Fourth Study Conference on BALTEX Scala Cinema Gudhjem

While the number of smallest drops measured by the OD is
independent of wind speed, the number of detected small
drops drastically decreases with wind speed for the JW
measurements.
Figure 3. Same as in Figure 2, but now the spectral
resolution of the OD was reduced to that of the JW.
a) b)
Figure 4. (a) gives the spectral rain rates of the OD
and the JW for situations with wind speeds less than
5ms -1 and (b) for situations with wind speeds ranging
from 5 to 10ms -1 .
4. Measured drop size spectra
Drop size spectra were measured in Westermarkelsdorf on
the island of Fehmarn, in Zingst, on a building of the IFM-
GEOMAR, and on the R/V Alkor by ODs. Measured drop
size distributions are analyzed for different ranges of rain
rates under the assumption that low rain rates are more
likely connected with stratiform rain, while high
precipitation rates are more typical for convective
precipitation events.
Examples of measured drop size spectra are given in Figure
5 for the Baltic Sea area, R/V Alkor, and for a coastal
station, Westermarkelsdorf. Differences between coastal
measurements and those over the Baltic Sea occur mainly in
the number of small drops. Measurements over the sea
contain less small drops than measurements over land.
5. Conclusions
Measurements of drop size spectra over land and sea
indicate significant differences. This indicates that relations
like the Z/R-relation differ over land and sea, which should
have an impact on precipitation rates retrieved from remote
sensing measurements like radar estimates.
- 49 -
Figure 5. Drop size spectra measured over sea on board
the R/V ALKOR (top) and over land in
Westermarkelsdorf (bottom) for different precipitation
rates.
6. Acknowledgements
This work is funded by the Bundesministerium für
Forschung und Bildung within the frame of DEKLIM
(APOLAS). We thank the Deutscher Wetterdienst (DWD)
in Westermarkelsdorf and the Umweltbundesamt in Zingst
for the possibility to perform measurements at their
stations. The Joss-Waldvogel data were made at our
disposal by A. Wagner and J. Seltmann (both DWD-
Hohenpeißenberg), Micro rain radar data by G. Peters
(Meteorological Institute Hamburg).
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