Il contributo del GPS nelle previsioni di eventi meteorologici significativi

The precision of GPS measurements is influenced by different effects acting on the observed signal; one of these is troposphere refraction. The study of spatial/temporal variability of such effect either allows to improve the positioning precision, and offers important information to forecast significant meteorological events. In the present work a strategy was tested so that, starting from the estimation of precipitable water contents altogether present in atmosphere by means of the inversion of GPS observations, the saturation conditions of single atmospheric layers may be analysed to evaluated real precipitable water vapour at different altitude. At this purpose models of atmospheric profiles of mixing ratio (mr) and of saturated mixing ratio (mrs) were built starting from radiosaunding performed during the Mesoscale Alpine Programme (MAP). The forecast of significant meteorological events was tested with success in the experimentation for Genoa city during the quarter September-November 1999; in particular, concerning the relevant event on 3rd November 1999, an advantage of 5 hours was obtained, estimating rain height of 36 mm versus 53.4 mm observed at the ground. The analysed strategy, using punctual GPS observations, wants to provide an integrative contribution to study the forecast of significant meteorological events. Particular interest will assume spatial analysis that, following the continuous development of GPS Permanent Station Networks, will allow to estimate horizontal atmospheric gradients associated to the vertical ones.