ИСТИНА

The cross-over height, i.e. an intersection between daily and nocturnal profiles of wind velocity V, is an important feature of the lower troposphere wind structure almost everywhere except, probably, only Polar regions. As it is known the value of ∂V/∂z in the surface air layer is as a rule higher at night than in the afternoon because of more intensive vertical turbulent exchange and more intensive downward transfer of momentum from one air layer to another under unstable stratification. Long-term continuous sounding by Doppler sodar ‘MODOS’ of METEK production is carried out at Moscow University since 2004. On a base of the sodar data the cross-over height dynamics and all possible kinds of correspondence between nocturnal and daily wind profiles have been studied in details. Case studying of extremely low and extremely high cross-over height, absence of it, coincidence of nocturnal and daily wind profiles, multiple intersection between them, an inverse cross-over height, etc. will be discussed with the account of synoptic conditions. In average cross-over height in Moscow is equal to 60-80 m in cold season and nearly to 100-110 m in warm season. Among others, it depends on an averaging time but the scatter between estimations due to different temporal averaging is not significant (usually – in limits of 10-20 m).