Natural Sources of Electromagnetic Radiation

 

Sunspot Number

Sunspot number simply represents the number of observed sunspots and sunspot groups on the solar surface. It is computed according to the Wolf Sunspot Number formula: R = k (10g + s), where 'g' is the number of sunspot groups (regions), s is the total number of individual spots in all the groups, and k is a scaling factor that corrects for seeing conditions at various observatories. Sunspot number varies in phase with the solar flux. Sunspot numbers can vary between zero (for sunspot minimum periods) to values in excess of 350 or 400 (in the very active "solar max" period of the suns 11 year cycle). Solar flux is related to the sunspot number, since sunspots produce radio emissions at 10.7 cm wavelengths (as well as at other wavelengths).

Sunspot Classifications

Sunspots are classified according to size, shape and spot density. They are classified using a set of three coded letters (Zpc) as follows:

Z - Modified Zurich class, labelled A through F plus H.

A - Single small spot (single magnetic polarity).

B - Very small distribution of small spots.

C - Two or more small spots, at least one of which has a detectable penumbra.

D - Moderately sized group of spots, several of which may have noticable penumbrae. Magnetic complexity of D-type regions are usually capable of producing C and low-intensity M-class flares.

E - Moderate to large area of a fairly complex system of sunspots, several of which have noticable penumbrae and good definition. Often capable of producing minor C-class as well as major M-class flares.

F - Large to very large area of a complex system of sunspots. These regions are often capable of producing major X-class flares as well as numerous major M-class and many C-class events (depending on their magnetic complexity).

H - Single large to very large sunspot (not usually capable of producing significant energetic events). This type of sunspot is usually manifest in the dying phase of a sunspot group.

p - Penumbra type of the largest spot in the group.

x - Single spot.

r - Rudimentary.

s - Small symmetric.

a - Small asymmetric.

h - Large symmetric.

k - Large asymmetric.

c - Relative sunspot distribution or compactness of the group.

x - Single spot.

o - Open group (separated by quite a wide space).

i - Intermediate (moderate sunspot compactness in the group).

c - Compact (very dense and complex spots within the group).

Example: A sunspot group classified as type DKO would be of moderate overall size (that is, the region encompassing all of the sunspots within the group would be of moderate size), the penumbra of the largest spot within the group would be large and asymmetric in shape, and the group would be "open" indicating that the sunspots within the region are not notably close together.

Magnetic Class

The magnetic class of sunspots is important in determining how potentially volatile particular active regions may be. Sunspots are regularly observed using instruments capable of determining the magnetic polarity of sunspots and active regions. By also applying laws which have been formulated over the years, visual observations can also be used to establish the magnetic polarity and complexity of spot groups. There are basically 7 magnetic types of sunspots that are classified. They are described as follows:

Type

A - Alpha (single polarity spot).

B - Beta (bipolar spot configuration).

G - Gamma (atypical mixture of polarities).

BG - Beta-Gamma (mixture of polarities in a dominantly bipolar configuration).

D - Delta (opposite polarity umbrae within single penumbra).

BD - Beta with a Delta configuration.

BGD - Beta-Gamma with a Delta configuration.

Example: A region labelled as having a magnetic classification of BG indicates that the sunspot region contains a mixture of magnetic polarities, but the dominant polarity of the group is bipolar. Potentially very powerful and potent regions are those which have classifications of BG, BD and BGD. As magnetic complexity increases, the ability of an active region to spawn major energetic events likewise increases.

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Prepared by the YES I Can! Science Team,