J1.3 Micrometeorological measurements at an alpine slope

Thursday, 10 August 2000: 8:30 AM
Eva van Gorsel, Univ. of Basel, Basel, Switzerland; and A. Christen, E. Parlow, and R. Vogt

Slopes play an important role in modifying the distribution of energy in a valley and fluxes of heat, mass and momentum result from their interaction with the atmosphere. These fluxes contribute to the development of the valley circulation and to typical warming and cooling patterns. In modeling studies the turbulent exchange between slope surface and atmosphere is in general parameterized with (flux-gradient) relationships, which were derived from ideal (flat, smooth and homogeneous) surfaces. Simplifying assumptions are applied in order to extend these relations to slopes or, more general, to complex terrain. Experimental evidence, however, which would justify that simplified approach or give an idea of the error, is missing.

In order to investigate the energy balance of an alpine slope the MCR Lab of the University of Basel carried out micrometeorological measurements at five sites located between 800 and 2000m on the westward facing slope (30-35°) of the Riviera valley close to Bellinzona, Switzerland. The activities were part of the MAP-Riviera project (Mesoscale Alpine Project, objectives and setup of the whole MAP Riviera are presented elsewhere in this conference).

Five towers were equipped with sonic anemometers (22m/6 levels; 12/2, 10/2, 6/1, 5/1). Momentum and sensible heat fluxes were measured at all sites, net radiation at four and latent heat flux only at two. The 22m tower stood in a mixed forest (birch, chestnut) and supported profile measurements of wind speed (8 levels) and temperature and humidity (6). The power supply was solved via batteries and solar panels, with increasing time, however, the addition of a gas power generator was necessary. The main measurement period was August and September 1999. Beside micrometeorological peculiarities of slopes, this presentation reports results from standard meteorological analysis of the data set. Fluxes and exchange conditions are characterized and compared to relations found at ideal sites (e.g. integral statistics, empirical functions from Monin-Obukhov theory). Furthermore questions concerning measurement and calculation of fluxes in complex terrain will be addressed.

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