Enhancement in the upper tropospheric humidity associated with aerosol loading over tropical Pacific

Many modeling studies have indicated that aerosol interactions with clouds increase the upper tropospheric humidity (UTH), but observational evidences are sparse. Using satellite datasets of upper tropospheric humidity and aerosols, this study shows that aerosols increase the upper tropospheric humidity over the tropical North West Pacific (NWP) and North East Pacific (NEP). The observations show an increase in the UTH by 2.8%RH over NEP for an increment of 0.12 in aerosol optical depth (ADD) and 2%RH increase in UTH over NWP for an increment of 0.19 in AOD. The study also quantifies the change in longwave cloud radiative forcing (LWCRF) as a consequence of the increase in UTH due to aerosols. The LWCRF increases by 3.38 W m(-2) over NEP and by 4.46 W m(-2) over NWP. The result that aerosols increase the upper tropospheric humidity is significant since the latter plays a crucial role in regulating the Earth's radiation budget and water vapor feedback. (C) 2015 Elsevier Ltd. All rights reserved.