The Simulation of Stratospheric Water Vapor Over the Asian Summer Monsoon in CESM1(WACCM) Models.

Previous observational studies have found a persistent maximum in stratospheric water vapor (SWV) in the upper troposphere lower stratosphere (UTLS) confined by the upper‐level anticyclone over the Asian summer monsoon region. This study investigates the simulation of SWV in the Community Earth System Model, version 1 with the Whole Atmosphere Community Climate Model as its atmospheric component [CESM1(WACCM)]. CESM1(WACCM) generally tends to simulate a SWV maximum over the central Pacific Ocean, but this bias is largely improved in the high vertical resolution version. The high vertical resolution model with increased vertical layers in the UTLS is found to have a less stratified UTLS over the central Pacific Ocean compared with the low vertical resolution model. It therefore simulates a steepened potential vorticity gradient over the central Pacific Ocean that better closes the upper‐level anticyclone and confines the SWV within the enhanced transport barrier. Key Points: The discrepancies in simulating SWV over the Asian summer monsoon region are commonly found in WACCM experimentsThe UTLS temperature over the central Pacific Ocean is crucial in confining the SWV within the Asian summer monsoon anticycloneModel with high vertical resolution resolves the UTLS temperature more accurately which better confines the SWV within the transport barrier [ABSTRACT FROM AUTHOR]