Modeling the Depletion and Recovery of the Outer Radiation Belt During a Geomagnetic Storm: Combined MHD and Test Particle Simulations. Issue 7 (28th July 2018)

• Record Type: Journal Article
• Authors: Sorathia, Kareem A.; Ukhorskiy, Aleksandr Y.; Merkin, Viacheslav G.; Fennell, Joseph F.; Claudepierre, Seth G.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 7(2018)
• Page Start: 5590
• Page End: 5609
• Publication Date: 2018-07-28
• Subjects: radiation belt -- geomagnetic storms -- dropout -- magnetopause loss -- radial transport; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2018JA025506
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: During geomagnetic storms the intensities of the outer radiation belt electron population can exhibit dramatic variability. Deep depletions in intensity during the main phase are followed by increases during the recovery phase, often to levels that significantly exceed their prestorm values. To study these processes, we simulate the evolution of the outer radiation belt during the 17 March 2013 geomagnetic storm using our newly developed radiation belt model (Conservative Hamiltonian Integrator for Magnetospheric Particles) based on test particle and coupled 3‐D ring current and global magnetohydrodynamic (MHD) simulations, and driven solely with solar wind and F10.7 flux data. Our approach differs from previous work in that we use MHD information to identify regions of strong, bursty, and azimuthally localized earthward convection in the magnetotail where test particles are then seeded. We validate our model using in situ Van Allen Probe electron intensities over a multiday period and show that our model is able to reproduce meaningful qualitative and quantitative agreement. Analysis of our model enables us to study the processes that govern the transition from the prestorm to poststorm outer belt. Our analysis demonstrates that during the early main phase of the storm the preexisting outer belt is largely wiped out via magnetopause losses, and subsequently, a new outer belt is created during a handful of discrete, mesoscale injections. Finally, we demonstrate the potential importance of magnetic gradient trapping in the transport and energization of outer belt electrons using a controlled numerical experiment. Plain Language Summary: During geomagnetic storms the intensity of the outer radiation belt, a population of high‐energy electrons trapped within the near‐Earth space environment, can vary by a factor of 1, 000 over a day. Often observed is the near disappearance of the belt at the onset of the storm and its intensification in the aftermath. Not yet understood is the relationship between the prestorm and poststorm belt and the mechanisms that create the more energetic poststorm electrons or equivalently: are the electrons that disappeared the ones that came back? and where did this new energy come from? We introduce our new radiation belt model, Conservative Hamiltonian Integrator for Magnetospheric Particles, and study the 2013 St. Patrick's Day Storm to address these questions. We find that at the onset of the storm the existing belt is annihilated and swept into interplanetary space and that during the course of the storm a new, stronger belt is created. Traditional thinking on belt energization has focused on processes acting on either individual electrons or the global magnetosphere. We show that there is room in the middle by demonstrating, using our high‐resolution simulations, that electrons can become trapped and energized within bursty, confined flow channels that erupt near Earth during the course of the storm. Key Points: Our radiation belt model broadly reproduces observed electron intensity throughout the 17 March 2013 storm During the storm the existing belt is lost and rebuilt via a handful of intense injections Mesoscale structure in the inner magnetosphere can play a role in electron transport and energization