Multitimescale variations in modeled stratospheric water vapor derived from three modern reanalysis products

Abstract

Stratospheric water vapor (SWV) plays important roles in the radiation budget and ozone chemistry and is a valuable tracer for understanding stratospheric transport. Meteorological reanalyses provide variables necessary for simulating this transport; however, even recent reanalyses are subject to substantial uncertainties, especially in the stratosphere. It is therefore necessary to evaluate the consistency among SWV distributions simulated using different input reanalysis products. We evaluate the representation of SWV and its variations on multiple timescales using simulations over 1980-2013 based on the Chemical Lagrangian Model of the Stratosphere (CLaMS) driven by three recent reanalyses: ERA-Interim, JRA-55 and MERRA-2. We find reasonable consistency among simulations of the distribution and variability of SWV with respect to the annual cycle (AC) and quasi-biennial oscillation (QBO). However, the amplitudes of both signals are systematically weaker in the lower and middle stratosphere when CLaMS is driven by MERRA-2. This difference is attributable to relatively slow tropical upwelling in the lower stratosphere based on MERRA-2, which is related to the large long-wave radiative effect and the unique assimilation process in MERRA-2. The impacts of ENSO and volcanic aerosol on H2O entry variability are qualitatively consistent among the three simulations despite differences of 50-100 % in the magnitudes. Trends show large discrepancies among the three simulations. CLaMS driven by ERA-Interim produces a neutral to slightly positive trend in H2O entry values over 1980-2013 (+0.01 ppmv decade-1), while both CLaMS driven by JRA-55 and by MERRA-2 produce negative trends but with significantly different magnitudes (−0.22 ppmv decade-1 and −0.08 ppmv decade-1, respectively).