Ground magnetic effects of the equatorial electrojet simulated by the TIE-GCM driven by TIMED satellite data

Quiet time daily variations of the geomagnetic field near the magnetic equator due to the equatorial electrojet are simulated using the National Center for Atmospheric Research Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIE-GCM) and compared to those observed by ground-based magnetometers. Simulations are run both with and without tidal forcing at the height of the model lower boundary (similar to 97km). When the lower boundary forcing is off, the wind that generates an electromotive force in the model is primarily the vertically nonpropagating diurnal tide, which is excited in the thermosphere due to daytime solar ultraviolet heating. The lower boundary tidal forcing adds the effect of upward propagating tides, which are excited in the lower atmosphere and propagate vertically to the thermosphere. The main objective of this study is to evaluate the relative importance of these thermospherically generated tides and upward propagating tides in the generation of the equatorial electrojet. Fairly good agreement is obtained between model and observations when the model is forced by realistic lower boundary tides based on temperature and wind measurements from the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite, as determined by Wu et al. (2012). The simulation results show that the effect of upward propagating tides increases the range of the geomagnetic daily variation in the magnetic-northward component at the magnetic equator approximately by 100%. It is also shown that the well-known semiannual change in the daily variation is mostly due to upward propagating tides, especially the migrating semidiurnal tide. These results indicate that upward propagating tides play a substantial role in producing the equatorial electrojet and its seasonal variability.