Vertical Structure and Radiative Forcing of Monsoon Clouds Over Kanpur During the 2016 INCOMPASS Field Campaign

摘要

An overview of cloud vertical structure (CVS) and cloud radiative forcing (CRF) during Indian summer monsoon is obtained over Kanpur, through observations made during the Interaction of Convective Organisation and Monsoon Precipitation, Atmosphere, Surface and Sea field campaign of 2016. Associations of CVS parameters with CRF at surface and top of atmosphere (TOA) are also investigated. One hundred thirty-seven radiosondes were launched at Indian Institute of Technology Kanpur, between 5 and 28 July 2016. CVS is determined using an algorithm that identifies cloud layers from vertical profiles of relative humidity, with altitude-dependent relative humidity thresholds. CVS is analyzed by separating the campaign period on the basis of presence and absence of depressions/low-pressure systems. Compared to nondepression periods, low-pressure events showed significant difference in all CVS and CRF parameters except cloud top height. CVS was multilayered in ～75% launches, with deep, mixed-phase clouds being present in ～70% launches. CRF was calculated from clear-sky measurements and TOA observations from Clouds and the Earth’s Radiant Energy System satellite retrievals, and surface measurements. A net cooling effect was found overall, with instantaneous shortwave CRF (mean values of ?95.92 and ?101.89 W/m~2 at surface and TOA, respectively) dominating longwave cloud radiative forcing (LWCRF) (mean values of 15.33 and 66.55 W/m~2 at surface and TOA, respectively). Results suggest that shortwave CRF depends on total depth of cloud layers and is independent of cloud altitude, whereas LWCRF depends on both depth and vertical location of cloud layers, with base and top heights regulating LWCRF at surface and TOA, respectively.