1. Workshop on Extension of the European Neutron Monitor Database October 13-15, 2010 Newark, Delaware Spaceship Earth John W. Bieber Bartol Research Institute and Department of Physics and Astronomy University of Delaware University of Delaware Collaborators: John Clem, Paul Evenson, Roger Pyle Visit our Website: http://neutronm.bartol.udel.edu/

2. WHAT IS A NEUTRON MONITOR ? A large instrument, weighing ~32 tons (standard 18-tube NM64) Detects secondary neutrons generated by collision of primary cosmic rays with air molecules Detection Method: –Older type – proportional counter filled with BF 3 : n + 10 B → α + 7 Li –Modern type – counter filled with 3 He: n + 3 He → p + 3 H Neutron Monitor in Nain, Labrador Construction completed November 2000

3. SPACESHIP EARTH NEUTRON MONITOR ARRAY 12 Stations on 4 continents Multinational participation: USA, Russia, Australia, Canada Optimized to measure angular distribution of GeV solar cosmic rays –9 stations view equatorial plane at 40-degree intervals –Thule, McMurdo, Barentsburg provide crucial 3-dimensional perspective Below: Solid symbols denote station geographical locations. Average viewing directions (open squares) and range (lines) are separated from station locations because particles are deflected by Earth's magnetic field. STATION CODES IN: Inuvik, Canada FS: Fort Smith, Canada PE: Peawanuck, Canada NA: Nain, Canada BA: Barentsburg, Norway MA: Mawson, Antarctica AP: Apatity, Russia NO: Norilsk, Russia TB: Tixie Bay, Russia CS: Cape Schmidt, Russia TH: Thule, Greenland MC: McMurdo, Antarctica The Instrument is the Array

4. Why are all the stations at high latitude? Prime Reason: Excellent directional sensitivity for solar cosmic rays Trajectories are shown for vertically incident primaries corresponding to the 10-, 20-, … 90-percentile rigidities of a typical solar spectrum

5. Modeling Solar Cosmic Rays: The January 20, 2005 GLE Transport modeling (preliminary) performed in collaboration with Dr David Ruffolo and Dr Alejandro Sáiz Mahidol University, Bangkok

6. THE RECORD-SETTING JANUARY 20, 2005 GROUND LEVEL ENHANCEMENT (GLE) Terre Adelie increase (not shown) was 46X over 6 min – largest increase at sea level since famous 1956 event South Pole increase was 56X, largest ever recorded by a neutron monitor! This distinction is partly owing to South Pole’s unique location at high latitude and high altitude (2820 m) Event was enormously anisotropic: Neutron rate increase at other high-latitude stations was an order of magnitude smaller – “only” 3X or so

7. STATION VIEWING DIRECTIONS AT GLE ONSET STATION CODES FS: Fort Smith, Canada TH: Thule, Greenland MC: McMurdo, Antarctica NA: Nain, Canada SP: South Pole, Antarctica BA: Barentsburg, Norway MA: Mawson, Antarctica AP: Apatity, Russia NO: Norilsk, Russia TB: Tixie Bay, Russia CS: Cape Schmidt, Russia IN: Inuvik, Canada Squares show the asymptotic viewing direction of a median energy (1.4 GeV) solar cosmic ray. Lines encompass the central 80% of detector energy response, extend- ing from the direction of a 0.5 GeV particle to that of a 4.6 GeV particle. Directions of the nominal inward (“O”) and outward (“X”) Parker spiral are also shown.

8. DENSITY, ANISOTROPY, AND CURVATURE EXTRACTED FROM NETWORK DATA Data of the 12 individual stations were used to derive the cosmic ray pitch angle distribution, which we characterize as a Legendre polynomial expansion out to 2 nd order. The zeroth-order coefficient is simply the cosmic ray density. We term the first-order coefficient “weighted anisotropy.” It is simply density times the ordinary anisotropy. We sometimes term the second- order Legendre coefficient “curvature.” Curvature provides insights into the possible influence of trapping or mirroring by magnetic structures.

9. TRANSPORT MODELING WITH BOLTZMANN EQUATION Standard Parker field assumed Transport is modeled using numerical solutions of the Boltzmann equation for cosmic ray transport, including effects of focusing and pitch angle scattering (sometimes called Roelof’s equation) Quantities derived by least- square fitting: –Interplanetary scattering mean free path –Injection function at Sun (here characterized by a piecewise linear function)

10. A downstream magnetic bottleneck on the flanks of ejecta can produce mirroring resulting in the density “bump” and enhanced “curvature”

11. TRANSPORT MODELING WITH BOLTZMANN EQUATION Parker field with downstream magnetic bottleneck Quantaties derived from modeling: –Scattering mean free path –Injection profile –Distance to downsteam bottleneck –Reflection coefficient of bottleneck

12. SUMMARY OF TRANSPORT MODELING

13. A Downstream Magnetic Bottleneck Is Supported by a “Fearless Forecast” of the IMF Configuration A “Fearless Forecast” (above) suggests Earth was connected to a downstream compression region at ~1.6 AU at event onset This is reminiscent of the Bastille event, in which transport was affected by a downstream magnetic bottleneck (Bieber et al., J. Geophys. Res., 567, 622-634, 2002) Fearless forecast from http://gse.gi.alaska.edu/recent/archive/20050119/ec8_recent.pdf

14. 2005 January 20 Type III Burst

15. DERIVED INJECTION PROFILE (PRELIMINARY) COMPARED WITH SOLAR RADIO BURST Derived injection profile is remarkably similar to 5 MHz radio profile 8 min has been added to injection profile to facilitate comparison with radio data Universal Time 2005 January 20

16. Space Weather Uses of Spaceship Earth

17. SPACESHIP EARTH STATIONS ARE WELL SITUATED TO ALERT / MONITOR RADIATION HAZARD ON POLAR AIRLINE ROUTES Line shows Chicago-Beijing great circle route. Squares are Spaceship Earth stations. (Two in Antarctica are not shown.)

18. Neutron Monitors Can Provide the Earliest Alert of a Solar Energetic Particle Event In the January 20, 2005 GLE, the earliest neutron monitor onset preceded the earliest Proton Alert issued by the Space Environment Center by 14 minutes.

19. In this study, a GLE alert is issued when 3 stations of Spaceship Earth (plus South Pole) record a 4% increase in 3-min averaged data With 3 stations, false alarm rate is near zero GLE Alert precedes SEC Proton Alert by ~ 10-30 min For details, see Kuwabara et al., Space Weather, 4, S10001, 2006.

20. GLE Alarm Implemented (Beta version) Developed primarily by Dr Takao Kuwabara To receive automated e- mail alerts of possible GLE, send e-mail request to: jwbieber@bartol.udel.edu

21. 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.

23. Spaceship Earth SCIENCE OUTCOMES Precise, high-time- resolution measurement of solar cosmic ray angular distribution Numerical modeling of interplanetary transport –Key source of information on the parallel mean free path Role of mirroring from structures in disturbed interplanetary medium –Magnetic bottleneck on flanks of ICME –Closed magnetic loop inside ICME Determination of injection profile at Sun, for comparison with radio and optical signatures –Relativistic solar cosmic rays present the clearest picture of the acceleration process because of their fast speed and large mean free path Earliest alert of a particle event, in case of a GLE –Precedes earliest GOES proton alert by ~10-30 minutes –Mapping radiation exposure in Earth’s polar regions

24. ENERGY SPECTRUM: POLAR BARE METHOD South Pole station has both a standard neutron monitor (NM64) and a monitor lacking the usual lead shielding (Bare). The Polar Bare responds to lower particle energy on average. Comparison of the Bare to NM64 ratio provides information on the particle spectrum. This event displays a beautiful dispersive onset (lower panel), as the faster particles arrive first. Later, the rigidity spectrum softens to ~P – 5 (where P is rigidity), which is fairly typical for GLE.

25. ENERGY SPECTRA Spectra are shown for the first three 5-min averages (arrows at right). Velocity dispersion effects are much in evidence as the lower energy particles struggle to “catch up.”

26. ENERGY SPECTRA Spectra are shown for the GOES peak and decay phase (arrows at right). The neutron monitor extrapolates roughly to the GOES 54 MeV and 110 MeV channels.