Dependency of the Cusp Density Anomaly on the Variability of Forcing Inside and Outside the Cusp

Abstract:

The Earth's magnetospheric cusp provides direct access of energetic particles to the thermosphere. These particles produce ionization and kinetic (particle) heating of the atmosphere. The increased ionization coupled with enhanced electric fields in the cusp produces increased Joule heating and ion drag forcing. These energy inputs largely determine the neutral density structure in the cusp region. Measurements by the CHAMP satellite (460-390- km altitude) have shown a region of strong enhanced density attributed to the combination of cusp particle and Joule heating. The Streak mission (325-123 km), on the other hand, observed a relative depletion in density in the cusp.

While particle precipitation in the cusp is comparatively well constrained, the characteristics of the steady and fluctuating components of the electric field in the cusp are poorly constrained. Also, the significance of harder particle precipitation in areas adjacent to the cusp in particular at lower altitudes has not been addressed as it relates to the cusp density anomaly. We address the response of the cusp region to a range electrodynamical forcing with our high resolution two-dimensional time-dependent nonhydrostatic nonlinear dynamical model. We take advantage of our model’s high resolution and focus on a more typical cusp width of 2 degrees in latitude. Earlier simulations have also shown a significant contribution from soft particle precipitation. We simulate the atmospheric response to a range of realizable magnitudes of the fluctuating and steady components of the electric field to examine the dependence of the magnitude of the cusp density anomaly on a large range of observed characteristics of the electrodynamical forcing and examine, in particular, the importance of particle heating relative to Joule heating. In addition we investigate the role of harder particle precipitation in areas adjacent to the cusp in determining the lower altitude cusp density and wind structure. We compare the model results to CHAMP and Streak observations and assess the distinctive features of the observations in terms of the various dependencies involved.

Acknowledgements: This research was supported by The Aerospace Corporation’s Technical Investment program