Statistical Properties of Whistler-Mode Hiss Waves in the Inner Radiation Belt

Using the Van Allen Probes A and B observations from 01 January 2013 to 28 February 2018, we surveyed statistically the occurrence rate, intensity, and propagation properties of hiss waves in the inner radiation belt (1.1 L <= 2). Like the outer plasmaspheric hiss (L > 2), the occurrence rate and amplitude of lower-band hiss (<600 Hz) are higher in the dayside high-L region (L > 1.3 and magnetic local time [MLT] = 6-20 hr) than the nightside (MLT similar to 20-6 hr) and increase with enhanced substorm activities (AE increases). Furthermore, their peak power spectral densities are located nearly in the same band (similar to 200-500 Hz). The equatorward propagation of middle-latitude hiss suggests that the lower-band hiss waves in the inner radiation belt mostly originate from the outer plasmaspheric hiss at high latitudes. Although the outer plasmaspheric hiss is also a likely source of weak upper-band hiss (>= 600 Hz) in the dayside high-L region (L > 1.3 and MLT = 6-20 hr), the intense upper-band hiss waves mostly appear in the dayside low-L region (L < 1.3) and most nightside regions. In the low-L region, the amplitude of the upper-band hiss has no obvious substorm dependence, and the average of its wave normal angles is comparable to that of lightning-generated whistlers reported in the past.