EFFECTS OF WIND SHEAR ON ATMOSPHERIC GRAVITY WAVE SPECTRUM

The effects of constant wind shear on atmospheric gravity wave spectrum are examined.At first a three-dimensional equilibrium spectral model of gravity waves is established in which wind shear rate β is implicit.Based on this model,the expressions for one-dimensional frequency spectrum of atmospheric gravity waves are derived in which β is explicit.Numerical results show that (1) if we assume that mean wind U(z)=βz(z represents the altitude) and the internal gravity wave spectrum at the altitude of U=0 (that is,z=0) is VanZandt one,then the effect of Doppler shifting due to mean wind may be ignored;(2) when Richardson number J(J=N2/β2,N is Brunt-Väisälä frequency,and is equal to 10-2s-1 in this paper) satisfies J≥10.0,the effects of wind shear arealso ignored;(3)for f22N2 (f is the inertia frequency,and f=10-4s-1in this paper,and ω is the observed frequency),the wind shear only affects the spectral amplitude,and does notalter the spectral shape;and (4) as wind shear becomes strong,a part of wave potential energy turns into wavekinetic one,and a part of the vertical kinetic energy further turns into the horizontal one.