Abstract
Abstract. Clouds affect the radiative energy balance of the earth–atmosphere system by reflecting and trapping the radiation. The cooling occurs over the earth by reflecting the incoming solar radiation and warming by trapping the outgoing longwave terrestrial radiation. In this paper an attempt has been carried out to understand the clouds and cloud radiative forcing over the windward side of the Madagascar mountain chain. The study was carried out using the Clouds and Earth’s Radiant Energy System (CERES) data June–September from 2000 to 2016. Over the windward side, clouds tend to cool whereas on the leeward side, clouds tend to warm marginally. During this period, peak value of shortwave cloud forcing and the longwave cloud forcing are −45 W m−2 and +15 W m−2 respectively. Generally, the clouds are restricted to low level in the windward side. We also examined the association between the cloud radiative forcing and cloud physical properties such as cloud optical depth, cloud, cloud top temperature and cover amount. The cloud optical depth (−0.74 correlation value) and cloud cover amount (−0.51 correlation value) show better correlation with net cloud radiative cooling. The surface pressure of the Madagascar is also correlated with the net cooling over the windward side.
Highlights
Clouds are composed of liquid droplets and frozen ice particles suspended in the atmosphere
The 9-year average (2000-2008) monthly total cloud cover amount and cloud top pressure obtained from ISCCP cloud data during June to September (JJAS) months over the Madagascar and surrounding region have been shown in Fig.4 (a-b)
The cloud radiative forcing (CRF) components are plotted for different cloud cover amount (CCA) and cloud optical depth (COD) bins for the east box for JJAS months for the 9-year analysis period (Fig.11)
Summary
Clouds are composed of liquid droplets and frozen ice particles suspended in the atmosphere. Several studies made attempts to estimate the net radiative effect of clouds with satellite measured radiation budget data (Hartmann, et al, 1986; Ramanathan, et al, 1989; Sathiyamoorthy et al, 2004; 2007; 2011). Rajeevan and Srinivasan (2000) noted that the Indian summer monsoon clouds exert a net cooling effect which otherwise is unique in the tropical belt They suggested that large amount of high level clouds found over this region with high optical depth may be the reason for the radiative cooling. In Fig., visible channel imagery of MODIS onboard Terra satellite for a typical day during June-September months (10 September 2016) is shown On this Day, clouds are seen over the east coast of Madagascar and the eastern parts of mountain chain. As Madagascar mountain chain is isolated from nearby land or orographic features of Africa, it is an ideal place to study the characteristics of the orographically generated clouds and their radiative forcing
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