A graph of sunspot counts from 1700 to 1993.
Click on image for full size
Image courtesy NOAA/NGDC.
Metrics & Indices that Describe Space Weather
As with weather on Earth, there are space weather reports and forecasts. In these reports and forecasts, scientists use metrics and indices.
Just what are these metrics and indices? They are numbers that have to do with the different players in the space weather scene during that time period. One example might be the number of sunspots on the Sun at that time. The higher the number of sunspots, the more active the Sun is likely to be. The more active the Sun, the more flares or coronal mass ejections we might see coming from the Sun. So, you can see that number of sunspots is a good metric for telling how active the Sun will be.
Other metrics and indices deal with the solar wind, the magnetic field out in space (IMF), the Earth's magnetic field and the Earth's atmosphere.
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