Fourth Study Conference on BALTEX Scala Cinema Gudhjem

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Observation of Clouds and Water Vapour with Satellites
M. Reuter 1 , P. Lorenz 2 , J. Fischer 1
1 Institut fuer Weltraumwissenschaften, Freie Universitaet Berlin, max.reuter@wew.fu-berlin.de
2 MPI fuer Meteorologie Hamburg
1. Introduction
Most interaction processes between earth surface and
atmosphere as well as those between different atmospheric
layers are significantly affected by clouds. This interaction
results on the one hand from the dynamic and
thermodynamic processes connected to clouds and on the
other hand from their dominant feedback on the radiation
and water budget. For this reason it is indispensable to
achieve a realistic representation of clouds and their
properties and of the atmospheric water vapour content in
climate models. Precondition for improving existing climate
models and their physical parameterizations is their
validation by comparing with observations. In this context
the following parameters are of special interest: cloud
optical thickness (COT), broadband albedo (BB-albedo),
integrated water vapour (IWV), cloud droplet number
concentration (CDNC), cloud top pressure (CTP), cloud
droplet effective radius (CER), fractional cloud coverage
(FCC). Modern temporally, spatially and spectrally high
resolving sensors like SEVIRI on MSG, MODIS on AQUA
and MERIS on ENVISAT offer an excellent access to these
parameters. Sensors like METEOSAT that have been
working operationally for long time provide important data
also especially in respect of long time series. The multitude
of available sensors on different satellites allows
predications on the product quality by intercomparison. The
geostationary operating satellites METEOSAT and MSG
provide a high time resolution and are therefore suitable for
deriving diurnal cycles and analyzing processes on short
time scales. The sensors on the polar orbiters AQUA and
ENVISAT provide higher spatial and spectral resolution and
therefore more information on spatial scales far below the
horizontal resolution of regional climate models like
BALTIMOS (BALTEX Integrated Model System) as well
as superior access to microphysical cloud parameters.
The investigation of those parameters above including the
comparison with the climate model BALTIMOS is object of
the subproject “observation of clouds with satellites” of the
BALTIMOS project embedded in the DEKLIM project.
2. Results
Comparisons of the parameter IWV and FCC derived from
satellite data with those from the climate model BALTIMOS
will be presented. BALTIMOS was driven in “climate
mode” unlike in “forecast mode”. This causes that only
statistical comparisons are applicable. Spatial distributions
of the average, standard deviation (Figure 1. ) and the data
density as well as histograms (Figure 2. , left), contour
diagrams (Figure 3. ), diurnal (Figure 2. , right), and annual
cycles will be shown. The differences will be discussed
considering the characteristics of the climate model and the
satellite data algorithms.
Figure 1. Spatial distribution of IWV standard deviation
in 2002 (cloud free cases over land only). Left:
BALTIMOS; right: MODIS.
Figure 2. Data from cloud free cases over land in 2002.
Red: MODIS, black: BALTIMOS. Left: Histogram of
IWV. Right: Annual cycle of IWV, bars representing the
standard deviation.
Figure 3. Annual and diurnal distribution of FCC
derived from METEOSAT in the period from 01.1998 to
12.2002