M-I Coupling Physics: Issues, Strategy, Progress

1. M-I Coupling Physics: Issues, Strategy, Progress William Lotko, David Murr, John Lyon, Paul Melanson, Mike Wiltberger Dartmouth founded 1769 FO+ = 2.14x107·S||1.265 Energization Regions EM Power In  Ions Out Evans et al., ‘77 Log (Flux, # / m2-s) Log (Flux, # / m2-s) r = 0.755 r = 0.721 9 10 11 13 12 9 10 11 12 Conductivity Modifications The “Gap” Zheng et al. ‘05 Effects onMI Coupling (issues!) CollisionlessDissipation Paschmann et al., ‘03 Alfvénic Electron Energization Energy Flux mW/m2 Mean Energy keV J|| A/m2 Strangeway et al. ‘05 Alfvén Poynting Flux, mW/m2 Chaston et al. ‘03 Cosponsored by NASA HTP 8.5 simulation hours Oct 97 – Mar 98 North South Polar perigee AVERAGE ION NUMBER FLUXES LFM with H+ Outflow (8 hours of CISM “Long Run”) compared with Polar Perigee Data (6 months Austral Summer) • A 1 RE spatial “gap” exists between the upper boundary of TING (or TIEGCM) and the lower boundary of LFM. • The gap is a primary site of plasma transport where electromagnetic power is converted into field-aligned electron streams, ion outflows and heat. • Modifications of the ionospheric conductivity by the electron precipitation are included global MHD models via a “Knight relation”; but other crucial physics is missing: • Collisionless dissipation in the gap region; • Heat flux carried by upward accelerated electrons; • Conductivity depletion in downward current regions; • Ion parallel transport outflowing ions, esp. O+. DUSK Lennartsson et al. 2004 2  1025 ions/s 3  1025 ions/s FLUENCE 2-3  1024 ions/s Where doesthe mass go? Progress Issues • Reconciled E mapping and collisionless Joule dissipation with Knight relation in LFM • Developed and implemented empirical outflow model with outflow flux indexed to EM power and electron precipitation flowing into gap from LFM (S|| Fe||) • Validations of LFM Poynting fluxes with Iridium/SuperDARN events (Melanson thesis) and global statistical results from DE, Astrid, Polar (Gagne thesis) The mediating transport processes occur on spatial scales smaller than the grid sizes of the LFM and TING/TIEGCM global Challenge: Develop models for subgrid processes using dependent, large-scale variables available from the global models as causal drivers. Priorities • Current-voltage relation in regions of downward field-aligned current; Strategy • Ion transport in downward-current and Alfvénic regions; (Four transport models) • Implement and advance multifluid LFM (MFLFM!) • Implement CMW (2005) current-voltage relation in downward current regions • Include electron exodus from ionosphere  conductivity depletion • Accommodate upward electron energy flux into LFM Advance empirical outflow model • Collisionless Joule dissipation and electron energization in Alfvénic regions – mainly cusp and auroral BPS regions; • Ion outflow model in the polar cap (polar wind). Alfvénic Ion Energization Empirical “Causal” Relations • Develop model for particle energization in Alfvénic regions (scale issues!) • Need to explore frequency dependence of fluctuation spectrum at LFM inner boundary • Full parallel transport model for gap region (long term) Lennartsson et al. ‘04 Keiling et al. ‘03