Earth Planets Space, Vol. 61 (No. 4), pp. 505-512, 2009
Thomas J. Immel1, Scott L. England1, Xiaoli Zhang2, Jeffrey M. Forbes2, and Robert DeMajistre3
1Space Sciences Laboratory, University of California, Berkeley
2Department of Aerospace Engineering, University of Colorado, Boulder
3Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland
(Received October 22, 2007; Revised April 7, 2008; Accepted May 14, 2008; Online published May 14, 2009)
Recent far-ultraviolet (FUV) observations of Earth have shown the remarkable spatial correspondence between the amplitude of non-migrating atmospheric tides originating in the troposphere and the density and morphology of the nighttime equatorial ionospheric anomaly (EIA). This is likely a result of the modulation of the $E$-region dynamo electric field in daytime by the tidal winds. FUV observations around the time of the vernal equinox of 2002 show that the signature of tidal influence, the wave-4 periodicity in the separation and density of the two EIA bands, itself exhibits significant temporal variability. Here, we seek to understand this variability, and whether (or not) it is linked to variations in the strength of the upward-propagating tides. This study relies on tidal measurements provided by the global observations from the TIMED-SABER instrument that measures the temperature variations in the MLT associated with the upward-propagating tides. TIMED-GUVI provides F-region density measurements concurrent to the MLT temperature retrievals. It is found that the atmospheric and ionospheric zonal wave-4 signatures very nearly covary over a 30-day period, strongly supporting the theory that the influence of the the diurnal eastward 3 (DE3) tide originating in the troposphere extends to the F-layer of the ionosphere. Additionally, a 6-day periodicity in the power of the ionospheric wave-4 signature is found that may originate with the tide's interaction with longer period planetary waves.
Key words: Atmospheric tides, tides and planetary waves, FUV, airglow, equatorial ionosphere, thermospheric dynamics.