Comparison of Fast In situ Stratospheric Hygrometer (FISH) measurements of water vapor in the upper troposphere and lower stratosphere (UTLS) with ECMWF (re)analysis data

摘要

An evaluation of water vapor in the upper troposphere and lower stratosphere(UTLS) of the ERA-Interim, the global atmospheric reanalysis produced by theEuropean Centre for Medium-Range Weather Forecasts (ECMWF), is presented.Water vapor measurements are derived from the Fast In situ StratosphericHygrometer (FISH) during a large set of airborne measurement campaigns from2001 to 2011 in the tropics, midlatitudes and polar regions, coveringisentropic layers from 300 to 400K (5–18km).The comparison shows around 87% of the reanalysis data are within afactor of 2 of the FISH water vapor measurements and around 30% havea nearly perfect agreement with an over- and underestimation lower than 10%.Nevertheless, strong over- and underestimations can occur both in the UT andLS, in particularly in the extratropical LS and in the tropical UT, where severeover- and underestimations up to 10 times can occur.The analysis data from the evolving ECMWF operational system is alsoevaluated, and the FISH measurements are divided into time periodsrepresenting different cycles of the Integrated Forecast System (IFS).The agreement with FISH improves over the time, in particular when comparingwater vapor fields for time periods before 2004 and after 2010. It appearsthat influences of tropical tropospheric and extratropical UTLS processes,e.g., convective and quasi-isentropic exchange processes, are particularlychallenging for the simulation of the UTLS water vapor distribution.Both the reanalysis and operational analysis data show the tendency of anoverestimation of low water vapor mixing ratio (⪅10ppmv)in the LS and underestimation of high water vapor mixing ratio(rapprox;300ppmv) in the UT.