|Polar Cap||0 - 40||40 - 100||100 - 160||160+|
|Auroral Zone||0 - 60||60 - 160||160 - 240||240+|
|Sub-Auroral Zone||0 - 20||20 - 40||40 - 80||80+|
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), ie 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).
For the benefit of those users who need to relate to the Kp index, we provide the following equivalences, which apply to all three of the zones used in our forecasts. In the diagram, the top layer indicates our forecast levels, the second and third layers indicate the Kp index and its subdivisions. It should be noted that the Kp index is defined for 3-hour intervals.