Journal article
Inward diffusion and loss of radiation belt protons
Journal of geophysical research. Space physics, Vol.121(3), pp.1969-1978
03/2016
DOI: 10.1002/2015JA022154
Abstract
Radiation belt protons in the kinetic energy range 24 to 76 MeV are being measured by the Relativistic Electron Proton Telescope on each of the two Van Allen Probes. Data have been processed for the purpose of studying variability in the trapped proton intensity during October 2013 to August 2015. For the lower energies (≲32 MeV), equatorial proton intensity near L = 2 showed a steady increase that is consistent with inward diffusion of trapped solar protons, as shown by positive radial gradients in phase space density at fixed values of the first two adiabatic invariants. It is postulated that these protons were trapped with enhanced efficiency during the 7 March 2012 solar proton event. A model that includes radial diffusion, along with known trapped proton source and loss processes, shows that the observed average rate of increase near L = 2 is predicted by the same model diffusion coefficient that is required to form the entire proton radiation belt, down to low L, over an extended (∼103 year) interval. A slower intensity decrease for lower energies near L = 1.5 may also be caused by inward diffusion, though it is faster than predicted by the model. Higher‐energy (≳40 MeV) protons near the L = 1.5 intensity maximum are from cosmic ray albedo neutron decay. Their observed intensity is lower than expected by a factor ∼2, but the discrepancy is resolved by adding an unspecified loss process to the model with a mean lifetime ∼120 years.
Key Points
Radiation belt protons with E = 24‐76 MeV were measured by REPT on Van Allen Probes during 2013‐2015
Increasing intensity at low E near L = 2 is consistent with inward diffusion of trapped solar protons
Low intensity levels at high E near L = 1.5 indicate faster than expected loss of CRAND protons
Details
- Title: Subtitle
- Inward diffusion and loss of radiation belt protons
- Creators
- R. S Selesnick - U.S. Air Force Research Laboratory Space Vehicles DirectorateD. N Baker - University of Colorado BoulderA. N Jaynes - University of Colorado BoulderX Li - University of Colorado BoulderS. G Kanekal - Goddard Space Flight CenterM. K Hudson - Dartmouth CollegeB. T Kress - University of Colorado Boulder
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Space physics, Vol.121(3), pp.1969-1978
- DOI
- 10.1002/2015JA022154
- ISSN
- 2169-9380
- eISSN
- 2169-9402
- Number of pages
- 10
- Grant note
- National Science Foundation (AGS-1455470) JHU/APL (967399) NASA (NNH14AX18I; NAS5-01072; NNX15AF54G) Air Force Research Laboratory Heliophysics Guest Investigators Program
- Language
- English
- Date published
- 03/2016
- Academic Unit
- Physics and Astronomy; University College Courses
- Record Identifier
- 9984199715602771
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