Anticipating Solar Flares

TL;DR

This paper introduces a method to predict solar flares by detecting a precursor event called HOPE using soft X-ray data, enabling early alerts with minimal false positives.

Contribution

The study develops a flare anticipation index (FAI) based on the HOPE detection, providing a new tool for near-real-time solar flare prediction.

Findings

FAI offers lead times of a few minutes.

FAI produces very few false positives.

Effective detection of HOPE precursor event.

Abstract

Solar flares commonly have a hot onset precursor event" (HOPE), detectable from soft X-ray observations. Detecting this requires subtraction of pre-flare fluxes from the non-flaring Sun prior to the event, fitting an isothermal emission model to the flare excess fluxes by comparing the GOES passbands at 1-8 A and 0.5-4 A, and plotting the timewise evolution of the flare emission in a diagram of temperature \textit{vs} emission measure. The HOPE then appears as an initial "horizontal branch" in this diagram. It precedes the non-thermal impulsive phase of the flare and thus the flare peak in soft X-rays as well. We use this property to define a "flare anticipation index" (FAI), which can serve as an alert for observational programs aimed at solar flares based on near-real-time soft X-ray observations. This FAI gives lead times of a few minutes and produces very few false positive alerts even for flare brightenings too weak to merit NOAA classification.