WIND GUST STATISTICS IN THE ATMOSPHERIC SURFACE LAYER
The statistics of the wind gustiness factor in the surface atmospheric layer over an urban territory and natural landscape is discussed. The findings of ultrasonic anemometers-thermometers installed at heights of 5 and 10 n (natural landscape) and 17 m (urban territory) above the underlying surface were used for the analysis. Measurements were conducted continuously with the data output rate of 10–11 Hz. Three orthogonal components of the wind vector, temperature and relative humidity of air, and atmospheric pressure were measured. The results of the analysis have confirmed the rather obvious fact that the gustiness factor over an urban territory is higher than that over the natural landscape. The seasonal and diurnal dynamics of the gustiness factor was studied. It was found that the seasonal dynamics (variation of the monthly average value) is practically absent. This is characteristic, in the first turn, of the urban territory. The diurnal average dynamics of the gustiness factor (for every month separately) is quite pronounced in the summer months and nearly absent in the cold season. Its correlation with the average (for the processing period) wind velocity was briefly considered. It was found that in some situations the gustiness factor can be rather large at the relatively slight wind in gusts and, to the contrary, big wind gusts may occur at the relatively low gustiness factors. Two different gustiness modes were revealed: fast (frequently occurring) gusts and slow gusts (intervals with somewhat weaker mean wind flow existing between big gusts). The relation of the gustiness factor with the vertical turbulent heat flux, which can serve as an indicator of current stratification of the atmospheric surface layer, is briefly analyzed.