[1] Using data from the Medium Electrons A instrument on the Combined Release and Radiation Effects Satellite (CRRES), a survey of pitch angle distributions (PADs) of energetic electrons is performed. The distributions are classified into three categories: 90°-peaked, flattop, and butterfly. The categorizations are examined as a function of L-shell and orbit number and at electron energies of 153, 510, and 976 keV. The 90°-peaked distributions dominate at the lowest energy channel, and butterfly distributions are more prevalent at higher L values. The PADs on the dayside are predominately 90°-peaked distributions, while butterfly distributions become more common on the nightside at higher L-shells. Fitting the PADs to a sin n a form, where a is the local pitch angle, a profile of the parameter n versus L-shell is produced for local times corresponding to postnoon and midnight sectors for the 510-keV channel. We then compare the 510-keV data during times of moderate disturbance to the less disturbed case and the average case, and show an increase in butterfly distributions, which occurs at L > 6 for the nightside case and 3.5 < L < 5.5 for the dayside case. Comparing the profiles for n > 1 before and after the great storm on 24 March 1991, we find that there are significant differences before and after this event, the latter orbits being during a time of higher observed geomagnetic activity. Considering only those PADs with a calculated n > 1, the variation of the 90°-peaked distributions versus L-shell and orbit shows increased steepness at lower L-shell. For the lowest energy channel, the low L-shell variation of the steepness of the distributions visually correlates with the average 2-day minimum plasmapause location calculated from a model based on the D st index over the same time period. For the 510-keV electrons, a correlation can be seen with the development of flattop distributions inside of the calculated minimum plasmapause location.
Abstract. In this research, the geometrical structures of tilted current sheet and tail flapping waves have been analysed based on multiple spacecraft measurements and some features of the tilted current sheets have been made clear for the first time. The geometrical features of the tilted current sheet revealed in this investigation are as follows: (1) The magnetic field lines (MFLs) in the tilted current sheet are generally plane curves and the osculating planes in which the MFLs lie are about vertical to the equatorial plane, while the normal of the tilted current sheet leans severely to the dawn or dusk side. (2) The tilted current sheet may become very thin, the half thickness of its neutral sheet is generally much less than the minimum radius of the curvature of the MFLs. (3) In the neutral sheet, the field-aligned current density becomes very large and has a maximum value at the center of the current sheet. (4) In some cases, the current density is a bifurcated one, and the two humps of the current density often superpose two peaks in the gradient of magnetic strength, indicating that the magnetic gradient drift current is possibly responsible for the formation of the two humps of the current density in some tilted current sheets. Tilted current sheets often appear along with tail current sheet flapping waves. It is found that, in the tail flapping current sheets, the minimum curvature radius of the MFLs in the current sheet is rather large with values around 1 R E , while the neutral sheet may be very thin, with its half thickness being several tenths of R E . During the flapping waves, the current sheet is tilted substantially, and the maximum tilt angle is generally larger than 45 • . The phase velocities of these flapping waves are several tens km/s, while their periods and wavelengths are several tens of minutes, and several earth radii, respectively.Correspondence to: C. Shen (sc@cssar.ac.cn) These tail flapping events generally last several hours and occur during quiet periods or periods of weak magnetospheric activity.
[1] A comparison of MeV electron measurements at geosynchronous orbit, GEO, with solar wind shows that the MeV electron prediction model developed for GEO using data from the declining phase of solar cycle 22 (1995-1996) works well for the declining phase of solar cycle 23 (2006-2008), indicating that the MeV electron flux has a predictable and systematic response to the solar wind. The same comparison for solar maximum (2000)(2001)(2002)(2003) shows that the model works less well partly because it does not match the high flux cutoff seen in the data and partly because it does not reproduce the sudden drops in flux that occur when the magnetopause is close to GEO. The model also reproduces the nonlinear correlation of the solar wind speed with the log of the MeV electron flux seen at GEO. An examination of 15 yr of solar wind and the MeV electron data shows that geomagnetic activity driven by a southward orientation of the interplanetary magnetic field, IMF, is a necessary condition for MeV electron enhancements at GEO and that high-speed solar wind are not necessary. The reason that high-speed solar wind is almost always associated with the enhancement of MeV electrons is mainly because high-speed solar wind almost always has some southward components of the IMF.
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