Parametric Study on the Interplay Between ECH and Whistler Waves: Particle-In-Cell Simulations

Electron Cyclotron Harmonic (ECH) waves and whistler waves are common plasma waves in the Earth's magnetosphere, and they play an important role in regulating electron dynamics. Recent observations reveal that whistler waves can suppress ECH waves by reshaping the electron distribution, but a comprehensive study on the effects of various plasma parameters on their interplay is still lacking. Using a two-dimensional (2-D) particle-in-cell (PIC) simulation model, we have thoroughly studied the evolution of ECH waves under various initial plasma conditions by relaxing anisotropic hot electrons with a loss-cone distribution. Overall, ECH waves are significantly suppressed once whistler waves appear, and their damping rate is strongly dependent on the amplitude of whistler waves, which is positively correlated with the hot electron proportion and the temperature anisotropy. Moreover, the final amplitude ratio R between ECH and whistler waves tends to increase with a higher hot electron proportion $n_h/n_e$, lower temperature anisotropy $A$, and higher ratio of plasma frequency to electron cyclotron frequency $f_{\text{pe}}/f_{\text{ce}}$. However, it shows little dependence on the size of loss-cone width $\beta$ and parallel temperature $T_{\parallel }$. This study not only supports that the suppression of ECH waves by whistler waves is a common phenomenon but also provides some new insights into understanding the global distribution of ECH waves in the Earth's magnetosphere.