Bounce‐ and MLT‐averaged diffusion coefficients in a physics‐based magnetic field geometry obtained from RAM‐SCB for the 17 March 2013 storm

Abstract

AbstractLocal acceleration via whistler wave and particle interaction plays a significant role in particle dynamics in the radiation belt. In this work we explore gyroresonant wave‐particle interaction and quasi‐linear diffusion in different magnetic field configurations related to the 17 March 2013 storm. We consider the Earth's magnetic dipole field as a reference and compare the results against nondipole field configurations corresponding to quiet and stormy conditions. The latter are obtained with the ring current‐atmosphere interactions model with a self‐consistent magnetic field (RAM‐SCB), a code that models the Earth's ring current and provides a realistic modeling of the Earth's magnetic field. By applying quasi‐linear theory, the bounce‐ and Magnetic Local Time (MLT)‐averaged electron pitch angle, mixed‐term, and energy diffusion coefficients are calculated for each magnetic field configuration. For radiation belt (∼1 MeV) and ring current (∼100 keV) electrons, it is shown that at some MLTs the bounce‐averaged diffusion coefficients become rather insensitive to the details of the magnetic field configuration, while at other MLTs storm conditions can expand the range of equatorial pitch angles where gyroresonant diffusion occurs and significantly enhance the diffusion rates. When MLT average is performed at drift shell L=4.25 (a good approximation to drift average), the diffusion coefficients become quite independent of the magnetic field configuration for relativistic electrons, while the opposite is true for lower energy electrons. These results suggest that, at least for the 17 March 2013 storm and for L≲4.25, the commonly adopted dipole approximation of the Earth's magnetic field can be safely used for radiation belt electrons, while a realistic modeling of the magnetic field configuration is necessary to describe adequately the diffusion rates of ring current electrons.