Spatial and temporal variability of deep convective clouds over the tropics using multi-year Megha - Tropiques – Sondeur Atmosphérique du Profil d’Humidité Intertropicale par Radiométrie (SAPHIR) observations

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.

Acknowledgements

The authors thank Dr. K. Rajeev, SPL, VSSC, Trivandrum for fruitful discussions. The CloudSat geometrical profile (2B-GEOPROF) product, which contains RADAR reflectivity data utilizing algorithms to identify weak cloud reflections from background instrument noise was obtained from (www.cloudsat.cira.colosate.edu). The SAPHIR level-1A1 and ScaRaB/3 level-2 data is obtained from MOSDAC through the website (www.mosdac.gov.in). MODIS monthly mean SST and ASCAT wind products were obtained from podaac-tools.jpl.nasa.gov. Sisma Samuel acknowledges ISRO Research Fellowship.

Disclosure statement

No potential conflict of interest was reported by the authors.