Characteristics of gusty wind disturbances and turbulent fluctuations in windy atmospheric boundary layer behind cold fronts

Statistical analysis of turbulent and gusty characteristics in the atmospheric boundary layer with strong mean wind behind cold fronts has been carried out. The data used in the analysis were the multilevel ultrasonic anemometer-thermometer observations for 5 years during spring in East Asia. The results show: (1) there is systematical descending component of the basic flow in the lower part and ascending component in the upper part of the boundary layer; (2) the turbulent fluctuations (period less than 1 min) are nearly random and isotropic with weak coherency, but the gusty wind disturbances (1 min < period < 10 min) are anisotropic with rather strong coherency; (3) the kinetic energy of gusty wind disturbances and the related downward flux of momentum reach their maximum at some level below h*, where h* is the level separating the descending and ascending components of the mean flow; and (4) the turbulent kinetic energy and related downward flux of momentum increase first in the lowest layer and then decrease with height, if the fastest sampling frequency is 10 Hz, although the reason is unclear yet.