Fluctuations in wind direction at Venice, related to the origin of the air masses

Abstract

At Venice, sited in the middle of a lagoon facing the Adriatic sea, the wind and the atmospheric stability are characterized by Alps-sea interactions and by cold outbreaks through particular gaps of the Alps chain. As a consequence, radiosonde launchings show thermal profiles different from those usually observed over the mainland and also the fluctuations of the wind direction vary with the origin and dynamics of the air masses. In this paper the relationships between thermal and dynamic stability in terms of standard deviation of the wind direction σ θ are discussed, since they are of particular interest in managing industrial emissions. The σ θ shows a poor diurnal trend, especially during winter; the seasonal trend is slightly more marked. However, it is possible to divide the σ θ into stability classes, draw stability roses and relate the latter to the local dynamic climatology and in particular to the different origins of the air masses.