Lagrangian Diagnostics of Tropical Deep Convection and Its Effect upon Upper-Tropospheric Humidity
Lagrangian Diagnostics of Tropical Deep Convection and Its Effect upon Upper-Tropospheric Humidity
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热带深对流的拉格朗日诊断及其对对流层上层湿度的影响
DOI：
10.1175/2007jcli1786.1
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发表时间：
2007
影响因子：
4.9
通讯作者：
B. Soden
中科院分区：
文献类型：
--
作者：
Á. Horváth;B. Soden
这项研究将地球静止水汽图像与光学云特性反演和微波海面观测相结合，以便在拉格朗日框架内研究(1)卷云顶端升华对热带上对流层湿度的重要性和(2)深对流发展对海表面温度的依赖。虽然欧拉分析表明，月平均卷云冰水路径与对流层上层湿度之间有很强的空间相关性，但拉格朗日分析表明，这些量之间没有因果联系。最大对流层湿度出现在峰值对流后5h，与最大卷云冰水路径高度同步，滞后不超过1.0h，考虑到卷云冰水的特征e折叠衰减时间为4h，这一短时间滞后不允许有显著的升华增湿作用。此外，趋势分析表明，卷云的衰变和增长分别伴随着对流层上层的干燥和增湿，这与卷云冰是主要水汽来源的预期相反。此外，研究还发现，海洋表面温度每升高2℃，深对流中心的频率、空间范围和含水率都会显著增加。温暖海洋上的较大风暴也与较冷海洋上的对应物相对应的较大的顶区有关；然而，单位积云面积的顶区面积，即卷云的脱出效率，随着SST的增加而降低。
This study combines geostationary water vapor imagery with optical cloud property retrievals and microwave sea surface observations in order to investigate, in a Lagrangian framework, (i) the importance of cirrus anvil sublimation on tropical upper-tropospheric humidity and (ii) the sea surface temperature dependence of deep convective development. Although an Eulerian analysis shows a strong spatial correlation of 0.8 between monthly mean cirrus ice water path and upper-tropospheric humidity, the Lagrangian analysis indicates no causal link between these quantities. The maximum upper-tropospheric humidity occurs 5 h after peak convection, closely synchronized with the maximum cirrus ice water path, and lagging behind it by no more than 1.0 h. Considering that the characteristic e-folding decay time of cirrus ice water is determined to be 4 h, this short time lag does not allow for significant sublimative moistening. Furthermore, a tendency analysis reveals that cirrus decay and growth, in terms of both cloud cover and integrated ice content, is accompanied by the drying and moistening of the upper troposphere, respectively, a result opposite that expected if cirrus ice were a primary water vapor source. In addition, it is found that an 2°C rise in sea surface temperature results in a measurable increase in the frequency, spatial extent, and water content of deep convective cores. The larger storms over warmer oceans are also associated with slightly larger anvils than their counterparts over colder oceans; however, anvil area per unit cumulus area, that is, cirrus detrainment efficiency, decreases as SST increases.