A Statistical Survey of Lower Hybrid Wave by Van Allen Probe

Abstract:

The lower hybrid (LH) waves are an electrostatic emission near the lower hybrid resonant frequency. These emissions propagate almost perpendicularly to the ambient magnetic field with small wavelength. They are ubiquitously observed in many plasma environments, such as the Earth’s magnetosphere, auroral region, magnetopause, Bow shock, comets and Tokamaks. These emissions can convert to the whistler mode wave though linear mode conversion process, heat thermal electrons/ions, produce cross-field particle diffusion and contribute to anomalous resistivity. LH waves are very common in the Earth’s inner magnetosphere and its role in wave-particle interaction is still an open question. In this study, we provide a global distribution of LH waves in the inner magnetosphere by using the WFR data of two Van Allen Probes from 2012 to 2018. We find that (1) typical amplitudes of LH waves are 0.01~0.1 mV/m. (2) Most of the LH waves confines in the nightside with |Mlat|< 5° and L>4. (3) The LH waves are much stronger in the inner L regions with larger plasma density. (4) The LH waves extend to inner L shell regions and wave amplitude increases when the geomagnetic activity level (AE index) increases. (5) The Occurrence rates of LH waves decrease with increasing AE index.