Aerosol, clouds and water vapor transport across the tropopause: observations and model results

Aerosols can affect cloud particle size and lifetime, which impact precipitation, radiation and climate. Increased aerosols may cause higher water vapor abundance in air that enters the stratosphere by increasing tropopause temperature and altering cloud properties in the tropical tropopause layer. We have analyzed recent satellite observations from Aura Microwave Limb Sounder (MLS) and other instruments, focusing on the polluted regions over South and East Asia. We found that polluted ice clouds have smaller ice effective radius, and higher temperature and specific humidity near the tropopause than clean clouds, suggesting a possible enhancement in water vapor transport from the troposphere to the stratosphere by aerosol effects. The stratospheric water vapor is observed to have a slightly increasing trend during Aura observation period from 2004 to 2010, coincidental with the Asian aerosol trend. The contributions of atmospheric dynamics and aerosol effects to the stratospheric water vapor trend are investigated. Simulations from a coupled aerosol-climate model also show that increasing black carbon and sulfate causes increased temperature and water vapor in the upper troposphere and lower stratosphere.