This plot contains the estimated planetary K-index. This index is derived, at the U.S. Air Force Space Forecast Center, using data from ground-based magnetometers at Meanook, Canada; Sitka, Alaska; Glenlea, Canada; Saint Johns, Canada; Ottawa, Canada; Newport, Washington; Fredericksburg, Virginia; Boulder, Colorado; and Fresno, California. These data are made available through the cooperation of the Geological Survey of Canada (GSC) and the US Geological Survey. K-indices of 5 or greater indicate storm-level geomagnetic activity. Geomagnetic storms have been associated with satellite surface charging and increased atmospheric drag.