Global structure of the lunar tide in ionospheric total electron content

Abstract

The global structure of the lunar tide in the ionosphere is studied based on observations of the global positioning system (GPS) total electron content (TEC). The unprecedented spatial and temporal resolution afforded by the GPS TEC observations enables illustration of the latitude, longitude, solar local time, and seasonal variability of the lunar tide in the ionosphere. Based on analysis of the multi‐year mean from 1999–2008, the dominant component is generally the semidiurnal lunar tide. However, a significant diurnal variation is also observed in some instances. The semidiurnal component achieves a maximum amplitude of ∼6% in the equatorial ionization anomaly crest regions and a slight hemispheric asymmetry is present with larger amplitudes in the Northern Hemisphere. Furthermore, the maximum amplitudes in the semidiurnal lunar tide are found to occur during Northern Hemisphere winter and during 9–15 solar local time. During certain years, a secondary maxima in solar local time is also observed demonstrating the influence of the lunar tide on the prereversal enhancement. Lastly, the observations reveal significant longitudinal variability in the semidiurnal lunar tide that is most prominent between November and February. The presence of a longitudinal variation reveals the existence of nonmigrating components in addition to the dominant migrating semidiurnal lunar tide.