Recent Investigations of Hydromagnetic Emissions Part II. Theoretical Interpretation

Abstract

Recent experimental and theoretical work suggests the hypothesis that hydromagnetic (hm) emissions are hydromagnetic wave packets guided by field lines as they bounce back and forth between hemispheres of the earth. As such they are analogous to whistlers, and one test of the hypothesis is the quantitative calculation of plasma densities in the outer magnetosphere and their comparison with whistler densities closer to the earth.Many hm emission exhibit measurable dispersion when displayed in the form of sonagrams (frequency vs time displays). In such cases, the measurement of group bounce times at two different emission frequencies can be combined with an accurate model of the magnetosphere to determine the zero-frequency (Alfven) bounce period and the equatorial cyclotron frequency above which the wave cannot propagate. These two quantities uniquely define the field line along which the hm emission propagated and the integrated plasma density along that field line.Analysis of 9 events showed they occurred on field lines crossing the equatorial plane between 4 and 10 earth radii, and showed equatorial plasma densities in agreement with extrapolated whistler "knee" densities.

A systematic study of structured micropulsations

“…In all of these models, the basic resonance takes place at some fraction of the cyclotron frequency owing to Doppler shifting, and the spacing is indicative of the latitudinal bounce time of either the field-guided energy packet or of the particles that are amplifying the wave [Tepley and Wentworth, 1965]. It has been demonstrated by several authors [Obayashi, 1965;Gendrin and Troitskaya, 1965;Wentworth, 1965] that protons, not electrons, are the most reasonable source for this interaction.…”

Determination of the Magnetospheric Plasma Density by the use of Long-Period Geomagnetic Micropulsations

“…Thus the plasma density can be determined almost uniquely (within the accuracy of present observation), in particular at the longer periods (for example, longer (b) Comparison with other results. Much information on the magnetospheric plasma density based on ground observations has been obtained from whistler investigations (Carpenter 1963, Carpenter and Smith 1964, Angerami and Carpenter 1966, and also from micropulsation studies (Obayashi and Jacobs 1958, Wentworth 1965, Watanabe 1965. Whistler studies have suggested that the electron density suddenly drops by a factor of 50 or more at distances between 3 and 5 Re (the knee), and has comparatively low values beyond the knee.…”

“…Whistler studies have suggested that the electron density suddenly drops by a factor of 50 or more at distances between 3 and 5 Re (the knee), and has comparatively low values beyond the knee. Wentworth (1965Wentworth ( , 1966 and Watanabe (1965) also deduced relatively low values of the plasma density (0.5-50 particles/cm3 in the region L=5-9) using pearl micropulsations (period 0.2-5 sec.). Since micropulsations of this period are believed to be generated at a distance of L=4-6 in the equatorial region (Jacks 1966) the resulting lower values of plasma density agree with the lower values in the outer region of the knee estimated from whistler studies.…”

“…micropulsations. Wentworth (1965Wentworth ( , 1966 and Watanabe (1965) have considered short period Present address * Department of Electronics, Doshisha University, Kyoto, Japan. ** Killam Memorial Professor of Science , the University of Alberta, Edmonton, Canada.…”

Substorm aspects of magnetic pulsations

“…But, for the same reasons, the field of diagnosis that can be made from ULF observations covers a wide range of magnetospheric problems Troitskaya and Gul'elmi, 1967;. We are not interested here in the determination of electron density profiles (Dowden and Emery, 1965;Watanabe, 1965;Wentworth, 1966;Kenneyetal., 1968;Liemohn etal., 1968). We will deal only with questions which are related to the understanding of magnetospheric storms: localization and bulk motion of the region of interaction, energy and flux of the interacting particles.…”