LF radio noise from the Earth's magnetosphere

Abstract

Gyro-synchrotron radio noise emitted by electrons trapped in the Earth's magnetosphere has been a subject of extensive research. Previous efforts, which considered frequencies greater than 1 MHz, have shown that this noise should not be detectable in the MF to HF range because its intensity is below the cosmic background noise level. This author, however, has investigated the LF range and has found that appreciable noise is generated at these frequencies. In fact, the theoretical results for this LF noise agree very well with experimental data obtained by the Goddard Space Flight Center radio astronomy experiment aboard the IMP 6 spacecraft. A comparison showed that the model predicted both variation in the observed noise intensity with Kp and the noise spectral characteristics. Consequently, it is concluded that detectable LF radio noise is emitted, by means of the cyclotron-synchrotron mechanism, by electrons trapped in the Earth's magnetosphere, and that this noise is observable only for frequencies below about 300 kHz. For higher frequencies, the theoretical model and the experimental data reconfirm that this noise is below that of cosmic origin. 991 992 MICHAEL S. FRANKEL The energy radiated by the trapped electrons and propagated to 32 earth radii is calculated using the equation of radiative transfer. To solve this equation, models for the thermal and superthermal electron densities throughout the Earth's magnetosphere are derived from in-situ and indirect measurements made of these particle populations. The analysis shows that appreciable radio noise in the LF range is emitted by electrons in the Earth's outer radiation belt, and that the intensity of this noise is positively correlated with K? (the planetary three-hour range index). This correlation is due to the enhancement of stably trapped electrons during periods of sustained geomagnetic activity. For a frequency [ in Hz (30 _< [ _< 110 kHz) the average calculated intensity I•([) is given by

Narrowband electromagnetic emissions from Saturn's magnetosphere

“…At Earth it has been known for many years that a relatively weak type of broadband radio emission called continuum radiation is generated within the magnetosphere (5,11,12). This radiation has a relatively smooth steady temporal structure, and when analyzed with spectral resolution comparable to that obtained from the Voyager 16-channel spectrum analyzer, the overall appearance is very similar to the electromagnetic emissions shown in Fig.…”

The Earth as a radio source: Terrestrial kilometric radiation

“…A rough ca!culation shows that the power radiated by incoherent cyclotron radiation from energetic auroral electrons is too small by a factor of about 10 ø. Similarly, the power radiated by incoherent Cerenkov radiation [Taylor and Shawhan, 1974] and by incoherent gyrosynchrotron radiation [Frankel, 1973] appears to be much too small to account for the observed intensities of the kilometric radiation.…”

Source locations of narrowband radio emissions detected at Saturn

“…Like the directly generated auroral radio emissions, the narrowband radio emissions are present at all five radio planets of the solar system and are also found to be emitted by the Jovian moon, Ganymede [ Kurth et al , 1997]. The characteristics of nonthermal continuum (NTC) radiation, Jovian narrowband kilometric radiation (n‐KOM) and narrowband emissions from other outer planets are similar to each other, and they are believed to be generated by the same type of mechanism: mode conversion from electrostatic upper hybrid bands, most likely in regions with steep density gradients [ Gurnett and Shaw , 1973; Frankel , 1973; Gurnett , 1975; Shaw and Gurnett , 1975; Jones , 1976; Kurth , 1982; Fung and Papadopoulos , 1987; Jones , 1988; Kurth , 1992; Reiner et al , 1993; Menietti et al , 2003, 2005a, 2005b].…”