Characterizing Interplanetary Shocks at 1 AU

1. Characterizing Interplanetary Shocks at 1 AU J.C. Kasper1,2, A.J. Lazarus1, S.M. Dagen1 1MIT Kavli Institute for Astrophysics and Space Research 2jck@mit.edu Shocks: Daniel Berdichevsky, Chuck Smith, Adam Szabo, Adolfo Vinas ACE: John Steinberg, Ruth Skoug

2. Outline • Identifying shocks • Analysis of shocks • Methods • Selection of data • Timing • Compare methods • As a function of spacecraft separation • Validity of methods • Magnetic coplanarity • Velocity coplanarity • Radius of curvature • As a function of spacecraft separation • Compare with numerical simulation • Survey of shocks • Conclusions

3. How well can we analytically model shocks? • How well can we predict transit times of shocks? • How planar are interplanetary shocks? • How uniform are shock properties along shock surface?

4. Shock database • Catalogue all FF, SF, FR, SR, (& exotic) interplanetary shocks • Wind 300+ events online • ACE 200+ events online • IMP-8 300+ events (coming soon) • Voyager (ingested) • Helios, Ulysses (possibly) • Run every analysis method and save results • Each shock rated as “publishable” is online • http://space.mit.edu/~jck/shockdb.shockdb.html • Currently “living document” with frequent updates

5. Conservation of MHD equations

6. Rankine-Hugoniot Jump conditions

7. Prescription for RH analysis Combine some number of the remaining conservation equations and calculate deviation of jumps from zero A given direction determines the shock speed given density and velocity measurements Minimum in 2 determines shock direction Depth of minimum determines uncertainty Mass conservation equation is fulfilled explicitly

8. Simple methods Magnetic Coplanarity Velocity Coplanarity (VC)

9. Shock analysis: Science VS Art • What intervals do you select upstream and downstream? • 10 minutes unless there is a periodic fluctuation, than an integer number of oscillations • How many of the Rankine-Hugoniot equations should we use? • Add normal momentum flux and energy separately • What weighting to use for each equation? • Estimate measurement uncertainties • Standard deviation of equation differences • How valid are the simpler methods? • Survey as a function of shock parameters • Example – 1998 DOY 238 FF shock

10. Data selection

11. Shock orientation

12. Derived parameters

13. Shock inflow and outflow

14. Sometimes things aren’t as clear! • Small uncertainties in derived shock normals • Huge disagreement in shock direction • When are methods valid? • What’s the real uncertainty in the derived parameters?

15. Wind distant prograde orbit (DPO) • From mid 2000 to mid 2002 • Wind moves to ygse +/- 300 RE • yz up to 400 RE • An excellent database for studies of transverse structure

16. 110 events seen by ACE and Wind

17. Shock timing • The observed propagation time • spacecraft can be determined by lining up high resolution magnetic field data • 16 s ACE, 3 s Wind • The propagation delay can be predicted • using the locations and the derived shock parameters • Assumptions • Shock is planar • Spacecraft motion ra(ta) rw(ta) rw(tw)

18. Examples of timing delays

19. Examples of timing delays

20. Average timing error in minutes • Blue is average of the timing errors • Red is the average of the absolute values of the timing errors

21. Timing error for 110 events

22. Magnetic Coplanarity

23. Velocity Coplanarity

24. Compression ratio Wind ACE

25. Fast Mach numbers Wind ACE

26. θBn Wind ACE

27. Timing error and spacecraft separation • Examine timing error as a function of separation • Separation along shock surface • Minimum timing error 1 minute for small separations • Error increases with distance to 15 minutes at 250 RE • Non-planar shock or error in shock normal?

28. Radius of curvature of shock wave • To what extent is the shock surface not planar? • Calculate radius of curvature using shock normals determined at multiple locations • Could be sensitive to • Global structure • Local ripples • Error in shock normals Rc

29. Radius of curvature • Record shock normal and speed at ACE • Record shock normal and speed at Wind • Calculate propagation delay between ACE and Wind • Calculate location of ACE point at Wind observation time • Determine radius of curvature

30. Radius of curvature • All bets are off if Rc is smaller than then spacecraft separation • But larger separation leads to better determination of Rc

31. Comparison of Rc calculations • Determine observed time delay • Propagate one shock to time observed at other spacecraft • Compare Rc determined using each spacecraft • Minimum values are clustered at spacecraft separation • Maximum values at ~ 1 AU

32. Distribution of Rc • Different methods give different range in Rc • For MC, Rc is clustered at nominal spacecraft separation • RH has larges values of Rc on average MC VC RH Number of events Radius of curvature [AU]

33. Simulation of radius of curvature • Pick Rc and σθ • Place spacecraft • Calculate normals to give Rc • Draw angles from distribution and rotate • Calculate new Rc

34. Variation of Rc with separation • Error in the shock normal directions determines the rollover at small separations • Typical Rc sets asymptotic value • Consistent with typical Rc of 0.07-0.1 AU • Uncertainty in direction of 10 degrees

35. Statistical indicators of geoeffectiveness Following Jurac et al study in 2001 – 150 more events Minimum SYMH θBn θBn

36. Conclusions • Compared 110 shocks seen by Wind and ACE • In general very good agreement • Timing analysis • MX3 and RH08 perform best overall • Predict propagation to within 3 minutes • Survey methods • MC performs poorly for oblique and perpendicular shocks • VC performs poorly for low Mach number shocks • Radius of curvature consistent with 5o uncertainty in normals and Rc 0.1 AU • Results for all methods posted online • http://space.mit.edu/~jck/shockdb/shockdb.html