Middle atmosphere water vapour and dynamical features in aircraft measurements and ECMWF analyses D. G. Feist1,*, A. J. Geer2,**, S. Müller1, and N. Kämpfer1 1Institute of Applied Physics, University of Bern, Switzerland 2Data Assimilation Research Centre, University of Reading, UK *now at: Max Planck Institute for Biogeochemistry, Jena, Germany **now at: European Centre for Medium-Range Weather Forecasts (ECMWF), Reading, UK
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
in-depth 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.
Citation: Feist, D. G., Geer, A. J., Müller, S., and Kämpfer, N.: Middle atmosphere water vapour and dynamical features in aircraft measurements and ECMWF analyses, Atmos. Chem. Phys., 7, 5291-5307, doi:10.5194/acp-7-5291-2007, 2007.