CloudSat observations of cloud-type distribution over the Indian summer monsoon region

K V Subrahmanyam,K K Kumar

doi:10.5194/angeo-31-1155-2013

Abstract

Abstract. The three-dimensional distribution of various cloud types over the Indian summer monsoon (ISM) region using five years (2006–2010) of CloudSat observations during June-July-August-September months is discussed for the first time. As the radiative properties, latent heat released and microphysical properties of clouds differ largely depending on the cloud type, it becomes important to know what types of clouds occur over which region. In this regard, the present analysis establishes the three-dimensional distribution of frequency of occurrence of stratus (St), stratocumulus (Sc), nimbostratus (Ns), cumulus (Cu), altocumulus (Ac), altostratus (As), cirrus (Ci) and deep convective (DC) clouds over the ISM region. The results show that the various cloud types preferentially occur over some regions of the ISM, which are consistent during all the years of observations. It is found that the DC clouds frequently occur over northeast of Bay of Bengal (BoB), Ci clouds over a wide region of south BoB–Indian peninsula–equatorial Indian Ocean, and Sc clouds over the north Arabian Sea. Ac clouds preferentially occur over land, and a large amount of As clouds are found over BoB. The occurrence of both St and Ns clouds over the study region is much lower than all other cloud types.The interannual variability of all these clouds including their vertical distribution is discussed. It is envisaged that the present study opens up possibilities to quantify the feedback of individual cloud type in the maintenance of the ISM through radiative forcing and latent heat release.

Highlights

These authors emphatically showed that the cloud-type variations are as important as cloud cover in modifying the radiation field of the earth–atmosphere system and further showed that the largest annual mean changes of the global top-of-atmosphere and surface shortwave radiative fluxes are produced by stratocumulus, altostratus, and cirrostratus clouds; whereas cirrus, cirrostratus, and deep convective clouds cause most of the annual mean changes in the global top-of atmosphere longwave radiative fluxes
During the Indian summer monsoon (ISM), the convective storms over most northern parts of Bay of Bengal (BoB) produce copious amounts of Ci clouds, which are spread over the ISM region by the strong Tropical Easterly Jet (TEJ)
The drought year of 2009, it can be noticed that the frequencies of occurrence of all cloud types are reduced compared to other years, and it is very interesting to note that the vertical distribution of deep convective (DC) clouds reflects the monsoon rainfall

Summary

Introduction

The height profiles of frequency of occurrence in each grid box provided the 3-D distribution of cloud types over the ISM region. It is important to know the diurnal variation in occurrence of cloud types, if any, as CloudSat observations cover only two local times over the ISM region.

Results

Conclusion