SM026-06
ULF Wave Driven Radial Diffusion During Geomagnetic Storms

Thursday, 10 December 2020: 20:50
Virtual
Jasmine Kaur Sandhu, Mullard Space Science Laboratory, University College London, Dorking, United Kingdom, Jonathan Rae, Northumbria University, Newcastle, United Kingdom, Clare Watt, Northumbria University, Newcastle-upon-Tyne, United Kingdom, Richard Bertram Horne, British Antarctic Survey, Cambridge, United Kingdom, Louis Ozeke, University of Alberta, Edmonton, AB, Canada, Marina Georgiou, National and Kapodistrian University of Athens, Athens, Greece, John R Wygant, University of Minnesota, Minneapolis, MN, United States, Aaron W Breneman, The University of Minnesota, Minneapolis, MN, United States, Sheng Tian, University of Minnesota Twin Cities, School of Physics and Astronomy, Minneapolis, MN, United States and Maria-Theresia Walach, University of Leicester, Leicester, United Kingdom
Recorded Presentation
Abstract:
The impact of radial diffusion in storm time radiation belt dynamics is well-debated. In this study we quantify the changes and variability in radial diffusion coefficients during geomagnetic storms. A statistical analysis of Van Allen Probes data is conducted for the time period spanning 2012 - 2019 to obtain measurements of the magnetic and electric power spectral densities for Ultra Low Frequency (ULF) waves. These values are used to estimate corresponding radial diffusion coefficients. The results show that global wave power enhancements occur during the main phase, and continue into the recovery phase of storms. Local time asymmetries show sources of ULF wave power are both external solar wind driving as well as internal sources from coupling with ring current ions and substorms. Wave power enhancements are also observed at low L values. The accessibility of wave power to low L is attributed to a depression of the Alfvén continuum. Overall, the increased wave power drives enhancements in both the magnetic and electric field diffusion coefficients by more than an order of magnitude. Significant variability in diffusion coefficients is observed, with values ranging over several orders of magnitude.

A comparison to the Kp parameterised empirical model of Ozeke et al. [2014] is conducted and indicates important differences during storm times. Although the electric field diffusion coefficient is relatively well described by the empirical model, the magnetic field diffusion coefficient is approximately ~ 10 times larger than predicted. Alternative storm-time radial diffusion coefficients are provided as a function of L* and storm phase.

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