Equatorial electrojet as part of the global circuit: a case-study from the IEEY

Abstract

Abstract. Geomagnetic storm-time variations often occur coherently at high latitude and the day-side dip equator where they a ect the normal eastward Sq ®eld. This paper presents an analysis of ground magnetic ®eld and ionospheric electrodynamic data related to the geomagnetic storm which occured on 27 May 1993 during the International Equatorial Electrojet Year (IEEY) experiment. This storm-signature analysis on the auroral, mid-latitude and equatorial ground ®eld and ionospheric electrodynamic data leads to the identi®cat-ion of a sensitive response of the equatorial electrojet (EEJ) to large-scale auroral return current: this response consists in a change of the eastward electric ®eld during the pre-sunrise hours (0400±0600 UT) coherently to the high-, mid-, and equatorial-latitude H decrease and the disappearance of the EEJ irregularities between the timeinterval 0800±0950 UT. Subsequent to the change in h'F during pre-sunrise hours, the observed foF2 increase revealed an enhancement of the equatorial ionization anomaly (EIA) caused by the high-latitude penetrating electric ®eld. The strengthening of these irregularities attested by the Doppler frequency increase tracks the H component at the equator which undergoes a rapid increase around 0800 UT. The DH variations observed at the equator are the sum of the following components: S R , DP, DR, DCF and DT.

Low-latitude ionospheric-thermospheric response to storm time electrodynamical coupling between high and low latitudes

“…The afternoon CEJ is seen shortly after the EEJ peak value of ∼220 nT which coincides with the main phase of the storm. The northward turning of IMF Bz results in to the reversal of the electric fields at midlatitudes and low latitudes [Rastogi and Patel, 1975;Kelley et al, 1979;Fejer et al, 1979;Gonzales et al, 1979;Kobea et al, 2000;Kikuchi et al, 2000bKikuchi et al, , 2003 Rastogi, 1977, 1997; Kobea et al, 1998Kobea et al, , 2000Kikuchi et al, 2000bKikuchi et al, , 2003Kikuchi et al, , 2008. Figure 4 shows the diurnal variation plot of IMF Bz and EEJ on 15 May 2005.…”

Statistical study of the DP2 enhancement at the dayside dip-equator compared to low latitudes

“…The geomagnetic disturbances observed generally at low latitudes are attributed to the magnetospheric electric fields and currents that connect the high-latitude ionosphere with the low-latitude ionosphere penetrating through the middle latitude (Nishida et al, 1966;Reddy et al, 1979;Kikuchi et al, 1996;Kobea et al, 1998). Studies by Nishida et al (1966) found that a type of disturbance called DP2, is associated with fluctuations in north-south component of interplanetary magnetic field.…”

Penetration of the convection and overshielding electric fields to the equatorial ionosphere during a quasiperiodic DP 2 geomagnetic fluctuation event

“…[3] Nishida's results and subsequent analyses based on high time-resolution magnetometer data [Kikuchi et al, 1996;Kobea et al, 1998] showed no significant shielding effects during DP 2 fluctuations. Moreover, Huang et al [2005], demonstrating that the convection electric field was observed at the dayside equator during the entire period of the main phase of a storm, concluded that the shielding did not work for several hours during the storm main phase.…”