Statistical Properties of Lower Hybrid Waves Within Foreshock Transient Boundaries

Abstract

AbstractLower hybrid waves (LHWs) are plasma waves commonly observed within the foreshock transient environment. Using Magnetospheric Multiscale in situ measurements, we present a statistical analysis of LHWs regarding their spatial distribution, wave properties, occurrence rate, and potential impact on plasmas at the density boundaries of foreshock transients. LHWs are mostly localized at the low‐density side of the boundaries, with a typical wave electric field below 2 mV/m. The occurrence rate of LHWs decreases as the density gradient length scale (Ln) normalized to the ion gyroradius (ρi) increases and the plasma beta (β) increases. This dependence of the wave occurrence is consistent with the linear growth rate of LHWs. The occurrence rate of LHWs exhibits a preference for conditions characterized by Ln/ρi < 3 and β < 3. In the case of a strong gradient (Ln/ρi ≲ 0.5), the occurrence rate exceeds 0.2. These findings provide valuable statistical evidence shedding light on the average behavior of LHWs within foreshock transients.