Solar Magnetospheric Coordinates Research Articles

Spatial distribution of energetic plasma sheet electrons

The spatial distribution of energetic plasma sheet electrons (E ≥ 50 kev) out to a radial distance of 24 RE using data from the University of California at Los Angeles electron spectrometer and fluxgate magnetometer experiments on Ogo 5 is presented. A comparison of distributions in geocentric solar magnetospheric coordinates (GSM) prepared with and without the use of a neutral sheet model indicates that the use of such a model facilitates organization of plasma sheet data. The distribution in the YGSM- ZN plane, where ZN is the distance above or below the neutral sheet in the ZGSM direction, for limited values of XGSM shows a tendency for the energetic electrons to concentrate near the neutral sheet. However, no characteristic behavior is seen in electron fluxes during individual neutral sheet crossings. The percentage of flux occurrence above a given flux threshold falls off rapidly with distance from the neutral sheet. Contours of constant percentage of occurrence diverge slightly from the neutral sheet at local times away from midnight. This effect decreases with increasing flux threshold. Contours in the XGSM-YGSM plane for a limited range in ZN are extended toward dawn, and thus a limited dawn-dusk asymmetry is indicated. This effect is limited to the extent that percentages of occurrence comparable to those on the dawnside are found in the region about midnight. The degree of asymmetry increases as the flux threshold is increased. The contours in the XGSM-ZN plane converge toward the neutral sheet with increasing distance in the antisolar direction (−XGSM). A comparison of this result with the results from Imp 1 indicates that XGSM is preferable to the radial distance R for organizing tail data.

Transverse structure of the Earth’s magnetotail and fluctuations of the tail magnetic field

The analysis is based on 5.46-min magnetic field averages measured by the IMP 3 satellite. The effect of the inclination χ of the earth's magnetic axis with respect to the Y, Z-plane of solar magnetospheric coordinates (perpendicular to the earth-sun line) is studied in detail, and a thick sheet of magnetic field depression is shown to exist around the neutral sheet at distances of 30 to 38 RE in the antisolar direction. The location of the region of magnetic field depression varies with the value of χ; the thickness of the depression region is about 10 RE in the central parts of the tail, Y≈0, and is probably higher for Y>10 RE. The region of magnetic field depression is identified with the plasma sheet. The sheet of magnetic field depression is characterized by very large, long time-scale fluctuations parallel to the average local magnetic field. A ‘flapping motion’ of the neutral sheet may be responsible for the large values of some of these fluctuations. The fluctuations perpendicular to local magnetic field are nearly independent of position in the magnetotail. Both types of fluctuations are enhanced during and/or after sudden storm commencements (ssc) and sudden impulses (si) observed at ground stations. The effect is more clearly seen in the perpendicular fluctuations. The information from the interaction between the magnetosphere and a discontinuity in the interplanetary medium is transferred mainly along the lines of force.

Vela 2 measurements of the magnetopause and bow shock positions

Extensive measurements of the positions of the earth's magnetopause and bow shock have been performed with the Vela 2 satellites at ∼17 RE (earth radii) and at ecliptic latitudes up to ±63°. It has been found that these positions are highly variable in time; there is evidence that some of this variability is due to the changing character of the solar wind. In particular, the average positions of the magnetopause and shock appear to be related to the magnetic disturbance index Kp and thus also to solar wind velocity. Specific examples of data have been found that can be interpreted as showing gross motions of either the magnetopause or shock at times of sudden changes in plasma pressure within the magnetosheath. Despite the large variations in the magnetopause and shock positions, it has been found that solar magnetospheric and solar ecliptic coordinates are both useful coordinate systems for ordering the boundary positions. However, solar magnetospheric coordinates appear to be slightly preferable at high latitudes. In either system, both the magnetopause and the shock exhibit an east-west tilt of about 2–4° relative to the sun-earth line.