Let us note, that the expected frequency of FEP events in the last column of Table 2.1 is averaged over solar cycle. Really, this frequency is much higher in periods of high solar activity than in periods of low solar activity (Dorman et al., 1993; Dorman and Pustil’nik, 1995, 1999).
4. On-line search of the start of great Flare Energetic Particle (FEP) events, automatically formation of Alerts, estimation of probability of false alerts and probability of missing alerts (realized in Israel Cosmic Ray Center and Emilio Segre’ Observatory). 4.1. Why we need to use solar high energetic particles for FEP forecasting and determine the time of their arriving?
It is well known that in periods of great flare energetic particle (FEP) ground events, fluxes of energetic particles can be so big that memory of computers and other electronics in space may be damaged, and satellite and spacecraft operations can be seriously degraded. In these periods it is necessary to switch off some part of electronics for a few hours to protect computer memories. The problem is how to forecast exactly these dangerous phenomena. We show that exact forecasts can be made by using high-energy particles (few GeV/nucleon and higher) whose transportation from the Sun is characterized by much bigger diffusion coefficients than lower energy particles. High-energy particles arrive from the Sun much earlier (8-20 minutes after acceleration and escaping into solar wind) than the lower energy particles that damage electronics (about 30-60 minutes later). We describe here the principles and operation of automated programs "FEP-Search-1 min", "FEP-Search-2 min",and "FEP-Search-5 min", developed and checked in the Emilio Segre' Observatory (ESO) of the Israel Cosmic Ray Center (2025 m above sea level, =10.8 GV). The determination of increasing flux is made by comparison with the intensity, averaged from 120 to 61 minutes, prior to the current one-minute data. For each minute of data the program "FEP-Search-1 min" is run. If the result is negative (no simultaneous increase in both channels of total intensity ≥ 2.5, where is the standard deviation for one minute of observation in one channel [for ESO =1.4 %]), start the program "FEP-Search-2 min", using two minute averages with = /?2, and so on. If any positive result is obtained, the "FEP-Search" programs check the next minute of data. If the result is again positive, automatically run the on-line the programs "FEP-Collect" and "FEP-Research" that determine the expected flux and spectrum and generate automatic alerts. These programs are described in Dorman and Zukerman (2001).
4.2. Short description of Israel Cosmic Ray Center and Emilio Segre' Observatory
The Israel Cosmic Ray Center (ICRC) and Emilio Segre' Observatory (ESO) were established in 1998, with affiliation to Tel Aviv University, to the Technion (Israel Institute of Technology, Haifa) and to the Israel Space Agency (under the aegis of the Ministry of Science). The Mobile Cosmic Ray Neutron Monitor of the Emilio Segre' Observatory, was prepared in collaboration with scientists of the Italian group in Rome, and transferred in June 1998 to the site selected for the Emilio Segre' Observatory (3318'N, 3547.2'E, 2025 m above sea level, vertical cut-off rigidity =10.8 GV). The results of measurements (data taken at one-minute intervals of cosmic ray neutron total intensities at two separate 3NM-64, as well as similar one-minute data about the intensities relating to neutron multiplicities m≥1, ≥2, ≥3, ≥4, ≥5, ≥6, ≥7 and ≥8) have been computer-stored. Similar one-minute data relating to the atmospheric electric field, wind speed, air temperature outside, and humidity and temperature inside the Cosmic Ray Observatory have also been recorded and archived. Each month one-hour data of the Emilio Segre' Observatory (short title ESO) are sending to the World Data Center in Boulder (USA, Colorado), to the WDC C-2 for cosmic rays (Japan) and to many Cosmic Ray Observatories in the world as well as are putting to our website. We established the automatic system of electric power supply using a diesel generator for providing continuous power for the Emilio Segre' Observatory. We finished the foundation of direct radio-connection in real time scale of the Emilio Segre' Observatory with our Laboratory in Qazrin, and with the Internet. In Figure 4.1 we show a block-scheme of the main components of the Emilio Segre' Observatory (ESO) and their connection with the Central Laboratory of Israel Cosmic Ray Center in Qazrin and with the Internet.
Let us consider the problem of automatically searching for the start of ground FEP events.Of course, the patrol of the Sun and forecast of great solar flares are very important, but not enough: only very small part of great solar flares produce dangerous FEP events. In principal this exact forecast can be made by using high-energy particles (few GeV/nucleon and higher) whose transportation from the Sun is characterized by much bigger diffusion coefficient than for small and middle energy particles. Therefore high-energy particles arrive from the Sun much earlier (8-20 minutes after acceleration and escaping into solar wind) than the lower energy particles that cause a dangerous situation for electronics ( at least about 30-60 minutes later). The flux of high-energy particles is very small and cannot be dangerous for people and electronics.
Fig. 4.1: Schematic of the main components of the Emilio Segre' Observatory (ESO) and their connection with the Central Laboratory of Israel Cosmic Ray Center (ICRC) in Qazrin and with INTERNET.
The problem is that this very small flux cannot be measured with enough accuracy on satellites to use for forecast (it needs very large effective surfaces of detectors and thus large weight). High-energy particles of galactic or solar origin are measured continuously by ground-based neutron monitors, ionization chambers and muon telescopes with very large effective surface areas (many square meters) that provide very small statistical errors. It was shown on the basis of data in periods of great historical FEP events (as the greatest of February 23, 1956 and many tens of others), that one-minute on-line data of high energy particles could be used for forecasting of incoming dangerous fluxes of particles with much smaller energy. The method of coupling (response) functions (Dorman, 1957; Dorman et al., 2000; Clem and Dorman, 2000) allows us to calculate the expected flux above the atmosphere, and out of the Earth's magnetosphere from ground based data. Let us describe the principles and on-line operation of programs "FEP-Search-1 min", "FEP-Search-2 min","FEP-Search-5 min", developed and checked in the Emilio Segre' Observatory of ICRC. The determination of increasing flux is made by comparison with intensity averaged from 120 to 61 minutes before the present Z-th one-minute data. For each Z minute data, start the program "FEP-Search-1 min" (see Figure 2). The program for each Z-th minute determines the values
where and are one-minute total intensities in the sections of neutron super- monitor A and B.
2.5, 2.5, (4.3)
the program "FEP-Search-1 min" repeat the calculation for the next Z+1-th minute and if Eq. (4.3) is satisfied again, the onset of great FEP is determined and programs "FEP-Collect" and "FEP-Research" described in the next section, are started.
Fig. 4.2. Schematic of programs "FEP-Search".
If Eq. (4.3) is not satisfied, the program "FEP-Search-2 min" searches for the start of an increase by using two-min data characterized by . In this case the program "FEP-Search-2 min" will calculate values
If the result is negative (no simultaneous increase in both channels of total intensity ≥ 2.5, i.e. the condition ≥ 2.5, ≥ 2.5 fails), then "FEP-Search-3 min" uses the average of three minutes Z-2, Z-1 and Z with . If this program also gives a negative result, then the program "FEP-Search-5 min" uses the average of five minutes Z-4, Z-3, Z-2, Z-1 and Z with . If this program also gives negative result, i.e. all programs "FEP-Search-K min"(where K=1,2,3,5) give negative result for the Z-th minute, it means that in the next 30-60 minutes there will be no radiation hazard (this information can be also very useful). After obtaining this negative result, the procedure repeats for the next, Z+1-th minute, and so on. If any positive result is obtained for some Z=Z', the "FEP-Search" programs checked the next Z'+1-th minute data. If the result obtained is again positive, then the programs, described in Section 4, are started to determine the expected flux and spectrum and to send automated alerts. The block-scheme of programs "FEP-Search" is shown in Figure 4.2.