Radiation balance over low-lying and mountainous areas in south-west Germany |
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| Authors: | M G Iziomon H Mayer W Wicke A Matzarakis |
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| Institution: | (1) Meteorological Institute, University of Freiburg, Freiburg, Germany, DE |
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| Abstract: | Summary Surface radiative fluxes play a major role in the energy exchange process between the atmosphere and earth surface and are
thus very crucial to climatic processes within the atmospheric boundary layer. Based on four years REKLIP (REgio-KLIma-Project)
data set of measured radiative fluxes and additional supporting meteorological variables, the surface radiation regime for
selected lowland site (Bremgarten 212 m a.s.l.) and mountain sites (Geiersnest at 870 m a.s.l.; Feldberg 1489 m a.s.l.) in
the southern Upper Rhine valley region (south-west Germany) has been reported. Time series of radiative fluxes and surface
albedo showed significant inter-site differences. Possible reasons for the observed differences have been made. Downward atmospheric
radiation A
l
at the study sites was parameterised in terms of air temperature, vapour pressure and cloud amount, all of which strongly
govern the variation of A
l
. Effective terrestrial radiation amounted to about 50% of absorbed shortwave radiation at the study sites annually. During
clear sky conditions, global solar irradiance G
s
constituted about 76.0% of the incident extraterrestrial solar irradiance at Feldberg mountain site but only 68.5% of that
at Bremgarten lowland site. Annual cumulative of net radiative flux R
n
amounted to 1722 MJm−2 yr−1 at the lowland site, while that at Geiersnest and Feldberg mountain sites constituted 84% and 73% respectively of the corresponding
magnitude for the lowland site. In the same vein, annual mean of radiation efficiency (defined here as R
n
/G
s
) amounted to 0.32 in Feldberg, 0.37 in Geiersnest and 0.41 in Bremgarten. Consequently the annual available energy, of which
net radiative flux is representative, was smaller at the mountain ous sites relative to the lowland site during the study
period. Inter-annual variability of net radiative flux, its constituent variables and derivatives at the study sites were
generally below 10%, with longwave fluxes showing the lowest fluctuation. This renders the measured data quite suitable for
modelling purposes. In winter, mean daily sums of R
n
showed a slow rise with cloud amount N at the lowland site but a sharp rise with N at Feldberg mountain site. In summer however, mean daily sums of R
n
declined significantly with N as well as Linke turbidity factor at the study sites.
Received June 24, 1999 Revised November 2, 2000 |
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