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

Abstract

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 (∼97 km). 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.

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

“…Thus, the negative-mode diurnal tide was considered to be the primary driver of the Sq currents. Later, Richmond and Roble (1987), Yamazaki and Richmond (2013), and Yamazaki et al (2014b) numerically evaluated the importance of upward-propagating tides from the lower atmosphere. These upward-propagating tides are generated in the stratosphere by absorption of solar radiation by ozone, and in the troposphere by absorption of infrared radiation and latent heat release (Zhang et al 2010a(Zhang et al , 2010b, and references therein).…”

“…As the waves propagate upward from the source regions, they grow exponentially with height, and at dynamo region altitudes, they attain amplitudes of several tens of meters per second in the horizontal wind. Yamazaki and Richmond (2013), and Yamazaki et al (2014b) showed that about one third of Sq currents and about one-half of EEJ are driven by the upward-propagating tides. That Çelik (2014) is, Sq variations are significantly affected by the tidal waves of lower atmospheric origin; this is why Sq studies are important for understanding of vertical atmospheric coupling.…”

“…The discrepancy could be due to the inaccuracy of the upward-propagating tides in these simulations. Yamazaki et al (2014b) discussed the importance of the upward-propagating tides in the simulation of geomagnetic daily variations.…”

“…39 (after . Recently, Yamazaki et al (2014b) conducted TIE-GCM simulations, successfully reproducing the semiannual variation in the magnetic-northward (N ) . From Rastogi et al (1994 component of the geomagnetic field near the magnetic equator.…”

“…In Fig. 40 (from Yamazaki et al 2014b), the top panels show observed and simulated ground-level geomagnetic perturbations N at Tirunelveli (8.7°N, 77.8°E), India for the year 2008. The model well captures the semiannual variation in N that is most significant at 10-11 LT.…”