5:15 PM - 7:15 PM
[PEM12-P23] Response of evening EEJ/CEJ to pre-reversal enhancement
Keywords:pre-reversal enhancement, equatorial electrojet
Equatorial plasma bubbles (EPBs) are ionospheric disturbances that occur in the magnetic equator. They are generated by the Rayleigh–Taylor instability, and the zonal electric field plays a crucial role. In particular, the enhancement of the eastward electric field before sunset, known as the pre-reversal enhancement (PRE), is known to be related to EPBs . In the E region, there are both the eastward current of the equatorial electrojet (EEJ) and the westward current of the counter electrojet (CEJ). These currents about two hours before sunset (as the evening EEJ/CEJ) has been shown to control the intensity of the PRE and to affect EPB occurrence [Uemoto et al., 2010].
In this study, in order to clarify the daily/regional/seasonal variation of evening EEJ/CEJ corresponding to the onset of PRE, we analyzed the EE-index, which consists of the magnetic field variation due to globally similarly varying magnetospheric currents (EDst) and the localized ionospheric magnetic field variations (EUEL) [Uozumi et al., 2008; Fujimoto et al., 2016]. Furthermore, in this study, semidiurnal lunar tidal variations were calculated from EUEL using the method of Fujimoto et al. (2019).
The composite waveforms of semidiurnal lunar tides and Sq currents were analyzed for each lunar time. As a result, characteristic waveforms combining CEJ and evening EEJ were observed when tidal effects are strong (e.g., during SSW). This result suggests that the superposition of semidiurnal lunar tides and Sq currents may promote the formation of eastward currents before sunset, i.e., PRE.
In this presentation, we will discuss whether the evening EEJ/CEJ contribution to PRE is due to independent current systems or to the superposition of semidiurnal tides and Sq currents through a comparative analysis of the Asian and South American regions.
In this study, in order to clarify the daily/regional/seasonal variation of evening EEJ/CEJ corresponding to the onset of PRE, we analyzed the EE-index, which consists of the magnetic field variation due to globally similarly varying magnetospheric currents (EDst) and the localized ionospheric magnetic field variations (EUEL) [Uozumi et al., 2008; Fujimoto et al., 2016]. Furthermore, in this study, semidiurnal lunar tidal variations were calculated from EUEL using the method of Fujimoto et al. (2019).
The composite waveforms of semidiurnal lunar tides and Sq currents were analyzed for each lunar time. As a result, characteristic waveforms combining CEJ and evening EEJ were observed when tidal effects are strong (e.g., during SSW). This result suggests that the superposition of semidiurnal lunar tides and Sq currents may promote the formation of eastward currents before sunset, i.e., PRE.
In this presentation, we will discuss whether the evening EEJ/CEJ contribution to PRE is due to independent current systems or to the superposition of semidiurnal tides and Sq currents through a comparative analysis of the Asian and South American regions.