Geomagnetic activity and wind velocity during the Maunder minimum
نویسنده
چکیده
Following a given classi®cation of geomagnetic activity, we obtained aa index values for the Maunder minimum (1645±1715). It is found that the recurrent and ̄uctuating activities were not appreciable and that the shock activity levels were very low. The aa index level was due almost entirely to the quiet days. Calculated average solar-wind velocities were 194.3 km s from 1657 to 1700 and 218.7 km s from 1700 onwards. Also, the coronal magnetic ®eld magnitude and southward interplanetary magnetic ®eld component Bz were lower. It is concluded that the nearly absent levels of geomagnetic activity during this period were due to lower coronal and Bz magnetic ®eld magnitudes as well as to the continuous impinging on the Earth of a slow wind.
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