Penetration of magnetospheric electric fields to the equator during a geomagnetic storm

Abstract

[1] Penetration of the magnetospheric electric field to the equatorial ionosphere was examined for the geomagnetic storm on 6 November 2001, by analyzing the difference in magnitude of the geomagnetic storm recorded at the dayside geomagnetic equator, Yap (À0.3°GML) and low latitude, Okinawa (14.47°GML). The penetrated electric field caused the DP2 currents at the equator, i.e., eastward currents during the main phase of the storm, while the overshielding currents, i.e., westward currents dominated during the recovery phase. It is shown that the ring current started to develop simultaneously with the onset of the equatorial DP2 within the temporal resolution of a few minutes. These results imply prompt transmission of the dawn-to-dusk convection electric field to the inner magnetosphere as well as to the equatorial ionosphere. It is found that the equatorial DP2 started to decrease one hour after the onset of the ring current development, indicating shielding effects becoming effective at the equator during the latter half of the storm main phase. The DP2 was then overwhelmed by the overshielding, which resulted in the counter electrojet (CEJ) in the beginning of the storm recovery phase. The IMAGE magnetometer chain data indicate that the westward auroral electrojet (AEJ) in the dawn sector was driven over midlatitude centered at 57°corrected geomagnetic latitude (CGML) during the main phase, while the AEJ shifted rapidly poleward to the auroral latitude centered at 67°CGML in the beginning of the recovery phase. The overshielding must be caused by the abrupt poleward shift of the R1 FACs as inferred from the poleward shift of the AEJ, in addition to the decrease in their magnitude due to the decrease in magnitude of the southward IMF. The geomagnetic storm at the dayside geomagnetic equator was enhanced in amplitude with the ratio of 2.7 as compared with the geomagnetic storm at low latitude. This amplification is a result of both effects of the DP2 currents and the CEJ associated with the main and recovery phases, respectively. It is suggested that the electric field associated with the DP2 currents contributed to the development of the ring current during the main phase, while the overshielding electric field may contribute to cease developing the ring current during the recovery phase.

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

“…During geomagnetically active periods, a counter electrojet is sometimes caused by the penetration of the polar-region electric field to equatorial latitudes (Rastogi and Patel 1975;Rastogi 1977Rastogi , 1997Kikuchi et al 2003Kikuchi et al , 2008. Besides, storm-time thermospheric winds tend to drive a westward electric field in the dayside equatorial region through the mechanism known as disturbance dynamo (Blanc and Richmond 1980;Fuller-Rowell et al 2002).…”

“…Rastogi (1977), analyzing the difference in H at Huancayo (12.0°S, 75.3°W) and Fuquene (5.4°, 73.7°), recognized the occurrence of the counter electrojet during geomagnetic storms. Later, Kikuchi et al (2003Kikuchi et al ( , 2008 demonstrated how the penetration of high-latitude electric fields to lower latitudes can cause an enhancement and reduction (or reversal) in the equatorial electrojet. High-latitude electric fields penetrate to lower latitudes, most evidently when the magnetospheric convection suddenly increases or decreases.…”

Studies of ionospheric F-region response in the Latin American sector during the geomagnetic storm of 21–22 January 2005

“…As described by Abdu (1997;see also Buonsanto, 1999) major modifications in the equatorial ionosphere-thermosphere system during magnetospheric disturbances are produced by (a) prompt equatorward penetration of magnetospheric/high latitude electric fields (see also Senior and Blanc, 1984;Spiro et al, 1988), and (b) disturbance dynamo driven by enhanced global thermospheric circulation resulting from energy input at high latitude (see also Blanc and Richmond, 1980). Recently, Kikuchi et al (2008) and Veenadhari et al (2010) have investigated penetration of magnetospheric electric fields to the equator during magnetic disturbances.…”

The transition to overshielding after sharp and gradual interplanetary magnetic field northward turning

“…[4] The overshielding scenario can successfully explain some observations in space [e.g., Goldstein et al, 2002Goldstein et al, , 2003] and on the ground [e.g., Kikuchi et al, 2000Kikuchi et al, , 2008. However, the physics behind overshielding still require more extensive study.…”