Dartmouth Events

Title:  One and Two Dimensional Hybrid Simulations of Whistler Mode Chorus in Dipole Field"

 

Abstract: We simulate whistler mode chorus waves using an electron hybrid code in dipole geometry in both one and two dimensions. Simulations in two dimensional Cartesian coordinates are also performed and compared with full dynamics particle-in-cell simulations. There are four species in the simulations, hot ring current electrons initialized with an anisotropic bi-Maxwellian distribution with the perpendicular temperature greater than the parallel temperature, warm electrons, cold inertialess fluid electrons and protons as an immobile background. The density of the hot population is a small fraction of the total plasma density. Comparison between the dispersion relation of our model and other dispersion relations shows that our model is more accurate for lower frequency whistlers than for higher frequency whistlers. Simulations in 2-D Cartesian coordinates agree very well with those using a full dynamics code. In the one dimensional simulations along the dipole magnetic field, the predicted frequency and wave number are observed. Rising tones are observed in the 1/14 scale simulations that have larger than realistic magnetic field spatial inhomogeneity. However, in the full scale 1-D simulation in a dipole field, the waves are more broadband and do not exhibit rising tones. In the two dimensional simulations, the waves are generated with propagation approximately parallel to the background magnetic field. However, the wave fronts become oblique as they propagate to higher latitudes. Simulations with different plasma density profiles across L-shell are performed to study the effect of the background density on whistler propagation. With constant total plasma density or total plasma density that decreased moderately with respect to L, the waves refract toward larger L. With a steeper gradient of total density in L, the refraction is inward toward smaller L.