A technique for short‐term warning of solar energetic particle events based on flare location, flare size, and evidence of particle escape

Abstract

We have developed a technique to provide short‐term warnings of solar energetic proton (SEP) events that meet or exceed the Space Weather Prediction Center threshold of J (>10 MeV) = 10 pr cm−2 s−1 sr−1. The method is based on flare location, flare size, and evidence of particle acceleration/escape as parameterized by flare longitude, time‐integrated soft X‐ray intensity, and time‐integrated intensity of type III radio emission at ∼1 MHz, respectively. In this technique, warnings are issued 10 min after the maximum of ≥M2 soft X‐ray flares. For the solar cycle 23 (1995–2005) data on which it was developed, the method has a probability of detection of 63% (47/75), a false alarm rate of 42% (34/81), and a median warning time of ∼55 min for the 19 events successfully predicted by our technique for which SEP event onset times were provided by Posner (2007). These measures meet or exceed verification results for competing automated SEP warning techniques but, at the present stage of space weather forecasting, fall well short of those achieved with a human (aided by techniques such as ours) making the ultimate yes/no SEP event prediction. We give some suggestions as to how our method could be improved and provide our flare and SEP event database in the auxiliary material to facilitate quantitative comparisons with techniques developed in the future.

Solar flares, coronal mass ejections and solar energetic particle event characteristics

“…Finally, for intermediate cases, where 1/3 < I 10 /I p < 0.85, the integration ends when the SXR peak flux had dropped by 1/3. This approach differs from the one presented in Laurenza et al (2009) who, instead of the flare start, used as the start time of the integration the 1/3 power point of the rise, under the argument that the SXR maximum is immediately obtained for real-time space weather forecasts and hence, the computed parameters are useful for such purposes. On the other hand, we applied a different criterion since we noticed that in some ''brief-duration'' cases the integration with the use of the 1/3rd criterion stopped at an earlier time that was not representative of the overall radio characteristics of these events.…”

“…This is evident for forecasting systems of SEP events that rely either on remote-sensing observations of the Sun (Laurenza et al 2009;Núñez 2011;Papaioannou et al 2015) or on in situ measurements (Posner 2007). In particular, the achieved warning time at a subset of common SEP events between the technique furnished by Laurenza et al (2009) and the concept of Posner (2007) has shown that the former leads to a median warning time of 55 min and the latter of 50 min in advance of the National Oceanic and Atmospheric Administration (NOAA) event threshold crossing (10 pfu at >10 MeV).…”

“…For the ''extended-duration'' flares, depending on their I 10 /I p ratio, we have used a fixed decay time (t dec ). In particular, the decay times, presented in Table 2 (supplementary online material) of Laurenza et al (2009), were utilized. For the cases where I 10 /I p > 1.0, the t dec = 38 min; in case 0.85 < I 10 / I p < 0.90, t dec = 68 min; when 0.90 < I 10 /I p < 0.95, t dec = 104 min, and for 0.95 < I 10 /I p < 1.00, t dec = 214 min.…”

“…Given that the complexity of the underlying physical processes of the acceleration and propagation of SEP events is still a very active research area, the prognosis of SEP event occurrence and their corresponding characteristics (e.g., peak flux, duration, fluence) mostly relies on near real-time observations of SFs and CMEs and makes use of the aforementioned empirical relations (Smart & Shea 1989;Balch 1999;Garcia 2004aGarcia , 2004bLaurenza et al 2009;Núñez 2011;Papaioannou et al 2015). In addition, the work from Posner (2007) has proven the concept of short-term forecasting of the appearance and intensity of solar ion events by means of relativistic electrons, making use of the higher speed of these electrons propagating from the Sun to 1 AU.…”

The firstSEPServerevent catalogue ~68-MeV solar proton events observed at 1 AU in 1996–2010

“…Intensity enhancements of protons in the energy range 54.8-80.3 MeV (average energy 67.7 MeV) were searched for. 7 The energy channel was purposely chosen well above the typically-used >10 MeV proton channel (e.g., Laurenza et al 2009) available from GOES satellites. This was considered appropriate for the goals of the SEPServer project from the point of view of space-weather relevance, as discussed in the Introduction.…”