Fluxes of particles with energies ≥ 10 MeV can reach 43,500 protons/cm2/sec/ster. During an SPE, satellites experience dramatically increased bombardment by high-energy particles. SPEs result from fast coronal mass ejections. Solar Proton Events at Earth can occur throughout the solar cycle but are most frequent in solar maximum years. Higher threshold products for ≥100 MeV flux levels, such as 100 pfu, are being considered for future implementation. Because flux levels can drop slowly, the time of a "confirmed" drop below threshold can sometimes take several hours to determine. Once the Proton Flux has dropped below a given threshold, a Proton Event SUMMARY is issued, specifying the start, maximum, end times, and maximum flux observed for the event, along with the corresponding NOAA S-scale. Higher threshold ≥10 MeV ALERTS are also issued for threshold exceedance of 100, 1,000, 10,000, and 100,000 pfu, matching the thresholds described in the NOAA S-scale. Initial ALERTS for ≥10 MeV and ≥100 MeV energies are issued for integral flux reaching or exceeding 10 pfu and 1 pfu, respectively. Proton Event ALERTS are issued upon confirmation of ≥10 Mev or ≥100 MeV Integral Flux exceeding certain thresholds. The ≥10 MeV Integral Flux WARNING includes the predicted level of activity based on the NOAA S-scale.
EXTENDED WARNINGS always have the same “Valid From” time as the original WARNING, with a revised “Now Valid Until” time specified in the message. If needed, the warning period may be extended by means of an EXTENDED WARNING. The WARNING period is expressed in terms of “Valid From” and “Valid To” times. Proton Event WARNINGS include a specific indication of what condition - Onset or Persistence - applies to the WARNING. The ≥100 MeV Integral Flux WARNING is issued based on the expectation of reaching or exceeding flux levels of 1 pfu. The ≥10 MeV Integral Flux WARNING is issued based upon the expectation of reaching or exceeding flux levels of 10 pfu. Proton Event WARNINGS are forecasts of a proton event and are issued by SWPC under two conditions: warning of the expected ONSET of a Proton Event, and warning of the expected PERSISTENCE of a Proton Event that is already in progress. The ≥100 MeV products are based on a single flux threshold of 1 proton flux unit (pfu). The ≥10 MeV products match the NOAA Solar Radiation Storm (S-scale) thresholds (10, 100, 1000, 10000, 100000 pfu), based upon values observed or expected on the primary GOES satellite. Proton Event products are issued for several thresholds and for two particle energy levels.
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