Determining temperature lapse rates over mountain slopes using modified GWR in the Pyrenees area

Improve the temperature forecasts in complex terrain areas provided by NWP is the aim of this project.

Temperature is an important variable, specially in mountain areas, as it provides changes in several meteorological phenomena and effects on human activities.

This study takes place in the Pyrenees range, in the north-eastern Iberian Peninsula. Pyrenees extents longitudinally separating the Iberian peninsula from the rest of Europe, and high peaks around 3000 meters arise from deep valleys. As a mountain range it supposes a barrier to the advections, in this case from the north and south, and typical meteorological phenomenon in mountainous areas occurs within it (inversions, foehn effect, extremely wind-chill, snow storms, etc).

Thus, two specific valleys in Catalonia are considered, Val d'Aran and Cerdanya, where in both automatic weather stations are available in similar heights. However, the main reason is that NWP have problems when forecasting temperatures in these areas, mainly in the valley floor in winter season. Furthermore, their climates are pretty different despite they are approximately 100 km far from each other.

Firstly, different equations based on a multilinear regression are obtained for each weather station. Multilinear regression is considered in this case as the most suitable downscaling method and data used is provided by automatic weather stations, radiosonde stations and MM5 model, and only winter period is analyzed.

These equations are applied within a modified Geographically Weighted Regression (GWR) in order to obtain a vertical temperature profile and further an improved freezing level between the valley floor and mountain tops.