ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-9-23-2009 A daytime climatological distribution of high opaque ice cloud classes over the Indian summer monsoon region observed from 25-year AVHRR data Devasthale A. 1 3 Grassl H. 1 2 Meteorological Institute, University of Hamburg, Hamburg, Germany Max Planck Institute for Meteorology, Hamburg, Germany now at: Swedish Meteorological and Hydrological Institute, Norrkoping, Sweden 05 01 2009 9 1 23 58 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/9/23/2009/acpd-9-23-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/9/23/2009/acpd-9-23-2009.pdf

A daytime climatological spatio-temporal distribution of high opaque ice cloud (HOIC) classes over the Indian subcontinent (0–40&deg; N, 60&deg; E–100&deg; E) is presented using 25-year data from the Advanced Very High Resolution Radiometers (AVHRRs) for the summer monsoon months. The HOICs are important for regional radiative balance, precipitation and troposphere-stratosphere exchange. In this study, HOICs are sub-divided into three classes based on their cloud top brightness temperatures (<I>BT</I>). Class I represents very deep convection (<I>BT</I>&lt;220 K). Class II represents deep convection (220 K&le;BT&lt;233 K) and Class III background convection (233 K&le;<I>BT</I>&lt;253 K). Apart from presenting finest spatial resolution (0.1&times;0.1 degrees) and long-term climatology of such cloud classes from AVHRRs to date, this study for the first time illustrates on 1) how these three cloud classes are climatologically distributed during monsoon months, and 2) how their distribution changes during active and break monsoon conditions. It is also investigated that how many overshooting convective clouds reach the tropopause layer during individual monsoon months. It is seen that Class I and Class II clouds dominate the Indian subcontinent during monsoon. The movement of monsoon over continent is very well reflected in these cloud classes. During monsoon breaks strong suppression of convective activity is observed over the Arabian Sea and the western coast of India. On the other hand, the presence of such convective activity is crucial for active monsoon conditions and all-India rainfall. It is found that a significant fraction of HOICs (3–5%) reach the tropopause layer over the Bay of Bengal during June and over the north and northeast India during July and August. Many cases are observed when clouds penetrate the tropopause layer and reach the lower stratosphere. Such cases mostly occur during June compared to the other months.

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