Transcript Ionospheric Convection Response to High-Latitude Reconnection and Electrodynamics of a Split-Transpolar Aurora S.

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, USA
of Leicester, Leicester, UK
3AFRL, Hanscom AFB, MA, USA
4SSC, University of New Hampshire, Durham, NH, USA
5Rutherford Appleton Laboratory, Chilton, UK
6NASA/GSFC, Greenbelt, MD, USA
7Istituto di Fisica dello Spazio Interplanetario, Roma, Italy
8JHU/APL, Laurel, MD, USA
9Centre d’Etude Spatiale des Rayonnements, Toulouse, France
10The Blackett Laboratory, Imperial College, London, UK
2University
Contact: [email protected]
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 Schematic
Dungey [1963]
(courtesy of J. C. Dorelli, UNH)
Side view
19
View from above
20 UT
18
Solar Direction
Cluster C1
Cluster C2
Cluster C3
Cluster C4
Solar Direction
Solar Direction
Cusp Schematic - Cluster FGM
Lobe field
Cluster C1
Cluster C3
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


v  B / 0
x-comp
y-comp
z-comp
Bx
By
Bz
Walen Test: Quantitative agreement with
high-latitude magnetic reconnection
magnetosheath
Bn
magnetotail lobe
z
x


v  B /  0

 
Rx   v v
YZ GSM Plane
B
Vx
Jpar
Vy
YZ GSM Plane
B
Vx
Jpar
Vy
Cluster C1 position
~1800-1900 UT
Vx
Vy
XZ GSM Plane
P
XZ GSM Plane
XZ GSM Plane
Cluster C3 18, 19, 20 UT
Cluster C1 18, 19, 20 UT
SuperDARN noon-sector flow in agreement with Cluster C3 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?
78o
13
12
11 MLT
80o
82o
78o
13
12
11 MLT
80o
82o
IMF during
SuperDARN highlatitude noon
convection changes
TPA: Transpolar Aurora (Polar UVI)
Red Vertical Line: Time of DMSP F13
TPA Observation
TPA
TPA
IMF during
SuperDARN 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
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 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
R2
R1
NBZ
R1 R2
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 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
R1
NBZ
Clockwise Lobe Cell
R1
R2
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 splitTPA. 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:
  VB cos  2

2
4
l02
0