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

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 400 K (5-18 km).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 quasiisentropic 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 ( 10 ppmv) in the LS and underestimation of high water vapor mixing ratio ( 300 ppmv) in the UT.

Intercomparison of mid-latitude tropospheric and lower stratospheric water vapor measurements and comparison to ECMWF humidity data

“…This is in agreement with previous studies, e.g., by Kunz et al (2014) and Dyroff et al (2015). The latter study shows a good agreement between measurement and model for vertical distances to the tropopause of 6 km and higher and model wet bias between 2 and 6 km above the tropopause for the extratropics.…”

“…In that regime, mean deviations are in the order of 100% with an IQR of 70 to 140%. The large wet bias of the model in the tropopause region is consistent with findings in previous studies, e.g., by Kunz et al (2014) or Dyroff et al (2015). The model wet bias decreases substantially at higher potential temperatures leading to a mean difference of only 17% at potential temperatures above 370 K. The fact that the model bias 30…”

“…Kunz et al (2014) found a similar feature with good agreement between FISH measurements and EMCWF reanalysis data at altitudes higher than 6 km above the tropopause.…”

Sensitivities of Lagrangian modelling of mid-latitude cirrus clouds to trajectory data quality

“…As it is known that the moisture content in weather prediction models is very uncertain in the upper troposphere (Kunz et al, 2014), simulations with different specific humidity at the trajectory starting points were performed. We used initial humidities between 90 and 110 % of the values calculated by the COSMO-2 model.…”

“…The humidity is usually retrieved from stateof-the-art NWP models, although with large uncertainties in E. Kienast-Sjögren et al: Sensitivities of Lagrangian modelling of mid-latitude cirrus clouds 7431 the upper troposphere (Kunz et al, 2014). As ice nucleation occurs at a certain ice supersaturation, humidity errors can lead to significant shifts in the onset of ice nucleation as well as in the number of nucleated ice crystals (Dinh et al, 2015).…”