Predicted Dst index since the time of the last measurement

The graph shows our predictions of the Dst index since the last available measurement.

• The points to the left of the dotted line on the graph are the most recent ``quick-look'' Dst measurements available from the World Data Centre for Geomagnetism (WDC-C2), Kyoto, Japan.
• The points within and to the right of the dotted lines are predictions of Dst made by the forecasting method of O'Brien and McPherron, using real-time solar wind data from the ACE spacecraft.
  1. The point within the vertical dashed lines is our ``nowcast''-our prediction for the current hour. We make this prediction as soon as we have enough solar wind data to do so.
  2. The last point on the plot is our ``forecast''-our prediction for the next hour.

See how our predictions have compared with the measured values of Dst over the last 24 hours, 7 days, or 28 days.

The coloured bar on the right hand side of the graph indicates an activity level corresponding to the Dst value. Low activity is defined as Dst > -20 nT, medium activity is -20 nT > Dst > -50 nT and high activity Dst < -50 nT.

We define a magnetic storm as any interval for which Dst is less than -20 nT and during which Dst drops below -50 nT (into the high activity zone). Thus green indicates no storm, a green - amber sequence may indicate the start of a storm, but a full green - amber - red sequence is needed to identify a storm conclusively.

The resultant magnetic storm forecast is used to produce a satellite risk forecast.