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arXiv · 2407.04567

Anticipating Solar Flares

Hugh S. Hudson
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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.

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Hugh S. Hudson. 2024-07-05. Anticipating Solar Flares. https://arxiv.org/abs/2407.04567

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