ABSTRACT

Multi-year seasonal mean diurnal variation of the occurrence frequency of Deep Convective Clouds (DCCs) over the tropical belt for various climatic regions including land and ocean are studied, using Level-1 brightness temperature ($T_{\mathrm{B}}$) data from Sondeur Atmosphérique du Profil d’Humidité Intertropicale par Radiométrie (SAPHIR) payload, aboard the Megha-Tropiques (MT) satellite for the period 2011 to 2018. The low inclination orbit of MT which provides the measurements at different local times makes the study of the diurnal cycle of DCCs possible from a single platform over the entire tropics. The spatial and temporal distribution of DCCs are derived for different seasons including measurements at all possible local time (LT) unlike measurements from a payload aboard polar-orbiting satellites. The seasonal variation of DCCs is in concurrence with the position of sun with maximum occurrence frequency in the summer months of the respective hemisphere. The largest occurrence of DCCs are found over the west Pacific and the northeast Bay of Bengal with a maximum occurrence frequency of around 4.0% during Northern Hemispheric summer. Central African landmasses, the South Pacific Convergence Zone, and the Amazon region also show a higher occurrence during their summer seasons. From the occurrence frequency maps, different regions are identified to estimate the seasonal mean diurnal variation of those regions. Over the continental regions, convective activity peaks during 15:00 to 18:00 LT and over the open ocean it peaks during 00:00 to 06:00 LT. Similarly, the convective activity is minimum over the oceanic region during 12:00 to 18:00 LT and over the land during 06:00 to 12:00 LT. The specific features associated with the distribution of DCC such as double Inter-Tropical Convergence Zone (ITCZ), the mean zonal diurnal variation of DCCs, the effect of El-Niño, the role of surface temperature and surface wind convergence on the occurrence of DCC are also presented.

摘要

利用1级亮度温度，研究了热带气候带（包括陆地和海洋）在热带带上深对流云（DCCs）的发生频率的多年季节性平均日变化（${Ť}_{\mathrm{乙}}$）的数据来自Megha-Tropiques（MT）卫星2011年至2018年期间的非洲国际辐射多变大气层（SAPHIR）有效载荷。对整个热带地区单一平台的DCC昼夜周期的研究。DCC的时空分布是针对不同季节得出的，包括在所有可能的本地时间（LT）进行的测量，这与极轨卫星上有效载荷的测量不同。DCC的季节变化与相应半球夏季月份中出现频率最高的太阳的位置有关。DCC的发生最多，发生在北太平洋的西太平洋和东北海湾，在北半球夏季最大发生频率约为4.0％。中部非洲大陆，南太平洋融合区和亚马逊地区在夏季也有较高的发生率。从发生频率图可以识别不同的区域，以估计这些区域的季节性平均日变化。在大陆地区，对流活动在中午15:00至18:00达到顶峰，而在远洋上，对流活动在中时00:00至06:00达到顶峰。同样，对流活动在LT的12:00至18:00期间在大洋区域最小，而在LT的06:00到12:00在陆地上对流最小。与DCC分配相关的特定功能，例如热带双热带融合带（ITCZ），