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Exploring Ionospheric Circulation and Merging Potential Due to Purely B y IMF

Exploring Ionospheric Circulation and Merging Potential Due to Purely B y IMF. Robert Bruntz, Ramon E. Lopez, Shree Bhattarai, and Kevin Pham University of Texas at Arlington; Arlington, Texas, USA 2014 AOGS - Sapporo, Japan. Background.

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Exploring Ionospheric Circulation and Merging Potential Due to Purely B y IMF

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  1. Exploring Ionospheric Circulation and Merging Potential Due to Purely By IMF Robert Bruntz, Ramon E. Lopez, Shree Bhattarai, and Kevin Pham University of Texas at Arlington; Arlington, Texas, USA 2014 AOGS - Sapporo, Japan

  2. Background Clear ionospheric circulation patterns and transpolar potentials (TPP) due to purely y-component (By) interplanetary magnetic field (IMF) are difficult to obtain from observations In nature, effects from By, Bz, and the viscous interaction are generally inextricably combined Mitchell et al. (2010) found that TPP is constant for small values of purely-By IMF, then rises linearly, but the cause was unclear An MHD simulation can help explore these topics

  3. Lyon-Fedder-Mobarry global MHD simulation • X: [25, -300] RE • Y, Z: [100, -100] RE • BCs: solar wind, supersonic outflow, 2-D ionospheric simulation • No dipole tilt • Input idealized solar wind, examine steady-state conditions

  4. Superposition of potentials Lopez et al. (2014) showed that By-driven reconnection, Bz-driven reconnection, and the viscous interaction are essentially independent, and can be combined to recreate full-IMF ionospheric flows and potentials

  5. Obtaining By circulation patterns and potentials from superposition By, Bz, and viscous patterns are independent:Full IMF  (By + Bz – Viscous) Subtracting the viscous components from By-only LFM runs leaves only the By-driven components

  6. Viscous potential dominates By potential for (relatively) small By Negative Bz: reconnection and viscous potentials add to produce one peak of each sign (+, -) Positive Bz: reconnection and viscous potentials are independent and largest of each sign eclipses the other By (positive or negative): reconnection and viscous potentials add, but peaks are not aligned, so one dominates over the other Smaller By values: viscous dominates reconnection Larger By values: reconnection dominates viscous Transition from viscous-dominated to By-dominated depends on the value of the viscous potential: VP = μ*n0.44V1.3 (Bruntz et al., 2012)

  7. Viscous potential dominates By potential for (relatively) small By TPP = transpolar potential VP = viscous potential Reconnection dominates Viscous dominates Low By values: viscous dominates reconnection Larger By values: reconnection dominates viscous

  8. Viscous potential is independent of IMF By Viscous dominated +ve cell ≈ -ve cell TPP for low values of By is constant and apx. equal to viscous potential – but could positive and negative cells be changing?E.g., 100 kV = 50 kV – (-50 kV) = 75 kV – (-25 kV) = same TPP No – both viscous cells have same value for various By values

  9. Symmetry of +/- By Change of sign of By IMF changes signs of circulation cells, but not comparative values

  10. Symmetry of +/- By North, +5 nT By South, -5 nT By North, -5 nT By South, +5 nT By Change of hemisphere changes signs of circulation cells, but not comparative values

  11. By reconnection patterns after viscous subtraction Northern polar cap. By = 1, 2, 3, 4, 5, 7.5 nT

  12. By reconnection patterns after viscous subtraction N. polar cap. By = 10, 12.5, 15, 17.5, 20, 25 nT

  13. By potentials after viscous subtraction The reconnection potential from IMF By shows signs of saturation, just like the potentials from IMF Bz

  14. Summary Superposition in LFM allows subtraction of the viscous-driven ionospheric circulation to find the By-driven ionospheric circulation and potentials. We are not aware of any other technique that allows for the isolation of the purely By-driven circulation patterns and potentials (that exclude the effect of the viscous interaction) Viscous potential dominates reconnection in TPP for relatively low values of By, so TPP is apx. constant; then reconnection dominates and TPP rises Viscous potential is constant with changing By (like negative Bz; unlike positive Bz)

  15. References Bruntz et al. (2012) Lopez et al. (2014) Mitchell et al. (2010)

  16. To do list Show reconnection ionospheres for a variety of By values Add labels to axes on all Excel plots REL: note that Bz runs show why extrapolation VP doesn’t match 0 IMF VP (extrema don’t quite coincide)

  17. Data table

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