Individual daytime traveling ionospheric disturbances (TID's) in the F‐layer are studied using three ionosondes mutually approximately 150 km apart in northern New Hampshire and Vermont. The ionosondes were operated continuously for long periods of time, making ionograms every two minutes. Methods of scanning the continuous data for TID's, and of analyzing them, are described. Iso‐height contours are emphasized as superior to iso‐ionic contours for analysis. It is found that the direction toward which a TID travels is essentially independent of height within the disturbance and that the directions of travel cluster about the south‐southeast. Other parameters are found to be height‐dependent and will be the subject of future papers.
The height dependence of amplitude and both horizontal and vertical phase trace speeds, for individual spectral components of F region TID's, are obtained for the first time by means of a three‐station network of rapid‐run ionosondes. The corresponding causative gravity wave parameters are derived using a previously developed inversion technique, which is extended by incorporating the effects of dissipation and ion diffusion. Reasonable agreement is achieved between the height variation of the real part of the vertical component of the gravity wave phase propagation vector, kzr, obtained from the inversion process, and solutions of a dissipative dispersion relation for kzr at different heights. Height dependent values of the imaginary part of the vertical component of the gravity wave phase propagation vector, kzi, which are required for the inversion, are computed from the dissipative dispersion relation. Values of kzi obtained from analytic formulae which assume an isothermal atmosphere and small dissipation yield erroneous results for the waves considered, suggesting that care should be exercised when interpreting previous theoretical results that have employed these assumptions.
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/Ne)(∂Ne/∂z) and to the dissipation which counteracts the exponential growth, with height, of the gravity wave.
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