High‐latitude irregularities of the magnetospheric electric field and their relation to solar wind and geomagnetic conditions

Abstract

[1] Having processed high-resolution electric field measurements of the low-altitude spacecraft Dynamic Explorer 2 in order to reveal and study signatures of rapid magnetospheric streams, we found that along with a regular large-scale electric field there exists an irregular one with amplitudes of 50-200 mV m À1 and transverse scale sizes varying from several to a hundred kilometers. This component behaves quite differently compared to the regular field: In particular, it is most common and of highest intensity under strong northward B z interplanetary magnetic field (IMF) and low AE and Dst conditions. Thus low average electric field (as expected and observed at quiet times) does not mean low variance. Large-amplitude electric field fluctuations typically occur at or around the convection reversal boundary, expanding to the central polar region or shifting to the equator depending on B z IMF direction. They are accompanied by large variations of the magnetic field component, with one-to-one correspondence of peaks and valleys of electric and magnetic field oscillations. The field-aligned currents inferred are on the order of 10 -100 A km À2 , which is large enough to be associated with discrete arcs.

Dynamical critical scaling of electric field fluctuations in the greater cusp and magnetotail implied by HF radar observations of F-region Doppler velocity

“…In fact, spatial fluctuation of electric fields in the high-latitude ionosphere are strongest during IMF northward conditions, when coupling to the solar wind is weakest (Golovchanskaya et al, 2002). This was attributed to the interchange instability acting over extended regions of closed magnetic flux when B z is northward.…”

“…Gravity waves might be generated with periods similar to the electric field fluctuations driving them via the Lorentz force, whereas the effects of tides and planetary waves occur at longer time scales than analysed here. Golovchanskaya et al (2002) used Dynamics Explorer 2 (DE 2) observations to show the high-latitude convection is more likely to be smooth when it is strongly driven under B z southward conditions, and that electric field fluctuations increase in intensity on closed field lines under B z northward conditions. They propose that when B z is northward, interchange instability develops within closed field line regions mapping to high latitude.…”

Scaling of electric field fluctuations associated with the aurora during northward IMF

“…There is a dependence on the Bz IMF as well, but it is not so well pronounced. The relation of the electric field turbulence to the Bz IMF was earlier revealed by Golovchanskaya et al [2002]. The IMF dependence of PDF shape can be explained if we assume that the turbulence under study is associated with the Birkeland field-aligned currents/large-scale convection velocity shears.…”

“…By now, after some controversy, it has been accepted that the observed frequencies of the fluctuations are Doppler shift frequencies in the satellite reference frame resulting from a satellite's motion through predominantly electrostatic coherent structures [Tam et al, 2005, and references therein]. There is evidence of a cause-to-effect relationship between the turbulence displayed in the electric and magnetic fields and auroral structuring [Frank et al, 1986;Golovchanskaya et al, 2002]. As was convincingly demonstrated by Frank et al [1986] for all cases when simultaneous optical observations were available, the most intense spikes in the fluctuating fields observed by DE2 were coincident with the occurrence of auroral arcs.…”

“…As was convincingly demonstrated by Frank et al [1986] for all cases when simultaneous optical observations were available, the most intense spikes in the fluctuating fields observed by DE2 were coincident with the occurrence of auroral arcs. A similarity between the turbulence and discrete auroral features with respect to the global distribution, seasonal variation, relation to solar wind, IMF and geomagnetic conditions has been pointed out by Heppner [1973], Saflekos and Potemra [1978], Golovchanskaya et al [2002], and Matsuo et al [2003]. Recently, Tam et al [2005] have performed intermittency analysis on the electric field data obtained by a sounding rocket in the auroral zone.…”