Storm Time Global Thermosphere: A Driven-Dissipative Thermodynamic System
AIR FORCE RESEARCH LAB HANSCOM AFB MA
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Orbit-averaged mass densities p and exospheric temperatures T infinity, inferred from measurements by accelerometrs on the Gravity Recovery and Climate Experiment GRACE satellites are used to investigate global energy Eth and power IIth, inputs to the thermosphere during two complex magnetic storms. Measurements show p, T infinity, and Eth, rising from and returning to prevailing baselines as the magnetospheric electric field EpsilonVS and the Dst index wax and wane. Observed responses of Eth, and T infinity, to Epsilonvs driving suggest that the storm time thermosphere evolves and a driven-but- dissipative thermodynamic system, described by a first-order differential equation that is identical in form to that governing the behavior of Dst Coupling and relaxation coefficients of the Eth, T infinity, and Dst equations are established empirically. Numerical solutions of the equations for Tinfinity and Eth, are shown to agree with GRACE data during large magnetic storms. Since Tinfinity and Dst have the same EpsilonVs driver, it is possible to combine their governing equations to obtain estimates of storm time thermospheric parameters even when lacking information about interplanetary conditions. This approach has the potential for significantly improving the performance of operational models used to calculate trajectories of satellites and space debris and is also useful for developing forensic reconstructions of past magnetic storms. The essential correctness of the approach is supported by agreement between thermospheric power inputs calculated from both GRACE-based estimates of Eth, and the Weimer Poynting flux model originally derived from electric and magnetic field measurements acquired by the Dynamics Explorer 2 satellite.
- Atmospheric Physics