Improving Solar Flare Nowcasting with the Hot Onset Precursor Event Technique

Abstract This study investigates the statistical behavior of plasma properties during hot onset precursor events (HOPEs) of solar flares and evaluates their potential for improving flare nowcasting. Two data sets are analyzed: (a) new soft X-ray (SXR) spectra of 25 flares (C2.6–M1.0) obtained from the Dual-zone Aperture X-ray Solar Spectrometer (DAXSS) and (b) SXR irradiance data from 137 flares (C5.0–X7.1) recorded by the X-Ray Sensor on the Geostationary Operational Environmental Satellite (GOES-XRS). Plasma temperature, emission measure (EM), and low first ionization potential (e.g., Mg, Si, Fe) elemental abundance factors (AFs) are derived from DAXSS using Astrophysical Plasma Emission Code model fitting. Isothermal plasma temperature and EM are derived from GOES-XRS using the XRS-A/XRS-B ratio method. Results indicate that the HOPE phase exhibits elevated temperatures (10–15 MK) and an order-of-magnitude increase in EM before the impulsive phase. Elemental AFs show a transition from coronal to photospheric values as the flare progresses. Using GOES-XRS data, we develop an improved nowcasting algorithm that detects flares utilizing HOPE signatures. The algorithm is tested across three categories of flares (C5.0–M1.0, M1.0–X1.0, and X1.0+), consistently predicting flare alerts 5–15 minutes ahead of the flare peak. We also explore the possibility of approximate flare magnitude prediction by calculating the correlation between onset parameters and flare peak magnitude. This HOPE-based system shows potential for earlier warnings than current NOAA R3 alerts, which could be useful for high-frequency communication systems operators and targeted flare observation campaigns.