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Determination of 3D CME Trajectories using Stereoscopy

Paulett Liewer, Jeff Hall, Eric DeJong, JPL

Vahab Pournaghsband, UCB

Arnaud Thernisien and Russ Howard, NRL

SECCHI Consortium, Orsay, March 2007

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Summary

• We use synthetic stereoscopic white light image pairs to test 3D trajectory determination using “triangulation”– Image sequences created from flux rope CME model by

A. Thernisien, et al (ApJ 2006)

• We obtained good agreement with model parameters for CME velocity, longitude and latitude for 6 blind tests

• We address why triangulation works on “features” resulting from LOS integration

STEREO/SECCHI will provide stereoscopic images of CME propagation from the Sun to Earth

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STEREO/SECCHI has 5 Telescopes1 EUV & 4 White Light

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CME Model & Synthetic White Light Images A. Thernisien, et al ApJ 2006• Start with Flux Rope Model

CME with density only near surface. CME moves out radially at constant prescribed velocity

• Assume a spacecraft separation & calculate time sequence for 3 SECCHI FOVs

• Calculate white light images using Thomson scattering

Left: view along LOS arrow shown in on right. Black disk is occultor. From Thernisien et al 2006

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CME Blind Tests

• Thernisien gave us 7 CME cases:– White lights images for COR2, HI1 & HI2

for SC A&B (time sequence of stereo pairs) – SC locations (longitudes, latitude, and

distance from Sun)

• CME direction and velocity unknown

• We used tiepointing, loop tracing and triangulation to track these model CMEs

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A/Cor2A/Hi1A/Hi2

B/Cor2 B/Hi2B/Hi1

2008 07 08 14:33:18 UT

Sample Synthetic White Light Image SequenceEach frame shows A&B SC + 3 FOVs (Cor2, Hi1, Hi2)

2008 07 08 17:04:38 UT

2008 07 09 10:43:44 UT

(a) (b)

(c) (d)

y

-x

SC A

SC BEarth

Sim 03 -separation 110°

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3D Reconstruction of CME LoopStep 1: User selects ‘seed’ point (X) on the bright CME

leading edge in each image of the stereo pair with cursor tool restricts movement to same latitude

Step 2: Routine sunloop traces bright “loop” and uses triangulation on points on the loop to obtain 3D reconstruction of the arcs in the two images

Repeated for each stereo pair in time sequence

sim04_144046_

cor2/Acor2/B

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Step 3: View the Results of the 3D Reconstruction

• Tool creates a 3D object: the reconstructed leading edge• 3D object can be rotated with cursor/trackball

• Edge coordinates are also written to an ascii file• Files analyzed to find Rmax and its latitude & longitude to track “location” of CME vs time

Note: Original model was a 3D flux tube surface whereas our

reconstruction is a curve in 3D

Here, CME leading edge at two times

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Tracked and Model TrajectoriesLatitude & Longitude at

different times

Radius, Velocity vs Time(model is dashed line)

Sim 03 again

Model XC2 + H1 * H2

SC A

SC BEarth

y

-x

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Summary Results from Six Simulations

SIMSep Angle (degrees)

Velocity (tracked)

Velocity (model)

velocity error (%)

latitude (tracked)

longitude (tracked)

latitude (model)

longitude (model)

latitude error

(degrees)

longitude error

(degrees)

1 100 666.26 620 7.5 -23.06 177.17 -28.5 173 5.4 4.2

2 75 552.87 545 1.4 49.43 335.14 64 313 14.6 22.1

3 110 643.23 690 6.8 2.56 244.51 1.50 259.00 1.1 14.5

4 110 773.50 789 2.0 -9.31 178.75 -9.00 178.50 0.3 0.2

5 120 636.53 643 1.0 44.80 286.42 48.00 292.00 3.2 5.6

6 90 739.92 703 5.3 18.09 27.21 19.50 24.50 1.4 2.7

Why are the results so good? Bright leading edge is a LOS effect!

Very good agreement: <10% error on velocities and < 10º on latitude

and longitude for most

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Why does this work?

• Stereoscopy works when tiepoint same feature from 2 viewpoints

• CME bright leading edge is not a real feature, but rather a result of LOS integration through a diffuse object

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Early Test on hemisphere CME

for Tiepointing Bright

Leading Edge

Result: • Leading Edge

at 15.1 Rsun vs actual 15 Rsun

• Angle of 72° vs actual 60°

COR2 - SC B at +20°COR2 - SC A at -20°

60°

x

y

+20°

-20°

SC A

SC B

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Consider Large SC Separations with CME in between

x

y

SC A

SC B

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Consider Large SC Separations

x

y

SC B

SC A

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Consider Large SC Separations

Increasing Separation Angle

• Brings tangent points closer together

• LOS “tiepoint” moves closer to true leading edgex

y

SC A

SC B

SIMS 1,3,4,5,6 had separation ≥ 90 degrees

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Sim02 had largest error in LongitudeEach frame shows A&B SC + 3 FOVs (Cor2, Hi1, Hi2)

Lines cross (1) out front of CME and(2) At larger (towards 360 °) longitude as obtained with tracking

A/Cor2A/Hi1A/Hi2

B/Cor2 B/Hi2B/Hi1

(a)

(b)

SC ASC B

Earth

y

x

Sim 02- separation 75°, latitude=64°Model longitude 313 ° Tracked longitude 335 °

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Sim02: Tracked & Model TrajectoriesLatitude & Longitude at

different timesRadius, Velocity vs Time

(model is dashed line)

SC ASC B

Earth

y

x

Lines cross (1) out front of CME and

(2) At larger longitude, as obtained with tracking

Model XC2 + H1 * H2

separation 75°

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Sim07: New case with 30º separation• We are still analyzing this case• For this much smaller separation angle case, Sunloop

automatic loop tracing led to false solution• Reconstructed curve was off by very large angles (50-70°)

in both latitude and longitude

• Tiepointing WITHOUT use of automatic loop tracing gave good results

• More to do!

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Conclusions• Can determine CME trajectory (speed, direction)

using stereoscopy on white light images for large separation angles

• For large angles, errors relatively small - <10% on velocity, a few degrees on direction

– Size of error depends on viewing geometry

• Now analyzing results for smaller separation angles

• Ready to test on STEREO/SECCHI data!

• May lead to improved Space Weather prediction