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## Characterizing Interplanetary Shocks at 1 AU

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**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**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**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?**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**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**Simple methods**Magnetic Coplanarity Velocity Coplanarity (VC)**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**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?**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**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)**Average timing error in minutes**• Blue is average of the timing errors • Red is the average of the absolute values of the timing errors**Compression ratio**Wind ACE**Fast Mach numbers**Wind ACE**θBn**Wind ACE**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?**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**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**Radius of curvature**• All bets are off if Rc is smaller than then spacecraft separation • But larger separation leads to better determination of Rc**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**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]**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**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**Statistical indicators of geoeffectiveness**Following Jurac et al study in 2001 – 150 more events Minimum SYMH θBn θBn**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