Alpine cloud climatology using long-term NOAA-AVHRR satellite data |
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| Authors: | M Kästner K T Kriebel |
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| Institution: | Institut für Physik der Atmosph?re, DLR Oberpfaffenhofen, Germany, DE
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| Abstract: | Summary Three different climates have been identified by our evaluation of AVHRR (Advanced Very High Resolution Radiometer) data
using APOLLO (AVHRR Processing scheme Over Land, Clouds and Ocean) for a five-years cloud climatology of the Alpine region.
The cloud cover data from four layers were spatially averaged in boxes of 15 km by 14 km. The study area only covers 540 km
by 560 km, but contains regions with moderate, Alpine and Mediterranean climate. Data from the period July 1989 until December
1996 have been considered. The temporal resolution is one scene per day, the early afternoon pass, yielding monthly means
of satellite derived cloud coverages 5% to 10% above the daily mean compared to conventional surface observation. At non-vegetated
sites the cloudiness is sometimes significantly overestimated. Averaging high resolution cloud data seems to be superior to
low resolution measurements of cloud properties and averaging is favourable in topographical homogeneous regions only. The
annual course of cloud cover reveals typical regional features as foehn or temporal singularities as the so-called Christmas
thaw. The cloud cover maps in spatially high resolution show local luff/lee features which outline the orography. Less cloud
cover is found over the Alps than over the forelands in winter, an accumulation of thick cirrus is found over the High Alps
and an accumulation of thin cirrus north of the Alps.
Received December 17, 1999 Revised July 18, 2000 |
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