The GOES 12 through 15 spacecraft each carry a sophisticated X-ray telescope called the Solar X-ray Imager (SXI) to monitor the Sun’s hot outer atmosphere, or corona. X-ray photons are created in the million-degree plasma of the solar corona and are not visible from the ground, due to the absorption of the Earth’s atmosphere. Observations of solar X-rays aids in the early detection of solar flares, coronal mass ejections (CMEs), and other phenomena that impact the geospace environment.
X-ray photons travel at the speed of light and are the first indication we receive at Earth of solar magnetic eruptions and the associated flares. These flare related X-rays cause changes to the Earth’s ionosphere and can result in significant degradation of radio communications, including complete black outs at some frequencies, beginning only 8 minutes (time for light to travel from the Sun to Earth) after a flare.
The early warning given by the SXI observations comes at least 15 hours before the associated shockwave of the solar eruption arrives at Earth, allowing the forecasters at SWPC to issue the appropriate watches, warnings, and alerts for geomagnetic storming which is the cause of the most significant space weather effects at Earth.
The SXI telescopes are mounted on the Sun-pointing solar array gimbles of the GOES weather satellites. These satellites are in geosynchronous orbits that allow continuous solar viewing, 24 hours/day, 7 days/week. The only exception to this is around equinox dates when the GOES satellites enter Earth's shadow for up to one hour each day.
Each SXI collects a solar X-ray image once per minute, and the exposure settings follow a sequence that is optimized to observe three primary phenomenon as they are reflected in the Solar atmosphere: coronal structures, active regions, and solar flares.
SWPC processes and presents the images and animations of the GOES SXI instruments in near-real-time, and uses them in analyzing events and in issuing space weather watches, warnings, and alerts.