Solar Wind Speed

Solar wind speed measures how fast the continuous stream of charged particles flowing outward from the Sun is traveling when it reaches Earth's vicinity, typically expressed in kilometers per second. Under normal, calm conditions, the solar wind moves at roughly 300 to 500 kilometers per second, but speeds can climb to 700 or 800 kilometers per second in fast streams flowing from coronal holes, and can spike even higher, sometimes exceeding 1,000 kilometers per second, at the leading edge of a fast coronal mass ejection. Solar wind speed is one of the most important single numbers in space weather forecasting because faster solar wind generally means more energy is available to disturb Earth's magnetosphere, and because a sudden increase in speed often signals the arrival of a shock front that can trigger a geomagnetic storm within minutes. NOAA's DSCOVR and ACE spacecraft continuously measure solar wind speed from a vantage point upstream of Earth, giving forecasters a crucial early warning window. Historically, high-speed solar wind streams from long-lived coronal holes are notorious for causing a recurring pattern of minor to moderate geomagnetic activity approximately every 27 days, matching the Sun's own rotation period as the same coronal hole rotates back into view.