Global large scale structures in the F region

Abstract

Measurements of neutral densities, neutral temperature, ion density and ion temperature by the Atmosphere Explorer C and E satellites exhibit fluctuations made up of coherent waves of scale sizes from hundreds to thousands of kilometers. The fluctuations in the AE‐C data are found at times of low magnetic activity to extend from the auroral region in one hemisphere across the equator to the corresponding region in the other hemisphere with little change in apparent wavelength. The fluctuations in the AE‐E data similarly exhibit at times of low magnetic activity nearly uniform wave structure encircling the equatorial belt. Typical examples of 2000 km waves in the AE‐C data and 1500 km waves in the AE‐E data are discussed. To explain these observations, it is suggested that during quiet periods the auroral belts excite quasi‐stationary waves distributed about the earth with coherent periods, possibly tidal, and scale lengths determined by the structure of the belts. According to this interpretation, TID's are manifestations of the transient waves that result from changes in magnetic activity with periods and scale sizes associated with the auroral excitation.