Listings and characterizations of solar x-ray flares

Collection includes a variety of indices related to solar activity contributed by a number of national and private solar observatories located worldwide. This metadata record is currently under construction.[SolarIndices A]

Solar Indices Bulletin is a prompt monthly information product that is distributed within two weeks after the observation month closes. For the month just ended, this 2-page circular tabulates daily values of sunspot numbers and 10.7 cm solar radio flux observed at Penticton (previously at Ottawa); flux measurements at eight other wavelengths are included. Page 2 of the Bulletin gives a table of smoothed monthly mean sunspot numbers for the current solar cycle--a table that begins with smoothed observed values for each month and ends with predictions.

Collection includes a variety of indices related to solar activity contributed by a number of national and private solar observatories located worldwide. This metadata record is currently under construction.[SolarIndices A]

Collection includes a variety of solar feature datasets contributed by a number of national and private solar observatories located worldwide.

Collection includes a variety of indices related to solar activity contributed by a number of national and private solar observatories located worldwide. This metadata record is currently under construction.[SolarIndices A]

Collection includes a variety of indices related to solar activity contributed by a number of national and private solar observatories located worldwide. This metadata record is currently under construction.[SolarIndices A]

Scientists monitor the structure of the solar corona, the outer most regions of the Sun's atmosphere, using radio waves (100’s of MHz to 10’s of GHz). Variations in the radiowave spectrum reveal characteristics of the corona and upper chromosphere in terms of altitude profile for the local plasma temperature, density and magnetic field. Typically, the lower the frequency then the higher the height of origin. The frequency, like the solar electron density, decreases uniformly outwards with 245 MHz originating high in the corona whereas 15,400 MHz originates in the low corona. Radio bursts are associated with solar flares. The delay at Earth of the different radio frequencies during burst events is due to the outward movement of the source. Bursts can have temperatures of 10xE12 degrees Kelvin. Large bursts last 10 to 20 minutes on average. Longer radio noise storms of persistent and variable high levels of radiation originate in sunspot groups, areas of large, intense magnetic fields. These storms are strongly circularly polarized due to the intense magnetic fields. The microwave wavelength 2800 MHz daily radio flux correlates highly with the daily sunspot number and the two databases are used interchangeably. The 2800 MHz, or 10.7 cm, responds to the same conditions that produce changes in the visible and X-ray wavelengths. Schmahl and Kundu (1995) find that the solar radio fluxes in the spectral range 1000-9400 MHz correlate well with the total solar irradiance. The intermediate frequencies (at 2800 and 3750 MHz) are produced mainly by free-free gyroresonance emission from sunspot structures, while 1000 and 9400 MHz flux are produced mainly by free-free processes from structures associated with plages. They can distinguish plage-associated emission from spot-associated emission in the time series of microwave flux, both contributing opposing effects on the total solar irradiance.

Collection includes a variety of indices related to solar activity contributed by a number of national and private solar observatories located worldwide. This metadata record is currently under construction.[SolarIndices A]

A solar flare is a short-lived sudden increase in the intensity of radiation emitted in the neighborhood of sunspots. For many years it was best monitored in the H-alpha wavelength and occurs in the chromosphere, though occasionally white light flares are seen in the photosphere. In modern times the solar X-ray wavelengths are monitored via satellite for solar flares. Flares are characterized by a rise time of the order of minutes and a decay time of the order of tens of minutes. The total energy expended in a typical flare is about 1030 ergs; the magnetic field is extraordinarily high reaching values of 100 to 10,000 gauss. Optical flares in H-alpha are usually accompanied by radio and X-ray bursts and occasionally by high-energy particle emissions. The optical brightness and size of the flare are indicated by a two-character code called "importance." The first character, a number from 1 to 4, indicates the apparent area. For areas of less than 1, an "S" is used to designate a subflare. The second character indicates relative brilliance: B for bright, N for normal and F for faint. A general discussion of solar flares is found in Svestka [1976]. The NOAA National Centers for Environmental Information (formerly NGDC) holds archives for about 80 stations, covering the period 1938 to the present. Currently 5 stations send their data to NGDC Boulder on a routine monthly basis -- the current main observing emphasis for Space Weather has transitioned to Coronal Mass Ejections (CMEs) which directly impact the Earth's geomagnetic field. Solar flares impact the Earth's upper atmosphere and can eject high energy particles that can cause satellite failures. The flare reports were processed and published in the monthly report "Solar-Geophysical Data" and in a different format in the IAU "Quarterly Bulletin on Solar Activity."