Legacy data generated or curated by NOAA for solar events such as solar flares, solar ionospheric disturbances and solar radio emissions. NOAA NCEI has acquired these legacy datasets 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.
Questions and comments may be directed to ncei.info@noaa.gov.
Solar Flares
A solar flare is a localized, short-lived, sudden brightening in solar atmospheric radiation. Solar flares usually occur near sunspots and active regions. 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 1030ergs; 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.
Historically, solar flares were monitored by ground-based telescopes in the H-alpha wavelength. These telescopes measure a chromospheric emission line, or measure in white light, observing emissions from the photosphere. Today, solar flares are most commonly observed in X-ray or EUVS wavelengths from instrumentation aboard of satellites
Visit GOES-R EXIS and SUVI pages to find current solar data products, and the GOES 1-15 page for solar data from 1975 to 2020).
Legacy Solar Flare Datasets
NCEI archives legacy solar flare datasets from approximately 80 stations, from 1938 to 2017. Please find the descriptions and references at the Read me file, and in the documents available in each archive directory. Some of the flare reports presented here were processed and published in the monthly NOAA National Geophysical Data Center (NGDC) (precursor of NCEI) report "Solar Geophysical Data" and, in a different format, in the IAU "Quarterly Bulletin on Solar Activity".
Solar Flare Reports
- H-alpha flare event multiple station list (1955-2010)
- H-alpha flare event multiple station tables (1955-2010)
- H-alpha flare event list - Kanzelhohe.txt files (1948-2015)
- H-alpha flare report - SOON (USAF Solar Observing Optical Network) .txt files (2010-2017)
- H-alpha flare merged list, multiple stations .txt files (1938 - 2010)
- H-alpha and optical flare event list: .txt files (1938-2015). Data source from 1938–1999: NASA SPDS and NOAA ESDIM Data Rescue projects.
- H-alpha Flare Patrol.txt files and monthly graphs from worldwide stations (1955-2010)
- Flare Index - Kandilli Solar Observatory: .txt files (1976-2024)
- Comprehensive Flare Index - CFI: .txt files (1955-1980)
- GOES X-ray flare reports - X-ray Sensor: .txt files (1975-2017)
- GOES X-ray flare reports - Soft X-ray Imager: .txt files (2004 -2007)
- SOLRAD flare reports: .txt files (1968-1974)
Sudden Ionospheric Disturbances (SIDs)
Sudden Ionospheric Disturbances (SIDs) are abrupt enhancements of ionization/plasma density in the lower layer of the diurnal ionosphere (D-region), caused by a solar flare. SIDs impact the propagation of radio-waves in the Earth-Ionosphere waveguide and can be detected in Very Low Frequency (VLF) data.
NCEI archives legacy SID datasets from the International Ursigram and World Days Services (IUWDS) and private interested individual VLF observers from AAVSO, covering the period from 1938 to 2017.
Please find the descriptions and references at the Read me file, and in the documents available in each archive directory.
Data Access
Solar Radio Emissions
The structure of the solar corona, the outermost region of the Sun's atmosphere, can be monitored using radio waves (100’s of MHz to 10’s of GHz). Variations in the radio wave 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, the higher the height of origin.
Radio bursts are associated with solar flares. The signal arrival time delay at Earth of the different radio frequencies during burst events is due to the outward movement of the source. 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.
NOAA NCEI has solar radio legacy datasets from multiple sources, including the United States Air Force (USAF) Radio Solar Telescope Network (RSTN) stations. RSTN uses four widely spaced antennae to observe the Sun between 18 MHz and 15 GHz to measure solar radio bursts: Palehua (Ka'ena Point), Learmoth, San Vito and Sagamore Hill.
Data Access
- Radio bursts from Culgoora Observatory: .txt files (2011-2014)
- Radio bursts at fixed frequencies, RSTN: .txt files (1960 - 2010) | Read me
- Radio bursts, spectral data, RSTN: .txt files (1967 - 2011)
- Type II from Weissenau station: .pdf and .txt files (1966 - 1987)
- Type II from RSTN: .txt files (1967 - 2009)
- Radio bursts summary, RSTN: .txt files (2012)
- Noontime Radio flux, multiple stations, including RSTN: .txt files (1947 - 2019)
- Daily mean Radio flux, multiple stations from IAU "Quarterly Bulletin of Solar Activity" and Ottawa: .txt files (1949 - 1986) Data source: NOAA/ESDIM and NASA/SPDS data rescue projects.
- Daily Solar Radio Maps from Nobeyama Observatory: .pdf files (2002 - 2011)
- Daily Solar Radio Maps from Stanford: .txt files (1962 - 1973) | Read me