Tropical Tropopause Layer Cloud Formation, Convection and Stratospheric Dehydration

Mark R Schoeberl, Science and Technology Corporation, Earth Sciences, Boulder, CO, United States, Andrew E Dessler, Texas A&M Univ, College Station, TX, United States, Tao Wang, Texas A & M University, College Station, United States, Melody A Avery, NASA Langley Research Ctr, Hampton, VA, United States and Eric J Jensen, National Center for Atmospheric Research, Atmospheric Chemistry Observations and Modeling Laboratory, Boulder, CO, United States
Abstract:
Using MERRA reanalysis winds, temperatures and anvil cloud ice, we use our domain-filling, forward trajectory model to study the impact that more realistic cloud formation and convective water injection has on stratospheric water vapor. Our model computed cloud fraction shows reasonable agreement with cloud frequency observed by HIRDLS and CALIOP in the tropical troposphere layer (TTL). Our results suggest that ~64% of the cirrus formed in the TTL are due convection. Overall we find that inclusion of cloud microphysical processes increases stratospheric water vapor by 0.5 ppmv. Adding anvil ice increases stratospheric water vapor by an additional 0.5-0.6 ppmv but has a bigger impact on cloud formation with an increase of ~20-30% in TTL cloud fraction. With convection and cloud dehydration global 18-30 km average water vapor is ~5-7% higher than MLS water vapor observations. Adding waves to the MERRA temperature fields reduces stratospheric water vapor bringing our estimates to within 3% of MLS.
Back to: Processes Controlling Upper Troposphere / Lower Stratosphere Composition and Structure V