Fourth Study Conference on BALTEX Scala Cinema Gudhjem

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Clouds and Water Vapor over the Baltic Sea 2001-2003: First Results of the
new Preliminary DWD Climate Monitoring Programme
Peter Bissolli, Helga Nitsche and Wolfgang Rosenow
Deutscher Wetterdienst (DWD, German Meteorological Service), P.O. Box 10 04 65, D-63004 Offenbach, Germany
Email: peter.bissolli@dwd.de
1. DWD Climate Monitoring Programme
The German Meteorological Service (DWD) starts a new
Climate Monitoring Programme this year. The main
objective of this programme is combining climate data of
various sources (satellite measurements, ground-based
observations at weather and climate stations, model output
results of weather forecast models) to value-added climate
monitoring products.
The climate elements which are considered in this
programme are preferably those which are in particular
important for the hydrological cycle and the energy balance
on the earth and in the atmosphere. They are listed in Fig. 1.
Clouds
• fractional cloud cover
• cloud cover in layers
• frequency of cloud type
Water vapour content (PW)
Frequency of fog
Radiation at the Surface
• Global radiation
• Downward longwave radiation
• Radiation balance
Heat fluxes
at the surface
Radiation balance
at the top of the atmosphere
Energy balance
in an atmospheric volume
Energy balance
at the surface
Figure 1. Climate elements of the new DWD Climate
Monitoring Programme.
The climate monitoring programme will run operationally
on a monthly basis. Presently it is still under construction. In
a first stage the system will be implemented only with the
two elements total fractional cloud cover and water vapor
content (precipitable water). Later on, the other elements
will be added to the system, so that finally the whole energy
balance at the earth’s surface and in an atmospheric volume
(column) from the earth to the top of the atmosphere can be
derived. The evaluation area covers Europe and the North
Atlantic, so the Baltic Sea area is included.
The basic concept of the monitoring programme consists at
the moment of constructing maps of monthly averages and
their anomalies in comparison to the reference period 1971-
2000, and also diagrams of daily averages and monthly
mean diurnal cycles. A continuous validation and
homogeneity checks are also planned. Other evaluation
methods, e.g. derivation of special climate indices and time
series analysis will be implemented later. More details of the
climate monitoring programme with first examples are
described by Bissolli et al. (2002).
Some preliminary products of cloud cover and precipitable
water exist already for recent years and are generated
operationally every month. This paper concentrates on an
evaluation and interpretation of a selection of these products
for the time period 2001-2003. It refers in particular to the
Baltic Sea region and its surroundings, to contribute to the
understanding of present climate variability in this region in
comparison to other parts of Europe.
2. Cloud Cover Results
The present operational cloud cover product is based on
the so called DWD “Satellite Weather”. The “Satellite
Weather” is an assimilation procedure using hourly
METEOSAT satellite data, observations at synoptical and
radiosonde stations, but also numerical weather prediction
results. The method is described by Rosenow et al. (2001).
In regions with a high density of synoptical data, the
analysis results are mainly determined by these data, in
other areas, e.g. over the oceans, cloud cover is derived
directly from classified (clustered) satellite information
using threshold value tests.
The algorithm is fast and it provides immediately hourly
products in METEOSAT pixel resolution (ca. 10 km over
the Baltic Sea) which can be used for nowcasting
purposes. Here, in this context, daily, monthly, seasonal,
half-yearly and yearly averages are taken for
climatological analyses.
As an example, monthly averages of selected months from
each season are shown in Fig. 2 for the years 2001-2003.
Jan 2001 Jan 2002 Jan 2003
Apr 2001
Apr 2002
Apr 2003
Jul 2001 Jul 2002 Jul 2003
Oct 2001 Oct 2002 Oct 2003
Figure 2. Monthly averages of cloud cover over the
Baltic Sea area based on the DWD “Satellite
Weather” product for selected months of each
season of the years 2001-2003. Colours are half octa
intervals (see legend on the right).
The results show a high year-to-year variability of the
monthly mean cloud pattern in all seasons. The cloudiness
over the Baltic Sea is influenced by cloud advection from
the east, but it profits also from lee effects due to the
mountain chain in western Scandinavia.