Abstract
The flux of relativistic electrons in the Earth's radiation belts is highly variable and can change by orders of magnitude on timescales of a few hours. Understanding the drivers for these changes is important as energetic electrons can damage satellites. We present results from a new code, the British Antarctic Survey (BAS) Radiation Belt model, which solves a 3‐D Fokker‐Planck equation, following a similar approach to the Versatile Electron Radiation Belt (VERB) code, incorporating the effects of radial diffusion, wave‐particle interactions, and collisions. Whistler mode chorus waves, plasmaspheric hiss, and lightning‐generated whistlers (LGW) are modeled using new diffusion coefficients, calculated by the Pitch Angle and Energy Diffusion of Ions and Electrons (PADIE) code, with new wave models based on satellite data that have been parameterized by both the AE and Kp indices. The model for plasmaspheric hiss and LGW includes variation in the wave‐normal angle distribution of the waves with latitude. Simulations of 100 days from the CRRES mission demonstrate that the inclusion of chorus waves in the model is needed to reproduce the observed increase in MeV flux during disturbed conditions. The model reproduces the variation of the radiation belts best when AE, rather than Kp, is used to determine the diffusion rates. Losses due to plasmaspheric hiss depend critically on the the wave‐normal angle distribution; a model where the peak of the wave‐normal angle distribution depends on latitude best reproduces the observed decay rates. Higher frequency waves (∼1–2 kHz) only make a significant contribution to losses for L∗<3 and the highest frequencies (2–5 kHz), representing LGW, have a limited effect on MeV electrons for 2<L∗<5.5.
Highlights
The Earth’s radiation belts were discovered over 50 years ago [Van Allen and Frank, 1959; Van Allen, 1959] at the beginning of the space age but, despite much research since, many significant questions remain regarding their behavior during geomagnetic storms
Plasmaspheric hiss, and lightning-generated whistlers (LGW) are modeled using new diffusion coefficients, calculated by the Pitch Angle and Energy Diffusion of Ions and Electrons (PADIE) code, with new wave models based on satellite data that have been parameterized by both the AE and Kp indices
We have developed a new model for the Earth’s electron radiation belts including the effects of radial transport and wave-particle interactions with whistler mode chorus, plasmaspheric hiss, and LGW
Summary
The Earth’s radiation belts were discovered over 50 years ago [Van Allen and Frank, 1959; Van Allen, 1959] at the beginning of the space age but, despite much research since, many significant questions remain regarding their behavior during geomagnetic storms. The electron population in the inner belt is relatively stable, but the population in the outer belt is highly variable, especially during geomagnetic storms which are driven by the solar wind [Paulikas and Blake, 1979; Baker et al, 1986, 1994, 1997; Li et al, 1997; Reeves et al, 1998; Miyoshi and Kataoka, 2005]. In the outer belt the flux of relativistic electrons can vary by several orders of magnitude on a variety of different timescales ranging from minutes to tens of days [e.g., Blake et al, 1992; 1994]. Understanding and predicting the radiation belt response during geomagnetic storms and at other times are important since relativistic electrons damage satellites [Wrenn, 1995; Baker, 2001; Wrenn et al, 2002] and pose a risk to humans in space
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