Bibliography

The Implications of Temporal Variability in Wave-Particle Interactions in Earth s Radiation Belts

Changes in electron flux in Earth s outer radiation belt can be modeled using a diffusion-based framework. Diffusion coefficients D for such models are often constructed from statistical averages of observed inputs. Here, we use stochastic parameterization to investigate the consequences of temporal variability in D. Variability time scales are constrained using Van Allen Probe observations. Results from stochastic parameterization experiments are compared with experiments using D constructed from averaged inputs and an average of observation-specific D. We find that the evolution and final state of the numerical experiment depends upon the variability time scale of D; experiments with longer variability time scales differ from those with shorter time scales, even when the time-integrated diffusion is the same. Short variability time scale experiments converge with solutions obtained using an averaged observation-specific D, and both exhibit greater diffusion than experiments using the averaged-input D. These experiments reveal the importance of temporal variability in radiation belt diffusion.

Watt, C.; Allison, H.; Thompson, R.; Bentley, S.; Meredith, N.; Glauert, S.; Horne, R.; Rae, I.;

Published by: Geophysical Research Letters      Published on: 12/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020GL089962

probabilistic methods; stochastic parameterization; Van Allen Probes

Variability of Quasilinear Diffusion Coefficients for Plasmaspheric Hiss

In the outer radiation belt, the acceleration and loss of high-energy electrons is largely controlled by wave-particle interactions. Quasilinear diffusion coefficients are an efficient way to capture the small-scale physics of wave-particle interactions due to magnetospheric wave modes such as plasmaspheric hiss. The strength of quasilinear diffusion coefficients as a function of energy and pitch angle depends on both wave parameters and plasma parameters such as ambient magnetic field strength, plasma number density, and composition. For plasmaspheric hiss in the magnetosphere, observations indicate large variations in the wave intensity and wave normal angle, but less is known about the simultaneous variability of the magnetic field and number density. We use in situ measurements from the Van Allen Probe mission to demonstrate the variability of selected factors that control the size and shape of pitch angle diffusion coefficients: wave intensity, magnetic field strength, and electron number density. We then compare with the variability of diffusion coefficients calculated individually from colocated and simultaneous groups of measurements. We show that the distribution of the plasmaspheric hiss diffusion coefficients is highly non-Gaussian with large variance and that the distributions themselves vary strongly across the three phase space bins studied. In most bins studied, the plasmaspheric hiss diffusion coefficients tend to increase with geomagnetic activity, but our results indicate that new approaches that include natural variability may yield improved parameterizations. We suggest methods like stochastic parameterization of wave-particle interactions could use variability information to improve modeling of the outer radiation belt.

Watt, C.; Allison, H.; Meredith, N.; Thompson, R.; Bentley, S.; Rae, I.; Glauert, S.; Horne, R.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 10/2019

YEAR: 2019     DOI: 10.1029/2018JA026401

empirical; Magnetosphere; parameterization; stochastic; Van Allen Probes; wave-particle interactions

The Balloon Array for RBSP Relativistic Electron Losses (BARREL)

BARREL is a multiple-balloon investigation designed to study electron losses from Earth\textquoterights Radiation Belts. Selected as a NASA Living with a Star Mission of Opportunity, BARREL augments the Radiation Belt Storm Probes mission by providing measurements of relativistic electron precipitation with a pair of Antarctic balloon campaigns that will be conducted during the Austral summers (January-February) of 2013 and 2014. During each campaign, a total of 20 small (\~20 kg) stratospheric balloons will be successively launched to maintain an array of \~5 payloads spread across \~6 hours of magnetic local time in the region that magnetically maps to the radiation belts. Each balloon carries an X-ray spectrometer to measure the bremsstrahlung X-rays produced by precipitating relativistic electrons as they collide with neutrals in the atmosphere, and a DC magnetometer to measure ULF-timescale variations of the magnetic field. BARREL will provide the first balloon measurements of relativistic electron precipitation while comprehensive in situ measurements of both plasma waves and energetic particles are available, and will characterize the spatial scale of precipitation at relativistic energies. All data and analysis software will be made freely available to the scientific community.

Millan, R.; McCarthy, M.; Sample, J.; Smith, D.; Thompson, L.; McGaw, D.; Woodger, L.; Hewitt, J.; Comess, M.; Yando, K.; Liang, A.; Anderson, B.; Knezek, N.; Rexroad, W.; Scheiman, J.; Bowers, G.; Halford, A.; Collier, A.; Clilverd, M.; Lin, R.; Hudson, M.;

Published by: Space Science Reviews      Published on: 11/2013

YEAR: 2013     DOI: 10.1007/s11214-013-9971-z

RBSP; Van Allen Probes