Characteristics of low clouds over the Arabian Sea

Abstract

[1] This paper studies climatically important low clouds (with cloud top below 680 hPa) over the Arabian Sea using the Kalpana-1 satellite data and International Satellite Cloud Climatology Project cloud data. Characteristics and possible mechanisms behind low-cloud formation in the summer monsoon season are presented. The dominant lower tropospheric circulation over the Arabian Sea during the summer season is the monsoon low-level jet (LLJ). Low clouds are predominantly found on the exit portion of the LLJ with decelerating winds. We postulate that the moisture carried by the LLJ from the entrance region with accelerating winds converge at the exit region with decelerating winds. This low-level convergence (observed~925 hPa level) may be conducive for moisture convergence, parcel uplifting, and low-cloud formation. These clouds are unable to grow vertically due to the presence of lower tropospheric thermal inversion. Change in the spatial extent of low-level convergence is found to influence the spatial coverage of the low clouds. It is found that low cloud cover is inversely related to the Indian summer monsoon activity. It is speculated that the changes in the strength of the lower tropospheric stability and spatial extent of convergence may be possible causes behind the observed inverse relation between low cloud cover and monsoon activity. Based on Clouds and the Earth's Radiant Energy System data, we find that these low clouds exert a peak cooling of about À55 Wm À2 .

Analysis of an extreme weather event in a hyper-arid region using WRF-Hydro coupling, station, and satellite data

“…The summer season extends from June to August and is greatly impacted by the Indian monsoon depression. The monsoon is associated with the low-level jet (LLJ) affecting the southern part of the peninsula (Sathiyamoorthy et al, 2013). The Tropic of Cancer, located under the descending limb of the Hadley cell, leads to the region being dominated by subtropical anticyclones, associated with air subsidence, stable conditions, and high pressure (Mandoos, 2006).…”

Variability of monsoon low‐level jet and associated rainfall over India

“…The MLLJ is formed primarily from the cross‐equatorial flow induced by differential heating in the summer hemisphere (between the latitudes 20°N and 20°S), which creates pressure gradient forces of heat lows over the Indian subcontinent and Mascarene High (Krishnamurti and Bhalme, ; Murakami, ; Hart, ). MLLJ winds blow primarily at heights between 1,000 and 4,000 m, with a core of jet at around 1,500 m above mean sea level (Boos and Emanuel, ), transport moisture from the Southern to Northern Hemisphere (Cadet and Reverdin, ; Roxy et al ., ), and also control the formation and maintenance of monsoon inversion layers over the western central Arabian Sea (Sathiyamoorthy et al ., ; Dwivedi et al ., ). The MLLJ also plays a major role in modulating the amount of rainfall over the Indian subcontinent (Wu et al ., ), in the active‐break monsoon rainfall spells, and intra‐seasonal oscillations of the ISM (Sam and Vittal Murty, ; Joseph and Sijikumar, ).…”

Differences in the association of sea surface temperature—precipitating systems over the Bay of Bengal and the Arabian Sea during southwest monsoon season

“…() have shown that the atmospheric circulation and thermodynamical parameters (convective available potential energy and convective inhibition) are influenced by the sea surface temperature (SST). The variation of convection (Graham and Barnett, ; Woolnough et al, ; Masunaga and Kummerow, ; Krishnamurthy and Kirtman, ; Rajendran et al, ; Sabin et al, ; Rajendran et al, ) and cloudiness (Gadgil et al, ; Meenu et al, ; Rajendran et al, ; Sathiyamoorthy et al, ; Nair and Rajeev, ) with SST has been documented over the Indian Ocean. Gadgil et al .…”