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

A. Nightside results (most emphasis) Perigee observations – quasi-static vs. Alfvénic structures

Apogee observations – BBFs, ‘bubbles’, energy conversion

Polar cap observations – inverted-Vs, (ion outflow)

B. Dayside results (very briefly) Steady reconnection mapped to ionosphere

(FTEs mapped to ionosphere)

C. Prospects

Outline

A1A1 Nightside perigee observations A1A1

Marklund et al., 2001

Quasistatic 2D

Auroral Plasma Physics, ISSI

Alfvénic, as ‘opposed’ to quasistatic

Marklund et al., 2001Karlsson and Marklund, 1998

A1A1 Nightside perigee observations A1A1

Marklund et al., 2001Streltsov and Marklund, 2006

A1A1 Nightside perigee observations A1A1

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”.

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.

spatial spatial

temp

A1A1 Nightside perigee observations A1A1

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”.

A1A1 Nightside perigee observations A1A1

Cluster DMSPVaivads et al., 2003

Wright et al., 2008

A1A1 Nightside perigee observations A1A1

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

C4

C3

FAST

Weygant et al., 2000. Also Keiling et al., 2000, 2001, 2002; Weygant et al., 2002.

Alfvénic Poynting flux into the ionosphere at PSBL.

A1A1 POLAR observations A1A1

Lysak, 1998

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

A1A1 Theory A1A1

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).

A2A2 Nightside apogee observations A2A2

Figure from Amm et al. (2005), adapted after Nakamura et al. (2001)

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.

Bx

By

Bz

Vx

N

Figure from Amm et al., 2005, adapted after Nakamura et al., 2005

A2A2 Nightside apogee observations A2A2

Marghitu et al., 2006Hamrin et al., 2006

A2A2 Nightside apogee observations A2A2

A2A2 Nightside apogee observations A2A2

Preliminary statistical study of concentrated generator regions (CGRs) and concentrated

load regions (CLRs), Marghitu et al., 2009.

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?

A3A3 Polar cap observations A3A3

BB Dayside results BB

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.

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.

CC Prospects CC

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.

ReferencesMarghitu 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.