THE INFLUENCE OF BACKGROUND WINDS ON THE PROPAGATION OF MEDIUM-SCALE DUCTED GRAVITY WAVES

The full-wave solution method in a horizontally stratified atmosphere is adopted in the analysis of the propagation features of medium-scale atmospheric gravity waves, and the effect of background winds on gravity waves is considered. The dispersion and attenuation distance curves of ducted waves are calculated. The numerical results show that, the existence of strong background winds blowing against the propagating direction of gratrity waves can considerably prolong the attenuation distance of various ducted modes, within which mode W₁ and W₄ have the longest attenuation distance in short period area. Thus strong winds blowing against the propagating direction of gravity waves can support the propagation of mediumscale gravity waves. The attenuation distance decreases rapidly with the increasing of wave period, which shows that the ducted mechanism vanishes in long period range, and that the support of winds on the long-distance propagating of ducted waves is valid only in medium-scale range. The distribution in periods of Travelling Ionospheric Disturbances observed at Millstone Hill and Wuhan is statistically analyzed. The result shows that the superior distribution of TIDs both in Wuhan and Millstone Hill are mainly the mode W₁ and mode W₄, thus the experimental results confirm the existence of these superior distributions of ducted gravity wave modes.