Parameterization of middle atmospheric water vapor photochemistry for high-altitude NWP and data assimilation J. P. McCormack1, K. W. Hoppel2, and D. E. Siskind1 1Space Science Division, Naval Research Laboratory, Washington DC, USA 2Remote Sensing Division, Naval Research Laboratory, Washington DC, USA
Abstract. This paper describes CHEM2D-H2O, a new
parameterization of H2O photochemical production and loss
based on the CHEM2D photochemical-transport model of the middle atmosphere.
This parameterization accounts for the
altitude, latitude, and seasonal variations in the photochemical sources and
sinks of water vapor over the pressure region from 100–0.001 hPa (~16–90 km altitude).
A series of free-running NOGAPS-ALPHA forecast model simulations offers
a preliminary assessment of CHEM2D-H2O performance over the June 2007 period.
Results indicate that the CHEM2D-H2O parameterization improves global 10-day forecasts of upper mesospheric
water vapor compared to forecasts using an existing one-dimensional (altitude only)
Most of the improvement is seen at high winter latitudes where the
one-dimensional parameterization specifies photolytic H2O loss year round
despite the lack of sunlight in winter.
The new CHEM2D-H2O parameterization should provide a better
representation of the downwelling of dry mesospheric air into the stratospheric polar vortex
in operational analyses that do not assimilate middle atmospheric H2O
Citation: McCormack, J. P., Hoppel, K. W., and Siskind, D. E.: Parameterization of middle atmospheric water vapor photochemistry for high-altitude NWP and data assimilation, Atmos. Chem. Phys., 8, 7519-7532, doi:10.5194/acp-8-7519-2008, 2008.