Seasonal and local time variation of ionospheric migrating tides in 2007–2011 FORMOSAT‐3/COSMIC and TIE‐GCM total electron content

Abstract

This study examines the seasonal and interannual variation of the major migrating tidal components in midlatitude to low‐latitude total electron content (TEC) observations from the FORMOSAT‐3/COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) satellite constellation from 2007 to 2011. Although the absolute amplitudes of the TEC zonal mean and migrating tidal components show a strong positive relation to the increasing and decreasing phases of the solar cycle, the relative tidal amplitudes following normalization by maximum background values show a more varied response to solar activity levels. Features of ionospheric local time variation produced by individual migrating tidal components are consistent from year to year, with DW1 forming the equatorial daytime peak in TEC, SW2 corresponding to the generation of the equatorial ionization anomaly (EIA) crests, and TW3 contributing to the TEC trough between the EIA crests. Numerical experiments using Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM) are also performed to determine the sensitivity of the ionospheric migrating tides to upward propagating migrating tidal components from the neutral mesosphere and lower thermosphere (MLT). Zonal mean TECs decrease when MLT tidal forcing is applied and are particularly sensitive to the MLT DW1. Most of the ionospheric SW2 response is attributable to MLT SW2 forcing, enhancing the EIA crests by amplifying the equatorial fountain. TW3 in the model is generated through both in situ photoionization and nonlinear interaction between DW1 and SW2.