Criteria for Forecasting Proton Events by Real-Time Solar Observations

The sequence for overcoming the threshold values of a number of physical characteristics for proton event forecasting in real time is discussed. Each characteristic adds a new physical meaning that refines the forecast. To take into account all the characteristics, the following continuous patrol observations are necessary: (1) the magnetic field of the active region (ascent of the flux) and the total magnetic field of the Sun, which can predict the onset of flare activity several days prior to main events; (2) soft X-ray radiation in two channels to calculate the temperature (T) and emission measure of plasma, which can show preheating to T > 10 MK required to begin proton acceleration (the first few minutes before the start of hard X-ray (HXR) radiation with energies >100 keV); (3) HXR radiation >100 keV or microwave radiation (>3 GHz), which indicates the intensity and duration of operation of the electron accelerator (a few to tens of minutes before the arrival of protons with energies >100 MeV); (4) radio emission at plasma frequencies (<1000 MHz), showing the development of the flare process upward into the corona and leading to a coronal mass ejection (CME) several minutes before the onset of type II and IV radio bursts (the first tens of minutes before the appearance of a CME in the field of view of the coronagraph); (5) the direction and velocity of CME propagation, which determine the conditions to release accelerated protons into the heliosphere. These stages of solar proton flares are illustrated by observations of proton events on August 2–9, 2011. To quantitatively predict the onset time, maximum and magnitude of the proton flux, as well as its fluence, it is necessary to create statistical regression models based on all of the listed characteristics of past solar proton events.