Late frost events in an Alpine Valley: Measurements and characterisation of the process

Under the research project GEPRI, aimed at investigating and characterizing late frost events potentiallydangerous for cultivated areas, in the spring of 2004 an intensive meteorological field experiment has been made in the Adige River Valley in Trentino (Northern Italy). The project is aimed at a better characterization of the mechanism of late frost events in complex topography in order to improve the forecast of the occurrence of nocturnal temperature minima. In this work some preliminary results of the micrometeorological measurements performed at a target area within an appletrees orchard are presented and discussed. Measurements allowed the determination of the complete energy balance, as well as the identification of specific local-scale circulations which appear to be relevant in characterizing the night-time cooling process. In case of fair weather conditions, the latter displays a sequence of at least four different phases which seem to alternate rather than superimpose advective- and radiative-effects.