Increases and decreases in radiation belt electron content with geomagnetic activity

Forsyth, Colin

Increases and decreases in radiation belt electron content with geomagnetic activity

Thursday, 8 March 2018: 11:30

Longshot and Bogey (Hotel Quinta da Marinha)

Colin Forsyth, Mullard Space Science Lab., Dorking, United Kingdom, Clare Watt, University of Reading, Reading, United Kingdom, Mervyn P Freeman, British Antarctic Survey, Cambridge, United Kingdom, Chia-Lin Huang, University of New Hampshire, Durham, NH, United States, Alex J Boyd, New Mexico Consortium, Los Alamos, NM, United States, Michael M Lockwood, University of Reading, Reading, Berkshire, United Kingdom, Kyle R Murphy, NASA Goddard Space Flight Center, Greenbelt, MD, United States, Jonathan Rae, University College London, Mullard Space Science Laboratory, London, United Kingdom and Harlan E. Spence, Solar System Exploration Research Virtual Institute, NASA Ames Research Center, Moffett Field, CA, United States

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Abstract:

Earth’s radiation belts are highly dynamic on a range of timescales. Over timescales of days the number of MeV energy electrons in the radiation belts can vary by several orders of magnitude. In a previous study, Forsyth et al. [2015] showed that 50% of substorm intervals were followed by an increase in the radiation belts, but 75% of quiet intervals were followed by a decrease. Here, we examine the values of the changes in the total radiation belt electron content (TRBEC) calculated from the Van Allen Probes in 2013. We statistically determine that the highest skill for identifying increases or decreases in TRBEC occurs for a threshold of the SuperMAG AL (SML) index of -250 nT within the previous 3h window. We subsequently determine that if five out of the previous six 3-h intervals are active, the interval can be determined as persistently active. Following quiet intervals, TRBEC decreases by ~2% per 3 hrs. Following persistently active intervals, TRBEC increases by 4% per 3 hrs, but following transiently active periods TRBEC decreases by 2.5% per 3 hrs. Our results show that the radiation belts are inherently lossy at a relatively steady rate and that the persistence of elevated geomagnetic activity is critical for the acceleration of particles in the radiation belts.