**2. Topography of study region**

involves both scattering and absorption of radiation, and the relative importance of these processes depends on their chemical composition, refractive index, and size distribution [4, 5]. The indirect effect of aerosols on climate occurs by modifying the cloud optical properties [6]. Thus, the concentration, size, and composition of aerosols which can act as cloud condensation nuclei determine the cloud properties, evolution, and development of precipitation [7]. Aerosols modify cloud properties and precipitation via a variety of mechanisms with varying and

Cloud interactions with aerosols are hypothesized to be critical to understanding the climate change since clouds play a pivotal role in controlling incoming and outgoing radiation [9]. A large number of studies showed that the anthropogenic aerosols change clouds and their optical properties [4, 10, 11]. Atmospheric aerosols change the concentration and size of the cloud droplets which in turn lead to a change in cloud albedo, its lifetime and thereby affect the precipitation [6, 12]. Also, the reduction in cloud effective radius due to the increase in cloud droplet number concentration (CDNC) leads to the increase in cloud lifetime. The possible repercussion of this process is to decrease the rate of surface evaporation which results in stable and drier atmosphere as a result of the reduction in cloud formation [12]. Anthropo‐ genic aerosols influence mixed‐phase clouds in a number of ways and needs comprehensive study to understand the precise phenomenon. A great number of studies were conducted on the possible modification of cloud properties via the interaction with atmospheric aerosol particles, as this may lead to important changes in the Earth's climate. Biomass burning aerosols have been shown to affect clouds through both microphysical and radiative mecha‐ nisms [7, 13]. Biomass burning, from both deforestation and annual agricultural burning, is the largest anthropogenic source of such particles in the Southern Hemisphere. Biomass burning aerosols are hygroscopic and can serve as cloud condensation nuclei [14, 15]. More recently, satellite analyses have revealed a persistent correlation between cloud fraction and aerosol optical depth in regions influenced by marine aerosol, smoke, dust, and industrial air

The first indirect effect known as the Twomey effect produces the reduction in cloud effective radius due to the increase in aerosol loading for fixed liquid water path (LWP). Opposite of this effect (i.e., as aerosol loading increases cloud effective radius also increases) were observed over some parts of the world in certain environmental conditions [16]. The Twomey effect and Albrecht effect (i.e., lifetime effect) facilitate cooling of the atmosphere by increasing cloud optical depth (COD) and cloud fraction (CF), respectively [17]. This causes a reduction in the net solar radiation at the top of the atmosphere and hence at the surface. Several other studies have pointed out that the aerosol–cloud interactions are not determined by aerosols alone, but the regional meteorological conditions can play a significant role in this relationship [18]. Comparison of the modeled results and MODerate Resolution Imaging Spectroradiometer (MODIS) retrievals for aerosol indirect effect investigated by Myhre et al. [10] and Storelvmo et al. [18] showed a negative correlation between AOD and cloud effective radius (CER) while

a positive correlation was observed between AOD and cloud optical depth (COD).

Extensive studies were conducted on various mechanisms of cloud properties through the interaction of atmospheric aerosol particles with cloud parameters which further influence the

contradicting consequences [8].

170 Aerosols - Science and Case Studies

pollution [4].

The Deccan Plateau is a large region that covers most of South Central India. The average elevation is 1000–2000 feet (305 and 610 m) above sea level along the northern sections of the region and 2000–3000 feet (610 and 915 m) in the southern section. Red loam or sandy loam soil usually overlies the granites and metamorphic rocks resulting in less fertile and less moisture retentive soil than found in the North Deccan region. The region slopes generally eastward allowing the drainage to flow toward the Bay of Bengal. Water in the rivers fluctuates considerably during the monsoon and the dry seasons. Their only source of water is the monsoon rains unlike rivers flowing out of the Himalayas that have year‐round moisture from snow packs in the high mountains. In the winter or dry season, many of the rivers throughout the South Deccan become almost dry and are useless for irrigation. Also, some of the rivers flow through well‐incised valleys, allowing little space for a flood plain and making it nearly impossible to direct water for irrigation onto the adjoining uplands. The climate is generally semi‐arid with <35 inches (89 cm) of rainfall. Ironically, the Western Ghats are only 30–40 miles (48–64 km) away with annual precipitations exceeding 100 inches (254 cm).

In the Indian part of the Western Himalayas the surface weather elements, like precipitation and temperature, are intensely governed by local topography and local atmospheric circula‐ tions. The different altitude and orientation of the Himalayan ranges give rise to different thermo dynamical and dynamical forcing. Topography, heterogeneity, and land use variability are the characteristics of Western Himalayas (WH). Western disturbances (WDs), embedded in large‐scale westerlies are responsible for winter precipitation, mainly snow, in WH. The interplay of topography with WDs determines orographic precipitation over the Himalayan region.
