On the latitudinal variations of the ionospheric electric field during magnetospheric disturbances

Abstract

A joint alert campaign was organized during the month of October 1980 by the incoherent scatter radars in the American sector: namely, Jicamarca, Arecibo, Millstone Hill, and Chatanika. The campaign, which met with success, was designed to study the behavior of the ionospheric electric field as a function of latitude during magnetically active conditions. The Arecibo data in this campaign support present and previous observations at Jicamarca that suggest that when the convection E field suddenly decreases, the Alfvén layer shielding field becomes unbalanced and penetrates the plasmasphere. While this type of observation is reasonably convincing, others are more difficult to categorize. We suggest that, beside the high‐latitude electric fields, time‐varying auroral conductivity models will have to be considered in order to understand the morphology of the low‐latitude E field disturbances. We present the first correlation analysis and determination of the amplitude ratio of the disturbed zonal electric field at 30° geometric latitude (Arecibo) to the field at 0° (Jicamarca). Other highlights of the paper are a discussion of DP2, which may help clarify the controversy surrounding it, and a discussion of the sensitivity of low‐ and mid‐latitude radars to disturbances of magnetospheric origin. We show that this sensitivity maximizes at the magnetic equator.

Response of equatorial ionosphere to episodes of asymmetric ring current activity

“…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. The present results, therefore, constitute an addition to the growing experimental knowledge of the characteristics of short-lived equatorial electric ®eld disturbances associated with asymmetric ring current activity.…”

“…Sastri et al (1992a, b) emphasised the bipolar character of disturbances in equatorial electric ®eld with particular reference to isolated substorm activity. Gonzales et al (1979Gonzales et al ( , 1983 have also shown earlier that the equatorial zonal electric ®eld responds to both rapid decreases and increases in magnetospheric convection. The present work rea rms the view that at a given location, bipolar electric ®eld disturbances do occur with some, if not all, isolated events of asymmetric ring current activity (substorms).…”

“…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. Gonzales et al, 1983;Fejer et al, 1985). The geomagnetic activity-related disturbances in the equatorial zonal electric ®eld/currents are broadly classi®ed into two groups depending on their nature and duration (rapid changes of short duration or slowly varying and persistent changes), and on the timedelay of their appearance with reference to the causative geomagnetic disturbance (prompt or delayed e ects).…”

<i>F</i>-region ionospheric perturbations in the low-latitude ionosphere during the geomagnetic storm of 25-27 August 1987

“…eastward/westward on the day/night sides), penetrated in the equatorial ionosphere, is associated with a southward turning of the interplanetary magnetic field component, B z (Abdu et al, 1991;Abdu, 1997). The intensity and duration of the disturbance electric field is controlled by many factors, such as the time constants of the decay/formation of the shielding charges in the inner magnetosphere, and auroral conductivity (Vasyliunas, 1975;Kelley et al, 1979;Gonzales et al, 1983), and, as a result, there are still questions concerning the prediction of the storm-time dependence of ionospheric electric fields (Fejer, 2002).…”

Spike‐like change of the vertical E × B drift in the equatorial region during very large geomagnetic storms

“…[2] During geomagnetic storms the deviations of the electric fields from their quiet-time pattern (disturbance electric fields) are frequently observed in the low-latitude ionosphere [e.g., Gonzales et al, 1979Gonzales et al, , 1983Kobea et al, 2000;Huang et al, 2005]. The disturbance electric fields play a significant role for the plasma distribution and the plasma instabilities in the low-latitude ionosphere and are often referred to as the primary source mechanism for the storm-time ionospheric disturbances.…”