Frequency-Drifting Plasmaspheric Hiss: A Statistical Study From the Van Allen Probes Data

Plasmaspheric hiss, a whistler-mode emission confined in the high-density plasmasphere, is of great interest to the space community attributed to its important role in inner magnetospheric dynamics. Their frequency-time structures provide crucial evidence for understanding the wave origin. In this work, based on similar to 7-year Van Allen Probes data, we statistically studied the frequency-drifting plasmaspheric hiss characterized by an increasing lower cutoff frequency over a timescale exceeding 1 hr. Frequency-drifting hiss waves predominantly occur at 3 < L < 6 from predawn to noon during geomagnetic active times. Observations and theoretical analyses suggest the frequency-drifting hiss could result from the local excitation inside the plasmasphere by energy-dispersive injected electrons. This unique feature of plasmaspheric hiss waves serves, to a certain extent, as an "identifier" for discerning the wave origins and as a "marker" facilitating the link between hiss waves across a broad spatial range.