Equatorial ionospheric electric fields during magnetospheric disturbances: local time/longitude dependences from recent EITS campaigns

Response of the equatorial ionosphere in the South Atlantic Region to the Great Magnetic Storm of July 15, 2000

“…In this paper, we investigate the profound manner in which the ionization distribution, plasma dynamics and structuring in the equatorial ionosphere were affected on July 15, 2000 when the prompt penetration of the electric field into the equatorial ionosphere occurred in the presence of sustained disturbance dynamo effects. attributed to nighttime particle precipitation [Abdu et al, 1995], and the presence of a moderate level of electric field near Ascension Island. The large storm-driven vertical (perpendicular to geomagnetic field) drifts can be channeled into large parallel drifts at high altitudes.…”

Multi-technique investigations of storm-time ionospheric irregularities over the São Luís equatorial station in Brazil

“…This effect can be intensified if the eastward direct penetration occurs in conjunction with the regular post-sunset pre-reversal enhancement driven by F-region dynamo action (Batista et al, 1991) or with disturbance dynamo action at night. Previous studies of this effect have mainly relied exclusively on either ionosonde data (Somayajulu et al, 1987;Reddy and Nishida, 1992;Abdu et al, 1995), incoherent scatter radar data (Fejer, 1997a), or VHF ionospheric scintillations (Aarons, 1991), which alone cannot give a complete perspective of the processes involved.…”

Response of equatorial ionosphere to episodes of asymmetric ring current activity

“…A fairly large body of literature now exists to show that at the time of geomagnetic substorms/storms the ionospheric electric ®elds/currents and plasma density in the dip equatorial region depart quite signi®cantly on di erent time-scales from the geomagnetically quiet time patterns (see Abdu et al, 1991Abdu et al, , 1993Abdu et al, , 1995Fejer, 1991;Fejer and Scherliess, 1995;Reddy et al, 1990;Reddy and Nishida, 1992;Sastri et al, 1992a,b,c, and references therein). Geomagnetic activity is found to in¯u-ence preferentially the zonal rather than the meridional component of the ionospheric electric ®eld at dip equatorial locations (e.g.…”

“…These electric ®eld disturbances are currently understood as manifestations of direct penetration to low latitudes of electric ®elds of magnetospheric/high-latitude origin (e.g. Fejer et al, 1990a,b;Sastri et al, 1992a,b,c;Abdu et al, 1993Abdu et al, , 1995Fejer and Scherliess, 1995), based on the results of numerical and semi-analytical model studies of electric ®eld perturbations in the plasmasphere due to sudden changes in the magnetospheric convection (polar-cap potential drop) and in ®eld-aligned current (FAC) systems (e.g. Nopper and Carovillano, 1978;Senior and Blanc, 1984;Tsunomura and Araki, 1984;Spiro et al, 1988).…”

“…Against this background, the present work is done with the primary aim of evaluating the longitude/localtime dependence of the response of equatorial zonal electric ®eld to asymmetric ring current intensi®cations, using simultaneous ionospheric data of Indian (75°E) and Brazilian (45°W) sectors. While the earlier studies have documented the global nature and polarity pattern of electric ®eld disturbances associated with asymmetric (partial) ring current events (Tanaka, 1981(Tanaka, , 1986Gonzales et al, 1979;, recent studies have drawn particular attention to the high sensitivity of the electric ®eld in the dusk and postmidnight sectors to asymmetric ring current developments, using essentially single-station data (Sastri et al, 1992c;Abdu et al, 1993Abdu et al, , 1995 The current work substantiates this prominent feature of the local-time dependence of the electric ®eld disturbances associated with asymmetric ring current events. Moreover, though the polarity of the electric ®eld disturbances associated with asymmetric ring current substorm activity is known from earlier studies to be opposite in the day and night hemispheres (Gonzales et al, 1979(Gonzales et al, , 1983Sastri et al, 1992b), evidence for the simultaneous response, with opposite polarity, of electric ®elds in the predawn and dusk sectors, to asymmetric ring current activity is reported for the ®rst time here.…”