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). From the upper
chromosphere we receive the strongest signal in the Lyman-alpha line (at 121.6 nm) and the other members
of the Lyman series of hydrogen. Lower down in the solar atmosphere, line emission from the Balmer series
of hydrogen becomes dominant, with its most prominent member, the famous H-alpha line at 656.3 nm.
In fact, most flare observations have been made using this line, since it is situated near the
peak of the visible part of the solar spectrum and is thus easily accessible to ground-based
observers. That is the reason why for many years the area at the time of maximum H-alpha
brightness of flares and also their “importance” (faint, normal or brilliant) have been used for flare
classification. Many volumes of Solar and Geophysical Data beginning in 1938 (published by
NOAA) are filled with these data, and yet these lists are incomplete and suffer from non-objective
judgments of different observers. A typical H-alpha flare observed from the ground is shown in
Figure 13.
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http://www.livingreviews.org/lrsp-2006-2 |
© Max Planck Society and the author(s)
Problems/comments to |
http://www.oafa.fcefn.unsj-cuim.edu.ar/ELSchool_2005.htm