Microbursts have been found to be a common occurrence in the auroral zone. They occur typically in two episodes per day for several days following a geomagnetic storm and for a day or two following strong negative magnetic bays. Microbursts are shown to have a close relationship to the electron precipitation with 5–30‐second characteristic times called fast variations. Both now appear to be related to the same underlying plasma wave phenomenon. Microbursts have the same temporal structure at L = 8 as they do at L = 6. Direct rocket observations show that the electrons involved in this form of precipitation can be fit by an energy spectrum of exponential form with e‐folding energy of 20 kev.
Measurements of high‐energy solar‐wind electrons have been made from a low orbit around the moon. Solar‐wind electrons can be identified up to energies of ∼3000 ev, at which an electron population of entirely different characteristics becomes dominant. The solar‐wind cavity on the moon's antisolar side shows evidence of being filled by plasma coming from the downstream direction. When the direction of the interplanetary field corresponds to solar ecliptic azimuth angles of about 90°, a partial solar‐wind cavity extends across most of the eastern sunlitside of the moon within ∼20° of the noon meridian. There are localized increases in the ∼500‐ev electron flux over much of the sunlit hemisphere. These increases are highly persistent and stable in their location over a 2½‐day period and hence are not due to intrinsic variations in the solar wind. They are usually associated with disturbances in the magnetic field. These increases are interpreted to be the result of an interaction between the solar wind and the moon that deflects some of the solar‐wind flow and results in limb shocks.
Two sounding rockets were launched into auroral breakups near local midnight and one rocket was launched into a 2.5‐db riometer absorption event at local noon. The rockets were instrumented to measure the energy spectra of electrons and protons. Results show that electron fluxes in the auroral zone resemble electron fluxes in the plasma sheet, both in the shape of energy spectra and in the magnitude of flux, which indicates that the plasma sheet may be the source of auroral zone electrons. The proton fluxes in these two regions are quite different. Thus the plasma sheet probably is not the source of auroral zone protons. Time variations of 1‐kev electrons and protons were coherent, which indicates similar precipitation mechanisms for these two types of particles. The source of 1‐kev electrons was found to have a wider spatial extent than the source of 10‐kev electrons. During auroral breakup, electron precipitation was isotropic over the upper hemisphere while the protons were anisotropic, with more flux at 90° than at 0°.
We present the first direct observations of convection electric fields in the earth's magnetotail. The electric fields have been measured from lunar orbit by detection of the E × B/B² drift displacement of low‐energy electrons at the limb of the moon. We find the following. (1) Electric fields range in magnitude from ≲0.02 mV/m, the limit of sensitivity of the method, up to 2 mV/m. The typical value is 0.15 mV/m, and the corresponding convection velocity is 15 km/s. (2) The sense of the electric field is almost always dawn to dusk. (3) The electric field is often variable on a time scale of hours and sometimes minutes. (4) The observations indicate that the electric field is not uniform across the magnetotail. If it is assumed that the typical measured electric field value represents an average over the inhomogeneities, the potential drop across the entire tail is ∼40 kV.
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