Magnetosphere – Ionosphere Coupling in the Auroral Region: A Cluster Perspective

1. Magnetosphere – Ionosphere Coupling in the Auroral Region: A Cluster Perspective Octav Marghitu Institute for Space Sciences, Bucharest, Romania 17th Cluster Workshop, Uppsala, May 15, 2009

2. Outline • Nightside results (most emphasis) • Perigee observations – quasi-static vs. Alfvénic structures • Apogee observations – BBFs, ‘bubbles’, energy conversion • Polar cap observations – inverted-Vs, (ion outflow) • Dayside results (very briefly) • Steady reconnection mapped to ionosphere • (FTEs mapped to ionosphere) • Prospects

3. A1Nightside perigee observationsA1 Auroral Plasma Physics, ISSI Marklund et al., 2001 • Quasistatic • 2D • Alfvénic, as ‘opposed’ to quasistatic

4. A1Nightside perigee observationsA1 Marklund et al., 2001 Karlsson and Marklund, 1998

5. A1Nightside perigee observationsA1 Model based on a “2-D set of reduced, two-fluid MHD equations that describe shear Alfvén waves in the cold, low-altitude-magnetosphere plasma”. Marklund et al., 2001 Streltsov and Marklund, 2006

6. spatial spatial temp A1Nightside perigee observationsA1 • Event discussed by Karlsson et al. (2004), Johansson et al. (2004), Marklund et al. (2004). • Simulation by Streltsov and Karlsson (2008), based on the same algorithm as before.

7. A1Nightside perigee observationsA1 Vaivads et al., 2003 Cluster DMSP • Poynting flux at Cluster roughly equal to DMSP e- energy flux • Good agreement between DMSP e- energy and Cluster potential dip / ion energy, suggesting a static structure • Cluster E/B ~ 104 km/s, consistent with an Alfvén wave, but “for altitudes below Cluster can safely be regarded as a potential structure”.

8. C4 C3 FAST A1Nightside perigee observationsA1 • j/B at FAST is 0–0.3 A/m2T, while at Cluster 4 is 0.1 A/m2T => consistent with magnetic conjunction • Filamentary structure of the dwd current, 10–20 km, related (?) to the Ionospheric Alfvén Resonator Wright et al., 2008

9. A1POLAR observationsA1 Alfvénic Poynting flux into the ionosphere at PSBL. Weygant et al., 2000. Also Keiling et al., 2000, 2001, 2002; Weygant et al., 2002.

10. A1TheoryA1 • Cold plasma (inertial regime, below 5 RE), incident + reflected wave. • Small scale structures Alfvénic at low / high altitudes and electrostatic in between. Lysak, 1998

11. A2Nightside apogee observationsA2 Figure from Amm et al. (2005), adapted after Nakamura et al. (2001) • BBFs modeled as plasma bubbles – Pontius and Wolf (1990), Chen and Wolf (1993, 1999). • Field-aligned currents connect the bubble to the ionosphere at the flanks. • BBFs believed to be related to auroral streamers / polar boundary intensifications. • Comprehensive review of Cluster – ground observations, including ionospheric signatures of BBFs, in Amm et al. (2005). • Cluster papers e.g. by Grocott et al. (2004), Nakamura et al. (2005), Walsh et al. (2009).

12. Bx By Bz Vx N A2Nightside apogee observationsA2 Cluster data (left), Cluster configuration (middle), ionospheric equivalent current pattern (right). The most likely location of the conjugate ionospheric flow channel surrounded by the pink line and the center of the precipitation indicated in orange. Figure from Amm et al., 2005, adapted after Nakamura et al., 2005

13. A2Nightside apogee observationsA2 Marghitu et al., 2006 Hamrin et al., 2006

14. A2Nightside apogee observationsA2 Preliminary statistical study of concentrated generator regions (CGRs) and concentrated load regions (CLRs), Marghitu et al., 2009.

15. A3Polar cap observationsA3 • Left: Polar cap crossing by northward IMF on 18 March 2003 (no optical data), Maggiolo et al., 2006. • Polar cap crossing by northward IMF on 20 March 2003, Teste et al., 2007. • Typically low energies (< 1 keV) => difficult to cross-check with optical data. • Open or closed field lines? • Alfvénic structures, similar to ‘proper’ aurora?

16. BDayside resultsB • Steady reconnection captured by Cluster and IMAGE, Phan et al., 2003, Frey et al., 2003. • Cusp/LLBL papers, ionospheric fingerprint of FTEs => see e.g. the review of Amm et al., 2005.

17. CProspectsC • Relationship between Alfvénic and quasi-static structures. • The 3D auroral arc. • Energy conversion and BBFs / bubbles. • M–I coupling in the Harang region (FAC–EJ coupling, dominated by the Hall current ?) => to rely on THEMIS, Cluster, and low altitude satellites / GBOs.

18. References Amm et al., AG, 23, 2129, 2005. Chen and Wolf, JGR, 98, 21409, 1993. Chen and Wolf, JGR, 104, 14613, 1999. Frey et al., Nature, 426, 533, 2003. Grocott et al., AG, 22, 1061, 2004. Hamrin et al., AG, 24, 637, 2006. Johansson et al., AG, 22, 2485, 2004. Karlsson and Marklund, Phys. Space Plasmas, 15, 401, 1998. Karlsson et al., AG, 22, 2463, 2004. Keiling et al., GRL, 27, 3169, 2000. Keiling et al., JGR, 106, 5779, 2001. Keiling et al., JGR, 107, 1132, 2002. Lysak, GRL, 25, 2089, 1998. Maggiolo et al., AG, 24, 1665, 2006. Marghitu et al., AG, 24, 619, 2006. Marghitu et al., Proc. 15th Cluster Workshop, in press, 2009. Marklund et al., Nature, 414, 724, 2001. Marklund et al., NPG, 11, 709, 2004. Nakamura et al., JGR, 106, 10791, 2001. Nakamura et al., AG, 23, 553, 2005. Phan et al., GRL, 30, 1059, 2003. Pontius and Wolf, GRL, 17, 49, 1990. Streltsov and Marklund, JGR, 111, A07204, 2006. Streltsov and Karlsson, GRl, 35, L22107, 2008. Teste et al., AG, 25, 953, 2007. Vaivads et al., GRL, 30, 1106, 2003. Walsh et al., AG, 27, 725, 2009. Wygant et al., JGR, 105, 18675, 2000. Wygant et al., JGR, 107, 1201, 2002. Wright et al., JGR, 113, A06202, 2008.