This text provided by Arve Kylling, NILU.
Description of the method applied to find topographical and surface
inhomogeneity effects for EDUCE sites including description of
necessary input data.
Summary of intentions
=====================
To investigate and quantify the influence of topography on surface
irradiance meausurements for the EDUCE stations. This will be done
using state-of-the-art three-dimensional radiative transfer
calculations.
Model details
=============
The three-dimensional radiative transfer calculations will be
performed with MYSTIC (Monte Carlo code for the physically
correct tracing of photons in cloudy atmospheres), see e.g.
Kylling et al. 2000 for a short overview and http://www.bmayer.de for
examples of its use. The model domains will be 201X201 km^2 with a
resolution of 1 km. Elevation information will be taken from the
GTOPO30 data set (Global 30 Arc Second Elevation data set, available
at http://edcwww.cr.usgs.gov/landdaac/gtopo30/gtopo30.html) and
regridded to 1X1 km^2 resolution using the Generic Mapping Tools (GMT)
(Wessel and Smith, 1995}. Between these data points, the surface is
interpolated bilinearely by the model to calculate the appropriate
surface elevation and inclination at any location.
Input parameters
================
Three wavelengths will be considered:
305 nm, strongly affected by ozone
320 nm, somewhat affected by ozone
340 nm, not affected by ozone
Since stations are located at very different latitudes it is not
appropriate to use the same standard set of szas for all
stations. However, for comparison reasons calculations will be carried
out for sza=60 for all stations. For selected stations other sza may
be considered. The sun will be in the south for all simulations (note
that for a flat Lambertian surface the result would not depend on
solar zenith angle).
For sites significantly shadowed by mountains or in highly
inhomogeneous regions (high montains, fiords, glacier) additional
calculations will be performed e.g. with and without snow. Examples of
such sites are Andøya and Sonnblick.
The effect of topography may be different on cloudy and cloudless
days. For some sites with large topography effects some cloudy
calculations will be performed to see if there is a cloud effect.
The background atmosphere will be taken from the atmosphere model of
Anderson et al. (1986).
Sites considered
================
The following sites listed on the the EDUCE metadata pages will be
considered:
Sitename Latitude Longitude Altitude (m)
Thessaloniki 40.517 22.967 60.00
Potsdam 52.363 13.068 107.00
Lindenberg 52.210 14.120 121.00
Hohenpeissenberg 47.804 11.018 980.00
Brussels 50.800 4.350 120.00
fr_ustl_vda 50.650 3.100 60.00
Ispra 45.814 8.627 214.00
Sodankyla 67.220 26.390 179.00
Jokioinen 60.814 23.499 107.00
Trondheim 63.430 10.470 20.00
Nea_Michaniona 40.471 22.848 20.00
Rome 41.900 12.517 60.00
Reading 51.450 -0.930 66.00
Sonnblick 47.050 12.950 3106.00
Vienna-Grossenzersdorf 48.120 16.330 150.00
Andoya 69.483 16.017 380.00
Character of expected results.
=============================
Report on the characterisation and quantification of
topographical and surface inhomogeneity effects for all EDUCE sites.
Possible problems
=================
None known
References
==========
Anderson, G., S. Clough, F. Kneizys, J. Chetwynd, and E. Shettle, AFGL
atmospheric constituent profiles (0-120 km), Tech. Rep.
AFGL-TR-86-0110, Air Force Geophys. Lab., Hanscom Air Force Base, Bedford,
Mass., 1986.
Kylling, A., T. Persen, B. Mayer, and T. Svenøe,
Determination of an Effective Spectral Surface Albedo From Ground
Based Global and Direct UV Irradiance Measurements},
J. Geophys. Res., 105, 4949-4959, 2000.
Wessel, P., and W. H. F. Smith, New version of the Generic
Mapping Tools released, EOS Trans. AGU, 76-(33), 329, 1995.
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