Cloud Radiative Forcing at Earth's Surface at a Coastal Station in the Southwest Peninsular India during the Asian Summer Monsoon Season
Abstract
Southwest Peninsular India is the gateway for the massive Asian summer monsoon (ASM) flow over to the Indian subcontinent. Onset of ASM over this region is marked by the appearance of widespread rain-bearing cloud bands, which propagate northwards during the advancement of ASM over the Indian region. Radiative impact of clouds is the single largest geophysical factor controlling the variability of Earth Radiation Budget over tropics. Energy balance at the surface in the southwest Indian peninsula and west placeArabian Sea during ASM is mainly controlled by clouds, which decrease the downwelling shortwave radiative flux and increase the downwelling longwave flux. Instantaneous shortwave cloud radiative forcing (SWCRF) at surface is defined as the downwelling shortwave radiative flux reaching the earth's surface under the prevailing cloudy condition minus the corresponding values under clear sky condition. Similar is the definition for longwave cloud radiative forcing (LWCRF). Sum of the SWCRF and LWCRF is the net cloud radiative forcing (NCRF). Cloud radiative forcing at a given location is highly variable, depending on the coverage and properties of clouds. This paper presents temporal variations of the diurnal mean SWCRF and LWCRF over a tropical coastal station, placeCityTrivandrum (8.5oN, 77oE), during the May to September period of 2011, which encompasses the onset and evolution of the Asian summer monsoon. On average, the diurnal mean SWCRF rapidly changes from <-80Wm-2 to <-120Wm-2 during the onset phase of summer monsoon. The monthly mean values of SWCRF over Trivandrum are found to be -37±5Wm-2, -57±11Wm-2, -76±8Wm-2, and -59±7 Wm-2 during May, June, July and August respectively. On the contrary, magnitude of the LWCRF are substantially smaller than that of the SWCRF with a magnitude of 26.7±5 Wm-2, 21.4±7 Wm-2, 18.2±.4 Wm-2and 18.6±5.7 Wm-2 and the NCRF is negative, which causes a net cooling of the earth's surface throughout the period.
- Publication:
-
39th COSPAR Scientific Assembly
- Pub Date:
- July 2012
- Bibcode:
- 2012cosp...39.1322N