Migrating and nonmigrating tidal signatures in sporadic E occurrence rates

Abstract

We analyze sporadic E (ES) occurrence rates (OR) obtained from ionospheric radio occultation measurements by the FORMOSAT-3/COSMIC constellation. Maximum OR are seen at 95 – 105 km altitude at lower midlatitudes. Midlatitude ES are mainly due to wind shear in the presence of tides, and the strongest signals are a migrating diurnal and semidiurnal component. Especially at high latitudes of the southern hemisphere, nonmigrating components such as a diurnal westward wave 2 and a semidiurnal westward wave 1 are also visible. Near the equator, a strong diurnal eastward wavenumber 3 component and a semidiurnal eastward wavenumber 2 component is found in summer and autumn. Terdiurnal and quarterdiurnal components are weaker than the diurnal and semidiurnal ones.