Direct penetration of the polar electric field to the equator during a DP 2 event as detected by the auroral and equatorial magnetometer chains and the EISCAT radar

Abstract

The quasi‐periodic DP 2 magnetic fluctuations (period of 30–40 min) appearing coherently at the auroral and equatorial latitudes during the day are analyzed based on the high time resolution magnetometer data recorded at the International Monitor for Auroral Geomagnetic Effects (IMAGE) stations in Scandinavia and at the Brazilian and African equatorial stations. It is shown that the correlation between the DP 2 magnetic fluctuations at both latitudes is excellent (correlation coefficient of 0.9). No discernible time shift has been found within the resolution of 25 s. The European incoherent scatter (EISCAT) radar observations in Scandinavia show that the DP 2 fluctuations at auroral latitudes are caused by an ionospheric Hall current which is controled by the convection electric field. The DP 2 fluctuations exhibit a strong decrease in magnitude with decreasing latitude, however, it is enhanced considerably at the dip equator with an amplitude comparable to that at the subauroral latitude. The considerable equatorial enhancement of the magnitude of the DP 2 fluctuations with an enhancement ratio of 4 is due to the concentration of the electric current along the highly conductive dayside equatorial ionosphere. These observational facts can be explained in terms of an ionospheric current which is generated by the magnetospheric electric field at the high latitude and extends to the equatorial ionosphere almost instantaneously. From the viewpoint of the electric field penetration, we conclude that the magnetospheric electric field penetrates to the equatorial ionosphere through the polar ionosphere almost instantaneously within the time resolution of 25 s. The nearly instantaneous propagation of the electric field to the equator can be explained primarily by a parallel plane transmission line model composed of the conductive Earth and ionosphere. In addition to our finding of the fast propagation of the DP 2 electric field, it is found that an impulsive magnetic change with a timescale of 100 s appears at the dayside dip equator with a time delay of about 10 s, which requires to include the effect of the high conductivity of the dayside equatorial ionosphere in future studies of the propagation model.

Numerical analysis of global ionospheric current system including the effect of equatorial enhancement

“…The latitudinal pro®le for the case of 0.0 ratio is nearly the same as that shown in Fig. 7 of Kikuchi et al (1996). However, the enhancement rate of the magnetic variation at the equator with respect to that in high latitudes is a little higher in the case of 0.0 ratio than that of Kikuchi et al's (1996) result.…”

“…3.2 E ect of shielding by region 2 current Kikuchi et al (1996) discussed the equatorial enhancement of the DP2 type magnetic variation as a case study and showed that the equatorial enhancement was recognized at the daytime equator and even region 2 ®eld-aligned current, causing a shielding e ect, was expected to exist to some extent. Several authors theoretically estimated the shielding e ect of region 2 current for the dawn-to-dusk electric ®eld in the equatorial region associated with the DP2 magnetic uctuations (Nopper and Calovillano, 1978;Senior and Blanc, 1984;Denisenko and Zamay, 1992).…”

“…However, the enhancement rate of the magnetic variation at the equator with respect to that in high latitudes is a little higher in the case of 0.0 ratio than that of Kikuchi et al's (1996) result. Therefore, at the event analyzed by Kikuchi et al (1996), the ratio of the region 2 to 1 currents is thought to be between 0.0 and 0.5 and may be near 0.0.…”

Role of the magnetospheric and ionospheric currents in the generation of the equatorial scintillations during geomagnetic storms

“…(1985) the magnetospheric ring current intensity is strongly dependent on the variations of the B z IMF. The magnetospheric ring current cannot directly penetrate to the equatorial ionosphere, though these are models with closed partial ring current through the polar ionosphere (Kikuchi et al, 1996). The equatorial electric field strengthening, on the other hand, can be observed in the absence of the ring current.…”

“…They also showed that the location and intensity of the FAC are defined by the B z and B y components of the IMF. Zakharov et al (1989), Denisenko and Zamai (1992), in theory, Kikuchi et al (1996), Sizova (2002), using geomagnetic data, Sizova and Pudovkin (2000), using ionospheric data, had shown that the electric fields from the FAC could penetrate to the equatorial ionosphere and explain the equatorial electric field variations. In Fig.…”