效应和机械强迫效应在亚洲夏季风系统中的作用机理.然而现有的高原非绝热加热率资料存在较大不确定性.本文详细比较了NCEP和ERA40再分析资料"残差诊断法"计...深入理解青藏高原上空大气非绝热加热三维结构,有助于揭示高原热动力效应和机械强迫效应在亚洲夏季风系统中的作用机理.然而现有的高原非绝热加热率资料存在较大不确定性.本文详细比较了NCEP和ERA40再分析资料"残差诊断法"计算的大气非绝热加热数据,分析两种资料所反映的高原上大气非绝热加热的时空分布特点,重点比较了二者在高原南麓的差异,并结合TRMM PR降水和潜热资料分析了差异的可能原因.研究发现两种资料之间的差异在夏季最大:ERA40在高原南麓高海拔地区所诊断的非绝热加热显著大于NCEP.ERA40大气强加热区域从高原南部山脚向北延伸、越过海拔4000位势米直至高原主体的南部;而相应NCEP大气强加热区主要位于高原南麓低海拔地区,不超过海拔4000位势米界限.上述差异不仅限于贴地层(地表感热的直接影响区域),而在400~500 h Pa大气层也很显著.同时发现,ERA40所估计的夏季高原南麓降水显著大于NCEP和TRMM PR的观测,这种差异在时间、空间上都与非绝热加热的差异相吻合.这说明降水所释放的潜热是造成上述差异的主要原因.分析大气加热场和大气环流的经向垂直剖面发现,ERA40在南麓高海拔地区所诊断的大气非绝热加热可向上延伸至对流层高层~300 h Pa,而相应NCEP大气非绝热加热主要集中在较低大气层,相应ERA40诊断的大气垂直上升速度明显强于NCEP,200 h Pa的水平辐散也较强.高原南麓深对流降水及其潜热的不确定性是充分理解高原-大气相互作用的主要难点.展开更多
文摘In this study, we unveil atmospheric circulation anomalies associated with the large-scale tropical teleconnections using National Center for Environmental Prediction (NCEP) reanalysis dataset. Composite analyses have been performed to know the impact of large-scale tropical circulations on the Horn of Africa. The composite analysis performed at the geopotential height of 850 Mb and 200 Mb, and precipitation rate (mm/day) during six strong El Niño and La Niña episodes revealed that the large-scale tropical variability induced climate anomalies in space and time. A substantial decrease in upper-level height (200 Mb) has been observed in the study area during El Niño composite years as compared to the La Niña years. During El Niño conditions, the upper-level divergence initiates low-level vertical motion, thereby enhancing convection, however, during La Niña composite years, nearly contrasting situations are noticed in Belg (February to May) season in Ethiopia. However, geopotential height anomalies at 850 Mb are above-normal during the strong El Niño years, suggesting suppressed convection due to vertical shrinking and enhancement of divergence at the lower level. Compared to the Belg (February to May), geopotential anomalies were generally positive during the Kiremt (June to September) season, thereby suppressing the rainfall, particularly in Southern Ethiopia and Northern Part of Kenya. In contrast, an increase in rainfall was observed during the Belg season (February to May).
文摘利用常规气象观测资料和NCEP2再分析资料,对2016年1月24日广州白云机场出现的一次强冷空气过程的环流背景、主要影响系统以及期间降水多相态转换的天气特征进行了分析。结果表明:本次天气过程来源于一次横槽转竖型寒潮,冷锋、中低空切变线和低空急流给华南地区带来了较长时间的降水天气;白云机场上空存在多条0℃等温线和逆温层,探空廓线多次穿过0℃等温线,使得地面出现了雨和冰粒的相态转换;降水相态变化时暖层温度、0℃层高度、位势厚度、边界层高度、气柱云水量和地表抬升指数等指数均发生较大变化;当降水相态为雨时,暖层温度≥2℃,0℃层高度≤975 h Pa;当降水相态为冰粒时,暖层温度≤0℃,0℃层高度≌1000 h Pa。
文摘深入理解青藏高原上空大气非绝热加热三维结构,有助于揭示高原热动力效应和机械强迫效应在亚洲夏季风系统中的作用机理.然而现有的高原非绝热加热率资料存在较大不确定性.本文详细比较了NCEP和ERA40再分析资料"残差诊断法"计算的大气非绝热加热数据,分析两种资料所反映的高原上大气非绝热加热的时空分布特点,重点比较了二者在高原南麓的差异,并结合TRMM PR降水和潜热资料分析了差异的可能原因.研究发现两种资料之间的差异在夏季最大:ERA40在高原南麓高海拔地区所诊断的非绝热加热显著大于NCEP.ERA40大气强加热区域从高原南部山脚向北延伸、越过海拔4000位势米直至高原主体的南部;而相应NCEP大气强加热区主要位于高原南麓低海拔地区,不超过海拔4000位势米界限.上述差异不仅限于贴地层(地表感热的直接影响区域),而在400~500 h Pa大气层也很显著.同时发现,ERA40所估计的夏季高原南麓降水显著大于NCEP和TRMM PR的观测,这种差异在时间、空间上都与非绝热加热的差异相吻合.这说明降水所释放的潜热是造成上述差异的主要原因.分析大气加热场和大气环流的经向垂直剖面发现,ERA40在南麓高海拔地区所诊断的大气非绝热加热可向上延伸至对流层高层~300 h Pa,而相应NCEP大气非绝热加热主要集中在较低大气层,相应ERA40诊断的大气垂直上升速度明显强于NCEP,200 h Pa的水平辐散也较强.高原南麓深对流降水及其潜热的不确定性是充分理解高原-大气相互作用的主要难点.