The Culgoora Radiospectrograph
Observations of the Sun are a vital component in forecasting disturbances to the geomagnetic field and the ionosphere. These include not only optical observations of sunspots and solar flares but also observations from space with X-ray telescopes and from the ground with radio telescopes.
The Culgoora Radiospectrograph is a radio telescope which plays an important role in forecasting. The instrument is located at the SWS Culgoora Solar Observatory on the CSIRO "Australia Telescope" site near Narrabri in northern New South Wales. The radiospectrograph was originally built by CSIRO and used for pioneering scientific studies of radio bursts from the Sun. The observations also proved of interest to SWS which obtained access to the data in real-time from CSIRO. By 1986 the radiospectrograph had exhausted its scientific potential and the instrument was transferred to SWS for use in solar-terrestrial forecasting.
In 1991 SWS commenced work on a major upgrade to the instrument to update the electronics which were degrading performance. The new radiospectrograph was brought back into operation in May 1992 and has been performing its role effectively since that time.
The figure below shows the first significant solar radio burst observed with the upgraded instrument. The horizontal axis is time (in Universal or Greenwich Mean Time) showing an interval of 25 minutes between 0400 and 0425 UT on 4 June 1992. The logarithmic vertical axis is radio frequency spanning a range of 18 MHz up to 180 MHz (in August 1992 the frequency range was increased to 1800 MHz). The large dark areas in the figure show a radio burst originating from the Sun. The particularly important event for forecasting is the slanted burst on the right hand side. This kind of signal is known as a Type II burst and is produced by electrically charged material being ejected from the Sun after a solar flare, perhaps on its way to produce a disturbance here on Earth. The manner in which the radio frequency changes with time allows an estimate of the speed at which this cloud of material is travelling away from the Sun - important information in making terrestrial forecasts.
More spectrograph images can be found in the Culgoora spectrograph section.
Material prepared by Richard Thompson