Space-based studies of low-latitude ionospheric forcing originating in the lower atmosphere Thomas J. Immel, Scott L. England Space Sciences Laboratory, U. C. Berkeley Jeffrey M. Forbes Dept. of Aerospace Engineering, U. of Colorado J. D. Huba Naval Research Laboratory M. E. Hagan High Altitude Observatory, NCAR R. DeMajistre Applied Physics Laboratory, Johns Hopkins U. 12th International Symposium on Equatorial Aeronomy, May 18-24, Crete, Greece

Space-based imaging of the ionosphere affords different views of ionospheric variability. IMAGE-FUV Hourly, Weekly Variability TIMED-GUVI Daily, Seasonal Variability

TIMED-GUVI:3-day average After some initial analyses of the FUV data, it became clear that the equatorial ionospheric anomaly varied in a manner that directly corresponded to recent modeling results showing large variation of tidal winds and temperatures in the E-region around Earth. IMAGE-FUV:30-day average

TIMED-GUVI:3-day average After some initial analyses of the FUV data, it became clear that the equatorial ionospheric anomaly varied in a manner that directly corresponded to recent modeling results showing large variation of tidal winds and temperatures in the E-region around Earth. IMAGE-FUV:30-day average

Seasonal Ionospheric, Tidal Variability If atmospheric tides influence the EIA, then tidal variability should be reflected in the EIA morphology. England et al., in press Apart from effects driven by other sources (e.g., seasonally dependent interhemispheric winds) major changes in EIA morphology can apparently be attributed to changes in tides, here measured by TIMED-SABER. Forbes et al., 2008

On global scales, variability can follow trends on timescales of weeks, as seen by TIMED-GUVI. Is it possible that this variability is driven by shorter-term variability in tides? Again, compare to TIMED- SABER. There is a significant change in the zonal wave-4 pattern between days 90 and 99. “Weekly” variability

Residual deviation from zonal mean temperatures are shown vs. day of the year at 100 km altitude (and in 10º bins of latitude. There is a significant change in the tidal temperature signature over the time interval imaged by GUVI (e.g. days , marked in plots  ) SABER residual temperatures between ±10º are combined and analyzed with a FFT for: 1) Total wave power 2) Relative power in wave-4 (s=4)

-10º 0º 10º In terms of both total power in the wave signature, and power in the wave-4 component, the trend is similar.

There is a significant change in the zonal wave-4 pattern between days 90 and 99. Do a similar analysis of GUVI data, using the separation of EIA bands instead of temperatures as the FFT variable.

There is a significant change in the zonal wave-4 pattern between days 90 and 99. Do a similar analysis of GUVI data, using the separation of EIA bands instead of temperatures as the FFT variable. FFT Power

Tidal Temperatures vs. EIA Separation TIMED-GUVITIMED-SABER 100 km350 km FFT Power

Is the periodicity in wave-4 power indicative of a 6.5-day planetary wave? Observations of the 6.5-day wave in the MLT region from HRDI show that a peak in 6.5- day wave activity occurs in the February-April period.

Conclusions Seasonal variability in the global morphology of the equatorial ionospheric anomaly (EIA) can be attributed in part to variation in 24- and 12-hour tides in the E-region. Short-term variability in the s=4 signature in the latitudinal separation of the EIA peaks roughly matches the same s=4 signature in the diurnal tides, again in the E-region. Planetary wave modulation of the DE-3 tide thought responsible for the s=4 signature in the EIA may explain the 6.5- day variation in the global EIA morphology. Combined FUV (GUVI) and IR (SABER) observations of the low latitude ionosphere lead to understanding that neither can provide individually. 12th International Symposium on Equatorial Aeronomy, May 18-24, Crete, Greece