Trends of Convective Available Potential Energy over the Indian region and its effect on rainfall

• Published in: International journal of climatology 2012-07, Vol.32 (9), p.1362-1372
• Main Authors: Murugavel, P., Pawar, S. D., Gopalakrishnan, V.
• Format: Article
• Language: English
• Subjects: Convective Available Potential Energy; Earth, ocean, space; Exact sciences and technology; External geophysics; Indian monsoon rainfall; low-level mixing ratio; Meteorology; upper level temperature
• ISSN: 0899-8418; 1097-0088
• DOI: 10.1002/joc.2359

Many studies in recent times have suggested that long‐term changes in Convective Available Potential Energy (CAPE) are associated with the changes in convective activity and atmospheric energy budget and, hence, the changes in CAPE could be used as a potential indicator of climate change. Here, we analyse daily radiosonde data of 32 stations over the Indian region from 1984 to 2008 (25 years), to study the climatology and long‐term changes in CAPE, lower troposphere moisture content and upper tropospheric temperature. Using gridded daily rainfall data over this region, the relationship between average CAPE and average rainfall as well as the trends in CAPE and its effect on rainfall pattern are also examined during different seasons of this region. All the coastal and island stations, as well as some stations in the foothills of the Himalayas, show higher values of CAPE compared to other inland stations. This study clearly demonstrates that CAPE values have been systematically increasing over most parts of the Indian region during last 25 years. The increase in CAPE is found to be due to increase in low‐level moisture content and decrease in upper level temperature over the last 25 years. The seasonal variations show that the CAPE is higher during the monsoon compared to pre‐monsoon or post‐monsoon seasons and it suggests that thermodynamic conditions favourable for high CAPE together with large‐scale dynamics are necessary for organized monsoon convections over this region. In comparison with a large increase in the all‐India average of CAPE during monsoon season, which is about 38 J Kg−1 year−1, the all‐India summer monsoon rainfall increases about 1.3 mm year−1. The systematic increasing trend in CAPE may be compensating for weakening of monsoon circulation and, thus, maintaining the monsoon rainfall over the Indian region. Copyright © 2011 Royal Meteorological Society