Influences of Geomagnetic Activities and Solar Wind Parameters on Global Distributions of Low-frequency Plasmaspheric Hiss based on Van Allen Probe A Measurements

Plasmaspheric hiss plays a crucial role in shaping the structure and dynamics of the radiation belts in the plasmasphere. Recent researches indicated that the characteristics and excitation mechanisms of low-frequency hiss differ markedly from those of typical frequency bands. Using the wave data observed by Van Allen Probes A from September 2012 to March 2019, we conducted a comprehensive statistical analysis of the global distribution of the average amplitude and occurrence rate of low-frequency hiss waves. We also explore the relationship between low-frequency hiss and geomagnetic activities as well as solar wind dynamic pressures (P_dyn). Our results reveal significant differences in the amplitude and occurrence rate distributions between low-frequency hiss and broad-band hiss, particularly regarding the distribution on the L-shell. The large amplitude low-frequency hiss waves are primarily observed at the afternoon side of the L > 5 region, shifting towards the noon side as geomagnetic activity intensifies. Furthermore, both the amplitude and occurrence rate of low-frequency hiss diminish with increasing solar wind dynamic pressure, and the occurrence rate of large amplitudes low-frequency hiss exhibits a North-South asymmetry under conditions of strong solar wind dynamic pressure. Our statistical results are vital for complementing the existing global distribution model of plasmaspheric hiss and for investigating its generation mechanism.