1 SEP Timing Studies: An Excruciatingly Brief Review Allan J. Tylka US Naval Research Laboratory, Washington DC SHINE 2006 Where was the CME when the SEPs first departed from the neighborhood of the Sun? How well can we answer this question? What are the results to date? Background Information: 2000 km/s ~ 1 Rs / 5 minutes I will emphasize uncertainties in the SEP departure-time determinations. Uncertainties in the CME height-time profile (due to limited image cadence, limited radial FOV, assumptions about the functional form) not covered here. (Ask Angelos or Gopal or Jie!) Zermatt, Utah, 31 July - 4 August 2006

2 Three Methods for SEPTiming Studies SHINE “Ballistic” Method: T Sun = T Earth - (1.2 AU) / v particle Examples: Kahler 1994; Haggerty et al Velocity Dispersion Analysis (“time vs. 1/β” plots) Examples: Lin et al. 1981; Reames et al. 1985; Krucker et al. 1999; Tylka et al. 2003; Mewaldt et al Assessment of Accuracy: Saiz et al Detailed Particle Transport Modeling To-date, generally applied only to neutron monitor observations Examples: Bieber et al. 2002; Saiz et al Zermatt, Utah, 31 July - 4 August 2006 Likely increase in accuracy and reliability, due to more input data and physics

3 Velocity Dispersion Method Example from Tylka et al Observed onset time at Earth plotted vs. 1/  Observed onset time at Earth plotted vs. 1/  particle Linear Fit : y-intercept gives solar release time y-intercept gives solar release time Slope gives effective pathlength (including scattering) Slope gives effective pathlength (including scattering) Method can give spurious due to limited instrumental sensitivity Important to have cross-checks among instruments Important to have cross-checks among instruments Lower energy particles (ions < 1 MeV/nuc; electrons <100 keV) often don’t fit on the same line: Ion trapping near the shock Ion trapping near the shock Multiple electron sources Multiple electron sources (  = particle speed in units of light speed)

4 Results from Velocity Dispersion Analyses “SPR” = Solar Particle Release time Classic “Impulsive” Event: SPR agrees with flare time Ground Level Event: SPR after flare SPR when CME is at ~ 2 Rs

5 Accuracy of Velocity Dispersion Results Saiz et al., ApJ 626, , 2005 Simulated Particle Time Profiles at 1 AU Analyze velocity dispersion just like real data Repeat for different assumptions about: rate of rise injection duration scattering conditions background levels How Good are the Results? Inferred – Actual Injection Times Some disasters Most conditions allow uncertainty < 5 minutes

6 Timing Results from Detailed Modeling of Particle Transport: Results from the Spaceship Earth Neutron Monitor Network Bieber et al. 2002, 2004; Saiz et al Advantages: Employs a sophisticated focused transport model Uses more input data: angular distributions & time-intensity profiles Extracts more information: onset, injection profiles at the Sun, scattering parameters, large-scale interplanetary structures. To date, generally applied to neutron monitor data – high energy, comparatively little scattering Disadvantages (?): Unclear how to assess residual systematics due to the assumptions in the structure of the transport model. Neutron monitor analysis is an art in itself! 2001 April January 20 Time at the Sun (ST)

7 Timing Results from Detailed Modeling of Particle Transport: Results from the Spaceship Earth Neutron Monitor Network Bieber et al. 2002, 2004; Saiz et al April January 20 Estimated release time here is 2.6 minutes earlier than the result from velocity-dispersion analysis (Tylka et al. 2003) Estimated CME height at SEP release: Rs Estimated CME height at SEP release: Rs (using the CME height-time profile from Gopalswamy et al ) Time at the Sun (ST)

8 Some Results This list contains only ~15% of the very large SEP events of Cycle 23. More thorough survey is needed. Among these events, estimated CME height is typically ~2 – 6 Rs

9 Sentinels: SEP Onset Studies at 0.35 AU Results from simulations carried out by Saiz et al. at the request of the Sentinels STDT

10Summary 1.Results to date suggest that the typical CME height when SEPs first depart the Sun in a large gradual event is ~2 – 6 Rs. SEP modeling efforts must deal with coronal conditions and shock characteristics at these altitudes. 2.Given these low altitudes, uncertainties in CME height-time extrapolation also become important. 3.Sentinels at ~0.35 AU will reduce SEP timing uncertainties to less than 1 minute, corresponding to a few tenths of Rs. A tight constraint, provided we have also have adequate imaging CME cadence, FOV, and resolution.

11 Backups

12 Ballistic Method SHINE 2006 Haggerty & Roelof 2002; Simnett, Haggerty, & Roelof, 2002 Zermatt, Utah, 31 July - 4 August 2006 Used near relativistic (~250 keV) electrons from ACE/EPAM Minimized potential scattering delays by selecting “beamed” events. Associated CMEs typically at 2-3 Rs from Sun center at the inferred time of electron departure from the Sun

13 More Examples Tylka et al. Proc 28 th ICRC (2003) In each case, the onsets are consistent with a common origin for electrons >100 keV and ions with energies ranging at least from ~2 MeV/nuc to the highest observable energies.

14 Comment on ACENews #72 Mewaldt et al. showed this analysis of the 2 April 2001 particle event. Using only ACE data, they reported a ~20 minute delay between the release of ~300 keV electrons and >10 MeV/nuc ions. Additional data from Wind and IMP8 do not support this conclusion. Instead, they show a common release time for ions and high-energy electrons. It appears that the onsets in the higher-speed ACE/SIS ions were not correctly identified, perhaps because of the relatively high pre-event background.

15 Comment on ACENews #72 ~80 MeV at Onset ~17 MeV at Onset These plots show IMP8/Chicago proton onsets in the 2 April 2001 event. They are at energies comparable to those of the ACE/SIS ions. But the higher-energy protons have an earlier onset than suggested by ACENews #72. (See previous plot.)