On the Interplay Between Solar Wind Parameters and ULF Wave Power as a Function of Geomagnetic Activity at High‐ and Mid‐latitudes

Abstract

AbstractUsing ground magnetometer measurements from the IMAGE array over the timespan of one solar cycle, we apply wavelets to statistically assess the power of ultra‐low frequency (ULF) waves from L = 3.34 to L = 13.6 as a function of Kp, solar wind speed (), solar wind dynamic pressure (), Dst, and . We find that although geomagnetic storms account for the overwhelming majority of ULF wave power at mid latitudes, this effect decreases for higher L‐shells. We present analysis of the effect of interplanetary magnetic field (IMF) on ULF wave power for different values of Kp and , revealing a strong inter‐dependency especially in relation to . A parameterization additionally incorporating appears to be more important at large‐L. Further, analysis for positive reveals a perhaps unexpected additional dependence on which points to effects of the interplanetary magnetic field cone angle and Kelvin‐Helmholtz instabilities. Finally, we derive ULF wave radial diffusion coefficients from the measured ULF wave power spectral densities and briefly discuss their importance for radiation belt dynamics. Interestingly, in part because of the correlation between Dst‐defined storm times and high Kp, we find that the low‐Kp radial diffusion coefficients during storms are higher than previously assumed almost certainly because of the dominance of nonstorm epochs in the statistics of median ULF wave power under conditions of low Kp. These inter‐dependencies should be taken into account in future specification models for ULF wave radial diffusion coefficients when applied in storm time simulations.