The STEREO REleASE+ notification system

STERΕO REleASE+ makes use of both:

• electron measurements provided by the Solar Electron Proton Telescope (SEPT) and the High Energy Telescope (HET) onboard STEREO, and
• a radio module that qualifies type-III radio bursts from STEREO-A SWAVES real-time radio spectrograms which have the potential of causing near-Earth significant solar proton events and sets a forecasting window (FW), namely the maximum time interval within which a significant proton event is expected to occur after the onset of the qualified strong type-III radio burst

to issue forecasts, proton alerts and determine the expected radiation impact, shown in this webpage.

A gauge with a needle indicates in real-time and in a user-friendly mode the expected radiation impact labelled according to the following three discrete levels:

─    Quiet l Green color
─    Warning l Orange color
─    Alert l Red Color

determined from combined forecast conditions both from SEPT and HET instruments and the radio module when STERΕO REleASE+ operates, and from SEPT and HET instruments alone when we revert to STEREO REleASE, as defined in the accompanying table below.

At the top of the gauge, we indicate if the STEREO REleASE+ forecasting system is presently running, or if we have alternatively switched to STEREO REleASE due to the presence of significant gaps in STEREO/A SWAVES data. Below the gauge we indicate if a significant solar proton event (SEP) is presently on-going or not. The duration of an on-going SEP event is defined as the time interval between the proton event occurrence (when the 21-40 MeV HET proton flux first surpasses the 0.22 cm^-2 s^-1 sr^-1 MeV^-1 threshold) and the time that the one-hour averaged proton flux drops below 0.044 cm^-2 s^-1 sr^-1 MeV^-1.

The temporal validity of the current expected radiation impact is also provided below the SEP indicator. The Quiet state temporal validity is set at 20 min and ends earlier if a Warning or Alert occurs, for the Warning state at the resolution of the STEREO measurements until a new state is produced, and for the Alert state at 20 hours (if no-SEP occurs) or until the end of an SEP (as defined above) that occurred within the initially set 20-hour interval.

The STEREO REleASE+ Alert System can generate alerts which are distributed to registered users. You can register here.

Validation

A preliminary POD and FAR analysis conducted on 23 SEP events (with fluxes exceeding 0.22 cm^-2 s^-1 sr^-1 MeV^-1) and 32 non-SEP events (with maximum flux below the 0.22 cm^-2 s^-1 sr^-1 MeV^-1 threshold value), that occurred during the period of 2008 to mid-2022, results in POD and FAR values equal to 1 (100%) and 0.521 (52.1%), respectively, when no radio module is involved (STEREO REleASE). However, while POD remains the same, FAR becomes equal to 0.148 (14.8%), when the radio module is involved (STEREO REleASE+), suggesting a significant suppression of false alarms that would occur from STEREO REleASE alone. We note, however, that POD - which mainly depends on the number of SPEs - is expected to slightly decrease due to some missed events, and FAR - that mainly relates to the number of non-SPEs - is expected to substantially increase when a much larger number of proton events is identified and taken into consideration in the real-time STEREO REleASE+ forecasting system.

Posner A., Malandaki O., et al., 2025., STEREO REleASE+, Space Weather Journal, in preparation.