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This chart is updated every 15 minutes at 1, 16, 31, and 46 minutes past the hour. Use the browser Refresh or Reload option to ensure the latest data is shown. Boulder, Colorado and Fredericksburg, Virginia are mid-latitude stations. College, Alaska is a high-latitude station. Estimated Planetary is a combined measure of several mid- and high-latitude stations.
A-index Watches are issued when a Fredericksburg, Virginia (mid-latitude) A-index of greater than 20, 30, 50, or 100 is predicted. These thresholds are marked on the chart. When observed A-indices exceed 100, the charts are individually scaled as needed.
Fredericksburg, College, and Estimated Planetary A- and K-index since 1994
A- and K-indices for last 2 years from all geomagnetic stations available at SWPC
Space Weather Data at SWPC -- Alerts and Forecasts, Models, Reports and Summaries, Indices, and Measurements as both plots and lists
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