Ionospheric Convection Response to High-Latitude Reconnection and

Electrodynamics of a Split-Transpolar Aurora

S. Eriksson1, G. Provan2, F. J. Rich3, C. Mouikis4,M. W. Dunlop5, M. Kuznetsova6, S. Massetti7, B. Anderson8,

M. Lester2, J. T. Gosling1, H. Reme9, and A. Balogh10

1LASP, University of Colorado, Boulder, CO, USA2University of Leicester, Leicester, UK

3AFRL, Hanscom AFB, MA, USA4SSC, University of New Hampshire, Durham, NH, USA

5Rutherford Appleton Laboratory, Chilton, UK6NASA/GSFC, Greenbelt, MD, USA

7Istituto di Fisica dello Spazio Interplanetario, Roma, Italy8JHU/APL, Laurel, MD, USA

9Centre d’Etude Spatiale des Rayonnements, Toulouse, France10The Blackett Laboratory, Imperial College, London, UK

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”]

• SuperDARN noon response to IMF 1940-2200 UT: Schematic NBZ field-aligned current (FAC) and ExB flow driven by lobe reconnection

• Iridium Birkeland Currents

• Summary – Part I

Outline Part II – Electrodynamics

• Polar UVI & All-sky Camera observations

• DMSP F13 observations: 2107-2114 UT-- ExB drift velocity

-- FAC system

-- Electron precipitation

• Summary – Part II

Part I – Global Observations

Lobe Reconnection SchematicDungey [1963]

(courtesy of J. C. Dorelli, UNH)

Cluster C1Cluster C2Cluster C3Cluster C4

Solar DirectionSolar Direction Solar Direction

View from aboveSide view

18

1920 UT

Cusp Schematic - Cluster FGM

Cluster C3

Cluster C1

Direction of magnetic field

Lobe field

Dayside closed field

x

z

BxByBz

VxVyVz

BxByBz

VxVyVz 0/ Bv

x-compy-compz-comp

Walen Test: Quantitative agreement with high-latitude magnetic reconnection

Walen Test: Quantitative agreement with high-latitude magnetic reconnection

Bnz

xmagnetotail lobe

magnetosheath

vvR

Bv

x

0/

YZ GSM PlaneB

Jpar

Vx

Vy

YZ GSM Plane

Cluster C1 position~1800-1900 UT

B Vx

VyJpar

XZ GSM Plane

Vx Vy

P

XZ GSM Plane

Cluster C1 18, 19, 20 UTCluster C3 18, 19, 20 UT

XZ GSM Plane

SuperDARN noon-sector flow in agreement with Cluster C3 observations

at 1940 UT and 1950 UT….one clockwise lobe cell is present inthe 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?

11 MLT80o

1213

82o

78o

11 MLT80o

1213

82o

78o

IMF during SuperDARN high-latitude noon convection changes

TPA TPA

TPA: Transpolar Aurora (Polar UVI)

Red Vertical Line: Time of DMSP F13 TPA Observation

IMF during SuperDARN high-latitude noon convection changes

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 B

C D E

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

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

D: One counter- clockwise 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

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)

upward NBZdownward NBZ

Iridium Configuration

downward upward

Iridium Configuration

downward upward

R1NBZ

R2

R1 R2

MHD simulation of NBZ development

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

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

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 C1). 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 (C1 and C3) 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.

• SuperDARN ExB drift is sunward and dawnward across the 12 MLT meridian at the time of the Cluster C3 flow enhancements.

• The subsequent direction of SuperDARN 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

Polar UVI

All-sky Camera, Daneborg (DNB)

All-sky Camera, Daneborg (DNB)

All-sky Camera, Daneborg (DNB)

All-sky Camera, Daneborg (DNB)

Clockwise Lobe Cell

NBZR1 R1 R2

Clockwise Lobe Cell

DMSP Electron Precipitation

DMSP Electron Precipitation

DMSP Electron Precipitation

Summary Part I-II• SuperDARN 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 F13 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 R2 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:

0

2042 2cos

l

VB