Screen A — Ground Magnetometers (U.S. and Canadian Magnetic Observatory Data, last 12 hours)

What you’re looking at

• Multiple observatories spanning from the U.S. to Canada, each showing components X, Y, Z of the magnetic field.
• Many plots include dB/dt (rate of change). This is a measure of how fast the field is changing.
• The X and Y plots include local station K-index calculations. The local K-index varies from zero (very quiet) to 9 (extremely disturbed). The hourly K-index is shown as a bar and the current hourly K-index (0, 1-, 1o, 1+, 2-, 2o, 2+, etc) is displayed at the base of that bar. The running 3-hour K-index is shown as a solid white line. If you look close, each plot has a dotted grid that shows the K-index levels to help you determine the levels of the white line. Fluctuations of the magnetic field are in units of nano-Tesla's and the Range indicates how much the magnetic field component has changed during the last 12 hours. The station K-index is the higher of either the X or Y components. So for example, if the X-component K-index is 2- (equal to 1.667) and the Y-component is 3o (equal precisely to 3.0), the station K-index for that time period would be the higher 3.0 (3o) value.

How to interpret it

• Bigger wiggles usually mean stronger geomagnetic activity. There is a daily variation (even during quiet times) that these plots don't correct for. You can see the daily variation as slow-moving ups and downs.
• Faster wiggles (dB/dt) mean rapid change. Changes that produce dB/dt values of more than about 30 nT/minute can be associated with induced ground currents in some regions (depending on ground conductivity).
• Compare stations: widespread disturbances across stations usually indicate a broader or global event.

Practical tip: If Bz is southward and the auroral oval expands, magnetometers can be used to confirm the response. They help answer: “Is Earth actually reacting right now?” Fluctuations are strongest in the auroral zone.