Some Consequences of Stormtime, Global Energy Budgets
William J. Burke
Boston College and AFRL/RBXP
Hanscom AFB, MA 01731
Neutral mass densities ρ measured by the CHAMP and GRACE satellites, joined with information readily available from ACE at L1 and ground magnetometers, offer new opportunities to monitor the energetics of the magnetosphere-ionosphere-thermosphere system during magnetic storms. This presentation uses measurements of ρ from the GRACE satellite to drive Jacchia thermospheric models. Within the tables of the Jacchia model we identify internal quadratic relationships between ρ and exospheric temperatures T∞. We then demonstrate that T∞ is linearly related to Eth the total (gravitational and thermal) energy of the thermosphere. Further analysis shows that stormtime increases of Eth exceed, by a factor of four, the ring current’s energy estimated via the Dessler-Parker-Sckopke theorem. Thus, most stormtime energy deposition occurs at polar cap rather than auroral latitudes. This result profoundly affects understanding of the disturbance dynamo’s genesis.
Eth has two independent but additive contributions from solar ultraviolet radiation (EUV) and the solar wind (ESW). Up to now the dynamics of EUV are modeled better. During storms ESW evolves as a driven-dissipative system:
where EM is the driving magnetospheric electric field; α and τ are empirically established coupling and relaxation constants. The observed e-fold decay constant τ ≈ 6.5 hours is mostly due to infrared radiative losses. EM is estimated from routine ACE measurements. Similar equations describe the solar-wind’s contributions to T∞SW and the Dst index. Solving these simultaneous equations offer the possibility of estimating ESW, T∞SW, and EM during storms when interplanetary measurements are unavailable.