Response of equatorial ionosphere to episodes of asymmetric ring current activity

Abstract

Abstract. We present the characteristics of the response of equatorial ionospheric zonal electric ®eld and Fregion plasma density to the asymmetric ring current intensi®cations that occurred in succession on 16 December 1991, corresponding to the STEP/EITS-2 campaign period. The study is based on high-timeresolution (1-min) data of asymmetic ring current indices, ASY(H/D) and F-region vertical plasma drift, z measurements at Kodaikanal (10.25°N; 77.5°E; dip 4°), India and quarter-hourly ionosonde data of Fortaleza (4°S; 322°E; dip A9°), Brazil. It is shown that short-lived disturbances in F-layer vertical plasma drift, z and height (h¢F/hpF2) indicative of westward and eastward electric ®elds prevail simultaneously in the dusk (18±21 LT) and predawn (02±05 LT) sectors, respectively, in association with the decay phase of asymmetic ring current events. Electric ®elds of opposite polarity do also seem to manifest at these local times, particularly in the early-morning sector in conjunction with the intensi®cation of the asymmetric ring current. At a given location, electric ®eld disturbances associated with individual asymmetric ring current events are thus bipolar in nature, with ®elds of opposite polarity during the growth and decay phases. The nature and polarity structure of the observed electric ®eld disturbances are in agreement with the theoretical/model predictions of prompt penetration of high-latitude electric ®elds to the equatorial region.

Variability of total electron content near the crest of the equatorial anomaly during moderate geomagnetic storms

“…In the main phase of storm and around local sunset hours (1918 h IST being the subionospheric sunset time) an abrupt increase in AE index is supposed to be a proxy of prompt penetration (PP) eastward electric field at the equatorial latitude Scherliess, 1995, 1997;Abdu et al, 2007) in the ''undershielding'' condition. The same period is also marked by a sharp increase in the variation of ASY-H. Sastri et al (1997) reported a prompt upward perturbation of plasma drift at an equatorial station, Kodaikanal (geographic: latitude 10.251N, longitude 77.51E, dip 41N), in the dusk sector in association with the asymmetric ring current development for which ASY-H is a proxy index. The changes in AE and ASY-H indices observed under present investigation support the idea of PP electric field in the specified local time sector.…”

Electrodynamic coupling processes between the magnetosphere and the equatorial ionosphere during a 5-day HILDCAA event

“…Stormtime processes in the equatorial ionosphere have been extensively studied for locations all over the world in the past few decades Kelley et al, 1979;Abdu et al, 1985Abdu et al, , 1988Abdu et al, , 1995Fejer et al, 1990;Batista et al, 1991;Sastri et al, 1997Sastri et al, , 2002Sobral et al, 1997Sobral et al, , 2001Basu et al, 2001aBasu et al, , 2001b. The present study concerns equatorial ionospheric responses to enhanced auroral currents with an intense interplanetary magnetic field (IMF) B z fluctuation but in the absence of magnetic storm.…”

“…The prompt penetration effects have been extensively studied by many authors Fejer et al, 1990;Sobral et al, 1997Sobral et al, , 2001Sastri et al, 1997;Tsurutani et al, 2004;Verkhoglyadova et al, 2008). Wei et al (2008) carried out direct comparison study of the interplanetary electric field (IEF) with ionospheric zonal electric field using a 5-day-long HILDCAA event.…”

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

“…[2] During geomagnetically disturbed conditions, ionospheric electric fields and currents at equatorial and low latitudes have been observed to be modulated by the direct prompt penetration of a dawn-dusk electric field to equatorial and low-latitude ionosphere [Nishida, 1968;Spiro et al, 1988;Sastri et al, 1997] and by the ionospheric disturbance dynamo electric field [Blanc and Richmond, 1980;Fejer and Scherliess, 1997]. The storm time ionospheric electric field perturbations often affect the distribution of ionospheric plasma by creating positive ionospheric storm (increased electron density) and/or negative ionospheric storm (decreased electron density) and the occurrence of plasma density irregularities at equatorial and low latitudes [e.g., Fejer, 1986;Abdu et al, 1991;Abdu, 1997;Sastri et al, 2000;Basu et al, 2001a].…”