Recent Investigations of Hydromagnetic Emissions Part I. Experimental Observations

Abstract

A review is presented of some of the more important properties of Pc 1(0.2-5cps) emissions observed at middle and low latitudes. Special attention is given to fine structured These include latitude variations of emission frequency, fine structure repetition period, and signal amplitude.In addition to the aspects of the Pc 1 emissions outlined above, properties of two other types of emissions are briefly discussed. One of these signals, referred to here as a "continuous emission" also lies in the Pc 1 category. It is often observed continuously throughout the night and is characterized by a slow variation of f -t characteristics.The other signal, which might be placed in a Pc 1-Pi 1 transition category, is observed during magnetically disturbed periods. On sonagrams it is characterized by an irregularly spaced rising frequency fine-structure. When monitored aurally on time-compressed magnetic tape (speedup factor of 1000-2000, it is characterized by a sound similar to bubbles blown under water.

Irregular structure of thermal ion plasma near the plasmapause observed from Ogo 3 and Pc 1 measurements

“…This suggests that no amplification mechanisms are involved for IPDP events, but that the oscillation processes may be broken up in part because of dominant tarbulences, in contrast to Pc-1 micropulsations which req uire nearly constant `luctuations in the plasma concentrations or in the Alfven index irk an L-shell region. Specifically, the propagation region for IPDP events is located at L = 6 -13, having a strong maximum occurrence rate around 21:00 LT [Tepley, 1966;Troitskaya and Schepetnov, 1967;Reacock, 1967;Knaflich and Kenney, 1967) . This 4.…”

“…IPDP events do not display repetitive multihop pattern, but seem to appear more or less at random, supeeimposed on a broad-band noise source that gradually increases in average frequency over the lifetime of event [Troitskaya, 1961;Tepley, 1966;Heacock, 1967;Knaflich and Kenney, 19671. This suggests that no amplification mechanisms are involved for IPDP events, but that the oscillation processes may be broken up in part because of dominant tarbulences, in contrast to Pc-1 micropulsations which req uire nearly constant `luctuations in the plasma concentrations or in the Alfven index irk an L-shell region.…”

Recent Investigations of Hydromagnetic Emissions Part II. Theoretical Interpretation

“…This led to the discovery that many hm emissions are characterized by a remarkable frequency-time fine structure (Tepley, , 1962Gendrin and Stefant, 1962 a, b;Mainstone and McNicol, 1962;Wentworth, 1962 a, b, 1963;. experimental reviews have been written by Jacobs and Watanabe, 1963a;Campbell, 1964;, 1966. In particular, hm emissions consisting of a band of frequencies (typically d f/f=N0.5 where d f is the bandwidth and f is the center (257) can usually be interpreted as a series of repetitive overlapping wave trains of rapidly rising frequency (typically d f/dt varies between 0.1 and 0.5 cps/min; Tepley and Wentworth, 1962b).…”

Group Travel Time of EM Waves with Frequencies near the Ion Cyclotron Frequency in the Two-ion Magnetosphere

“…In diagnostics, computation of the wave group travel time in an e--H+ plasma can be used only for the rising tone fine structure of Pc 1-2. However, the Pc 1-2 spectra often show complicated structures (Tepley 1966;Dowden 1966;Fraser 1972;Fraser-Smith 1977). The heavy ion modification to the wave group travel time was used to explain the change of tones in observed spectra (e.g.…”