Seasonal variation of cloud activity and atmospheric profiles over the eastern part of the Tibetan Plateau
Seasonal variation of cloud activity and atmospheric profiles over the eastern part of the Tibetan Plateau
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DOI：
10.1029/2007jd009321
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发表时间：
2008-05
影响因子：
--
通讯作者：
K. Taniguchi;T. Koike
中科院分区：
文献类型：
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作者：
K. Taniguchi;T. Koike
[1]青藏高原积云活动有明显的季节变化规律。4月至5月中旬，高原东部活动频繁。从5月中旬到6月中旬，积云活动的频率急剧减少，然后在6月中旬后增加。现场无线电探空仪观测数据揭示了这种明确的季节性进展的原因。在早春，从地面到海拔7000米中午附近，位温的垂直分布几乎是均匀的，大气层结是垂直中性的干对流。在这样的条件下，干对流容易发生，并发展成经常观测到的积云。5月中旬至6月中旬，大气层结有条件不稳定，但大气相对干燥，几乎不饱和，积云活动较少。虽然大气在6月中旬后也有条件地不稳定，但总可降水量的增加使大气容易饱和，积云活动重新开始。同时，卫星资料和再分析资料表明，在青藏高原东部，积云活动、总可降水量和大气垂直不稳定度的季节变化具有一致的对应关系。天气尺度分析结果表明，印度北方积云对流和青藏高压的增强，使青藏高原水汽含量增加，高原上空积云活动频繁。
[1] Cumulus activity over the Tibetan Plateau has a clear pattern of seasonal progression. Activity occurs with significant frequency in the eastern part of the plateau from April to mid-May. From mid-May to mid-June the frequency of cumulus activity drastically decreases and then increases after mid-June. Causes of such definite seasonal progression are revealed by in situ radiosonde observation data. In early spring the vertical profile of potential temperature is almost uniform from the surface to 7000 m above sea level around noon, and atmospheric stratification is vertically neutral for dry convection. Under such a condition, dry convection easily occurs and develops cumulus cloud that is frequently observed. From mid-May to mid-June the atmosphere has conditionally unstable stratification, but the atmosphere is relatively dry and hardly saturated and cumulus activity occurs less frequently. Though the atmosphere is also conditionally unstable after mid-June, the increase in total precipitable water content allows easy atmospheric saturation and cumulus activity recommences. At the same time, satellite data and reanalysis data show, in the eastern part of the Tibetan Plateau, a consistent correspondence of the seasonal variation of cumulus activity, total precipitable water content, and vertical instability of the atmosphere. Results of synoptic-scale analysis indicate the enhancement of cumulus convection in the northern part of India and the Tibetan High cause a moisture increase over the Tibetan Plateau and leads to the recommencement of frequent cumulus activity over the plateau.