Plasma observations on Explorer 34

Abstract

This paper discusses results of the Explorer 34 plasma detector obtained during three magnetic storms, May 30, June 5, and June 25, 1967. Detailed comparisons with magnetic field observations on the same satellite are used to interpret the observations and to identify shocks and tangential discontinuities. A relation between the magnitude of such sudden changes in the earth's magnetic field and the solar wind parameters has been derived by Siscoe. Our observations are consistent with this relationship. The local shock speeds are derived from data obtained at the time of the sudden commencements. An example of an si+ si− pair is discussed, and in this case the negative impulse is shown to be due to a tangential discontinuity rather than a shock, whereas the positive impulse is associated with a shock. Helium observations are described that show that during the main phase of some geomagnetic storms the abundance ratio na/np shows a marked increase. In the May 30 storm it attained a value of 0.15 ± 0.02, 5½ hours after the sc, an increase of seven times over the value observed earlier.

Hydromagnetic shocks in the solar wind

“…The plasma instrument has been described by Ogilvie et al (1968), so only a very short account will be given here. It records protons and helium nuclei separately, a spectrum of each species taking approximately one minute to acquire and successive spectra are separated in time by 3.04 minutes.…”

“…Now consider Equation 3, which is a statement of conservation of momentum flux across a shock. Using (2), and the condition for continuity of tangential electric field in an infinitely conducting plasma, Wilkerson (1968) has obtained the following condition which must be satisfied if (3) is valid and if the discontinuities are shocks:…”

Solar wind interaction with Comet Bennett (1969i)

“…In fact, it is still not even known whther fast solar-wind streams come from active regions or~uite regions on the sun. Similarly, there is only a weak correlation between solar-wind conditions and geomagnetic activity as measured by the D<:P index (Snyder et al, 1963;Ogilvie et al, 1968). Thus, to obtain definitive results concerning the short-term variations in comet tails, it is necessary to relate comet observations directly to solar-wind measurements.…”

Geomagnetic sudden impulses at low latitude during northward interplanetary magnetic field conditions

“…As a consequence, on the ground a sudden impulse (SI) in the geomagnetic field is observed which, at middle and low latitudes, typically involves a step-like variation of the northsouth component H whose amplitude has been found to be roughly proportional to the change of the square root of the SW dynamic pressure [Siscoe et al, 1968;Ogilvie et al, 1968;Su and Konradi, 1975]. Sis recorded by ground magnetometers at geomagnetic latitudes between 15 ø and 30 ø have been analyzed by Russell et al [1992Russell et al [ , 1994 :40), the sense of polarization of low-frequency geomagnetic field fluctuations (0.8-3.6 mHz) is CCW in the morning and reverses to CW in the afternoon but the reversal is delayed by a few hours with respect to local noon; we explained this feature, suggesting that the observed waves could be mostly generated by SW discontinuities impacting the magnetopause in the early afternoon sector, as expected for corotating interplanetary structures [see Rostoker and Sullivan, 1987], rather than by the Kelvin-Helmholtz instability, whose effects at our latitude are strongly damped [Yurnoto, 1986].…”