CODES, TERMINOLOGY AND CLASSIFICATIONS
Sunspot Group Classification
The 3 component McIntosh classification (McIntosh, Sol. Phys. 125, 251-267,1990) is based on the general form 'Zpc', where 'Z' is the modified Zurich Class, 'p' describes the penumbra of the principal spot, and 'c' describes the distribution of spots in the interior of the group.
Z-values: (Modified Zurich Sunspot Classification). A - A small single unipolar sunspot. Representing either the formative or final stage of evolution. B - Bipolar sunspot group with no penumbra on any of the spots. C - A bipolar sunspot group. One sunspot must have penumbra. D - A bipolar sunspot group with penumbra on both ends of the group. Longitudinal extent does not exceeds 10 deg. E - A bipolar sunspot group with penumbra on both ends. Longitudinal extent exceeds 10 deg. but not 15 deg. F - An elongated bipolar sunspot group with penumbra on both ends. Longitudinal extent of penumbra exceeds 15 deg. H - A unipolar sunspot group with penumbra.
p-values: x - no penumbra (group class is A or B) r - rudimentary penumbra partially surrounds the largest spot. This penumbra is incomplete, granular rather than filamentary, brighter than mature penumbra, and extends as little as 3 arcsec from the spot umbra. Rudimentary penumbra may be either in a stage of formation or dissolution. s - small, symmetric (like Zurich class J). Largest spot has mature, dark, filamentary penumbra of circular or elliptical shape with little irregularity to the border. The north-south diameter across the penumbra is less or equal than 2.5 degrees. a - small, asymmetric. Penumbra of the largest spot is irregular in outline and the multiple umbra within it are separated. The north-south diameter across the penumbra is less or equal than 2.5 degrees. h - large, symmetric (like Zurich class H). Same structure as type 's', but north-south diameter of penumbra is more than 2.5 degrees. Area, therefore, must be larger or equal than 250 millionths solar hemisphere. k - large, assymetric. Same structure as type 'a', but north-south diameter of penumbra is more than 2.5 degrees. Area, therefore, must be larger or equal than 250 millionths solar hemisphere.
c-values x - undefined for unipolar groups (class A and H) o - open. Few, if any, spots between leader and follower. Interior spots of very small size. Class E and F groups of 'open' category are equivalent to Zurich class G. i - intermediate. Numerous spots lie between the leading and following portions of the group, but none of them possesses mature penumbra. c - compact. The area between the leading and the following ends of the spot group is populated with many strong spots, with at least one interior spot possessing mature peanumbra. The extreme case of compact distribution has the entire spot group enveloped in one continuous prenumbral area.
Mount Wilson Magnetic Classifications
Alpha. Denotes a unipolar sunspot group. Beta. A sunspot group having both positive and negative magnetic polarities, with a simple and distinct division between the polarities. Beta-Gamma. A sunspot group that is bipolar but in which no continuous line can be drawn separating spots of opposite polarities. Delta. A complex magnetic configuration of a solar sunspot group consisting of opposite polarity umbrae within the same penumbra. Gamma. A complex active region in which the positive and negative polarities are so irregularly distributed as to prevent classification as a bipolar group.
X-ray flare class
- Rank of a FLARE based on its X-ray energy output. Flares are classified by the order of magnitude of the peak burst inten- sity (I) measured at the earth in the 1 to 8 angstrom band as follows:
Class (in Watt/sq. Meter) B I less than (l.t.) 10.0E-06 C 10.0E-06 l.e.= I l.t.= 10.0E-05 M 10.0E-05 l.e.= I l.t.= 10.0E-04 X I g.e.= 10.0E-04
Optical flare classification
- The optical system approved by Commission 10 of the IAU in 1966 uses area (in degree of heliocentric latitude), as given in the table below. The area is supposed to be corrected for projection, but height effects make published areas of flares more than 65 degrees from central meridian passage quite inaccurate. A suffix (f,n or b) is added if the brightness (determined by visual estimate) is faint, normal or bright. (source: Astrophysics of the Sun, Harold Zirin)
Area Area Class Typical corresponding (sq deg) (10^-6 solar A) SXR Class <= 2.0 <= 200 S C2 2.1-5.1 200-500 1 M3 5.2-12.4 500-1200 2 X1 12.5-24.7 1200-2400 3 X5 >24.7 > 2400 4 X9
Radio emission storms
- Emissions of the sun in radio wavelengths from centimeters to dekameters, under both quiet and disturbed conditions.
Type I. A noise storm composed of many short, narrow-band bursts in the metric range (300 - 50 MHz). Type II. Narrow-band emission that begins in the meter range (300 MHz) and sweeps slowly (tens of minutes) toward deka- meter wavelengths (10 MHz). Type II emissions occur in loose association with major FLAREs and are indicative of a shock wave moving through the solar atmosphere. Type III. Narrow-band bursts that sweep rapidly (seconds) from decimeter to dekameter wavelengths (500 - 0.5 MHz). They often occur in groups and are an occasional feature of complex solar ACTIVE REGIONs. Type IV. A smooth continuum of broad-band bursts primarily in the meter range (300 - 30 MHz). These bursts are associated with some major flare events beginning 10 to 20 minutes after the flare maximum, and can last for hours.
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 A INDEX. A daily index of geomagnetic activity derived as the average of the eight 3-hourly a indices. K INDEX. A 3-hourly quasi-logarithmic local index of geomagnetic activity relative to an assumed quiet-day curve for the recording site. Range is from 0 to 9. The K index measures the deviation of the most disturbed horizontal component. Kp INDEX. A 3-hourly planetary geomagnetic index of activity generated in Gottingen, Germany, based on the K INDEX from 12 or 13 stations distributed around the world. AFred. Abbreviation for the A INDEX for Fredericksburg. Ap INDEX. An averaged planetary A INDEX based on data from a set of specific stations. Dst INDEX. A geomagnetic index describing variations in the equatorial ringcurrent.
Levels of geomagnetic activity
QUIET. With regard to geomagnetic levels, a descriptive word specifically meaning geomagnetic levels such that Ap is less than 8 (see Ap INDEX). UNSETTLED. A descriptive word specifically meaning that Ap is greater or equal to 8 and less than or equal to 15. ACTIVE. Geomagnetic levels such that AP is greater than 15 and less than 30. GEOMAGNETIC STORM. A worldwide disturbance of the earth's magnetic field, distinct from regular diurnal variations. Minor Geomagnetic Storm: A storm for which the Ap index is greater than 29 and less than 50. Major Geomagnetic Storm: A storm for which the Ap index is greater than 49 and less than 100. Severe Geomagnetic Storm: A storm for which the Ap index is 100 or more.
- NOAA's Space Environment Center Glossary of Solar-Terrestrial Terms
- Stanford's Solar Glossary
- IPS Radio & Space Services (IPS, Australia) Glossary
- Oulu Space Physics Textbook