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A 3-hourly "equivalent amplitude" index of local geomagnetic
A 3-hourly "equivalent amplitude" index of local geomagnetic activity; "a" is related to the 3-hourly K INDEX according to the following scale: K 0 1 2 3 4 5 6 7 8 9 a 0 3 7 15 27 48 80 140 240 400
A daily index of geomagnetic activity derived as the average of the eight 3-hourly a indices.
Geomagnetic levels such that 15 is less than Ap which is less than 29.
Solar activity levels with at least one geophysical event or several larger radio events (10cm) per day (Class M Flares)
ACTIVE DARK FILAMENT (ADF)
An ACTIVE PROMINENCE seen on the DISK.
The approximate center of a range of heliographic longitudes in which ACTIVE REGIONS are more numerous and more FLARE-active than the average.
A PROMINENCE displaying material motion and changes in appearance over a few minutes of time.
ACTIVE PROMINENCE REGION (APR)
A portion of the solar LIMB displaying ACTIVE PROMINENCEs.
ACTIVE REGION (AR)
A localized, transient volume of the solar atmosphere in which PLAGEs, SUNSPOTS, FACULAe, FLAREs, etc. may be observed.
ACTIVE SURGE REGION (ASR)
An ACTIVE REGION that exhibits a group or series of spike-like surges that rise above the limb.
Abbreviation for the A INDEX for Fredericksburg.
A unit of length = 1.0E-08cm.
An averaged planetary A INDEX based on data from a set of specific stations.
ARCH FILAMENT SYSTEM (AFS)
A bright, compact PLAGE crossed by a system of small, arched FILAMENTS, which is often a sign of rapid or contin- ued growth in an ACTIVE REGION.
ASTRONOMICAL UNIT (AU)
The mean earth-sun distance, equal to 1.496E+13cm or 214.94 solar radii.
A faint visual phenomenon associated with geomagnetic activity, which occurs mainly in the high-latitude night sky; typical auroras are 100 to 250 km above the ground.
An oval band around each geomagnetic pole which is the locus of structured AURORAe.
The equinox that occurs in September.