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On the relationship between polar cap flows and the IMF
W.A. Bristow, R.T. Parris, J. Spaleta, T. TheurerGeophysical Institute, University of Alaska Fairbanks
McMurdo SuperDARN
• McMurdo Station SuperDARN built January 2010
• Station Latitude 77.88° South Geographic (~80° Magnetic)
• Magnetic Pole near center of FOV at ~1200 km range
Convection Maps
•Ruohoniemi and Baker convection mapping routine
•McMurdo data fill in region over magnetic pole
Convection Dependance• Examine
dependance Earth-Sun component of velocity on the IMF
• Use line of sight velocity to eliminate model influence
• Average of all LOS vectors where λ>85° and kr ∙kE-S > 0.9
Imposed Potential
Bow Shock
Magnetopause
Sheath
Vsw ≈300 km/sVi ≈ 1 km/s
Polar cap ~4000 km(OCB at 70°)
Expected Velocity• About 1-hour of IMF maps into
the polar cap at any given time
• Might expect ionospheric velocity to vary from place to place depending on solar wind mapping
• Except... sound speed in ionosphere
Expected Velocity• About 1-hour of IMF maps into
the polar cap at any given time
• Might expect ionospheric velocity to vary from place to place depending on solar wind mapping
• Except... sound speed in ionosphere
Expected Velocity
• For B≈50 µ T, oxygen n=1011, VA≈860 km/s
• 860 km/s >> 1km/s (flow speed)
• Flow is incompressible
- ∇∙v = 0