Lunar Tide in the F Region Ionosphere

Abstract

AbstractIn this paper the magnetic latitude (±50°) and longitude, local solar time (LST), and month‐to‐month variability of the M2 lunar semidiurnal tide in the ionosphere is revealed through analysis of topside F region electron density measurements by the Planar Langmuir Probe instrument on the CHAMP satellite during the two 5‐year periods 2001–2005 and 2005–2009. The local time precession rate of CHAMP is such that 5 years is required to obtain full LST coverage for every month of the year at each latitude of interest. Thus, each 5‐year period is compressed into one equivalent year. M2 amplitudes, expressed in terms of percent residuals from a background value, range between about 3% and 20% and vary considerably with LST and magnetic longitude. Longitude variations in principle arise from zonal asymmetries in lunar tidal forcing due to Earth and ocean tides, as well as magnitude of Earth's magnetic field. The O1 diurnal tide is also discussed in the context of CHAMP and other measurements of the F region ionosphere.