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SHINE 2008 June, 2008 Utah, USA Visit our Websites: http://www.thaispaceweather.com http://neutronm.bartol.udel.edu/ E-mail: [email protected] Relativistic Solar Protons on 2006 December 13 David Ruffolo, 1 John W. Bieber, 2 John Clem, 2 Paul Evenson, 2 Roger Pyle, 2 Alejandro Sáiz, 1 & Maneenate Wechakama 3 Univ., Bangkok 2 Univ. Delaware 3 Kasetsart Univ., 1
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SHINE 2008 June, 2008 Utah, USA

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Relativistic Solar Protons on 2006 December 13. SHINE 2008 June, 2008 Utah, USA. David Ruffolo, 1 John W. Bieber, 2 John Clem, 2 Paul Evenson, 2 Roger Pyle, 2 Alejandro Sáiz, 1 & Maneenate Wechakama 3. - PowerPoint PPT Presentation
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Page 1: SHINE 2008                  June, 2008                      Utah, USA

SHINE 2008 June, 2008 Utah, USA

Visit our Websites: http://www.thaispaceweather.com http://neutronm.bartol.udel.edu/

E-mail: [email protected]

Relativistic Solar Protons on 2006 December 13

David Ruffolo,1 John W. Bieber,2

John Clem,2 Paul Evenson,2 Roger Pyle,2

Alejandro Sáiz,1 & Maneenate Wechakama3

1Mahidol Univ., Bangkok 2Univ. Delaware 3Kasetsart Univ., Bangkok

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Page 2: SHINE 2008                  June, 2008                      Utah, USA

The “maverick” GLE of December 13, 2006: It occurred near solar minimum, but it was a large event, exceeding 100% increase at Oulu

Page 3: SHINE 2008                  June, 2008                      Utah, USA

• A blow-up of the peak region reveals some strange features: Mawson initially recorded the fastest rise, but then decreased while Apatity continued rising

• We believe this may be caused small shifts in the angular distribution axis of symmetry, coupled with a highly anisotropic pitch angle distribution

Page 4: SHINE 2008                  June, 2008                      Utah, USA

Spaceship EarthAsymptotic Viewing Directions at Start of Event

• Circles show station geographical locations

• Open squares show asymptotic direction for a median rigidity solar particle

• Lines show range (10- to 90-percentile rigidity) of viewing directions for each station

• Circled dot and circled X denote nominalSunward and anti-Sunward Parker directions, respectively

Page 5: SHINE 2008                  June, 2008                      Utah, USA

MAPPING RADIATION INTENSITY IN POLAR REGIONS: METHOD

• First, the asymptotic viewing directions of the neutron monitor array are determined, and the cosmic ray pitch angle distribution (here modeled as a constant plus exponential function of pitch angle cosine) is computed in GSE coordinates by least-square fitting

• To form the map, a preliminary computation is done at each grid point to determine if a 1 GV proton is “allowed.” If it is, then that location is considered to have a geomagnetic cutoff below the atmospheric cutoff, and the grid point is included in the map.

• The asymptotic viewing direction at the center of the grid point is then computed in GSE coordinates for a median rigidity particle, permitting the “pitch angle” for the location to be determined.

• From the model pitch angle distribution, the predicted intensity for that grid point is computed and plotted by color code.

Page 6: SHINE 2008                  June, 2008                      Utah, USA
Page 7: SHINE 2008                  June, 2008                      Utah, USA

Event Modeling

• Step 1: Individual station data were fitted to an angular distribution of the form

f(μ) = c0 + c1 exp(b μ), with μ cosine of pitch angle, and c0, c1, and b free parameters. The

symmetry axis from which pitch angles are measured was also a free parameter.

Page 8: SHINE 2008                  June, 2008                      Utah, USA
Page 9: SHINE 2008                  June, 2008                      Utah, USA

Event Modeling

• Step 2: The first 3 Legendre coefficients, f0, f1, f2, of the derived distribution were computed from f(μ). They are shown at left as “Density”, “Weighted Anisotropy”, and “2nd Legendre.” Longitude and latitude of the derived symmetry axis are also shown, as is the ordinary anisotropy, f1/f0.

Page 10: SHINE 2008                  June, 2008                      Utah, USA

t: time, f: cosmic ray phase space density, μ: cosine of pitch angle, v: particle speed, z: distance parallel to mean field, L: magnetic focusing length, defined by L-1 = (-1/B) dB/dz, Ф(μ): Fokker-Planck coefficient for pitch angle scattering, q: source term

• The Boltzmann equation for cosmic ray transport is solved numerically to yield predictions for the cosmic ray density and anisotropy vs time. Fitting anisotropy as well as density is crucial for separating effects of interplanetary diffusion from extended acceleration or release at the Sun.

• Scattering strength is usually quantified by the parallel mean free path λ║ or diffusion coefficient K║ which are related to Ф(μ) by:

Page 11: SHINE 2008                  June, 2008                      Utah, USA

Event Modeling: Standard Parker Field• Step 3: The Legendre

coefficients as functions of time are fitted to numerical solutions of the Boltzmann equation. Free parameters are the scattering mean free path and profile of particle injection at the Sun, represented by a piecewise-linear function.

• A standard Parker IMF does not yield a satisfactory fit: The optimal mean free path of 0.23 AU provides a good fit to density, but not to weighted anisotropy or 2nd Legendre.

• Based on our experience modeling the Bastille event, we suspect a downstream magnetic mirror may be affecting transport in this event.

Page 12: SHINE 2008                  June, 2008                      Utah, USA

Magnetic Mirrors in the Solar Wind

• GLE particles are sometimes injected into a normal Parker background field, as in (a) – e.g., Easter GLE

• But frequently they are injected into a background that is highly disturbed as a result of earlier events from the same active region. In (b), particles mirror from a magnetic bottleneck downstream of Earth. We believe this configuration existed in the Bastille Day 2000 event [Bieber et al., Astrophys. J., 567, 622 (2002)].

• Sometimes particles are injected into a closed magnetic loop, as in (c). We believe this configuration explains the highly unusual October 22, 1989 event.

• Figure is from Ruffolo et al., Astrophys. J., 639, 1186 (2006).

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Page 13: SHINE 2008                  June, 2008                      Utah, USA

Event Modeling: Downstream Magnetic Bottleneck (Preliminary)

• A bottleneck fit works much better. Here, the optimal mean free path is much larger, 1.08 AU, and the optimal bottleneck location is at 1.52 AU.

Page 14: SHINE 2008                  June, 2008                      Utah, USA

A Downstream Magnetic Mirror Is Supported by a “Fearless Forecast” of the IMF Configuration

• A “Fearless Forecast” (left) suggests Earth was connected to a downstream compression region at ~1.5 AU at event onset

• This is reminiscent of the Bastille event, in which transport was affected by a downstream magnetic bottleneck [Bieber et al., Astrophys. J., 567, 622-634, 2002]

Fearless forecast from http://gse.gi.alaska.edu/recent/archive/20061212/ec8_recent.pdf 14

Page 15: SHINE 2008                  June, 2008                      Utah, USA

SUMMARY• Neutron monitors measure solar cosmic rays with

energy >400 MeV. Modeling data from a suitable array of stations permits determination of:– Injection onset to ~1 minute precision– Injection time profile– Interplanetary scattering mean free path– Scattering “q” parameter

• Two events were presented as examples– Start time of relativistic proton injection (0640 ST ± 2 min.

on 2005 Jan 20, 0240 ST ± 2 min. on 2006 Dec 13, for ST= solar time) can be compared with observations of electromagnetic radiation from flare and CME.

• Mirroring from large-scale interplanetary structures (e.g., loops, bottlenecks) is an important factor in modeling GLE transport (“Kings Do Not Travel Alone” – A. Belov)

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