Forecasting of radiation hazard: 1. Alerts on great FEP events beginning; probabilities of false and missed alerts; on-line determination of solar energetic particle spectrum by using spectrographic method

Abstract

We show that exact forecast can be made by using high-energy particles (few GeV/nucleon and higher) which transportation from the Sun is characterized by much bigger diffusion coefficient than for small and middle energy particles. Therefore, high-energy particles came from the Sun much more early (8–20 min after acceleration and escaping into solar wind) than main part of smaller energy particles caused dangerous situation for electronics (more than 30–60 min later). We describe here principles and experience of automatically working of program “FEP-Search”. The positive result which shows the exact beginning of FEP event on the Emilio Segre’ Observatory (2025 m above sea level, R c = 10.8 GV), is determined now automatically by simultaneously increasing on 2.5 St. Dev. in two sections of neutron supermonitor. The next 1-min data the program “FEP-Search” uses for checking that the observed increase reflects the beginning of real great FEP or not. If yes, automatically starts to work on line the programs “FEP-Research”. We determine also the probabilities of false and missed alerts. The first of programs “FEP-Research” is the program “FEP-Research/Spectrum”. We consider two variants: (1) quiet period (no change in cut-off rigidity), (2) disturbed period (characterized with possible changing of cut-off rigidity). We describe the method of determining of the spectrum of FEP in the 1-st variant (for this we need data for at least two components with different coupling functions). For the 2-nd variant we need data for at least three components with different coupling functions. We show that for these purposes can be used data of total intensity and some different multiplicities, but better to use data from two or three NM with different cut-off rigidities. We describe in details the algorithms of the program “FEP-Research/Spectrum”. We show how worked this program on examples of some historical great FEP events.