University of Crete Island of Crete

Space-based studies of low-latitude ionospheric forcing originating in the lower atmosphere

T. J. Immel1, S.L. England1, J. M. Forbes2, J. D. Huba3, M. E. Hagan4, and R. DeMajistre5
  1. University of California Berkeley, USA
  2. University of Colorado, Boulder, USA
  3. Naval Research Laboratory, Washington DC, USA
  4. High Altitude Observatory, Boulder, CO, USA
  5. Applied Physics Laboratory, Laurel, MD, USA

A significant portion of the energy and momentum propagating upward from the lower and middle atmosphere to ionospheric heights is carried by atmospheric tides. Since most upward-propagating tidal waves dissipate in the lower ionosphere, their direct influence on neutral and ion conditions in the main F-layer might be expected to be small. Recently however, a strong correlation between modeled tidal amplitudes at 100 km and F-layer conditions (~350 km) at low latitudes has been clearly observed in global-scale ionospheric imaging from the IMAGE, TIMED, and COSMIC missions. The modulation of electric fields in the E-region dynamo by tidal driven winds was identified as one likely mechanism for extending tidal forcing above ~150 km. This theory has been tested with the TIMEGCM and SAMI models, confirming the importance of the dayside E-region dynamo and producing changes in modeled F-layer densities with magnitudes comparable to observations. The daytime equatorial electrojet current has also been found to exhibit a strong 4- peaked zonal variation in concert with the nighttime FUV morphology. These observations support the idea that structuring of the equatorial ionospheric anomaly originates in large part during the daytime buildup of plasma densities. Only recently, however, have the global tides themselves been compared to the observed ionospheric variations. Initial comparisons with mesospheric/lower-thermospheric temperatures from TIMED show the remarkable correspondence of tides with ionospheric effects, and co-variation on the timescales of weeks and seasons. Furthermore, the global ionospheric measurements carry indications of planetary wave modulation of tidal amplitudes on timescales too short to be retrieved from the space-based temperature measurements themselves. These observations mirror the findings of earlier ground-based studies using ionosondes, with the advantage of global observations providing the zonal wavelength of the affected tidal structures, complimenting the capability of the ground-based radars to provide the wave periods. These and other results point the way to important new collaborations between space- and ground-based research teams to understand the connection of terrestrial weather to geospace

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