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อภิธานศัพท์: อภิธานศัพท์ฟิสิกส์ (อวกาศ)
A
a INDEXA 3-hourly "equivalent amplitude" index of local geomagnetic |
a INDEX 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
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A INDEX A daily index of geomagnetic activity derived as the average of
the eight 3-hourly a indices.
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ACTIVE Geomagnetic levels such that 15 is less than Ap which is less than 29.
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ACTIVE Solar activity levels with at least one geophysical event or
several larger radio events (10cm) per day (Class M Flares)
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ACTIVE DARK FILAMENT (ADF) An ACTIVE PROMINENCE seen on the DISK.
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ACTIVE LONGITUDE The approximate center of a range of heliographic
longitudes in which ACTIVE REGIONS are more numerous and more
FLARE-active than the average.
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ACTIVE PROMINENCE A PROMINENCE displaying material motion and changes
in appearance over a few minutes of time.
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ACTIVE PROMINENCE REGION (APR) A portion of the solar LIMB displaying
ACTIVE PROMINENCEs.
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ACTIVE REGION (AR) A localized, transient volume of the solar atmosphere
in which PLAGEs, SUNSPOTS, FACULAe, FLAREs, etc. may be observed.
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ACTIVE SURGE REGION (ASR) An ACTIVE REGION that exhibits a group or
series of spike-like surges that rise above the limb.
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AFRED Abbreviation for the A INDEX for Fredericksburg.
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ANGSTROM A unit of length = 1.0E-08cm.
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Ap INDEX An averaged planetary A INDEX based on data from a set of specific
stations.
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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.
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ASTRONOMICAL UNIT (AU) The mean earth-sun distance, equal to 1.496E+13cm
or 214.94 solar radii.
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AURORA 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.
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AURORAL OVAL An oval band around each geomagnetic pole which is the locus
of structured AURORAe.
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AUTUMNAL EQUINOX The equinox that occurs in September.
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