A theoretical study of the ionospheric F region equatorial anomaly—II. results in the American and Asian sectors

Abstract

When observed noontime values of the maximum electron density, NMAX( F2), in the ionospheric F2 region are plotted as a function of magnetic latitude, a curve is produced which has two peaks, one on either side of the dip equator at ±16° dip latitude. This paper theoretically investigates the daily variation of this latitudinal distribution in NMAX( F2) (the so-called Appleton or equatorial anomaly) and specifically attempts to account for the longitudinal differences observed between the American and Asian sectors. In Part II, models of the neutral atmosphere, production, loss and diffusion rates, neutral wind, and electric field are described and the electron densities obtained by solving the continuity equation utilizing these models are presented. In each sector, the extent to which the equatorial anomaly's daily variation is affected by changes in the geomagnetic field configuration, neutral wind, and E × B drift is examined. It is found that development of the anomaly is most sensitive to the electric field model assumed, and that the observed differences at the magnetic equator between the American and Asian sectors could be accounted for by an upward E × B drift which commences an hour or two earlier in the Asian sector.