Anti-parallel versus
Component Reconnection
at the Magnetopause
K.J. Trattner
Lockheed Martin Advanced Technology Center
Palo Alto, CA, USA
and the
Polar/TIMAS, Cluster/CIS, Image/FUV teams
Outline
•
•
•
•
Reconnection: When, Where and Why
Where: The Cusp for Northward IMF
- Anti-parallel Reconnection
- Component Reconnection
Where: The Cusp for Southward IMF
- Component Reconnection
- Anti-parallel Reconnection
Summary
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Magnetic Reconnection
• When does reconnection occur – “all the time” (i.e., it
is a “quasi-steady” process)
– We have poor knowledge of the changes in the reconnection
rate
• Where does reconnection occur – recent observations
appear to favor anti-parallel reconnection but some
previous observations suggest component reconnection
– Work in progress……. Stay tuned!
• Why does reconnection occur – DON’T KNOW!
– The answer appears to be in the electron diffusion region
– Future mission (e.g., MMS) will have the time resolution and
instrumentation to fully investigate this region
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Magnetic Reconnection Near the Earth: Field
Line Topologies (for Southward IMF)
Blue - Solar Wind Field Lines
Green - Closed Field Lines
Red - Open Field Lines
Focus on “dayside” reconnection
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Observe Reconnection In Two
Locations
Cusp: “foot” of the reconnected field lines
• Does reconnection stop?
• Where does reconnection occur?
Each location has
its advantages
and disadvantages
Magnetopause: “up close and personal”
• What is the reconnection rate?
• Where does reconnection occur?
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When is Magnetic Reconnection
Occurring?
WHEN
Cusp Ion Energy Dispersion for Southward IMF
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WHEN:
Low- and High Altitude Cusp Observations
MLT = 3h
UT = 5h
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Trattner et al. [2002]
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Direct Confirmation of Images of the
Foot of a Reconnecting Field Line
• Images of the footpoint from
the IMAGE spacecraft
• Simultaneous observations
at the reconnection site from
the Cluster spacecraft
(bi-directional ion flows)
• Magnetic field mapping
confirms the location of the
ionospheric “spot”
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Observations Mapping
Does Reconnection Stop? You
Decide…..
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IMF Rotation from North to South:
Observations and Predictions
Although there is a delay, in general, there is
a simple change in the location of the reconnection site
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IMF Rotation from South to North:
Observations and Predictions
Similar for south to north transition – a delay but reconnection
does not stop, even when conditions change
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Where is Magnetic Reconnection
Occurring?
“WHERE is reconnection occurring?” boils down to two
models….
Antiparallel Reconnection
before reconnection
MP
Magnetic Reconnection
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after reconnection
MP
Component Reconnection
before reconnection
MP
after reconnection
MP
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Remote Sensing the High
Latitude Reconnection
Site
Sunward Motion of
Reconnected Field Lines
Magnetopause
IMAGE
spacecraft
Fast Ion
Auroral “Spot”
Slow Ion
Earth's Magnetic
Field in the
Magnetosphere
Sunward Convection Produces
Two Effects:
Auroral “Spot” in the Ionosphere
Velocity Dispersion in the Cusp
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Proton aurora images from IMAGE/FUV taken just before and after the
arrival of an interplanetary disturbance in the ionosphere.
Fuselier et al. [2002]
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Mapping cusp foot points along geomagnetic field lines into the
magnetosphere (Fuselier et al. [1994]).
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Comparison of the location of field lines
mapped from the cusp foot points with the
location of anti-parallel reconnection sites.
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The Location of the Reconnection Line for
Northward IMF
Polar/TIMAS Cusp Crossings
•
•
•
•
240 Cusp Events for Northward IMF.
81 events analyzed.
Calculate the Distance to the X-Line.
Mapping the Distance along the
Geomagnetic Field.
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Cusp Ion Energy Dispersion for Northward IMF
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Ion Dispersion in the Cusp:
Distance to the Reconnection Site
Source Distribution
(magnetosheath)
e
to
M
Lobe
reconnection
site
Cu
sp
Shocked
Solar Wind
magnetosphere
Observer
Extended Source
(Magnetopause)
ne
ag
Reflecting Wall
(ionosphere)
reconnection
site
us
pa
Xr
2Ve
=
X m (Vm - Ve )
Observed Distribution
(cusp)
Vm
Ve
slowest ions are from nearest
the reconnection site
Assumes: “Instantaneous” Acceleration
Simple Field Line Structure
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log f(v) km -6 s 3 log f(v) km -6 s 3 log f(v) km -6 s 3
9
8
7 May 1996
Polar/TIMAS
A
- :55
Ve 0529:43
INVLAT=81.9
7
6
5
4
8
B
7
Ve
0526:50 - 27:02
INVLAT=81.6
Vm
Xr/Xm = 2Ve/(Vm-Ve)
6
5
4
8
0517:25 - :37
INVLAT=81.1
C
Onsager et al. [1990]
Fuselier et al. [2000]
7
6
5
4
-800
-400
0
400
800
Velocity (km/s)
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The Location of the Reconnection
Line for Northward IMF
Event 1: Sept. 22, 1997
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Time (UT)
Convection time to the MP: 22min
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Tsyganenko [1996] together with Cooling [2001] IMF draping model
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The Location of the Reconnection
Line for Northward IMF
Event 2: Oct. 30, 1997
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81 events analysed
67 events with useable 3D cutoffs
29 antiparallel, 23 component, 15 >>Bx
-Bx, +By
Antiparallel
Reconnection
29 events
Component
Reconnection
23 events
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+Bx, +By
-Bx, -By
+Bx, -By
9 events
15 events
5 events
1200-1430
MLT
0900-1200
MLT
1000-1140
MLT
3 events
2 events
2 events
16 events
0830-1030
MLT
0930-1130
MLT
1700-1730
MLT
1700-1730
MLT
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Southward IMF: Anti-Parallel and
Component Reconnection
Anti-parallel merging
15
Equinox
Equinox
10
10
5
5
ZGSM [RE]
ZGSM [RE]
Tilted X-line
15
0
-5
0
-5
IMF
-10
IMF
-10
View from the Sun
-15
-15
-10
-5
0
YGSM [RE]
5
10
15
-15
-15
-10
-5
0
5
10
YGSM [RE]
Can we determine the distance THAT accurately?
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15
Precipitation is Different for the
Two Types of Reconnection
Anti-Parallel
Tilted Line
The Key
Difference is
The Flux Near
Noon
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Fuselier et al. [2002]
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Example: “Double Cusp” Interval –
Component or Anti-Parallel?
Trattner et al. (2003)
showed these are
spatial features
(energy-time(latitude)
dispersion indicative of
reconnection)
Compute the distance
to the reconnection site
for the two dispersions
and see if they are
different
First dispersion
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Second dispersion
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Two Different Distances for the
Two Dispersions
First Dispersion
Second Dispersion
(One distance for each
measured distribution function)
The second dispersion
occurred closer to the
spacecraft than the
first dispersion
Compare these distances
to predictions from antiParallel reconnection
Cluster
View from the Sun
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How Do the Distances Compare
with Anti-Parallel Reconnection?
“Red” = Anti-Parallel
Reconnection
Doesn’t compare
Exactly with AntiParallel Reconnection
Second Dispersion
First Dispersion
Get Some Help With the Interpretation….
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The Cusp Images Tell the
Difference Tilted Neutral Line
Anti-Parallel
Observations
Looks more like antiparallel reconnection
but with a shift relative
to local noon
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Conclusion: Anti-Parallel Reconnection (with a Local
Noon Shift)
The pure T96 model
does not show how
the northern hemisphere
reconnection line is
shifted ~1/2 hour pre-noon
However, the cusp images
do!
Second Dispersion
First Dispersion
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Summary
• NORTHWARD IMF: Image/FUV and
Polar/TIMAS observations reveal that both
reconnection scenarios occur simultaneously.
• SOUTHWARD IMF: Both reconnection
scenarios observed. Unclear what triggers one or
the other.
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WHEN: Multiple Cusps
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Anti-Parallel Reconnection for
Northward IMF
Northward IMF
Solar Wind
Magnetic
Field
Solar Wind
Z
Earth's Magnetic
Field in the
Magnetosphere
antiparallel
reconnection
sites
Y
cusps
magnetosheath
field
View of the Dayside magnetopause from the Sun
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Northward IMF
Poleward Reconnection Site
Equatorward Reconnection Site
Observations in the cusp have indicated the possibility of component reconnection for
northward IMF (e.g., Onsager and Fuselier, 1994; Chandler et al., 1999; Fuselier et al., 2000)
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