[1] In this work, the magnetic variations simulated by the NCAR thermosphereionosphere-electrodynamics general circulation model (TIE-GCM) in the vicinity of the magnetic equator are examined to evaluate the ability of this model to reproduce the major features of the equatorial electrojet (EEJ) as observed on the ground as well as on board low-altitude orbiting satellites. The TIE-GCM simulates electric currents of various origins and reproduces their associated magnetic perturbations. We analyze the diurnal and latitudinal variations of the EEJ magnetic effects calculated on the ground in West Africa under approximately the same solar activity condition as in 1993 for the March equinox and June and December solstices. The latitudinal and local time structures of these simulated results correspond well to those that are observed. We also compare longitudinal variations of the midday EEJ magnetic perturbations observed by the CHAMP satellite with the model predictions. Although the simulations and observations both show multiple maxima and minima in longitude, the locations of these extrema often disagree. In the model most of the longitudinal variation of the magnetic variations is associated with nondipolar structure of the geomagnetic field. We find that the modeled contributions of the thermospheric migrating diurnal and semidiurnal tides to the magnetic perturbations have large longitudinal variations, and we suggest that an increase in the amplitude of these tides in the TIE-GCM may cause them to play a major role in explaining the morphology of the EEJ longitudinal variation.

In this short letter, we recall the differences between the counter electrojet (CEJ), which is a phenomenon observed on the magnetically quiet days and the disturbance dynamo (Ddyn), which can be observed during and after a geomagnetic storm. The CEJ is well known to occur near the geomagnetic dip equator. It can be identified by a reversal in the horizontal component (H) of the geomagnetic field daily regular variations. In contrast to equatorial electrojet (EEJ) that flows eastward in the daytime, the CEJ is considered to flow westward. The magnetic signatures of the reversed solar quiet (Sq) current at the low latitude during magnetic storms are due to the Ddyn. This disturbance (Ddyn) is produced by current systems that are driven by thermospheric storm winds originating from the Joule heating of enhanced high‐latitude currents. The DP2 is the magnetic effect of current systems at high latitudes. These currents are associated with the coupling of magnetosphere and ionosphere through geomagnetic field lines. They are associated to the magnetospheric convection. During intense magnetic storms these high‐latitude currents are enhanced and their magnetic effects can extend toward the low latitudes. This work shows that the study of magnetic perturbations makes it possible to understand the disturbances of the ionospheric electric currents. The use of an efficient treatment of the magnetic signals makes it possible to separate the magnetic effects of the different perturbations prompt penetration of the magnetospheric convection electric field and disturbance dynamo electric field. This was performed in the paper Nava et al. (2016).

Abstract. During magnetic storms, the auroral electrojets intensification affects the thermospheric circulation on a global scale. This process which leads to electric field and current disturbance at middle and low latitudes, on the quiet day after the end of a storm, has been attributed to the ionospheric disturbance dynamo (Ddyn). The magnetic field disturbance observed as a result of this process is the reduction of the H component amplitude in the equatorial region which constitutes the main characteristic of the ionospheric disturbance dynamo process, associated with a westward electric current flow. The latitudinal profile of the Ddyn disturbance dynamo magnetic signature exhibits an eastward current at mid latitudes and a westward one at low latitudes with a substantial amplification at the magnetic equator. Such current flow reveals an "anti-Sq" system established between the mid latitudes and the equatorial region and opposes the normal Sq current vortex. However, the localization of the eastward current and consequently the position and the extent of the "anti-Sq" current vortex changes from one storm to another. Indeed, for a strong magnetic storm, the eastward current is well established at mid latitudes about 45 • N and for a weak magnetic storm, the eastward current is established toward the high latitudes (about 60 • N), near the Joule heating region, resulting in a large "anti-Sq" current cell. The latitudinal profile of the Ddyn disturbance as well as the magnetic disturbance DP2 generated by the mechanism of prompt penetration of the magnetospheric convection electric field in general, show a weak disturbance at the low latitudes with a substantial amplification at the magnetic equator. Due to the intensity of the storm, the magnitude of the DP2 appears higher than the Ddyn over the American and Asian sector contrary to the African sector.

[1] The ionospheric disturbance dynamo signature in geomagnetic variations is investigated using the National Center for Atmospheric Research ThermosphereIonosphere-Electrodynamics General Circulation Model. The model results are tested against reference magnetically quiet time observations on 21 June 1993, and disturbance effects were observed on 11 June 1993. The model qualitatively reproduces the observed diurnal and latitude variations of the geomagnetic horizontal intensity and declination for the reference quiet day in midlatitude and low-latitude regions but underestimates their amplitudes. The patterns of the disturbance dynamo signature and its source "anti-Sq" current system are well reproduced in the Northern Hemisphere. However, the model significantly underestimates the amplitude of disturbance dynamo effects when compared with observations. Furthermore, the largest simulated disturbances occur at different local times than the observations. The discrepancies suggest that the assumed high-latitude storm time energy inputs in the model were not quantitatively accurate for this storm.