Real-time GLE alert in the ANMODAP Center for December 13, 2006

Abstract

Within the last years, a real-time system to monitor high energy cosmic rays for space weather use has been operated at Athens cosmic ray station. Neutron monitors and satellite high resolution data in real time are used, making it possible to observe cosmic rays in dual energy range observations. In large solar energetic particle (SEP) events, ground level enhancement (GLE) can provide the earliest alert for the onset of the SEP event. This system watches for count rate increases recorded in real time by 23 neutron monitors, which triggers an alarm if a ground level enhancement (GLE) of cosmic ray intensity is detected. Our effort is to determine optimal strategies for detecting the GLE event at a very early stage, while still keeping the false alarm rate at a very low level. We have studied past events to optimize appropriate intensity threshold values and a baseline to determine the intensity increase. We define three levels of alarm (watch, warning and alert) on the basis of the number of stations that record a significant intensity increase. For every station there is a program which every minute calculates in real time the mean value of the last sixty minutely measurements and compares this value with a threshold. If we have five pre-alert points in succession, we define a Station Alert. If we see at least three stations in station alert mode, another program provides a General GLE Alert. A statistical analysis on the last ten GLEs recorded from 2001 till 2006 using 1-min data from our database, produced GLE alarms for nine events in our system. Alarm times for these nine events are compared with satellite data separating if the event is GLE or magnetospheric one. The GLE alert precedes the earliest alert from GOES (100 MeV or 10 MeV protons) by 4–33 min. When the alert is final then an automated e-mail is sent to all the interested users. An alert signal was established at December 13, 2006 by the ANMODAP Center and for first time an automated e-mail alarm signal was sent out by our system determining the onset of the GLE70 event. A detailed analysis of this alert is discussed.