ORCID Profile
0000-0001-8819-4345
Current Organisation
Los Alamos National Laboratory
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Publisher: American Geophysical Union (AGU)
Date: 02-2011
DOI: 10.1029/2010JA015735
Publisher: American Geophysical Union (AGU)
Date: 03-2012
DOI: 10.1029/2011SW000729
Publisher: American Geophysical Union (AGU)
Date: 05-03-2014
DOI: 10.1002/2013GL058819
Publisher: American Geophysical Union (AGU)
Date: 03-2013
DOI: 10.1002/JGRA.50126
Publisher: American Geophysical Union (AGU)
Date: 10-2022
DOI: 10.1029/2022JA030751
Abstract: Dropout events are dramatic decreases in radiation belt electron populations that can occur in as little as 30 minutes. Loss to magnetopause due to a combination of magnetopause shadowing and outward radial transport plays a significant role in these events. We examine the dropout of relativistic electron populations during the October 2012 geomagnetic storm using simulated electron phase space density, evaluating the contribution of different processes to losses across the magnetopause. We compare loss contribution from outward transport calculated using a standard empirical radial diffusion model that assumes a dipolar geomagnetic field to an event‐specific radial diffusion model evaluated with a non‐dipolar geomagnetic field. We additionally evaluate the contribution of Shabansky type 1 particles, which bounce along magnetic field lines with local equatorial maxima, to the loss calculated during this event. We find that the empirical radial diffusion model with a dipolar background field underestimates the contribution of radial diffusion to this dropout event by up to 10% when compared to the event‐specific, non‐dipolar radial diffusion model. We additionally find that including Shabansky type 1 particles in the initial electron phase space density, that is, allowing some magnetic field lines distorted from the typical single‐minima configuration in drift shell construction, increases the calculated loss by an average of 0.75%. This shows that the treatment of the geomagnetic field significantly impacts the calculation of electron losses to the magnetopause during dropout events, with the non‐dipolar treatment of radial diffusion being essential to accurately quantify the loss of outer radiation belt populations.
Publisher: American Geophysical Union (AGU)
Date: 07-2020
DOI: 10.1029/2020SW002528
Abstract: We present a methodology to define moderate, strong, and intense space weather events based on probability distributions. We have illustrated this methodology using a long‐duration, uniform data set of 1.8–3.5 MeV electron fluxes from multiple LANL geosynchronous satellite instruments, but a strength of this methodology is that it can be applied uniformly to heterogeneous data sets. It allows quantitative comparison of data sets with different energies, units, orbits, and so forth. The methodology identifies a range of times, “events,” using variable flux thresholds to determine average event occurrence in arbitrary 11‐year intervals (“cycles”). We define moderate, strong, and intense events as those that occur 100, 10, and 1 time per cycle and identify the flux thresholds that produce those occurrence frequencies. The methodology does not depend on any ancillary data set (e.g., solar wind or geomagnetic conditions). We show event probabilities using GOES 2 MeV fluxes and compare them against event probabilities using LANL 1.8–3.5 MeV fluxes. We present some ex les of how the methodology picks out moderate, strong, and intense events and how those events are distributed in time: 1989 through 2018, which includes the declining phases of solar cycles 22, 23, and 24. We also provide an illustrative comparison of moderate and strong events identified in the geosynchronous data with Van Allen Probes observations across all L‐shells. We also provide a catalog of start and stop times of moderate, strong, and intense events that can be used for future studies.
Publisher: Wiley
Date: 09-06-2020
No related grants have been discovered for Gregory Cunningham.