A Global Model of Plasmaspheric Hiss Waves Inferred from Poes Observations

Abstract:

Accurate magnetospheric wave models are key to understanding the dynamic variability of the radiation belts. Statistical wave models are commonly used in diffusion codes to evaluate the effects of the wave parameters on the radiation belt dynamics. Statistical wave models, however, may not accurately reproduce the real, instantaneous global wave distribution. The ability of the diffusion simulations to accurately reproduce the changes in the radiation environment ultimately depends on the accuracy of the available global wave models. The specification of a global model of plasmaspheric hiss waves is the purpose of this investigation. 

Plasmaspheric hiss is an incoherent emission in the whistler band confined within the dense plasmasphere and dayside plasmaspheric plumes. Hiss is responsible for the formation of the slot region, and can also contribute to the scattering of outer belt electrons particularly during active geomagnetic periods. Additionally, following storm time enhancements, the slow decay of the outer radiation belt is also attributed to pitch angle scattering by hiss waves.

The methodology used to build a global model of plasmaspheric hiss waves is not based on in-situ wave observations but on low-altitude electron measurements from the POES spacecraft. The advantage of inferring hiss wave amplitudes from POES electron measurements is that multiple POES satellites provide extensive coverage in the inner magnetosphere, while in-situ wave observations in a particular storm are limited to a certain range in L-shell and MLT. More specifically, we use the ratio between precipitating and trapped electrons provided by the Medium Energy Proton and Electron Detector (MEPED) instrument onboard the POES spacecraft to infer the global dynamic amplitude of plasmaspheric hiss waves. The performance of the technique is evaluated by comparing its results with EMFISIS observations during conjunction events with the Van Allen Probes, as well as with the predictions from the most recent statistical models of plasmaspheric hiss. The sensitivity of the methodology to the input parameters (hiss frequency spectrum, cold plasma density, and electron energy spectrum) is also analyzed in the present study.