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Early Alert of Solar Radiation Hazard Paul Evenson (email@example.com), 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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