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The Magnetospheric Cusp: Solar Wind – Magnetosphere – Ionosphere – Thermosphere Coupling

The Magnetospheric Cusp: Solar Wind – Magnetosphere – Ionosphere – Thermosphere Coupling. R. J. Strangeway IGPP & ESS /UCLA. Special Acknowledgement to J. Raeder, UNH, and the Community Coordinated Modeling Center. Outline. Introduction – why talk about the cusp?

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The Magnetospheric Cusp: Solar Wind – Magnetosphere – Ionosphere – Thermosphere Coupling

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  1. The Magnetospheric Cusp: Solar Wind – Magnetosphere – Ionosphere – Thermosphere Coupling R. J. StrangewayIGPP & ESS /UCLA Special Acknowledgement to J. Raeder, UNH, and the Community Coordinated Modeling Center. GEM - Cusp Tutorial - R. J. Strangeway

  2. Outline • Introduction – why talk about the cusp? • Reconnection topology and the cusp – where is the cusp? • Cusp ion dispersion at middle altitudes – where is the reconnection? • Cusp ion dispersion at low altitudes – multiple cusps? • Field-aligned currents – Force balance and cusp dynamics • Ion outflows – Joule dissipation and electron precipitation • Neutral upwelling – Important for satellite drag • Summary GEM - Cusp Tutorial - R. J. Strangeway

  3. What is so Special About the Cusp? • The cusp is the region that provides the most direct path from the solar wind to the ionosphere and thermosphere • The cusp requires an understanding of several processes: • Reconnection topology and Interplanetary Magnetic Field direction effects (IMF By) • Steady-state, multi-point, and time-varying reconnection • Particle kinematics (time-of-flight, velocity dispersion) • Field-aligned current generation • Joule Dissipation – ion and neutral upwelling and outflows GEM - Cusp Tutorial - R. J. Strangeway

  4. Outline • Introduction – why talk about the cusp? • Reconnection topology and the cusp – where is the cusp? • Cusp ion dispersion at middle altitudes – where is the reconnection? • Cusp ion dispersion at low altitudes – multiple cusps? • Field-aligned currents – Force balance and cusp dynamics • Ion outflows – Joule dissipation and electron precipitation • Neutral upwelling – Important for satellite drag • Summary GEM - Cusp Tutorial - R. J. Strangeway

  5. Anti-parallel merging [Luhmann, 1984] Luhmann et al. [1984] used Spreiter gas dynamic model to map IMF to the magnetopause Contours show regions of anti-parallel merging (up to 90˚) Crooker [1985] used superposition of IMF and Chapman-Ferraro field at magnetopause, considered component merging Cooling [2001] extended Luhmann et al. [1984] to allow for component merging B = (0,0,1)(northward) B = (0,1,0)(By only) B = (0,0,-1)(southward) B = (0,-1,-1) GEM - Cusp Tutorial - R. J. Strangeway

  6. Cooling Model – Component Merging Luhmann et al. [1984] Cooling et al. [2001] GEM - Cusp Tutorial - R. J. Strangeway

  7. Outline • Introduction – why talk about the cusp? • Reconnection topology and the cusp – where is the cusp? • Cusp ion dispersion at middle altitudes – where is the reconnection? • Cusp ion dispersion at low altitudes – multiple cusps? • Field-aligned currents – Force balance and cusp dynamics • Ion outflows – Joule dissipation and electron precipitation • Neutral upwelling – Important for satellite drag • Summary GEM - Cusp Tutorial - R. J. Strangeway

  8. Trattner et al. [2012] component and anti-parallel merging • Characteristic signature of cusp is energy dispersed ions • Plot shows Polar data at ~ 5.5 Re • Mapping to magnetopause (source region) uses time-of-flight energy dispersion comparing downgoing to reflected [Onsager et al., 1990] • Multiple dispersion events could be because of: • Multiple reconnection sites • Time-varying reconnection • High latitude and low-latitude reconnection (different history) GEM - Cusp Tutorial - R. J. Strangeway

  9. Trattner et al. [2012], different topology By-dominated – nearly anti-parallel, multiple X-lines? Southward Bz – anti-parallel, multiple injections from same point Northward Bz – component merging, extended region GEM - Cusp Tutorial - R. J. Strangeway

  10. IMF By – Hemispherical Asymmetry Østgaard et al. [2005] investigate cusp proton precipitation asymmetry using IMAGE (viewing north) and Polar (viewing south) Cusp precipitation consistent with locus of anti-parallel merging Bx contributes to hemi-spherical differences GEM - Cusp Tutorial - R. J. Strangeway

  11. Outline • Introduction – why talk about the cusp? • Reconnection topology and the cusp – where is the cusp? • Cusp ion dispersion at middle altitudes – where is the reconnection? • Cusp ion dispersion at low altitudes – multiple cusps? • Field-aligned currents – Force balance and cusp dynamics • Ion outflows – Joule dissipation and electron precipitation • Neutral upwelling – Important for satellite drag • Summary GEM - Cusp Tutorial - R. J. Strangeway

  12. Newell et al. [2007] – Forward Dispersion DMSP “FAST” Note: At low altitudes the spacecraft moves through structures GEM - Cusp Tutorial - R. J. Strangeway

  13. Newell et al. [2007] – Reverse Dispersion DMSP “FAST” GEM - Cusp Tutorial - R. J. Strangeway

  14. Newell et al. [2007] – Double Cusp DMSP “FAST” GEM - Cusp Tutorial - R. J. Strangeway

  15. Double Cusp – Wing et al. [2001] Wing et al. [2001] argue that double cusps are because the dispersing ions come from two different reconnection sites DMSP data from Newell et al. [2007] (not the same event) GEM - Cusp Tutorial - R. J. Strangeway

  16. Outline • Introduction – why talk about the cusp? • Reconnection topology and the cusp – where is the cusp? • Cusp ion dispersion at middle altitudes – where is the reconnection? • Cusp ion dispersion at low altitudes – multiple cusps? • Field-aligned currents – Force balance and cusp dynamics • Ion outflows – Joule dissipation and electron precipitation • Neutral upwelling – Important for satellite drag • Summary GEM - Cusp Tutorial - R. J. Strangeway

  17. Force Balance For simplicity assume neutrals at rest (frame of reference) Ionospheric flow: Frozen-in electrons: GEM - Cusp Tutorial - R. J. Strangeway

  18. IMF By-Dependent Convection Currents Convection By > 0 By < 0 Burch et al. [1985] GEM - Cusp Tutorial - R. J. Strangeway

  19. Weimer [2001] FAC morphology GEM - Cusp Tutorial - R. J. Strangeway

  20. FAST Orbit 8276 – Strong IMF By GEM - Cusp Tutorial - R. J. Strangeway

  21. MHD FAC Predictions GEM - Cusp Tutorial - R. J. Strangeway

  22. Field Topology – Shock Passage GEM - Cusp Tutorial - R. J. Strangeway

  23. FAST Orbit 8284 – Double Cusp? GEM - Cusp Tutorial - R. J. Strangeway

  24. Outline • Introduction – why talk about the cusp? • Reconnection topology and the cusp – where is the cusp? • Cusp ion dispersion at middle altitudes – where is the reconnection? • Cusp ion dispersion at low altitudes – multiple cusps? • Field-aligned currents – Force balance and cusp dynamics • Ion outflows – Joule dissipation and electron precipitation • Neutral upwelling – Important for satellite drag • Summary GEM - Cusp Tutorial - R. J. Strangeway

  25. Ion Outflows Type 1 Type 2 Type 1 and Type 2 defined by Wahlund et al. [1992] GEM - Cusp Tutorial - R. J. Strangeway

  26. Ion Outflows – Including Alfvén Waves Type 1 Type 2 Type 1 and Type 2 defined by Wahlund et al. [1992] GEM - Cusp Tutorial - R. J. Strangeway

  27. Joule Dissipation and Heating Rates Plasma frame: Neutral frame: Rate of temperature increase: Minority species temperature increases more rapidly See [Strangeway, JGR, 2012] GEM - Cusp Tutorial - R. J. Strangeway

  28. Outline • Introduction – why talk about the cusp? • Reconnection topology and the cusp – where is the cusp? • Cusp ion dispersion at middle altitudes – where is the reconnection? • Cusp ion dispersion at low altitudes – multiple cusps? • Field-aligned currents – Force balance and cusp dynamics • Ion outflows – Joule dissipation and electron precipitation • Neutral upwelling – Important for satellite drag • Summary GEM - Cusp Tutorial - R. J. Strangeway

  29. Cusp Statistics – Knipp et al. [2011] Poynting flux statistics from DMSP Southern hemisphere is mirror-reflected about noon as a function of IMF By Events required |By| > 10 nT (a) N:By < 0, Bz < 0; (b) N:By > 0, Bz < 0 (c) N:By < 0, Bz > 0; (d) N:By > 0, Bz > 0 Red is 100 µW/m2 GEM - Cusp Tutorial - R. J. Strangeway

  30. Thermospheric Response – Crowley et al. [2011] CHAMP sees strongly neutral density modulation near the cusp Modified TIME-GCM using real-time AMIE data shows enhanced densities too GEM - Cusp Tutorial - R. J. Strangeway

  31. Poynting Flux Versus Neutral Density – Crowley et al. [2011] GEM - Cusp Tutorial - R. J. Strangeway

  32. Small scale FACs – Lühr et al. [2004] CHAMP also sees large-amplitude small-scale FACs in the Cusp Lühr et al [2004] argue that these can significantly enhance the heating Heating rate depends on E2, But there is an issue with time scales, neutrals heat much more slowly than ions GEM - Cusp Tutorial - R. J. Strangeway

  33. Summary • Reconnection topology controls the location of the cusp • There is both a high latitude (anti-parallel merging) and low latitude (component merging) source of dispersing ions – depends on IMF orientation • Field-aligned currents and Joule dissipation in the ionosphere strongly affected by IMF By – I suggest this is high latitude merging • Ion outflows and neutral upwelling both appear to be associated with Joule dissipation – question of timescales for the neutrals GEM - Cusp Tutorial - R. J. Strangeway

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