Auroral Boundaries: Finding Them in Data and Models

1. Auroral Boundaries: Finding Them in Data and Models Gang Lu High Altitude Observatory National Center for Atmospheric Research Joint CEDAR/GEM Workshop, Santa Fe, June 29, 2005

2. Outline • Plasma Convection & Convection Reversal Boundary (CRB) • Plasma Boundary Layers & Auroral Boundaries • Auroral Boundaries from HF Radar Measurements • Auroral Boundaries from IS Radar Measurements • Auroral Boundaries in Global MHD Models • Advanced Modular Incoherent Scatter Radar (AMISR)

3. Noon-Midnight Meridional Plane High-Latitude Ionosphere V Equipotential Contour V Equatorial Plane V OPEN-CLOSE FIELD LINE BOUNDARY Topology of Plasma Convection CRB and Open/Closed boundary do not always coincide (Lyons & Williams, 1984)

4. Southward IMF Bz CRB Northward IMF Bz CRB Ion Drifts Measured by DMSP Satellites

5. Ion Drifts Measured by Sondrestrom IS Radar CRB (Clauer & Ridley, 1995)

6. CRB Ion Drifts Measured by SuperDARN HF Radars

7. Convection Patterns Derived from SuperDARN

8. Convection Patterns Derived from AMIE Southward Bz Northward Bz (Lu et al., 1994)

9. Morphology of Plasma Boundary Layers (Vasyliunas, 1979)

10. Auroral Precipitation Boundaries from DMSP Satellites (Newell & Meng, 1988)

11. Relation Between Auroral Precipitation & Convection Bz < 0 By < 0 Bz > 0 By < 0 Bz > 0 By > 0 Bz < 0 By > 0 (Newell et al, 2004)

12. IMAGE FUV Polar UVI Jan. 9, 1997 (LBHL) Km2 x106 0534:47 GW 0651:27 nT 0719:40 0749:16 Magnetic Latitude (degree) 0759:32 0839:24 05:00 06:00 07:00 08:00 09:00 10:00 Time (UT) (Brittnacher et al, 1999) (Mende et al, 2003)

13. (Baker et al, 1995) Geo. Latitude Width (m/s) Number of Events MSP @ 630 nm Intensity (kR) Geo. Latitude (Milan et al, 1999) Spectral Width (m/s) Auroral Boundaries from HF Radar Measurements • A sharp latitudinal gradient in the Doppler spectral width has been associated with: • - dayside Cusp

14. Based on 6 HF radars between October 1996 – May 1997 (Villain et al, 2002) Auroral Boundaries from HF Radar Measurements • A sharp latitudinal gradient in the Doppler spectral width has been associated with: • - dayside Cusp • - the boundary between the CPS and the BPS • - the LLBL • - the open-closed boundary

15. Cusp Boundary Auroral Boundary Auroral Boundaries from HF Radar Measurements • A sharp latitudinal gradient in the Doppler spectral width has been associated with: • - dayside Cusp • - the boundary between the CPS and the BPS • - the LLBL • - the open-closed boundary (Villain et al, 2002)

16. Cusp Boundary Auroral Boundary Auroral Boundaries from HF Radar Measurements • A sharp latitudinal gradient in the Doppler spectral width has been associated with: • - dayside Cusp • - the boundary between the CPS and the BPS • - the LLBL • - the open-closed boundary • Advantage: • The wide coverage allows to image the auroral boundaries continously and globally • Limitation: • The high spectral width can be observed both on closed and open regions (e.g., Lester et al., 2001; Woodfield et al., 2002; Andre et al., 2002) (Villain et al, 2002)

17. Altitude (km) 3x104 cm-3 Electron Density (de la Beaujardiere et al, 1991) Invariant Latitude (degree) Intensity [R] Ne [103 cm-3] (Blanchard et al, 1996) Auroral Boundaries from IS Radar Measurements • Ti and/or Te, and E-region electron density have been used to identify: • - dayside Cusp • - nightside auroral poleward boundary

18. Altitude (km) Invariant Latitude (degree) Intensity [R] Ne [103 cm-3] (Blanchard et al, 1996) Auroral Boundaries from IS Radar Measurements • Ti and/or Te, and E-region electron density have been used to identify: • - dayside Cusp • - nightside auroral poleward boundary • Advantage: • Not affected by “blackouts”; • able to observe several important plasma parameters (e.g., Ne, Ti, Te, Vi) • Limitation: • - limited availability of IS radars • - Expensive to operate (de la Beaujardiere et al, 1991) (Blanchard et al, 1996)

19. Auroral & Open-closed Boundaries in MHD Models Energy flux for diffuse e- Energy flux for discrete e- NH energy flux SH energy flux Electric Potential Field-aligned current Electric potential Field-aligned current (Fedder et al, 1995) (Courtesy of Jimmy Raeder)

20. IMAGE FUV MHD POLAR VIS Auroral & Open-closed Boundaries Compared BATSRUS UCLA-GGCM (Rastätter et al, 2005)

21. Why should we care about auroral boundaries? • Observations of auroral boundaries can be used to remotely monitor magnetospheric processes (e.g., reconnection rate) • Auroral boundaries may be used as a dynamical coordinate system to better organize some physical parameters (e.g., Poynting flux, ion upflow/outflow) • Auroral precipitation and ionospheric plasma convection represent two of the major magnetospheric forcings on the ionosphere/thermosphere dynamics and electrodynamics • Let’s not forget about the ionospheric feedback effects

22. 80 Ion upflow (Vi > 800 m/s) Magnetic Latitude (deg) 76 72 Why should we care about auroral boundaries? Poleward auroral Boundary derived from FUV

23. Ion Outflow (Dynamic Coordinates) 18 18 00 00 Pole. boundary Eq. boundary Why should we care about auroral boundaries? Ion Outflow (ILAT/MLT Coordinates) 60 60 18 60 60 18 00 00

24. AMISR Advanced Modular Incoherent Scatter Radar 384 Panels, 12,288 AEUs 3 DAQ Systems 3 Scaffold Support Structures (Courtesy of Craig Heinselman)

25. 1500 PULSES 800 Altitude (km) 0 -400 0 400 Ground Distance (km) Plasma Parameter Maps (Courtesy of Craig Heinselman) V7-6 END

26. 160 140 ALTITUDE (km) 120 100 0.10 0 E-FIELD (V m–1) –0.10 10:00 11:00 12:00 TIME (UT) AMISR Ion Velocity Estimation Vector Scale :3000 ms–1 3 positions, 3 km & 3 m intervals E East E North 3 positions, 3 m intervals (Courtesy of Craig Heinselman) v12

27. AMISR Coverage – Global Context A Great Observatory: ISRs SuperDARN Optical Instruments (MSPs & All-sky imagers) + DASI + Satellites (Courtesy of Craig Heinselman) v21B