The climatology of low-latitude ionospheric densities and zonal drifts from
IMAGE-FUV.

T.J. Immel, E. Sagawa, H.U. Frey, S.B. Mende, and J. Patel


The IMAGE satellite was the first dedicated to magnetospheric imaging, but has
also provided numerous images of the nightside  ionosphere with its
Far-Ultraviolet (FUV) spectrographic imager. Nightside emissions of O I at
135.6-nm originating away from the aurora are due to recombination of
ionospheric O+, and vary in intensity with (O+^{2}. IMAGE-FUV, operating in a
highly elliptical orbit with apogee at middle latitudes and >7 Re altitude,
measures this emission globally with 100-km resolution. During each 14.5 hour
orbit, IMAGE-FUV is able to monitor nightside ionospheric densities for up to
6-7 hours. Hundreds of low-latitude ionospheric bubbles, their development and
drift speed, and a variety of other dynamical variations in brightness and
morphology of the equatorial anomalies have been observed during this mission.
Furthermore, the average global distribution of low-latitude ionospheric plasma
densities can be determined in 3 days. Imaging data collected from February
through June of 2002 are used to compile a dataset containing a variety of
parameters (e.g., latitude and brightness of peak plasma density, zonal bubble
drift speed) which can be drawn from for climatological studies. Recent results
indicate that the average ground speed of low-latitude zonal plasma drifts vary
with longitude by up to 50%, and that a periodic variation in ionospheric
densities with longitude suggests the influence of a lower-thermospheric
non-migrating tide with wave number = 4 on ionospheric densities. An excellent
correlation between zonal drift speed and the magnetic storm index Dst is also
found.

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Presentation, Fall A.G.U. Meeting, San Francisco, CA, 13-17 December 2004