Importance of Cumulus Parameterization for Precipitation Simulation over East Asia in June
Importance of Cumulus Parameterization for Precipitation Simulation over East Asia in June
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DOI：
10.2151/jmsj.79.939
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发表时间：
2001-08
影响因子：
3.1
通讯作者：
S. Emori;T. Nozawa;A. Numaguti;I. Uno
中科院分区：
文献类型：
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作者：
S. Emori;T. Nozawa;A. Numaguti;I. Uno
利用NIES/CCSR RAMS区域气候模式，以ECMWF客观分析资料为边界条件，模拟了东亚地区6月的降水型，包括与白乌锋相伴的降水型。在对照试验中，模拟的降水型不符合实际，主要表现在两个方面：一是白乌锋降水太弱，二是20°N附近北太平洋副热带高压降水较强。根据ECMWF资料，副高上空维持着较强的潜在不稳定，在这种情况下，模式中使用的积云参数化预报强降水，以稳定大气。由于副热带高压上空的低层自由大气非常干燥，在真实的大气中，这种干燥空气抑制了深积云对流的发展。当积云参数化被修改为包括这一假设，在拜厄锋的降水强度以及副热带高压上的不切实际的降水型明显改善。分析认为，巴乌锋面降水的增强是由于水汽向巴乌锋面输送的增加，以及巴乌锋面附近湿对流稳定性的减弱。在CCSR/NIES AGCM的半预报实验中，发现这种修改在地球仪的许多其他地方也有效。由于在降水分布中存在类似的问题，在许多其他的气候模式中，积云参数化的修改建议，在这些模式中也可能是有效的。
A regional climate model, NIES/CCSR RAMS, was used with the ECMWF objective analysis data as boundary conditions to reproduce the precipitation pattern over East Asia in June, including that accompanying the Baiu front. In the control experiment, the simulated precipitation pattern was unrealistic, mainly in two respects: precipitation over the Baiu front was too weak, and strong precipitation was found over the North Pacific subtropical high at around 20°N. According to the ECMWF data, strong potential instability is maintained over the subtropical high, under which condition, the cumulus parameterization used in the model predicts strong precipitation to stabilize the atmosphere. Because the lower free atmosphere is very dry over the subtropical high, it is conjectured that the development of deep cumulus convection is suppressed by this dry air in the real atmosphere. When the cumulus parameterization was modified to include this assumption, the intensity of precipitation over the Baiu front as well as the unrealistic precipitation pattern over the subtropical high was clearly ameliorated. The intensification of precipitation over the Baiu front is considered to be due to the increased water vapor transport to the Baiu front, and the decreased stability with respect to the moist convection around the Baiu front. In semi-prognostic experiments with CCSR/NIES AGCM, this modification was found to be also effective in many other parts of the globe. Because problems in precipitation distribution similar to that discussed in the present study are found in many other climate models, the modification of cumulus parameterization suggested here could also be effective in those models.