Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm44a..03s&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SM44A-03
Physics
2704 Auroral Phenomena (2407), 2716 Energetic Particles: Precipitating, 2740 Magnetospheric Configuration And Dynamics, 2764 Plasma Sheet, 2778 Ring Current
Scientific paper
In previous work we have investigated the spatial structure of the electron diffuse aurora during storms by comparing drift-loss simulations with precipitating particle data and auroral images. In such past simulations we have computed the bounce-averaged drift motion and precipitation-flux distribution of plasmasheet electrons in Dungey's model magnetosphere, which consists of a dipole field plus a uniform southward Bz (which we have treated as time-independent). In our present study, we improve upon the underlying magnetic- field model by allowing it to be time-dependent, taking account also of (1) the B field produced by the developing ring current and (2) the day-night asymmetry imposed on the magnetosphere by solar-wind flow. Specifically, we allow the southward Bz in Dungey's model magnetosphere to vary with the field-line labels L and φ (MLT), as well as with ordinary time (UT) during the storm. This approach allows us to estimate the magnetic field produced by ring-current ions and electrons from drift simulations of equatorially mirroring particles. We have developed the tools needed to compute mean drifts of electrons undergoing strong pitch-angle diffusion in this dynamic magnetic-field model. Specifically, we have formulated semi-analytical fits to the flux-tube volume as a function of L and φ, given the equatorial magnetic-field intensity B0 as a function of φ and r0 (equatorial radial distance). The flux-tube volume depends on the relative amounts by which the field line of interest and field lines infinitesimally nearby in the same MLT meridian are stretched relative to dipolar field lines with the same L values. We have evaluated the simulated precipitating electron energy flux at an ionospheric altitude of 127 km in a model for which electron pitch-angle diffusion is everywhere strong. By comparing distributions of precipitating electron flux in the original static Dungey magnetic field model with those found in our present (dynamic) magnetic-field model, which takes account of the developing ring current, we take a first step toward investigating how the ring current affects the spatial structure of distributions of electron precipitation during geomagnetic storms, of which we adopt the storm of 19 October 1998 as a prototypical example for the present study.
Chen Margaret W.
Schulz Michael
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