Climatology of Warm Rain and Associated Latent Heating Derived from TRMM PR Observations
Climatology of Warm Rain and Associated Latent Heating Derived from TRMM PR Observations
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DOI：
10.1175/2009jcli2575.1
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发表时间：
2009-09-21
影响因子：
4.9
通讯作者：
Ueda, Hiroaki
中科院分区：
文献类型：
--
作者：
Kodama, Yasu-Masa;Katsumata, Masaki;Ueda, Hiroaki
利用来自热带降雨测量任务降水雷达观测的9年数据集，研究了热带、亚热带和部分中纬度地区降水和潜热剖面的大尺度分布，重点研究了暖雨的贡献。暖雨的分布表现出不同于其他类型雨和向外长波辐射的特征。暖雨在陆地上偏弱，但在海洋上分布广泛，特别是在热带辐合带和副热带海洋西部。观测到的暖雨量取决于降雨强度，而不是暖雨事件的频率。海洋暖雨量与海表温度呈显著正相关；海温对总雨量的依赖性主要存在于热带、亚热带和部分中纬度地区，而海温对总雨量的依赖性仅限于热带地区。总雨和暖雨都集中在沿局地海温极大值延伸的ITCZ。副热带辐合带（白锋面区、南太平洋辐合带和南大西洋辐合带的副热带部分）有少量暖雨，总雨量充足。然而，在这些区域的低纬度侧，在流向这些区域的低空水汽流的上游部分观测到更多的暖雨。暖雨可以通过加深湿润边界层和增加水汽通量来培育亚热带辐合带。暖雨与低层云量的统计关系表明，低层云量在20% ~ 30%时暖雨量大，低层云量大于40%时暖雨量小。这表明，在大量云量的条件下，强烈的暖雨是由对流云而不是层状云提供的。尽管暖雨对总降雨量的贡献很小，但在大多数热带和亚热带海洋保持正LH值。暖雨造成的LH掩盖了层状雨中观测到的低层降温，维持了熔融层以下低层大气LH正。由于暖雨只限于海洋，沿岸维持强烈的LH对比；这种对比在某些地方达到1-2 K第21天的值，并可能影响大陆沿岸的局地和季风环流。
The large-scale distribution of precipitation and latent heating (LH) profiles in the tropics, subtropics, and part of the midlatitudes was studied using a 9-yr dataset derived from Tropical Rainfall Measuring Mission precipitation radar observations, with emphasis on the contribution of warm rain. The distribution of warm rain showed features unique from those of rain in other categories and those of outgoing longwave radiation. Warm rain was weak over land but widely distributed over oceans, especially along the intertropical convergence zone (ITCZ) and the western part of the subtropical oceans. The observed amount of warm rain depended on the rainfall intensity rather than on the frequency of warm rain events. The amount of warm rain over ocean was positively correlated with sea surface temperature (SST); this dependency was found in the tropics, subtropics, and part of the midlatitudes, whereas dependency of SST on total rain was confined to the tropics. Both total rain and warm rain were concentrated in the ITCZ, which elongated along the local SST maximum. Small amounts of warm rain were found along subtropical convergence zones (the baiu frontal zone and subtropical portions of the South Pacific convergence zone and the South Atlantic convergence zone) with ample total rainfall. However, larger amounts of warm rain were observed at the lower-latitude sides of these zones in the upstream portions of low-level moisture flow toward the zones. Warm rain may cultivate the subtropical convergence zones by deepening the moist boundary layer and increasing moisture flux toward the zones. The statistical relationship between warm rain and low-level cloudiness showed that the warm rain amount was large when low-level cloudiness was 20%-30% and small when low-level cloudiness was greater than 40%. This indicates that intense warm rain is provided by convective clouds, not by stratiform clouds, in conditions of substantial cloudiness. Despite the small contribution to total rain, warm rain maintained positive LH values over most of the tropical and subtropical oceans. The LH by warm rain masked low-level cooling observed in stratiform rain and maintained positive LH in the lower atmosphere below the melting layer. Because warm rain was confined to oceans, a strong LH contrast was maintained along the coast; this contrast reached values of 1-2 K day 21 in certain places and may affect local and monsoonal circulation across continental coasts.