| Solar Magnetic Field |
| The solar magnetic field is approximately a dipole at high latitudes and is highly
irregular at middle and low latitudes. The field apparently gives rise to a coupling
between solar differential rotation and the 11-year cycle of solar activity; the field
also governs the evolution of individual active regions. Field magnitudes range from
a few gauss in quiet regions to a few thousand gauss in some active regions. Longitudinal
(line-of-sight) components of the solar magnetic field are measured by magnetographs
which use the Zeeman effect. The solar magnetic fields are photographically or computer
drawn contours of the solar longitudinal magnetic field distribution across the whole
sun at different levels of nanotesla (gauss). The computer plotted contours use solid
lines for positive and dotted lines for negative field polarities. The polarities
on the photographs are indicated by bright areas as positive and dark areas as negative.
The data also can be drawings of individual sunspot regions with coordinates, polarity
and intensity in nanotesla of each spot indicated. The National Geophysical Data Center
(NGDC) archives (from about 14 stations): 1) once-daily (Scout) measurements of sunspot
magnetic fields. These may be marked-up sunspot maps, large-scale magnetic maps or
tables. If sunspot maps, the magnetic field intensity and polarity is indicated. If
tables, the heliographic position of the spot is given followed by the magnetic classification,
or the maximum strength and polarity, or both; 2) solar magnetograms of the whole
disk, both Kitt Peak and Mt. Wilson daily magnetograms appear in Solar-Geophysical
Data (SGD), a monthly NGDC publication; 3) data on the mean solar magnetic field from
sun-as-a-star integrated light measurements. Stanford daily data appear in SGD. Mean
daily measurements are reported in monthly tables.
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