Middle atmosphere water vapour and dynamical features in aircraft measurements and ECMWF analyses

Abstract

Abstract. The European Centre for Medium-Range Weather Forecasts (ECMWF) provides global analyses of atmospheric humidity from the ground to the lower mesosphere. Unlike in the troposphere, in the stratosphere no humidity observations are assimilated. Humidity analyses here are essentially the results of a free-running model constrained by the ECMWF's analysed wind fields. So far only the broad-scale features of the resulting stratospheric water vapour distribution have been validated. This study provides the first indepth comparison of stratospheric humidity from ECMWF with observations from an airborne microwave radiometer that has measured the distribution of stratospheric water vapour over an altitude range of roughly 15-60 km on several flight campaigns since 1998. The aircraft measurements provide a horizontal resolution that cannot be achieved by current satellite instruments. This study examines dynamical features in the moisture fields such as filamentation and the vortex edge, finding that features in the ERA-40 humidity analyses often do correspond to real atmospheric events that are seen in the aircraft measurements. However, the comparisons also show that in general the ECMWF model produces an unrealistically moist mesosphere. As a result it cannot replicate the descent of relatively dry mesospheric air into the polar vortex in winter and spring.

The 2009 stratospheric major warming described from synergistic use of BASCOE water vapour analyses and MLS observations

“…Data assimilation has been used successfully to produce analyses of stratospheric constituents such as ozone and water vapour; evaluate observations of stratospheric chemical constituents; and evaluate chemical models. Papers describing this work include (the list is not exhaustive) Fisher and Lary (1995), Khattatov et al (2000), Errera and Fonteyn (2001), Dethof and Hólm (2004), Geer et al (2006Geer et al ( , 2007, Lahoz et al (2007a, b), Jackson (2007), McCormack et al (2008), Eckermann et al (2009), Thornton et al (2009) and Lahoz and Errera (2010). The review by Lahoz et al (2007a) includes a comprehensive list of references.…”

Validation of stratospheric water vapour measurements from the airborne microwave radiometer AMSOS

“…The change is done at the intersection point of the ERA40 profile and the USStandard profile in about 45 km altitude. From an earlier study (Feist et al, 2007) we know that ERA40 values at the top of the stratosphere diverge from observations. For the temperature and pressure profiles we used data from ECMWF continued by CIRA86 (Rees et al, 1990) for the altitude levels above the top of the ECMWF atmosphere.…”

“…4e the high values at the bottom of the plot in red color extend to 17 km in the tropics and 13 km in the Arctic. For additional dynamical discussions see (Feist et al, 2007).…”

“…The dataset overlaps several satellite experiments in time. In a previous work (Feist et al, 2007) this dataset was compared to the ECMWF model.…”

The COST 723 Action

“…D' Aulerio et al (2004) describe an intercomparison of water vapour retrievals between three Raman lidar stations. Feist et al (2007) describe a comparison between aircraft microwave humidity data and the ECMWF analysis, demonstrating that the mesosphere and upperstratosphere polar vortex are too dry in the ECMWF analyses, which are not based on direct observations. Feist et al also provide a better understanding of the limitations of microwave observation in the UTLS region.…”