Rapid rebuilding of the outer radiation belt

Abstract

[1] Recent observations by the radiation monitor (RDM) on the spacecraft Akebono have shown several cases of >2.5 MeV radiation belt electron enhancements occurring on timescales of less than a few hours. Similar enhancements are also seen in detectors on board the NOAA/POES and TWINS 1 satellites. These intervals are shorter than typical radial diffusion or wave-particle interactions can account for. We choose two so-called "rapid rebuilding" events that occur during high speed streams (4 September 2008 and 22 July 2009) and simulated them with the Space Weather Modeling Framework configured with global magnetosphere, radiation belt, ring current, and ionosphere electrodynamics model. Our simulations produce a weaker and delayed dipolarization as compared to observations, but the associated inductive electric field in the simulations is still strong enough to rapidly transport and accelerate MeV electrons resulting in an energetic electron flux enhancement that is somewhat weaker than is observed. Nevertheless, the calculated flux enhancement and dipolarization is found to be qualitatively consistent with the observations. Taken together, the modeling results and observations support the conclusion that storm-time dipolarization events in the magnetospheric magnetic field result in strong radial transport and energization of radiation belt electrons.

Impact of Solar Wind on the Earth Magnetosphere: Recent Progress in the Modeling of Ring Current and Radiation Belts

“…Based on careful data analysis from Akebono, TWINS and NOAA satellites, Glocer et al (2011) conclude that the time scale of these enhancements is about 2 hours and thus it is too short for wave associated energization. Additional analysis of AL index and magnetic field measurements from GOES 11,12 satellites suggests a substorm may play a role in this quick increase of outer belt electrons Glocer et al, 2011). The example of flux enhancement is shown on the Fig.…”

“…Therefore, a realistic description of these field variations is extremely important. This is the main motivation to couple the RBE model with global MHD model Glocer et al, 2011;. It is critical to use magnetic and electric fields from the two-way coupled MHD-ring current model for RBE, because ring current inflates inner magnetosphere magnetic field and changes electric field.…”

“…The Radiation Belt Environment (RBE) model has been rigorously developed over past 10 years (Fok et al, 2005;Fok et al, 2011;Fok, Moore & Spjeldvik, 2001;Fok et al, 2008;Glocer et al, 2011;Zheng et al, 2011;. It models both the radiation belts and ring current electrons.…”

“…Recently Fok et al (2011) andGlocer et al (2011) use coupled RBE-SWMF to examine 2 events with rapid radiation belt enhancements. Based on careful data analysis from Akebono, TWINS and NOAA satellites, Glocer et al (2011) conclude that the time scale of these enhancements is about 2 hours and thus it is too short for wave associated energization.…”

“…The Akebono data are averaged over 3 orbit periods (∼ 7.5 h). Fok et al (2011) andGlocer et al (2011) perform RBE-SWMF simulations to understand the cause of the flux enhancement seen in the Akebono electron data. Additionally, the RBE is run in stand-alone mode with empirical models as inputs.…”