anti-parallel versus component reconnection at the magnetopause

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

Magnetic Reconnection Cambridge, Aug., 2004

2

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…..

D:\data\ktrattne\Documents\presentations\ppt_other\2004_gem_Fuselier_Student_Tutorial\reconFINAL.mov


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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

magnetosphere

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]



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Event 1: Sept. 22, 1997


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Time (UT)Convection time to the MP: 22min


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26


27


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Tsyganenko [1996] together with Cooling [2001] IMF draping model


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Event 2: Oct. 30, 1997


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31


32


33


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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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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)

anti-parallel versus component reconnection at the magnetopause

Documents

reconnection line

reconnection ratewhere

region magnetic reconnection

reconnection siteimf

location of field lines

magnetic field mapping

geomagnetic field lines

field line topologies