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alpha.
A unipolar sunspot group.
beta.
A sunspot group having both positive and negative magnetic polarities
(bipolar), with a simple and distinct division between the polarities.
gamma.
A complex active region in which the positive and negative
polarities are so irregularly distributed as to prevent classification
as a bipolar group.
beta-gamma.
A sunspot group that is bipolar but which is sufficiently
complex that no single, continuous line can be drawn between spots of
opposite polarities.
delta.
A qualifier to magnetic class (see below) indicating that
umbrae separated by less than
2 degrees within one penumbra have
opposite polarity.
beta-delta.
A sunspot group of general beta magnetic classification but
containing one (or more) delta spot(s).
beta-gamma-delta.
A sunspot group of beta-gamma magnetic classification
but containing one (or more) delta spot(s).
gamma-delta.
A sunspot group of gamma magnetic classification but
containing one (or more) delta spot(s).
Type I.
A noise storm composed of many short, narrow-band bursts
in the meter wavelength range (300-50 MHz), of extremely variable
intensity. The storm may last from several hours to several days.
Type II.
Narrow-band emission (sweep) that begins in the meter range
(300 MHz) and sweeps slowly (tens of minutes) toward dekameter
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 occur with some major flare events;
they begin 10 to 20 minutes after the flare maximum and can last for
hours.
Type V.
Short-duration (a few minutes) continuum noise in the dekameter
range usually associated with Type III bursts.
P-angle (or P).
The position angle between the geocentric north pole and
the solar rotational north pole measured eastward from geocentric
north. The range in P is +/- 26.3l degrees.
Bo.
Heliographic latitude of the central point of the solar disk; also
called the B-angle. The range of Bo is +/- 7.23 degrees, correcting for
the tilt of the ecliptic with respect to the solar equatorial plane.
Example: If (P,Bo) = (-26.21 degrees, -6.54 degrees), the heliographic
latitude of the central point on the solar disk is -6.54 degrees (the
north rotational pole is not visible), and the angle between the
projection onto the disk of the geocentric north pole and the solar
north rotational pole is 26.21 degrees to the west.
Lo.
Heliographic longitude of the central point of the solar disk. The
longitude value is determined with reference to a system of fixed
longitudes rotating on the Sun at a rate of 13.2 degrees /day
(the mean rate of rotation observed from central meridian transits
of sunspots). The standard meridian on the Sun is defined to be the
meridian that passed through the ascending node of the Sun's equator
on 1 January 1854 at 1200 UTC and is calculated for the present day
by assuming a uniform sidereal period of rotation of 25.38 days.
Once P, Bo, and Lo are known, the latitude, central meridian distance,
and longitude of a specific solar feature can be determined as follows:
Latitude.
The angular distance from the solar equator, measured north
or south along the meridian.
Central meridian distance (CMD).
The angular distance in solar longitude
measured from the central meridian. This position is relative to the
view from Earth and will change as the Sun rotates; therefore, this
coordinate should not be confused with heliographic positions that
are fixed with respect to the solar surface.
Longitude.
The angular distance from a standard meridian (0 degrees
heliographic longitude), measured from east to west (0 degrees to
360 degrees) along the Sun's equator. It is computed by combining CMD
with the longitude of the central meridian at the time of the
observation, interpolating between ephemeris values (for 0000 UT) by
using the synodic rate of solar
rotation (27.2753 days, 13.2 degrees per day).
Return to HAO homepage.
-Revised 25 January 1996 by
webmaster@hao.ucar.edu.
Copyright 2000, NCAR.
- Written by Barry Knapp.
- Approved by Dick White.