| definition |
- The levels of geomagnetic field activity, or disturbance, currently used in the long-term (up to 27 days) forecasts are labelled qualitatively for general usage. For each of the three major zones (subauroral, auroral, polar cap), the range of activity is divided into four classifications: quiet, unsettled,
active, storm. The actual parameter used for reporting and forecasting magnetic activity is a daily index. It is known as DRX and is the average of the hourly ranges (maximum minus minimum during each hour) in the X (northward) component of the magnetic field intensity for a day (the UT [or GMT] day), i.e., DRX for the zone is the mean of 24 values. Because this averaging process has the effect of smoothing (filtering) the more rapid fluctuations in the field, the qualitative descriptors are defined rather differently than for the short-term forecasts.
Units are nanoteslas (nT).
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