Earth’s radiation belts consist of highly energetic protons and electrons trapped by Earth’s magnetic field in the region of 1.2~8 Re (Earth radii) away from Earth’s center, which can be hazardous for satellite equipment. Our group uses modelling approaches to better understand the dynamic evolution of the outer radiation belts. Specifically, we have developed physics-based 3D and 4D Versatile Electron Radiation Belt (VERB) codes to help us understand important mechanisms controlling the dynamic evolution of radiation belts, such as radial diffusion, local acceleration, local loss, magnetopause shadowing and electric convection.
Analysis of radiation belt observations present a major challenge, as satellite observations are often incomplete, inaccurate and have only limited spatial coverage. Nevertheless, through data assimilation observations can be blended with information from physics-based models, in order to fill gaps and lead to a better understanding of the underlying dynamical processes. We have developed a scheme that enables efficient data assimilation from multiple satellite missions into the state-of-the-art partial differential equation-based model of the inner magnetosphere Versatile Electron Radiation Belt (VERB-3D).
The ring current is an electric current encircling the Earth at the distances between ~3 and ~5 Earth’s radii from the center of the Earth in the equatorial plane. It is a crucial component in our understanding of the magnetosphere dynamics and geomagnetic storms, and it can also affect human infrastructures such as high-latitude power grids or currently operating communication or navigation satellites. In our group, we use the four-dimensional Versatile Electron Radiation Belt (VERB-4D) code to model the dynamics of the ring current.
Low energy electrons (up to a few 100s of keV) in the plasma sheet and in the ring current can be accelerated to higher energies by various processes and become the drivers of the radiation belts dynamics. Therefore, it is important to account for the dynamics of this so called low energy seed population in the simulations of radiation belt electrons. While low energy electrons in the magnetotail are transported towards the Earth due to magnetospheric convection, the dynamics of energetic electrons inside geosynchronous orbit are largely determined by diffusive processes. Most available physics-based models only compute the evolution of one of these electron populations. However, in order to better understand the particle interactions in the inner magnetosphere a link between these models is necesary. The tool presented here targets this task by combining the two physics-based models IMPTAM and VERB-3D.
The Inner Magnetospheric Particle and Transport Acceleration Model (IMPTAM) (Ganushkina et al. 2001, 2005, 2006) traces electrons from the plasma sheet into the inner magnetospheric region using the guiding center approximation together with time dependent electric and magnetic fields. The model accounts for a number of wave particle interacctions, coulomb colissions and losses to the atmosphere. Electron distributions modeled by IMPTAM provide realistic time dependent boundary conditions to drive radiation belt simulations with the VERB-3D code (Shprits et al. 2009 and Subbotin et al. 2009), which in turn calculates the evolution of energetic electrons due to diffusive processes occuring in the inner L-shells of the magnetosphere. The combination of these two models gives birth to the IMPTAM-VERB coupled model. This 6-day radiation belt nowcast of 0.9 MeV electrons is automatically generated every 1hour using the IMPTAM-VERB coupled model.
- Ganushkina N. Yu., T. I. Pulkkinen, V. F. Bashkirov, D. N. Baker, X. Li, Formation of intense nose structures, Geophysical Research Letters, 28, 491-494, 2001.
- Ganushkina, N. Yu., T. I. Pulkkinen, M. V. Kubyshkina, H. J. Singer, and C. T. Russell, Long-term evolution of magnetospheric current systems during storms, Annales Geophysicae, 22, 1317-1334, 2004.
- Ganushkina, N. Y.; Pulkkinen, T. I.; Milillo, A.; Liemohn, M. Evolution of the proton ring current energy distribution during 21-25 April 2001 storm, Journal of Geophysical Research, 111, A11S08, doi: 10.1029/2006JA011609, 2006.
- Shprits, Y. Y. , D. Subbotin, B. Ni (2009), Evolution of electron fluxes in the outer radiation belt computed with the VERB code, J. Geophys. Res., 114, A11209.
- Subbotin, D. A., Y. Y. Shprits (2009), Three-dimensional modeling of the radiation belts using the Versatile Electron Radiation Belt (VERB) code, Space Weather, 7, S10001.