Transcript Document

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
Outline
A.
B.
C.
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
A1 Nightside perigee observations A1
Marklund et al., 2001
 Quasistatic
 2D
Auroral Plasma Physics, ISSI
 Alfvénic, as ‘opposed’ to quasistatic
A1 Nightside perigee observations A1
Marklund et al., 2001
Karlsson and Marklund, 1998
A1 Nightside perigee observations A1
Marklund et al., 2001
Streltsov and Marklund, 2006
Model based on a “2-D set of reduced,
two-fluid MHD equations that describe
shear Alfvén waves in the cold, lowaltitude-magnetosphere plasma”.
A1 Nightside perigee observations A1
spatial
spatial
temp
 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.
A1 Nightside perigee observations A1
Cluster
Vaivads et al., 2003
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”.
A1 Nightside perigee observations A1
C4
C3
FAST
 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
A1 POLAR observations A1
Alfvénic Poynting flux into
the ionosphere at PSBL.
Weygant et al., 2000. Also Keiling et al.,
2000, 2001, 2002; Weygant et al., 2002.
A1 Theory A1
 Cold plasma (inertial regime, below 5 RE), incident + reflected wave.
 Small scale structures Alfvénic at low / high altitudes and electrostatic in between.
Lysak, 1998
A2 Nightside apogee observations A2
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).
A2 Nightside apogee observations A2
Bx
By
Bz
Vx
N
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
A2 Nightside apogee observations A2
Marghitu et al., 2006
Hamrin et al., 2006
A2 Nightside apogee observations A2
Preliminary statistical study of concentrated generator regions (CGRs) and concentrated
load regions (CLRs), Marghitu et al., 2009.
A3 Polar cap observations A3
 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?
B Dayside results B
 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.
C Prospects C
 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.
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.