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
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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
Magnetopause Current Sheet
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Observe Reconnection In Two Locations
Cusp: “foot” of the reconnected field lines• Does reconnection stop?• Where does reconnection occur?
Magnetopause: “up close and personal”• What is the reconnection rate?• Where does reconnection occur?
Each location hasits advantagesand disadvantages
When is Magnetic Reconnection Occurring?
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WHENCusp Ion Energy Dispersion for Southward IMF
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MLT = 3hUT = 5h
Trattner et al. [2002]
WHEN:Low- and High Altitude Cusp Observations
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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”
Observations Mapping
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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 isa 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 reconnectiondoes not stop, even when conditions change
Where is Magnetic Reconnection Occurring?
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Antiparallel Reconnection
MP MP
before reconnection after reconnection
Component Reconnection
MP MP
before reconnection after reconnection
“WHERE is reconnection occurring?” boils down to twomodels….
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Remote Sensing the High Latitude Reconnection Site
Earth's MagneticField in theMagnetosphere
Sunward Motion ofReconnected Field Lines
Fast Ion
Slow Ion
Auroral “Spot”
Magnetopause
Sunward Convection ProducesTwo Effects:Auroral “Spot” in the IonosphereVelocity Dispersion in the Cusp
IMAGEspacecraft
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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
Re
flect
ing
Wa
ll (
ion
osp
he
re)
Ext
en
de
d S
ou
rce
(M
ag
ne
top
au
se)
Observer
reconnection site
Source Distribution (magnetosheath)
Observed Distribution (cusp)
VeVm
slowest ions are from nearest the reconnection site
X r
X m=
e(V - V )m
2Ve
Shocked Solar Wind
Magnetopause
Lobe
magneto- sphere
Cusp
reconnection site
Assumes: “Instantaneous” Acceleration Simple Field Line Structure
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4
5
6
7
8
9
4
5
6
7
8
8004000-400-800
4
5
6
7
8
Velocity (km/s)
log
f(v
) k
m
s
-63
log
f(v
) k
m
s
-63
log
f(v
) k
m
s
-63
0529:43 - :55 INVLAT=81.9
0526:50 - 27:02 INVLAT=81.6
0517:25 - :37 INVLAT=81.1
A
B
C
Ve
Ve
Vm
7 May 1996 Polar/TIMAS
Xr/Xm = 2Ve/(Vm-Ve)
Onsager et al. [1990]
Fuselier et al. [2000]
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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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-Bx, +By +Bx, +By -Bx, -By +Bx, -By
Antiparallel
Reconnection
29 events
9 events
1200-1430
MLT
15 events
0900-1200
MLT
5 events
1000-1140
MLT
Component
Reconnection
23 events
3 events
0830-1030
MLT
2 events
0930-1130
MLT
2 events
1700-1730
MLT
16 events
1700-1730
MLT
81 events analysed67 events with useable 3D cutoffs29 antiparallel, 23 component, 15 >>Bx
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Southward IMF: Anti-Parallel and Component Reconnection
-15
-10
-5
0
5
10
15
ZG
SM
[R
E]
-15 -10 -5 0 5 10 15
YGSM [RE]
Equinox
IMF
Anti-parallel merging
-15
-10
-5
0
5
10
15
ZG
SM
[R
E]
-15 -10 -5 0 5 10 15
YGSM [RE]
Equinox
IMF
Tilted X-line
Can we determine the distance THAT accurately?
View from the Sun
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Precipitation is Different for the Two Types of Reconnection
Anti-Parallel
Tilted Line
The KeyDifference is
The Flux NearNoon
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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 arespatial features(energy-time(latitude) dispersion indicative of reconnection)
Compute the distanceto the reconnection sitefor the two dispersionsand see if they aredifferent
First dispersion Second dispersion
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Two Different Distances for the Two Dispersions
View from the Sun
First Dispersion Second Dispersion
The second dispersionoccurred closer to thespacecraft than thefirst dispersion
Compare these distancesto predictions from anti-Parallel reconnection
(One distance for eachmeasured distribution function)
Cluster
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How Do the Distances Compare with Anti-Parallel Reconnection?
Second Dispersion First Dispersion
“Red” = Anti-ParallelReconnection
Doesn’t compareExactly with Anti-Parallel Reconnection
Get Some Help With the Interpretation….
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The Cusp Images Tell the Difference
Looks more like anti-parallel reconnectionbut with a shift relativeto local noon
Observations
Anti-Parallel Tilted Neutral Line
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Conclusion: Anti-Parallel Reconnection (with a Local Noon Shift)
Second Dispersion First Dispersion
The pure T96 modeldoes not show howthe northern hemispherereconnection line isshifted ~1/2 hour pre-noon
However, the cusp imagesdo!
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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
antiparallel reconnection sites
Z
magnetosheath field
cuspsY
View of the Dayside magnetopause from the Sun
Magnetopause
Earth's Magnetic Field in the Magnetosphere
Solar Wind Magnetic Field
Solar Wind
Northward IMF
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Northward IMFPoleward Reconnection Site Equatorward Reconnection Site
Observations in the cusp have indicated the possibility of component reconnection fornorthward IMF (e.g., Onsager and Fuselier, 1994; Chandler et al., 1999; Fuselier et al., 2000)