DIURNAL WIND VARIATIONS, SURFACE TO 30 KILOMETERS

Abstract

Annual mean 12-hr wind differences are computed from monthly mean wind statistics at 27 levels between the surface and 10 mb for 105 radiosonde stations that have extended periods of record. The resulting wind difference vectors for 0000?1200 gmt and 0300?1500 gmt are plotted on constant pressure charts. At polar latitudes in both hemispheres, a simple pattern is observed, with flow directed across the Pole from the daytime hemisphere to the nighttime hemisphere at all levels. At low and middle latitudes, the wind difference patterns are strongly related to topography, even at stratospheric levels. Land-sea contrasts and terrain slope appear to be the controlling influences. Analysis of hodographs at individual stations shows that the topographically induced tidal fluctuations propagate downward at all levels above 1 km. This is indicative of an upward flux of tidal energy from the planetary boundary layer.