Influence of Solar Wind Dynamic Pressure on Distribution of Whistler Mode Waves Based on Van Allen Probe Observations

In this study, the effect of solar wind dynamic pressure (P-SW) on the global distribution of whistler mode waves (including chorus and hiss waves) while the absence of substorm activity is investigated using the data originating from the Van Allen Probes for nearly 5 years. After the effect of substorm activity is excluded, our statistical results indicate that the hiss and chorus waves exhibit different characteristics with the increase of P-SW. The amplitudes of chorus waves increase on the dayside with the P-SW strengthen, which can be explained through the local enhanced electron temperature anisotropy and more intense emission for the chorus in the inner magnetosphere. Interestingly, the amplitudes of hiss wave are reduced with the increase of P-SW. The weakness of hiss waves can be attributed to electrons at high L-shells which drift out of the magnetosphere on the dayside when the magnetopause's position decreases. It can significantly result in a reduced chorus inside the magnetopause that will evolve into hiss waves. In addition, the upper and lower cutoff frequencies of hiss waves will increase. This new finding is critical for understanding the generation and evolution of whistler mode waves and its responses to the intensity of P-SW.