The height dependence of wave‐normal depression and disturbance amplitude in TID's

Abstract

Experimental results obtained with multistation rapid‐run ionosondes are presented and discussed for seven large daytime traveling ionospheric disturbances (TID's). There is a sharp maximum in the amplitude of each disturbance in the inflection region of the electron density profile below the F layer peak, and the wave normal is depressed downward in this region from 55° to 85° below the horizontal. At the upper and lower fringes of the disturbance the wave‐normal depression is much less, ranging from 2° to 25°. The reduced depression at the upper side is attributed to a concomitant effect of dissipation of the causative gravity wave, and that at the lower side to trapping of the gravity wave energy below the thermopause. The TID amplitude peak is ascribed to a peak in (1/N_e)(∂N_e/∂z) and to the dissipation which counteracts the exponential growth, with height, of the gravity wave.