Effects of magnetic field configuration on the day-night asymmetry of chorus occurrence rate: A numerical study

Abstract:

Understanding the generation and distribution of chorus waves is important to quantify their effects on the radiation belt electron dynamics. In this work, effects of magnetic field configuration on the day-night asymmetry of chorus occurrence rate are investigated using a recently developed hybrid code DAWN. Previous observations demonstrate that dayside chorus occur in regions where background magnetic field is almost homogeneous, suggesting that the magnetic field configuration might play a significant role in the dayside chorus excitation. Using the DAWN code, we numerically study the threshold conditions of hot electron distributions to excite chorus waves with different magnetic field configurations. Our results demonstrate that in a magnetic field with smaller inhomogeneity, smaller temperature anisotropy and hot electron density are needed to excite chorus waves. This conclusion could help understand the higher occurrence rate of chorus waves on the dayside compared with that on the nightside especially during quiet times.