Abstract
Abstract. An evaluation of water vapor in the upper troposphere and lower stratosphere (UTLS) of the ERA-Interim, the global atmospheric reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF), is presented. Water vapor measurements are derived from the Fast In situ Stratospheric Hygrometer (FISH) during a large set of airborne measurement campaigns from 2001 to 2011 in the tropics, midlatitudes and polar regions, covering isentropic layers from 300 to 400K (5–18km). The comparison shows around 87% of the reanalysis data are within a factor of 2 of the FISH water vapor measurements and around 30% have a nearly perfect agreement with an over- and underestimation lower than 10%. Nevertheless, strong over- and underestimations can occur both in the UT and LS, in particularly in the extratropical LS and in the tropical UT, where severe over- and underestimations up to 10 times can occur. The analysis data from the evolving ECMWF operational system is also evaluated, and the FISH measurements are divided into time periods representing different cycles of the Integrated Forecast System (IFS). The agreement with FISH improves over the time, in particular when comparing water vapor fields for time periods before 2004 and after 2010. It appears that influences of tropical tropospheric and extratropical UTLS processes, e.g., convective and quasi-isentropic exchange processes, are particularly challenging for the simulation of the UTLS water vapor distribution. Both the reanalysis and operational analysis data show the tendency of an overestimation of low water vapor mixing ratio (⪅10ppmv) in the LS and underestimation of high water vapor mixing ratio (⪆300ppmv) in the UT.
Highlights
Water vapor is one of the most important greenhouse gases in the atmosphere and plays a key role in the atmospheric part of the climate system
Validation studies of the European Centre for Medium-Range Weather Forecasts (ECMWF) water vapor fields show that the operational analysis and forecasted upper troposphere and lower stratosphere (UTLS) water vapor fields might in some cases deviate significantly from independent in situ observations (Flentje et al, 2007; Schäfler et al, 2010)
A more climatological evaluation of water vapor fields based on the multiyear MOZAIC (Measurements of Ozone and Water Vapour by Airbus In-Service Aircraft) program was presented for the former ERA-40 data set by Oikonomou and O’Neill (2006) and for operational ECMWF analysis fields by Luo et al (2007)
Summary
Water vapor is one of the most important greenhouse gases in the atmosphere and plays a key role in the atmospheric part of the climate system. Validation studies of the ECMWF water vapor fields show that the operational analysis and forecasted UTLS water vapor fields might in some cases deviate significantly from independent in situ observations (Flentje et al, 2007; Schäfler et al, 2010). A more climatological evaluation of water vapor fields based on the multiyear MOZAIC (Measurements of Ozone and Water Vapour by Airbus In-Service Aircraft) program was presented for the former ERA-40 data set by Oikonomou and O’Neill (2006) and for operational ECMWF analysis fields by Luo et al (2007). The moist bias with an overestimation of the extratropical lower stratospheric specific humidity in the ECMWF operational analysis and forecast system has been intensively studied with CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) in situ measurements between 2005 and 2012 (Dyroff et al, 2014).
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