Global Change Abstracts The Swiss Contribution - SCNAT

58
ability and various significant trends of the time
series of seasonal cluster frequency. Tentative estimations
of central European temperature changes
based solely on seasonal cluster frequencies can
explain between 33.9% (summer) and 59.0% (winter)
of temperature variance on the seasonal time
scale. However, the signs of long- term changes
in temperature are correctly reproduced even on
multidecadal - centennial time scales. Moreover,
linear warming trends are reproduced, implying
from one- third up to one- half of the observed
temperature increase between 1851/ 52 and 2003
(except for summer, but with significant trends
for spring and autumn), indicating that changes
in daily circulation patterns contribute to the observed
overall long- term warming in the central
European region.
Journal of Climate, 2007, V20, N16, AUG 17, pp
4065-4095.
08.1-57
Remote sensing of aerosol optical depth over
central Europe from MSG- SEVIRI data and accuracy
assessment with ground-based AERO-
NET measurements
Popp C, Hauser A, Foppa N, Wunderle S
Switzerland, Germany
Remote Sensing , Meteorology & Atmospheric
Sciences
In this study, the remote sensing of aerosol optical
depth (tau(a)) from the geostationary Meteosat
Second Generation (MSG) Spinning Enhanced Visible
and Infrared Imager (SEVIRI) is demonstrated.
The proposed method is based on the analysis of
a time series of SEVIRI’s 0.6 µm channel images.
Top-of-atmosphere reflectance is precorrected for
the effect of atmospheric gases and a background
aerosol amount. Subsequently, surface reflectance
for each pixel is estimated by determining its lowest
precorrected reflectance within the observed
time period for each satellite observation time of
the day. The resulting diurnal surface reflectance
curve in combination with the radiative transfer
code SMAC are finally used to derive ta. This approach
is applied to SEVIRI subscenes of central
Europe (40.8 - 51.3 degrees N, 0.3 degrees W - 19.9
degrees E) from August 2004, daily acquired between
0612 and 1712 UTC in intervals of 15 min.
SEVIRI tau(a) are related to Aerosol Robotic Network
(AERONET) Sun photometer measurements
from nine sites. About 3200 instantaneous SEVIRI
and Sun photometer tau(a) are compared. An
overall correlation of 0.9 and a root mean square
error of 0.08 are obtained. Further, the spatial distribution
of SEVIRI tau(a) maps for August 2004
represent expectable features like higher concen-
Global Change Abstracts – The Swiss Contribution | Atmosphere
trations in industrialized regions or lower loading
in higher altitudes. It is concluded that the
described method is able to provide an estimate of
tau(a) from MSG-SEVIRI data. Such aerosol maps
of high temporal frequency could be of interest to
atmospheric related sciences, e. g., to track aerosol
particle transport.
Journal of Geophysical Research Atmospheres,
2007, V112, ND24, NOV 9 ARTN: D24S11.
08.1-58
Hydrological aspects of the Mesoscale Alpine
Programme: Findings from field experiments
and simulations
Ranzi R, Zappa M, Bacchi B
Italy, Switzerland
Modelling , Hydrology , Meteorology & Atmospheric
Sciences
The Mesoscale Alpine Programme (MAP) was a
unique initiative to improve the understanding
of processes involved in orographically influenced
precipitation events and in the related emergence
and mitigation of floods in the Alps. This study
presents a summary of the results from investigations
of hydrological relevance in areas to
the south (Lago Maggiore watershed) and north
(Ammer watershed) of the Alps. A special focus
is given to the 1999 Special Observing Period
(SOP) experiment. MAP has been an important
dialogue platform between the hydrological and
meteorological communities. A common goal
has been the verification and the assessment of
errors and sources of uncertainty of new coupled
techniques for flood forecasting in mountainous
environments. The ensemble multi-model
error in the hydrometeorological forecast, two
days in advance, was 30% of the observed peaks
and 15% of the observed runoff volumes, on average.
To provide some insight on the relative importance
and priority of observation strategies
of hydrological factors such as soil moisture and
reservoir volume in contributing to the flood intensity,
the MAP project ‘Hydrology’ focused also
on the role and magnitude of water storage in reservoirs.
The presented analyses indicate that for
the investigated basins and flood events, the storage
reservoirs may retain, on average, up to 10%
of the event runoff volume and are key elements
contributing to the mitigation of peak runoff.
The observed variability of soil moisture is large
and therefore it has been confirmed that severe
difficulties remain in instrumental monitoring of
soil moisture in mountainous environments. The
sensitivity of floods to soil moisture in the physiogeographic
context analysed here seems, however,
to be minor, due to the shallow soil layer covering