A sudden eruption of energy on the solar DISK lasting minutes to hours, from which radiation and particles are emitted.
Flare-Associated Events
The subdisciplines in this category provide information on solar and terrestrial phenomena at the time of solar flares. The instruments and types of observations are identical to those providing data in the other categories.
- H-alpha Flares
- Solar Magnetic Fields in Active Regions and Their Short-Term Changes
- Solar Radio Events, Fixed Frequency
- Solar Radio Spectrograms of Events
- Solar X-Ray Observations
- Sudden Ionospheric Disturbances--Ground Based Observations
- Solar Protons and Electrons--Direct Measurements
- Cosmic Ray Ground Level Increases
As in the Solar and Interplanetary Phenomena category, many of the data above have been regularly published since 1955 in Solar-Geophysical Data (SGD). Thus, the most efficient and economical means of satisfying data requests is frequently by means of SGD or extracts copied from it.
A major body of data, not in SGD, is the 35mm H-alpha flare patrol films. During patrol operations images of the sun are usually recorded cinematographically at various intervals depending on solar activity. The intervals can vary from a few seconds to only a few frames each hour. NGDC holds archives for years 1933 through 1990. We expect to archive digital solar imagery in the near future.
Flare-events discipline data on diskette or CD-ROM include solar flares, solar radio bursts, regions of solar activity and sudden ionospheric disturbances. Satellite data available on CD-ROM are X-ray and magnetic field data from the SMS/GOES satellites, and particle data from DMSP, NOAA/TIROS and SMS/GOES satellites. Other data in this discipline are held on paper tabular or graphical displays.
The United States Air Force Solar Observing Optical Network (SOON) supplies us with daily digital solar activity data from Palehua (Hawaii), Ramey (Puerto Rico), Holloman (New Mexico), and Learmonth (Australia). For further information on data availability, formats, and costs, please contact the data center.
ON-LINE GLOSSARY OF SOLAR-TERRESTRIAL TERMS of National Geophysics Data Center
Flare Classifications:
Flares are classified using one of two different systems. The first classification ranks the event by measuring its peak x-ray intensity in the 1-8 angstrom band as measured by the GOES satellites. This x-ray classification offers at least two distinct advantages compared with the second system of classification (optical): it gives a better measure of the geophysical significance of the event and it provides an objective means of classifying geophysically significant activity regardless of its location on the solar disk or near the solar limb. The classification scheme is as follows:
Class Peak Flux (1-8 Angstroms in Wm-2)
A < 10-7
B < 10-6 but > class A
C < 10-5 but > class B
M < 10-4 but > class C
X > 10-4
The letter designates the order of magnitude of the peak value. Following the letter the measured peak value is given. For descriptive purposes, a number from 1.0 to 9.9 is appended to the letter designation. The number acts as a multiplier. For example, a C3.2 event indicates an x-ray burst with a peak flux of 3.2 x 10-6 Wm-2. Since x-ray bursts are observed as a full-Sun value, bursts below the x-ray background level are not discernable. The background drops to class A level during solar minimum; only bursts that exceed B1.0 are classified as x-ray events. During solar maximum, the background is often at the class M level, and therefore class A, B and C x-ray bursts cannot be seen. Bursts greater than 1.2 x 10-3 Wm-2 may saturate the GOES detectors. If saturation occurs, the estimate peak flux values are reported.
The second system of classification involves a purely optical method of observation. A flare event is observed optically (in H-alpha light) and is both measured for size and brightness. This classification therefore includes two items of information: a descriptor defining the size of the flare and a descriptor defining the peak brightness of the flare. They are listed below:
Importance
S - Subflare area <= 2.0 square degrees.
1 - 2.1 <= area <= 5.1 square degrees.
2 - 5.2 <= area <= 12.4 square degrees.
3 - 12.5 <= area <= 24.7 square degrees.
4 - area >= 24.8 square degrees.
Brightness
F - Faint.
N - Normal.
B - Brilliant.
Example: A major flare rated as a class M7.4/2B event indicates that the flare attained a maximum x-ray intensity of 7.4 x 10-5 Wm-2. The "2B" portion of this specification indicates that the flare was an importance 2 flare (>= 5.2 and <= 12.4 square degrees) and was optically Brilliant. This sample flare is a powerful event. Flares that reach x-ray levels in excess of class M4 can begin to have an impact on the Earth. Likewise, flares rated 2B or greater are generally capable of influencing the Earth, particularly if accompanied by Type II and IV radio sweeps (discussed below).
Mr. Vaino K. Lehtoranta |
