RECREATING THE THREE DIMENSIONAL STRUCTURE OF INTERPLANETARY CORONAL MASS EJECTIONS

1. RECREATING THE THREE DIMENSIONAL STRUCTURE OF INTERPLANETARY CORONAL MASS EJECTIONS Timothy A. Howard and S. James Tappin Air Force Research Laboratory, Space Vehicles Directorate, National Solar Observatory, Sunspot, NM. AGU Fall Meeting, 15-19 December, 2008

2. SH13B-1531 ABSTRACT With the abundance of heliospheric image data in recent years from the Solar Mass Ejection Imager (SMEI) aboard Coriolis and the Heliospheric Imagers (HIs) aboard STEREO it is of critical importance that the appearance of Interplanetary Coronal Mass Ejections (ICMEs) in these images be thoroughly understood. At large distances from the Sun, many of the standard assumptions required for producing measurements from images of Coronal Mass Ejections (CMEs) in coronagraphs do not apply. To extract meaningful physical parameters from ICME images it is necessary to consider the physics responsible for their appearance. We have developed a model based on a theory that builds up a picture of the observed ICME from the Thomson physics of a single electron, to an integrated line of sight, to a complete ICME including the consequences of its geometry relative to the observer. This has allowed us to extract the physical parameters responsible for the ICME appearance (kinematic properties and geometry) for any ICME from which reliable leading edge measurements can be made. We present the theoretical framework for the model and demonstrate its utility by discussing two ICMEs that were observed by SMEI in February and November 2004. Our results indicate the model has produced a reliable convergence for these events and the extracted parameters corresponding to the structure and timing of the event observed with the heliospheric imagers and the available in-situ measurements from the ACE spacecraft. We conclude with a discussion of the physics responsible for the evolution of this ICME.

3. The Current Problem With Modeling Interplanetary Coronal Mass Ejections Models that produce simulated ICME images tend to couple two problems: • The physics of ICME appearance. This is a combination of the Thomson scattering physics determining white and polarized brightness, and relative geometry. • The physics of ICME evolution. This describes the kinematic and geometrical evolution in terms of the driving physics and those of the interaction with the interplanetary medium. This leads to confusion as it is unknown whether inadequacies in the model are due to incorrect evolution physics or simple the result of projection effects. We have devised a model that extracts the geometrical and kinematic features of ICMEs directly from the data, thus allowing the de-coupling of these two problems.

4. Appearance Two aspects: • Apparent Brightness. This is governed by the physics of Thomson scattering and is related to ICME location and direction. For a single electron, the scattered intensity is maximized along the locus of points forming a ½ AU sphere between the Observer (O) and the Sun (S). This is at the point P for the given line of sight (LOS), so any electron at Q will have a scattered intensity that is related to its distance from P. NOTE:The scattered light is maximized NOT because of the Thomson scattering itself, but because this happens to the point along the LOS that is closest to the Sun. That is, the point of maximum incident intensity and maximum density. In fact, the scattered light itself is MINIMIZED at this point, but the former two factors significantly overcome the latter.

5. Appearance Two aspects: • Geometry. For example, the leading edge of an ICME, the most common feature used for height-time and geometry measurements, changes significantly as the ICME moves outward. δr Here we demonstrate (using a simple spherical ICME structure) how the assumption of same location for leading edge measurement (the o’s) leads to a large discrepancy (δr) in distance approximation at large distance from the Sun (S). The actual leading edge (the x’s) moves closer to the observer (O) as distance increases.

6. The TH Model The Tappin & Howard (TH) model produces an estimation of ICME geometry and kinematics by comparing leading edges measured in heliospheric image data with those from simulated ICMEs. 1. Bubble • Two basic structures are chosen: • A sphere (bubble); • A spherical arc, solar centered (shell). • Then independent combinations of: • Speed • Distance • Central Latitude • Central Longitude • Latitude Width • Longitude Width • Distortion Parameter • Are combined to produce ICME simulated images from which leading edges are produced relative to a fixed observer. Observer Sun 2. Shell Observer Sun

7. The TH Model The product is a 6 (5) dimensional hypercube containing elongation-position angle (ε,PA) traces of leading edges for simulated ICMEs for each combination of parameters. Over 300 000 traces are included. Then the hypercube is compared with a sequence of leading edge measurements from actual ICMEs observed in heliospheric image data. A genetic algorithm is used to perform the correlation between data and model, with the objective of minimizing the elongation and position angle difference between. A simplex method application completes the convergence. The end result is a unique combination of parameters describing the ICME that best matches the leading edge trace sequence from the data.

8. The TH Model The TH model is run in 2 stages: Stage 1 converges to a solution containing a unique combination of each of the parameters. Along with a fixed direction and structure, this also produces a single speed, allowing only for a constant speed ICME. Stage 2 considers smaller subsets of data measurements, leaving the direction and structure fixed, but allowing the speed parameter to vary from one combination to another. Employing Stage 2 allows us to monitor small changes in the kinematics of the ICME, particularly variations in speed and acceleration. D t D t

9. Results Event 1: 15-18 February, 2004 The CME Component Coronagraph (LASCO) Parameters Onset Date Time Speed Central PA PA Width 2004/02/15 03:54 UT 450 km/s 36°S 101°W

10. Results Event 1: 15-18 February, 2004 The ICME Component Converging parameters: Shell Speed Central Central Latitude Longitude Latitude Longitude Width Width 450 km/s 36°S 101°W 35° 30°

11. Results Event 1: 15-18 February, 2004 Sun Earth From the perspective of the Ulysses spacecraft

12. Height and Speed Plots Event 1: 15-18 February, 2004 SMEI Model LASCO Data

13. Results Event 2: 30 November-05 December, 2004 The CME Component Coronagraph (LASCO) Parameters Onset Date Time Speed Central PA PA Width 2004/12/03 00:26 UT 1200 km/s N/A 360°

14. Results Event 2: 30 November-05 December, 2004 The ICME Component Converging parameters: Shell Speed Central Central Latitude Longitude Latitude Longitude Width Width 360 km/s 39°N 6°E 27° 39°

15. Results Event 2: 30 November-05 December, 2004 Sun Earth From the perspective of the Ulysses spacecraft

16. Height and Speed Plots Event 2: 30 November-05 December, 2004 SMEI Model ACE Shock LASCO Data

17. Discussion Event 1: The TH model independently converged to a solution with a size and location consistent with the solar surface data. The location, just behind the solar limb, is especially encouraging. Converged kinematic properties reveal a deceleration, then an acceleration in the ICME’s trajectory through the field of view of SMEI. The connection between LASCO CME and SMEI ICME is clear, and remarkable. Event 2: The TH model identified multiple separate ICMEs observed during the same time period observed by SMEI. We have only shown one here. The ICME could be connected with a LASCO ICME meeting the correct angular span, speed and time range of the SMEI events if we allow for a slight deceleration, and the location was consistent with the solar surface information. Projected time of arrival of the ACE shock for the Halo CME was remarkably accurate. We predict an arrival time at ACE only 19 minutes late.

18. Conclusions • The TH model worked remarkably well at identifying ICME, launch location, structure and kinematic evolution. • The model converged to a solution that allowed accurate CME association and prediction of arrival time at 1 AU. • We have successfully identified a method allowing for the de-coupling of the two problems of ICME appearance and evolution physics, thus allowing the first study of ICME evolution characteristics independent of appearance issues. • Given the latency of the model (~ 1 hour per event), the potential for the use of the TH model as a tool for space weather forecasting is clear and encouraging. References Papers to look out for... Howard, T.A., and Tappin, S.J., Interplanetary coronal mass ejections observed in the heliosphere: 1. Review of theory, Space Sci Rev., submitted. Tappin, S.J., and Howard, T.A., Interplanetary coronal mass ejections observed in the heliosphere: 2. Model and data comparison, Solar Phys., submitted. Howard, T.A., and Tappin, S.J., Interplanetary coronal mass ejections observed in the heliosphere: 3. Physical implications, in preparation. Howard, T.A., Tappin, S.J., and Hampson, M.M., Interplanetary coronal mass ejections observed in the heliosphere: 4. Statistical survey, in preparation.