热带地区云量日变化的气候特征

利用国际卫星云气候计划（ISCCP）1984—2003年共20年云量资料，统计分析了热带地区的云量日变化特征，研究结果表明，云量峰值时间和变化幅度在全球的分布都较为均匀，而海陆差异明显。高云和低云在变化机制上相对独立，其云量日变化并非同步。全球云量日变化由4类基本形式组成，分别为洋面高云型、陆面高云型、洋面低云型和陆面低云型。高云日变化与地表辐射加热状况密切相关，其形式在洋面和陆面类似，均为早晨出现云量最小值而午后到达云量峰值。相比于洋面，陆面高云的峰值在夜间持续时间较长，可发展至更为稳定深厚的云系。低云多在局地5时附近出现云量峰值，18时左右达到云量极小值，其中陆面低云在12时出现第二峰值。

THE CLIMATOLOGICAL FEATURE OF DIURNAL VARIATION OF CLOUD AMOUNT OVER THE TROPICS

The diurnal cycle of tropical cloud amount was analyzed by using a 20-year International Satellite Cloud Climatology Project (ISCCP) dataset. Both peak time and amplitude are shown to be spatially even, with evident contrast between the ocean and land. The diurnal mechanisms of high clouds and low clouds are independent to each other, which results in non-synchronous diurnal phases. Four distinct components of the diurnal cycle were revealed for representing maritime high clouds, terrestrial high clouds, maritime low clouds, and terrestrial low clouds. The diurnal variations of high clouds are similar over the ocean and land and highly correlated with surface thermal situation. Since terrestrial high clouds usually evolve to become steady cloud clusters, they tend to have a relatively long peak during nighttime. Most low clouds peak before sunrise, while the minimum is reached in late afternoon. It was also found that terrestrial low clouds have a peak at noon in addition to the primary early-morning peak.