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					Early Alert of Solar Radiation Hazard
Paul Evenson (evenson@udel.edu), T. Kuwabara, J. W. Bieber, J. Clem, R. Pyle
Bartol Research Institute and Department of Physics and Astronomy, University of Delaware

  Abstract            We describe our automated Ground Level                                 Algorithm for issuing an alarm                                     We define three levels of alarm (Watch, Warning,
  Enhancement (GLE) Alarm that is now operational in beta testing.                                                                                            and Alert) based on the number of stations that record a
  Using our neutron monitor stations at Fort Smith, Inuvik, McMurdo,                                                                                          significant intensity increase.
  Nain, Newark, Peawanuck, South Pole, and Thule, automated e-mail                                                                                             A threshold level Ith is set for the cosmic ray intensity
  alarms can be sent to subscribers within minutes of large GLE onsets.                                                                                       increase, and an alarm is generated when the number of
  In brief, the system generates a WATCH when one station observes an                                                                                         stations that exceed the threshold level is
  increase of 4% or more in a three minute moving average, a                                                                                                             1 - Watch, 2 - Warning, 3 –Alert.
  WARNING when two stations observe such an increase, and an                                                                                                   Baseline to calculate the intensity increase is defined
  ALERT when three or more stations record such an increase. (A higher                                                                                        by two parameters b and 0. Then, by using a trailing
  threshold for percent increase may be imposed for some stations with                                                                                        moving average value for the current count rate, the
  lower count rates.) A scientific discussion of the alarm system can be                                                                                      intensity at time t =  is calculated each minute from
  found in the article "Development of a Ground Level Enhancement                            Condition for issuing three levels of alarm. Intensity
                                                                                                                                                              the observed count rate N() averaged over the
  Alarm System Based upon Neutron Monitors", T. Kuwabara, J. W.                              increase recorded at three stations during a schematic
                                                                                                                                                              preceding c minutes, shown as left equation.
  Bieber, J. Clem, P. Evenson, and R. Pyle, Space Weather, 4, S10001,                        GLE are illustrated.
                                                                                                                                                               To reduce fluctuations and accurately detect the GLE,
  doi: 10.1029/2006SW000223, 2006. A web page specifically devoted                                                                                            all parameters (threshold and baseline) were optimized
                                                                                                              1                  1           0
                                                                                                                                                            
                                                                                                     I                 N t                   N t 
  to the GLE alarm, including graphical displays is available at:
  http://www.bartol.udel.edu/~takao/neutronm/glealarm/index.html                                                                                            as by backtesting against past neutron monitor data as
                                                                                                               c t   c        b t   0  b             c=3 min, b =75min, 0=10min, Ith = 4%.
   South Pole neutron monitor is supported by NSF award ANT-0838839                                                                                             At this condition, the false alarm rate for Watch,
  and McMurdo is supported by NSF award ANT-0739620                                            c : average time              0 : time interval between the  Warning, and Alert was ~40/yr, less than 1/yr, and 0/yr
                                                                                               b : duration of the                baseline and current time  respectively, during the 4.4-year period of our
                                                                                                    base-line                 Ith : threshold level           backtesting study,
 GLE event on January 20, 2005
                                                                                             Alarm issued for January 20, 2005 event                                   On Jan 20, 2005 event, alarm times for
                                                                                                                                                                     Warning and Alert are 6:49 and 6:50
                                                                                                                                                                     respectively; a separate Watch alarm was not
                                                                                                                                                                     generated. The SEC alert was issued at 7:02 from
                                                                                                                                                                     >10 MeV data, and 7:04 from >100 MeV data.
                                                                                                                                                                       Proton flux observed in the >10 MeV channel
                                                                                                                                                                     exceeds 100 pfu at 6:55. This flux level is defined
                                                                                                                                                                     as a “Moderate Storm” (S2 on NOAA Space
                                                                                                                                                                     Weather Scale for Solar Radiation Storms) that
                                                                                                                                                                     has the possibility to cause single-event upsets
                                                                                                                                                                     aboard satellites, and our system can produce
                                                                                                                                                                     alarm before this.
                                                                                                                                                                       http://www.sec.noaa.gov/alerts/archive.html
                                                                                                                                                                       Space Weather Message Code: ALTPX2
                                                                                                                                                                       Serial Number: 27
                                                                                                                                                                       Issue Time: 2005 Jan 20 0702 UTC

                                                                                        GOES proton flux and cosmic ray intensity increase. In upper                   ALERT: Proton Event 10MeV Integral Flux exceeded 100pfu
                                                                                                                                                                       Begin Time: 2005 Jan 20 0701 UTC
                                                                                        panel, black arrows indicate the onset time of SEP event(>100                  NOAA Scale: S2 - Moderate
                                                                                        MeV), and the start time of the Moderate storm. Vertical lines                 Space Weather Message Code: ALTPC0
                                                                                        drawn in lower panels also show the onset time of GLE.                         Serial Number: 17
                                                                                        Colored arrows indicate the time when each alarm is issued                     Issue Time: 2005 Jan 20 0704 UTC

                                                                                        (proton monitor) or generated (neutron monitor).                               ALERT: Proton Event 100MeV Integral Flux exceeded 1pfu
                                                                                                                                                                       Begin Time: 2005 Jan 20 0701 UTC


                                                                                              Comparison between the alert times from our system
                                                                                              and alarm issue times from proton data at SEC/NOAA for nine GLE events.

GLE event on January 20, 2005. Upper panel shows the low energy
proton integral flux recorded by the GOES-11 satellite (solid line >10MeV,
dotted line >100MeV). Lower panel shows neutron rates detected in
several neutron monitors. These data are normalized to average counting
rate at Inuvik (05:30-06:30).

 The GLE (Ground Level Enhancement) of January 20, 2005 was the largest
in half a century. The onset of the intensity increase in neutron monitors is
earlier than that of the low energy proton flux, and time to reach maximum
intensity is shorter for neutron monitors.
  The GLE particles have large mean free paths and travel almost at the
speed of light, and can be detected with high accuracy by detectors with
large volume such as ground-based neutron monitors. A GLE alarm can
provide a very useful early warning of an impending solar radiation storm.
We developed a system that watches (in real time) for count rate increases in
our data, and gives an alarm when a GLE is detected. We compare the alarm                      Number of Minutes by which each alert
                                                                                                                                                              Number of Minutes by which GLE Alert precedes
time produced in our system with that of the system operated by                                precedes Moderate Storm (>100pfu in >10
                                                                                                                                                              earliest SEC Proton Alert
SEC/NOAA by using the GOES proton data.                                                        MeV channel)

Eight neutron monitors are used in this work. The station name, detector                             Summary
type, average cosmic ray background count rate (in 2005),
                                                                                                     We have developed a real-time GLE detection system using eight high-latitude neutron monitors
geographical latitude, longitude, and altitude are listed.
                                                                                                       • GLE alarms are produced at three levels (Watch, Warning, and Alert) corresponding to the number of
Station                        Type          Count/hour        Lat., Long., Altitude                   stations that exceed the 4% intensity threshold
                                                                                                       • Intensity increase are calculated from a 3-minute moving average counting rate relative to a 75-minute
Inuvik, Canada                 18NM64         6.6×105          68.4 N, 133.7 W, 21 m                   baseline extending from 85 minutes to 10 minutes before the current time
Fort Smith, Canada             18NM64         7.4×105          60.0 N, 111.9 W, 203 m                  • During the 4.4-year period of our backtesting study, the false alarm rate for Watch, Warning, and Alert
Peawanuck, Canada              18NM64         7.3×105          55.0 N, 85.4 W, 52 m                    was ~40/yr, less than 1/yr, and 0/yr respectively
Nain, Canada                   18NM64         7.3×105          56.5 N, 61.7 W, 46 m                  Alert times decided from this algorithm in the past 9 GLE events were compared with the earliest alert issued
Thule, Greenland               18NM64         8.0×105          76.5 N, 68.7 W, 44 m                  by SEC/NOAA based upon GOES (100 MeV or 10 MeV protons) data
McMurdo, Antarctica            18NM64         9.4×105          77.9 S, 166.6 E, 48 m                    • Alert times produced by our system are ~10-30 minutes earlier than alert issue times from SEC/NOAA
                                                                                                        • Alert times are also substantially earlier (around 60 minutes) than the time when dangerous amounts of
South Pole, Antarctica         3NM64         10.3×105          90.0 S, 0.0 E, 2820 m                    low energy particles reach the satellite (S2 storm level)
South Pole Bares*              6NM64          3.2×105          90.0 S, 0.0 E, 2820 m
*Bare : Neutron counters without the usual lead shielding that respond to a slightly lower           These results suggest that our system can provide valuable added minutes of advance warning for radiation
energy primary cosmic ray than the standard monitor.                                                 events of concern for satellites, astronauts, and air crews.

				
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posted:12/11/2011
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