Electrostatic electron cyclotron harmonic instability due to energetic electrons in Jupiter's magnetosphere

Abstract

Electrostatic electron cyclotron harmonic instability in the magnetosphere of Jupiter is investigated using a kappa distribution with loss cone for energetic electrons in the tail of the distribution function. Temporal growth rates are calculated at two representative radial distances characterized by different temperatures of the thermal electron population. It is found that the frequency within the harmonic band shifts to a lower value as the temperature of the thermal electron population increases. Furthermore, higher harmonic bands are damped faster as the angle between the wave normal and the ambient magnetic field is decreased. Calculations are performed by changing various parameters appearing in the distribution function. The present study may be helpful in accounting for some of the observed features of the electron cyclotron harmonic bands in the magnetosphere of Jupiter. The observed features are as follows: (1) Maximum amplitudes are usually seen in the first harmonic band and at the highest frequency of emission near upper hybrid resonance, (2) Emissions are greatest at smaller radial distances and decrease with increasing distance, (3) The amplitude is observed to fluctuate over more than an order of magnitude on timescales of several seconds.