Ionospheric Convection Response to High-Latitude Reconnection and Electrodynamics

Ionospheric Convection Response to High-Latitude Reconnection and Electrodynamics of a Split-Transpolar Aurora S. Eriksson 1, G. Provan 2, F. J. Rich 3, C. Mouikis 4, M. W. Dunlop 5, M. Kuznetsova 6, S. Massetti 7, B. Anderson 8, M. Lester 2, J. T. Gosling 1, H. Reme 9, and A. Balogh 10 1 LASP, University of Colorado, Boulder, CO, USA of Leicester, UK 3 AFRL, Hanscom AFB, MA, USA 4 SSC, University of New Hampshire, Durham, NH, USA 5 Rutherford Appleton Laboratory, Chilton, UK 6 NASA/GSFC, Greenbelt, MD, USA 7 Istituto di Fisica dello Spazio Interplanetario, Roma, Italy 8 JHU/APL, Laurel, MD, USA 9 Centre d’Etude Spatiale des Rayonnements, Toulouse, France 10 The Blackett Laboratory, Imperial College, London, UK 2 University Contact: eriksson@lasp. colorado. edu

Outline Part I – Global Observations • Cluster lobe reconnection observations: 14 February 2003 1840 -2000 UT • BATSRUS MHD simulation 1830 -2030 UT http: //ccmc. gsfc. nasa. gov [c. f. “Stefan”] • Super. DARN noon response to IMF 1940 -2200 UT: Schematic NBZ field-aligned current (FAC) and Ex. B flow driven by lobe reconnection • Iridium Birkeland Currents • Summary – Part I

Outline Part II – Electrodynamics • Polar UVI & All-sky Camera observations • DMSP F 13 observations: 2107 -2114 UT -- Ex. B drift velocity -- FAC system -- Electron precipitation • Summary – Part II

Part I – Global Observations

Lobe Reconnection Schematic Dungey [1963] (courtesy of J. C. Dorelli, UNH)

Side view 19 View from above 20 UT 18 Solar Direction Cluster C 1 Cluster C 2 Cluster C 3 Cluster C 4 Solar Direction

Cusp Schematic - Cluster FGM Lobe field Cluster C 1 Cluster C 3 Dayside closed field z x Direction of magnetic field

Vx Vy Vz Bx By Bz

Walen Test: Quantitative agreement with high-latitude magnetic reconnection Vx Vy Vz x-comp y-comp z-comp Bx By Bz

Walen Test: Quantitative agreement with high-latitude magnetic reconnection magnetosheath Bn magnetotail lobe z x

YZ GSM Plane B Vx Jpar Vy

YZ GSM Plane B Vx Jpar Vy Cluster C 1 position ~1800 -1900 UT

Vx Vy XZ GSM Plane P

XZ GSM Plane

XZ GSM Plane Cluster C 3 18, 19, 20 UT Cluster C 1 18, 19, 20 UT

Super. DARN noon-sector flow in agreement with Cluster C 3 observations at 1940 UT and 1950 UT…. one clockwise lobe cell is present in the dayside sector with sunward and dawnward flow across 12 MLT.

How does the sunward flow in the noon sector respond as the IMF clock angle changes? 78 o 13 12 11 MLT 80 o 82 o

78 o 13 12 11 MLT 80 o 82 o

IMF during Super. DARN highlatitude noon convection changes TPA: Transpolar Aurora (Polar UVI) Red Vertical Line: Time of DMSP F 13 TPA Observation TPA

IMF during Super. DARN highlatitude noon convection changes A: Two-cell pattern B: Strong predominantly dawnward flow C: One clockwise global lobe cell C A B D E D: One counterclockwise postnoon dayside lobe cell E: Two dayside lobe cells (reverse dayside flow)

A: Two-cell pattern B: Strong predominantly dawnward flow C: One clockwise global lobe cell D: One counterclockwise postnoon dayside lobe cell E: Two dayside lobe cells (reverse dayside flow)

A: Two-cell pattern B: Strong predominantly dawnward flow C: One clockwise global lobe cell downward NBZ upward NBZ D: One counterclockwise postnoon dayside lobe cell E: Two dayside lobe cells (reverse dayside flow)

Iridium Configuration downward upward

Iridium Configuration R 2 R 1 NBZ R 1 R 2 downward upward

MHD simulation of NBZ development

Proposed model: The sunward flow and the bounding NBZ FAC system are directly driven by lobe reconnection. As the IMF By changes during positive Bz, so does the lobe reconnection site and thus the location and deflection of the joint sunward flow channel and NBZ system. A TPA is expected within the upward NBZ system. See also: Southwood, 1987; Vennerstrom et al. , 2005 B: Strong predominantly dawnward flow IMF clock angle +90 C: One clockwise global lobe cell IMF clock angle +45 E: Two dayside lobe cells (reverse dayside flow) IMF clock angle 0 F: One anti-clockwise global lobe cell ? ? ? IMF clock angle -45

Summary Part I • The IMF from ACE and Cluster is strongly northward and duskward. The IMF Bx is negative in the solar wind (ACE) and in the magnetosheath (Cluster C 1). Lobe reconnection is favored tailward of the northern cusp. Following a southward IMF Bz excursion, the IMF By decreases gradually toward By~0. • The Cluster s/c moved through the northern cusp at the beginning of the event. Two s/c (C 1 and C 3) observed enhanced sunward and dawnward velocity in agreement with high-latitude lobe reconnection tailward of the cusp. • MHD simulations confirm the general magnetic field and flow topology consistent with these Cluster observations. NBZ-type FACs are suggested on either side of the MHD lobe reconnection region and in the duskside ionosphere. • Super. DARN Ex. B drift is sunward and dawnward across the 12 MLT meridian at the time of the Cluster C 3 flow enhancements. • The subsequent direction of Super. DARN noon sector flows (after a southward excursion) tracks the IMF clock angle changes well with different time delays. A faster response time is suggested to the southward (100 to 156 deg) turning (3 -6 min) than either the duskward (135 to 34 deg) or due northward (45 to 8 deg) turnings that take 8 -9 min and 12 -14 min, respectively.

Part II – Electrodynamics

Polar UVI

All-sky Camera, Daneborg (DNB)

Clockwise Lobe Cell

R 1 NBZ Clockwise Lobe Cell R 1 R 2

DMSP Electron Precipitation

Summary Part I-II • Super. DARN verified a sunward flow channel over the TPA as part of a clockwise global lobe cell that covered much of the polar cap. This is consistent with the positive IMF By and northward IMF Bz (~30 -50 deg clock angle). • A DMSP F 13 dusk-to-dawn pass verified a structured sunward lobe cell flow channel over the split-TPA and an NBZ current system on either side of it [Iijima and Shibaji, JGR, 1987; Southwood, 1987]. The TPA was found within the upward NBZ region. • Two inverted Vs were detected in agreement with sunward flow shear and local upward FAC filaments at each of the two Sun-aligned arcs of the split. TPA. The high-latitude current system poleward of the duskside R 2 system was locally balanced assuming a Pedersen closure. • The increased Pedersen conductance at both arcs self-consistently explains the structured sunward drift velocity.

Summary Part I-II • The dual arc separation is consistent with a prior Akebono study [Obara et al. , 1996]. • The structure & dual-arc system is in general agreement with the Zhu et al. [1994, 1996] MI-coupling model. The second (poleward) arc is due to the ionospheric response to an initial magnetospheric flow shear. • We do not fully understand the cause and effect of the energy-dependence of the dual-arc separation. It may be related to stronger Hall current system relative to the Pedersen currents. • We propose the following response of high-latitude dayside electrodynamics during northward IMF. The sunward flow & the bounding NBZ FAC system are directly driven by lobe reconnection. As the IMF By changes, so does the lobe reconnection site and thus the location and deflection of the joint sunward flow channel & NBZ system. The (dayside) TPA is expected within the upward NBZ system [see also Vennerstrom et al. , 2005].

Mach number Plasma Beta Dynamic pressure Northward IMF epsilon: