Storm time distributions of diffuse auroral electron energy and X-ray flux: Comparison of drift-loss simulations with observations

Abstract

We investigate the spatial structure of the electron diffuse aurora during the 19 October 1998 storm by comparing drift‐loss simulations with precipitating particle data and auroral images. Distributions of precipitating diffuse aurora during magnetic storms depend on variation of the magnetotail electron distributions, electron transport, and electron pitch‐angle scattering. In our simulations we compute the bounce‐averaged drift motion and precipitation of plasma sheet electrons in Dungey's model magnetosphere (dipole plus uniform southward Bz). We use the Assimilative Model of Ionospheric Electrodynamics (AMIE) electric field. We evaluate the precipitating energy flux and X‐ray energy at ionospheric altitude h = 127.4 km for two different scattering rate models: (1) strong diffusion everywhere and (2) an MLT‐dependent model scattering rate less than everywhere strong. We compare the simulated distributions of electron energy flux with those obtained from Dst‐binned averaged NOAA‐12 data and the Polar/Ultraviolet Imager (UVI). The simulated distributions of X‐ray flux are compared with Polar/Polar Ionospheric X‐ray Imaging Experiment (PIXIE) images. The comparisons reveal that pitch‐angle scattering clearly plays a crucial role in determining the spatial distribution of the precipitating electron energy flux. The simulated storm time energy flux with strong diffusion tends to be much more intense in the evening sector and much weaker near dawn than what is statistically observed. The most intense electron precipitation under strong diffusion will occur where the electron drift times from the plasma sheet are on the order of the electron lifetime against strong diffusion. On the other hand, the model and data comparison shows that MLT‐dependent scattering less than everywhere strong produces a more realistic electron diffuse aurora than with strong diffusion. Our study strongly suggests that wave scattering is weak in the postdusk sector (∼2200 MLT) and strong in the morning sector (∼0400 MLT), which seems to be in general agreement with statistical and storm time wave observations.