Statistical Distribution of Whistler Mode Waves in the Radiation Belts With Large Magnetic Field Amplitudes and Comparison to Large Electric Field Amplitudes

Abstract

We present a statistical analysis with 100% duty cycle and non-time-averaged amplitudes of the prevalence and distribution of high-amplitude '50-pT whistler mode waves in the outer radiation belt using 5 years of Van Allen Probes data. Whistler mode waves with high magnetic field amplitudes are most common above L=4.5 and between magnetic local time of 0–14 where they are present approximately 1–6% of the time. During high geomagnetic activity, high-amplitude whistler mode wave occurrence rises above 25% in some regions. The dayside population are more common during quiet or moderate geomagnetic activity and occur primarily '5° from the magnetic equator, while the night-to-dawn population are enhanced during active times and are primarily within 5° of the magnetic equator. These results are different from the distribution of electric field peaks discussed in our previous paper covering the same time period and spatial range. Our previous study found large-amplitude electric field peaks were common down to L=3.5 and were largely absent from afternoon and near noon. The different distribution of large electric and magnetic field amplitudes implies that the low-L component of whistler mode waves observed previously are primarily highly oblique, while the dayside and high-L populations are primarily field aligned. These results have important implications for modeling radiation belt particle interactions with chorus, as large-amplitude waves interact nonlinearly with electrons, resulting in rapid energization, de-energization, or pitch angle scattering. This also may provide clues regarding the mechanisms which can cause significant whistler mode wave growth up to more than 100 times the average wave amplitude.