ALPTHERM - A PC-based Model for Atmospheric Convection over Complex Topography

Abstract

Forecasting soaring flight conditions in mountainous areas is more complex than over flat terrain due to the area-height distribution of topography. The resultant volume-effect is the reason why the apparent input of sensible heat is larger over mountain valleys than over flat terrain.  As a rule of thumb it was found for the Alps that the maximum day temperature at the bottom of the valley decreases by about 5C if the valley floor rises by 1000 m.  In order to assess the dynamics and the precise temporal evolution of convection the use of computers becomes advisable, in particular if topography should be considered.  This was the starting point for the development of “ALPTHERM”.  Topography is a key element for regionalized gliding forecasts.  Its detailed consideration in modeling atmospheric convection is possible with today’s personal computers.  The presented PC-based model “ALPTHERM” produces regionalized forecasts of the parameters important for gliding.  Used as a simulator, “ALPTHERM” illustrates effects like the convective enhancement of low-lying inversions in mountain valleys and the volume effect. Quantitative information of the mixing process in the boundary layer is also obtained for complex topography.