CODES, TERMINOLOGY AND CLASSIFICATIONS

  • ISES code book
  • Forecasting guide
  • Glossary
  • Sunspot Group Classification
  • Mount Wilson Magnetic Classifications
  • X-RAY flare class
  • Optical flare class
  • Radio emission storms
  • Geomagnetic indices
  • Levels of geomagnetic activity


  • 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.

    There are 60 valid McIntosh classifications (see table).
    Examples: Dao, Eao, Ekc, Fai, Fkc, Fko. (Images courtesy: Franky Dubois)

     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.
    

    Geomagnetic Indices
    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.
    

    Recommended glossaries
            
  • 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