Upward Propagating Tidal Effects Across the E- and F-Regions of the Ionosphere

The dayside ionospheric dynamo is driven largely by tidal winds in the E-region. These tides vary significantly during the year, but are highly structured during equinox, with a dominant non-migrating wave-4 signature at low latitudes. These tidal components originate in the troposphere with the release of latent heat and absorption of IR radiation in persistent tropical rainstorms. Recent observations by NASA TIMED and IMAGE satellites have reported the finding of the effects of these tides in the density and morphology of the equatorial ionospheric anomaly (EIA), reasonably attributed to the modulation of the E-region dynamo electric field in daytime by the tidal winds. However, significant day-to-day variability in the zonal wave-4 signature of the brightness and separation of the bands of the EIA is found. Here, we seek to understand this variability, whether it is tied to variations in the strength of the upward-propagating tides, or to some other effect that diminishes and/or overrides the effect of the tides on the EIA development. This study relies on global observations from the TIMED-SABER instrument that measures the temperature variations in the mesosphere and lower thermosphere (MLT) associated with the upward-propagating tides. F-region density measurements are made concurrent to the MLT temperature retrievals by both the TIMED-GUVI and IMAGE-FUV instruments. This initial study focuses on the March-April period in 2002 and on times of low magnetic activity where penetrating electric fields from high latitudes do not complicate the ionospheric observations.