Tropical Tropopause Layer Cloud Formation, Convection and Stratospheric Dehydration

Thursday, 18 December 2014: 11:05 AM
Mark R Schoeberl, Science and Technology Corporation, Boulder, CO, United States, Andrew E Dessler, Texas A&M Univ, College Station, TX, United States, Tao Wang, Texas A & M University, College Station, TX, United States, Melody A Avery, NASA Langley Research Ctr, Hampton, VA, United States and Eric J Jensen, NASA Ames Research Center, Moffett Field, CA, United States
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.