Forecasting GOES 15 >2 MeV Electron Fluxes From Solar Wind Data and Geomagnetic Indices. Issue 8 (25th August 2020) - Forsyth, C.
Abstract: The flux of > 2 MeV electrons at geosynchronous orbit is used by space weather forecasters as a key indicator of enhanced risk of damage to spacecraft in low, medium, or geosynchronous Earth orbits. We present a methodology that uses the amount of time a single input data set (solar wind data or geomagnetic indices) exceeds a given threshold to produce deterministic and probabilistic forecasts of the >2 MeV flux at GEO exceeding 1, 000 or 10, 000 cm −2 s −1 sr −1 within up to 10 days. By comparing our forecasts with measured fluxes from GOES 15 between 2014 and 2016, we determine the optimum forecast thresholds for deterministic and probabilistic forecasts by maximizing the receiver‐operating characteristic (ROC) and Brier skill scores, respectively. The training data set gives peak ROC scores of 0.71 to 0.87 and peak Brier skill scores of −0.03 to 0.32. Forecasts from AL give the highest skill scores for forecasts of up to 6 days. AL, solar wind pressure, or SYM‐H give the highest skill scores over 7–10 days. Hit rates range over 56–89% with false alarm rates of 11–53%. Applied to 2012, 2013, and 2017, our best forecasts have hit rates of 56–83% and false alarm rates of 10–20%. Further tuning of the forecasts may improve these. Our hit rates are comparable to those from operational fluence forecasts, that incorporate fluence measurements, but our false alarm rates are higher. This proof‐of‐concept shows that the geosynchronous electron flux can be forecast with a degree of success without incorporating a persistence element into the forecasts. Plain Language Summary: Spacecraft that orbit the Earth 36, 000 km above the equator take 24 hr to orbit the Earth, meaning they stay above the same point on the Earth's all the time. These "geosynchronous" orbits are incredibly useful, enabling satellites to have constant contact with the ground. As of 31 March 2019, over 500 spacecraft are in geosynchronous orbit (https://www.ucsusa.org ). Geosynchronous orbit is also on the edge of one of the most hazardous regions of space around the Earth—the Van Allen Radiation Belts. These belts contain highly energetic particles capable of damaging spacecraft in geosynchronous orbit and are highly variable. As such, predicting when the radiation belts at geosynchronous orbit are dangerous is a key concern in space weather. In this study, we create forecasts of the radiation belts based on simple measurements of upstream and local conditions of Earth's space environment. These simple forecasts provide the probabilities of high‐risk events at geosynchronous orbit over periods of up to 10 days, providing an interesting new mechanism for forecasting the conditions in near‐Earth space as well as helping us to understand the factors that control the dynamics of the radiation belts. Key Points: A simple method for deterministic or probabilistic forecasting of the geosynchronous >2 MeV electron flux exceeding set levels is examined Forecasts are based on the amount of time a single input variable exceeds a set threshold and do not include measured geosynchronous flux AL, SYM‐H, and solar wind pressure provide the most skilful forecasts when analyzed using standard forecasting metrics