Solar Radio Data

Scientists monitor the structure of the solar corona, the outer most regions of the Sun's atmosphere, using radio waves -- the surface of the Sun is 6,000 degrees Kelvin, while the high corona can reach several million degrees Kelvin. Solar radio emissions at different frequencies allow us to observe radiation from different heights in the atmosphere. The lower the frequency, the higher the height of origin. The frequency, like the electron density, decreases uniformly outwards: 245 MHz originates high in the corona, while 15,400 MHz originates in the low corona. The 5 MHz emission corresponds to about 10 solar radii height. For a detailed review, see McLean and Labrum (1985)SOLAR RADIOPHYSICS.

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.

For great movies of solar radio events and more information about Solar and Stellar Radio Astronomy, please visit the website of Dr. Stephen White. His PowerPoint talk The Radio Sun is also available.

1. Solar Radio Bursts Event Listings from a worldwide network of stations ---- Download Data

2. Solar Radio Flux -- Noon Flux Measurements from Ottawa/Penticton (10.7 cm/2800 MHz) and USAF stations (8 fixed frequencies between 245-15,000 MHz) 1947 to present ---- Download Data

3. International Astronomical Union (IAU) Quarterly Bulletin on Solar Activity (QBSA) daily solar radio noon flux values NASA SPDS and NOAA ESDIM Data Rescue -- from 55 stations, for the time period 1949-1986 (722 station-years, 16.6 Mbytes) ---- Download Data

4. USAF RSTN Radio Solar Telescope Network 1 second Data -- 8 selected frequencies from four worldwide station network -- for data 1980-2000, please check the rstn tape catalog. For earlier data on strip charts, 1977-1984, please check the solar radio charts catalog. ---- Download Data

5. Solar Radio Spectral Event Data 1967-present -- event listings from worldwide network ---- Download Data

6. RSTN Solar Radio Spectral Graphical Data from four Stations, with viewing software ---- Download Data

7. Stanford Daily Maps of Solar 9.1 cm Microwave Emission Jun 1962-Aug 1973 ---- Download Data
8. East-West Solar Radio Scans from several stations 1957 to present
   • East-west solar radio scans give the strip intensity distribution at radio wavelength from one limb of the solar disk, through the center of the disk, to the other limb. When daily drift profiles are compared, they reveal the movement and evolution of active regions near the solar equator.
   • NGDC archives several solar radio east-west scan databases, including Fleurs (Australia) 1966-1989, MIT (U.S.) 1983-1987, Nancay (France) 1957 to present, Nederhorst (The Netherlands) 1957-1970, Ottawa (Canada) (1968-1988), and Toyokawa (Japan) 1977-1989. Many of these are published in the monthly publication Solar-Geophysical Data (SGD). Please contact the data center for further information.