Air motions and the fading, diversity, and aspect sensitivity of meteoric echoes

A theory is presented which relates those properties of meteoric echoes that depend on distortion of the trail by winds. It is shown that existing results on the delay in the start of echo fading, the delay in echo appearance with aspect, the spectral composition of the received signal, and the regularity of the fading pattern are quantitatively explicable. In addition, the theory predicts that the ensemble-average rate of echo fading should rise characteristically with time and should then drop precipitously at the end of the ensemble echo; moreover, it predicts that the correlation of fading patterns at two ground receivers should be a gaussian function of the product of receiver spacing and echo fading cycle-number. Experimental results are given which confirm these predictions and make possible the determination of the principal properties of the wind profile. It is concluded that at the times of observation the small-scale cutoff wavelength of the turbulence spectrum was about a kilometer, that lack of correlation of wind velocities existed in a vertical range of about a scale height, that the rms variable component of N-S wind velocity was about 50 m/s, and that the rms value of the relative maxima of the vertical gradient of a component of the wind velocity was about 100 m/s. These figures agree with Whipple's photographic studies of meteor trails.