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Cycle 23 GLEs with ESPs

Cycle 23 GLEs with ESPs. Allan J. Tylka 11 February 2009. 4 - 8 November 2001. This event erupts from a source region near central meridian. It is not only a GLE, but also has a clear increase in intensity associated with the shock’s arrival at Earth.

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Cycle 23 GLEs with ESPs

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  1. Cycle 23 GLEs with ESPs Allan J. Tylka 11 February 2009

  2. 4 - 8 November 2001 • This event erupts from a source region near central meridian. • It is not only a GLE, but also has a clear increase in intensity associated with the shock’s arrival at Earth. • We are generally unable to track the neutron monitor response through the shock (large geomagnetic disturbances, etc.) • We therefore break the spectral analysis into two parts, each of which we fit with a Band function. • the “GLE” (the first 10 hours in this event, in which we have both satellite and NM data) and • the “ESP” (the rest of the event, based solely on GOES MEPAD+HEPAD).

  3. 4 - 8 November 2001 “GLE” “ESP” The “GLE” produces most of the fluence above ~1 GV, while the ESP dominates at lower rigidities.For dose-depth calculations, both parts should be included.

  4. Another Example: 14 - 18 July 2000 In this event, the ESP associated increase is not as large as in the previous example.

  5. 14 – 18 July 2000 “GLE” “ESP”

  6. Another Example: 28 – 29 October 2003 (The increase at ~21 UT on 29 October is the start of another GLE.)

  7. 28- 29 October 2003 “GLE” “ESP”

  8. Another Example: 24 -27 August 1998 This is one of the smallest GLEs of Cycle 23. We were unable to derive spectra from the NM data. Spectra are based solely on GOES MEPAD+HEPAD.

  9. 24- 27 August 1998 “GLE” “ESP”

  10. Band-Fit Parameters for the GLE-Associated ESPs of Cycle 23(Preliminary Results)

  11. How well do our Band fits reproduce the data? • Compare Band fits for ESPs to GOES/MEPAD datapoints at >10, >30, >50, >60, >100 MeV. • Calculate fractional residual: (Data-Fit)/Data • Mean Residual ~ 4% • RMS Width of Distribution of Residuals ~ 25 % (compared to 10% for GLEs). • This is a much wider distribution of residuals, probably because we do not have NM measurements to aide in the determination of the spectrum beyond 100 MeV. • Are these fits nevertheless adequate for dose calculations?

  12. How well do Exponentials reproduce the data? • Exponential fits did not use the GOES/MEPAD datapoint at 10 MeV in order to optimize the fit accuracy at above 30 MeV, which is more relevant threshold for many radiation hazards. • Mean Residual ~ 4%, same as with the Band fit • RMS Width of Distribution of Residuals ~12%, better than the Band fits’ ~25% • Since the exponential fits are constrained only by measurements in a limited energy (30-100 MeV), they do a better job than the Band fit at these energies. But the exponentials still seriously underestimate higher energies.

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