Premonsoon estimates of convective available potential energy over the oceanic region surrounding the Indian subcontinent

Abstract

Convective available potential energy (CAPE) and convective inhibition energy (CIN) are important parameters in determining the stability of the atmosphere for moist convection. This paper presents the estimates of CAPE and CIN during the premonsoon season over the oceanic region surrounding the Indian subcontinent. The high‐resolution radiosonde data used in this study were collected as a part of the Integrated Campaign for Aerosols gases and Radiation Budget (ICARB; March–May 2006), which covered the Bay of Bengal, Arabian Sea, and parts of North Indian Ocean. We discuss the spatiotemporal variability of CAPE and CIN during the premonsoon period and investigate the role of boundary layer, as well as free tropospheric parameters in controlling the CAPE and CIN values. During the convective event of 9 April the sensors on board the ship recorded 4 mm of rain and an overall reduction of CAPE by 620 J kg−1was seen. This corroborates with the concept that CAPE generated by the nonconvective processes is consumed by the convection for its intensification. However, the observed reduction in CAPE after this convective event is much less compared to the monsoon season reported elsewhere. CIN was found to be anticorrelated with the free convection depth (FCD), which is the distance through which the parcel ascends by its own buoyancy. Thus the variability in CAPE and CIN is found to be interlinked through the FCD. Apart from this, contribution to total CAPE from various levels are also estimated, which shows that the CAPE in the middle levels contributes most toward the total CAPE. Our investigations show that although the CAPE and CIN are related to the tropospheric parameters like temperature lapse rate, the variability in CAPE and CIN is essentially determined by the moisture in the atmospheric boundary layer. As the equivalent potential temperature (θE) in the ABL increases, CAPE increases, favoring the development of convection.