GOES x-ray sensor and its use in predicting solar-terrestrial disturbances

The X-Ray Sensor (XRS) on the Geostationary Orbiting Environmental Satellite (GOES) provides a standard referencefor essentially continuous monitoring solar activity and characterizing solar flares. Disk-integrated x-ray fluxes observed byXRS are used by forecasters and researchers around the world as a measure of the strength and duration of solar flares. Thepeak 0. 1-0.8 am x-ray flux during flares is used to distinguish between C, M, and X flares, flares that differ by an order ofmagnitude in the peak flux. Forecasters use this peak flux to predict the magnitude of proton events, and the x-ray duration isused to estimate whether coronal mass ejection may have occurred that could cause a geomagnetic disturbance if it hits theEarth. Recipients of the data use the peak flux and the duration of the flare to estimate the disturbances expected on radiocommunication systems. The magnitudes of XRS-observed flares are also used to determine when to issue alerts of changedionospheric conditions that can disrupt communications and GPS signals. XRS fluxes are also used to augment solar radioobservations to alert users of radio frequencies of times when the solar signal may interfere with their operations. The non-flaring x-ray flux, otherwise known as the x-ray background flux, is used as a proxy for the solar EUV emissions that are usedto predict the atmospheric density as satellite orbits; variations in the daily averaged solar x-ray flux are used to estimatechanges in the atmospheric drag on spacecraft orbits.Keywords: GOES, x-rays, solar physics, x-ray instruments, space weather, solar-terrestrial disturbances, flares