Publication: Journal of Geophysical Research: Space Physics; Authors: Benjamin Hogan, William Lotko, Kevin Pham
First author, William Lotko, reveals that the CHAMP satellite orbiting near 400 km altitude near the magnetic cusp routinely traversed thermospheric density enhancements (up to 50%) that are not predicted by empirical models. The density enhancements are well-correlated with kilometer-scale field-aligned currents interpreted as ionospheric Alfvén resonator modes.
Air density in the northern hemisphere on 27 March 2003 when CHAMP passes through the edge of a high-latitude density enhancement. A: Simulated air density (color) at the CHAMP altitude vs MLT and MLAT at the UT corresponding to “CHAMP Location” in panel B. B: Comparison of instantaneously observed, simulated and MSIS empirical air density vs. UT. C: % difference in CMIT air density with and without Alfvénic heating.
With this motivation, we investigated the effects of Alfvén wave energy deposition on thermospheric upwelling and density. A subgrid model for the altitude dependence of the Alfvén wave electric field, constrained by CHAMP data, was developed and embedded in the Joule heating module of the National Center for Atmospheric Research (NCAR) Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model. The CMIT model was then used to simulate the geospace response to an interplanetary stream interaction region (SIR) that swept past Earth on 26-27 March 2003. Simulation results show that 1) inclusion of Alfvénic Joule heating in CMIT improves its instantaneous density prediction (up to 15%) along the CHAMP orbit near the cusp heating region; and 2) Thermospheric density changes of 20-30% caused by the cusp-region Alfvénic heating sporadically populate the polar region through the action of co-rotation and neutral winds.