Gyroresonant interactions between the radiation belt electrons and whistler mode chorus waves in the radiation environments of Earth, Jupiter, and Saturn: A comparative study

Abstract

[1] In the current study we perform a comparative analysis of the gyroresonant interactions of whistler mode waves with radiation belt electrons in the magnetospheres of Earth, Jupiter, and Saturn. Our primary goal is to evaluate the effect of resonant wave-particle interactions with chorus waves and determine whether chorus waves can produce net acceleration or net loss of radiation belt electrons on the outer planets. The ratio of plasma frequency to gyrofrequency is a key parameter that determines the efficiency of the pitch angle and energy resonant scattering. We present a comparison of statistical maps of the ratio of plasma frequency to gyrofrequency for Jupiter, Saturn and Earth in terms of radial distance and latitude. Preliminary maps of the plasma frequency to gyrofrequency ratio and 2D simulations of pitch angle and energy diffusion using the Versatile Electron Radiation Belt (VERB) indicate that the Kronian plasma environment is not likely to support as efficient gyroresonant interactions with whistler mode chorus waves as in the Terrestrial or Jovian environments. Inefficiency of the local acceleration by whistler mode waves in the Kronian environment raises important questions about the origin of the relativistic electrons in the Saturn's radiation belts. Two-dimensional diffusive simulations of local acceleration and loss to the atmosphere using the VERB code confirm previous suggestions that the acceleration of electrons may be very efficient in the outer radiation belt of Jupiter. However, sensitivity simulations also show that the result of the competition between acceleration and loss in the Jupiter's magnetosphere strongly depends on the currently unknown latitudinal distribution of chorus waves that will be provided by the upcoming Juno mission. If waves extend to high latitudes, it is likely that the loss rates due to whistler mode waves will exceed energization rates.Citation: Shprits, Y. Y., J. D. Menietti, X. Gu, K. C. Kim, and R. B. Horne (2012), Gyroresonant interactions between the radiation belt electrons and whistler mode chorus waves in the radiation environments of Earth, Jupiter, and Saturn: A comparative study,

Electron acceleration at Jupiter: input from cyclotron-resonant interaction with whistler-mode chorus waves

“…In reality the initial conditions may already include acceleration and loss due to cyclotron-resonant interactions with chorus and other waves, but at present this contribution cannot be separated out of the observations. A useful discussion of this effect can be found in Shprits et al (2012). A dipole magnetic field was used in the model, which is a reasonable assumption for distances up to approximately 14 R J along the equator.…”

“…Since the plasma density drops significantly with increasing latitude (Bagenal, 1994), the conditions for acceleration may be more favorable at higher latitudes. Shprits et al (2012) showed that changing the theoretical latitudinal extent of the chorus waves plays a major role in the effectiveness of wave-particle interactions at Jupiter and Saturn. In this study we use data from the Galileo spacecraft to investigate in more detail the acceleration of electrons by wave-particle interactions at Jupiter in the region outside Io.…”

Probability of relativistic electron trapping by parallel and oblique whistler-mode waves in Earth's radiation belts

“…37,40,42,58,64,67 Multiple spacecraft observations of intense emissions of parallel (relative to the background magnetic field) whistler-mode waves during geomagnetic storms and substorms 1,33,38 have led to the suggestion that these parallel waves could be responsible for almost all the recorded variations of electron fluxes. In addition, oblique wave damping due to Landau resonance with a dense population of suprathermal electrons 20,36 often sensibly decreases the amplitudes of oblique whistler-mode waves along their propagation.…”

What characterizes planetary space weather?

“…Terrestrial life requires liquid water. The stability of liquid water at the surface of a planet defines a habitable zone around a star (see e.g., Dole 1964;Shklovskii and Sagan 1966;Huang 1959Huang , 1961Hart 1980). In the solar system, it stretches between Venus and Mars, but excludes these two planets.…”