Variability and Changes in Cloud Cover Over India During 1951-2010
Clouds have an enormous impact on weather and climate by reflecting sunlight, blocking outgoing long-wave radiation and producing precipitation. In addition, clouds also play an important role in the recycling of water vapour from the earth’s surface to the atmosphere and back again. Evaporation of water removes heat from the surface and represents an important cooling process. Clouds generally form in rising air, which expands and cools in the presence of condensation nuclei in the supersaturated air. The actual form of clouds so created depends on local conditions such as the strength of the uplift and air stability. In unstable atmospheric conditions, convection dominates, creating vertically developed clouds. Stable air produces horizontally homogeneous clouds. Due to high albedo, low-level clouds have a cooling effect, whereas high-level clouds trap outgoing long-wave radiation contributing to warming of the earth’s surface (Mace et al. 2006; Zelinka and Hartmann 2010).
Different cloud types contribute to total cloud amount and are associated with a wide variety of thermal and dynamic processes in the climate system. Clouds cover about two-thirds of the earth’s surface and exert great effects on earth’s radiation budget (Wild et al. 2004) and climate change by producing precipitation, reflecting short-wave solar radiation coming from the Sun and returning outgoing long-wave radiation from the surface (IPCC 2007). The effect of clouds on the earth’s radiation budget, the “cloud radiative forcing” (Ramanathan et al. 1989; Harrison et al. 1990), is generally negative in the daytime but positive at night. Therefore, knowledge of variations in cloud cover may improve our comprehension of the role of clouds in contemporary climate change (Warren et al. 2007).
A.K. Jaswal (H)
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M.N. Rajeevan and S. Nayak (eds.), Observed Climate Variability and Change Over the Indian Region, Springer Geology, DOI 10.1007/978-981-10-2531-0_7