Abstract
Abstract. Particles with different energies produce varying contributions to the total ring current energy density as the storm progresses. Ring current energy densities and total ring current energies were obtained using particle data from the Polar CAMMICE/MICS instrument during several storms observed during the years 1996-1998. Four different energy ranges for particles are considered: total (1-200keV), low (1-20keV), medium (20-80keV) and high (80-200keV). Evolution of contributions from particles with different energy ranges to the total energy density of the ring current during all storm phases is followed. To model this evolution we trace protons with arbitrary pitch angles numerically in the drift approximation. Tracing is performed in the large-scale and small-scale stationary and time-dependent magnetic and electric field models. Small-scale time-dependent electric field is given by a Gaussian electric field pulse with an azimuthal field component propagating inward with a velocity dependent on radial distance. We model particle inward motion and energization by a series of electric field pulses representing substorm activations during storm events. We demonstrate that such fluctuating fields in the form of localized electromagnetic pulses can effectively energize the plasma sheet particles to higher energies (>80keV) and transport them inward to closed drift shells. The contribution from these high energy particles dominates the total ring current energy during storm recovery phase. We analyse the model contributions from particles with different energy ranges to the total energy density of the ring current during all storm phases. By comparing these results with observations we show that the formation of the ring current is a combination of large-scale convection and pulsed inward shift and consequent energization of the ring current particles.
Highlights
The E×B drift is responsible for the basic transport and acceleration of ions moving from the magnetotail and the plasma sheet to the inner magnetosphere
Birn et al (1997), by tracing test particle orbits in the dynamic fields from a three-dimensional MHD simulation, found that most energization is caused by betatron acceleration as particles are transported into the stronger magnetic field region by a timedependent dawn-to-dusk electric field
In the present paper we study the role of the substormassociated electric fields in the transport of the plasma sheet protons to the ring current and their energization to higher energies (>80 keV)
Summary
The E×B drift is responsible for the basic transport and acceleration of ions moving from the magnetotail and the plasma sheet to the inner magnetosphere. In the present paper we study the role of the substormassociated electric fields in the transport of the plasma sheet protons to the ring current and their energization to higher energies (>80 keV). We model the injections by tracing protons numerically in the drift approximation in several combinations of the large-scale and smallscale stationary and time-dependent magnetic and electric field models and using different initial conditions. The storm on 2–4 May 1998 is used to discuss the conditions that are necessary for the magnetic and electric fields to account for the observed earthward transport and energization of ions
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