Role of cloud feedback in regulating the “pool of inhibited cloudiness” over the Bay of Bengal
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Cloud-circulation feedback by latent heating (LH) is a major contributor for driving atmospheric circulation. This study examines the potential role of spatial variations of LH in driving a mini-circulation for generating the “pool of inhibited cloudiness”, where cloud formation in the lower and middle troposphere is significantly inhibited over the southwest Bay of Bengal (BoB) during the Indian summer monsoon. Spaceborne observations show that LH rates in the deep convective regions of the head BoB are as high as 0.2 K/h, while that over the “pool” are about 5 times smaller. This differential heating results in modulating the mean circulation. 20 years of reanalysis data show good correlation between (a) upper troposphere (300 hPa) convergence and lower tropospheric (1000 hPa) divergence at the “pool” and (b) lower tropospheric divergence at the “pool” and lower tropospheric convergence at the head BoB as well as at the west coast of India. Besides the orographic influence, a portion of the air mass descending at the “pool” arises from deep convective regions in the north BoB and equatorial trough. This subsidence is responsible for the persistent inhibition to cloud formation at the “pool”. This case forms a classic example of the cloud-circulation feedback.
2B-GEOPROF data were obtained from the CloudSat Data Processing Center through its website (http://www.cloudsat.cira.colostate.edu). TRMM-rain rate, convective, and stratiform heating data were obtained from NASA-GES DISC through www.disc.sci.gsfc.nasa.gov/precipitation. QuikSCAT scatterometer data were obtained from CERSAT through ftp://ftp.ifremer.fr/ifremer/cersat/products. ECMWF interim reanalysis data were obtained from http://www.ecmwf.int website. GPCP precipitation data were obtained from the Physical Sciences Division, ESRL (NOAA), The authors acknowledge Prof. A. Jayaraman, Director, NARL and Dr. Radhika Ramachandran, Director, SPL for their suggestions. The authors also thank the valuable suggestions and comments by the anonymous reviewers.
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