A solar flare is a localized, short-lived, sudden brightening in solar atmospheric radiation, usually occurring near sunspots and active regions. Flares are characterized by a rise time on the order of minutes and a decay time on the order of tens of minutes to hours. The total energy expended in a typical flare is about 1030 ergs. Historically, flares were monitored in the H-alpha passband (656 nm) which is centered on a chromospheric emission line. Occasionally, white light flares are observed in the photosphere. Presently, flares are most commonly characterized by their X-ray wavelength signatures and are monitored via satellite.
Geostationary Operational Environmental Satellite (GOES) 1974-present
The GOES X-Ray Sensor (XRS) has measured X-Ray fluxes in the 1-8 Å and 8-20 Å bands since the 1970s.
- GOES-R (2016+) space weather data, including flare data, is available for XRS
- Data for GOES-1 through -15 XRS is available from the Irradiance tab
- GOES Solar X-Ray Imager (SXI, 2004–2007) data is available from the Solar Imaging tab
- All Data (1975–Present)
XRS (1975–2017) - Solar-Flares Documentation
SOLar RADiation (SOLRAD) 1968–1974
Each detected solar X-ray flare is listed, giving the starting date and time, the end time, the peak flux and time at which the peak occurs for the 0.5-3 Å, 1-8 Å, and 8-20 Å bands. The starting and ending times are determined at the time (UT) when the 1-8 Å flux first rises above and subsequently drops below the 3 x10-3 ergs cm-2 s-1 level. In general, a flare will not be listed unless the 1-8 Å flux remains above the 3 x10-3 ergs cm-2 s-1 level for four minutes or more. The peak flux values given for the 1-8 Å and 8-20 Å bands are based on a 2.0x106 degree Kelvin "Gray Body'' approximation, and the peak value given for the 0.5-3 Å band is based on a 1.0x107 degree Kelvin approximation. All detectors are in units of ergs cm-2 s-1.
Extreme Ultraviolet Flares
Product Details
NCEI archived approximately 80 stations, starting in 1938. Most ground-based station data is available through approximately 2017. Five stations still send data to NCEI on a monthly basis. 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.”
H-alpha Tables
Each folder contains monthly PDFs of text files generated from ground-based observations. Each table gives as many of the following measurements as possible: time of beginning; time of maximum brightness; time of any prominent secondary maxima; time of end (all times in UT); area at time of maximum brightness (square degrees of solar disk correct for foreshortening); importance class of flare (IAU 1964 report, updated in 1975); heliographic coordinates of center of gravity of flare at maximum brightness; source of data are noted as photographic, electronic or visual data. Also, when available, maximum width, and end of every observing period is given while distinguishing gaps of five minutes or more.
H-alpha Flare Events and Reports
Yearly text file reports consist of data for each flare or sub flare, and a day-by-day table of times when the Sun was under observation by photographic, electronic, or visual patrol.
- Flare Events, Multiple Observatories (1955-2010)
- Kanzelhöhe (1948–2015)
- SOON (2010–2017)
- Merged Flare Reports (1938-2015)
Flare Patrol
Includes text files and monthly graphs of flare patrol data from worldwide sources. Photographic patrols indicate the normal interval between exposures. Visual patrols (without photographic patrol) indicate whether continuous or intermittent, and specify the normal intervals.
Solar H-alpha Kandilli Flare Index
Flare index data compiled from the Kandilli Solar Observatory. This dataset was prepared by the Kandilli Observatory and Earthquake Research Institute at the Bogazici University, and made available through the NOAA National Geophysical Data Center (NGDC).
The Comprehensive Flare Index (CFI)
Helen W. Dodson and E. Ruth Hedeman of the McMath-Hulbert Solar Observatory developed the Comprehensive Flare Index (CFI) from 1966–2008. The first description is printed in WDC-A for STP's Report UAG-14, "An Experimental, Comprehensive Flare Index and Its Derivation for 'Major' Flares, 1955–1969." Subsequent volumes of CFI indices for more recent years are given in Reports UAG-52 (1970–1974) and UAG-80 (1975–1979).
Solar Flare Observations
Flares are characterized by a rise time on the order of minutes and a decay on 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.
For more recent flare data, see NOAA’s more recent satellite instruments such as EXIS.
For real-time data, users are directed to NOAA’s Space Weather Prediction Center.
NOAA/NCEI has acquired these legacy data sets from multiple sources over many decades. The data presented here are provided, ‘as is,’ and in most cases the linked documentation is the entirety of available information. In some cases, older data may also be found in the Space Weather Legacy Print Publications.
Questions and comments may be directed to ncei.info@noaa.gov.
