1 Determination of 3D CME Trajectories using Stereoscopy Paulett Liewer, Jeff Hall, Eric DeJong, JPL Vahab Pournaghsband, UCB Arnaud Thernisien and Russ Howard, NR L SECCHI Consortium, Orsay, March 2007

2 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

3 STEREO/SECCHI has 5 Telescopes 1 EUV & 4 White Light

4 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

5 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

6 A/Cor2A/Hi1A/Hi2 B/Cor2B/Hi2B/Hi :33:18 UT Sample Synthetic White Light Image Sequence Each frame shows A&B SC + 3 FOVs (Cor2, Hi1, Hi2) :04:38 UT :43:44 UT (a)(b) (c)(d) y -x SC A SC B Earth Sim 03 -separation 110°

7 3D Reconstruction of CME Loop Step 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/A cor2/B

8 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 R max 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

9 Tracked and Model Trajectories Latitude & Longitude at different times Radius, Velocity vs Time (model is dashed line) Sim 03 again Model X C2 + H1 * H2  SC A SC B Earth y -x

10 Summary Results from Six Simulations 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

11 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

12 Early Test on hemisphere CME for Tiepointing Bright Leading Edge Result: Leading Edge at 15.1 R sun vs actual 15 R sun 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

13 Consider Large SC Separations with CME in between x y SC A SC B

14 Consider Large SC Separations x y SC B SC A

15 Consider Large SC Separations Increasing Separation Angle Brings tangent points closer together LOS “tiepoint” moves closer to true leading edge x y SC A SC B SIMS 1,3,4,5,6 had separation ≥ 90 degrees

16 Sim02 had largest error in Longitude Each 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/Cor2B/Hi2B/Hi1 (a) (b) SC ASC B Earth y x Sim 02- separation 75°, latitude=64° Model longitude 313 ° Tracked longitude 335 °

17 Sim02: Tracked & Model Trajectories Latitude & Longitude at different times Radius, 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 X C2 + H1 * H2  separation 75°

18 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!

19 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