E × B Drifts at Midlatitudes

Abstract

At midlatitudes, vertical transport of ionization in the topside F region results from three mechanisms: first, ambipolar diffusion along the magnetic field, second, interaction between the ionization and the wind in the neutral atmosphere, and third, E × B drifts perpendicular to the magnetic field. The vertical velocity resulting from these three mechanisms was measured by determining the Doppler shift in the Thomson‐scattered power spectrum at altitudes between 450 and 900 km (Evans et al., 1970). Drift measurements were made at Millstone Hill Ionospheric Observatory. Electron‐density profiles and electron‐ and ion‐temperature profiles were made also. Drifts for the 24‐hour period of September 11–12, 1968, are examined for an altitude of 450 km. The diffusion velocity is calculated from the electron density and the thermal structure; the ion temperature at 300 km is taken as the neutral gas temperature for determination of the atomic oxygen density. With this diffusion velocity calculated and the vertical velocity measured, the combined effect of interaction with the neutral winds and E × B drifts can be determined. Through use of a model of the diurnal neutral wind behavior (Cho and Yeh, 1970), the effective E × B drift in the topside F region is estimated at midlatitudes. East‐west electric fields in the dynamo region that generate such E × B drifts are calculated from these results.