Direct comparison of nonmigrating tidal signatures in the electrojet, vertical plasma drift and equatorial ionization anomaly

Abstract

This paper presents for the first time a full decomposition of tidal signatures in three important ionospheric quantities, the equatorial electrojet (EEJ), vertical plasma drift and the crest-to-trough ratio (CTR) of the equatorial ionization anomaly. Data sources are the EEJM-2 model, ROCSAT-1 data and CHAMP electron density measurements. The analysis is based on data sampled around the solar maximum 23 (2000–2004). Full spectra of the predominant nonmigrating tides were determined. The tidal component DE3 is dominating the spectrum during the months around August in all three quantities. Conversely, DE3 disappears around December solstice everywhere. The August enhancement in EEJ strength is almost 3 times larger than that in plasma drift and CTR. The DE2 tide is strong during solstice months and shows minima around equinoxes. The relative amplitudes of the annual variations are much the same for the three investigated quantities. The EEJ and the zonal wind around 100km altitude exhibit almost identical DE2 and DE3 annual variations. Similarly, the vertical plasma drift and the zonal wind around 400km altitude show much the same DE2 and DE3 annual variations. But their phase values are quite different, making a direct interaction less probable. Clear DE2 and DE3 tidal signature are only found in ionospheric quantities during daylight hours. There is a suite of other nonmigrating tides, which can be explained by the interaction of migrating diurnal and semi-diurnal solar tides with stationary longitudinal structures. These tides are prominent during solstices and generally weak during equinoxes.