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 has played, and continues to play, an important role in forecasting. The instrument is located at the IPS 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 IPS who obtained access the data in real-time from CSIRO. By 1986 the Radiospectrograph had exhausted its scientific potential and the instrument was transferred to IPS for use in solar-terrestrial forecasting.

In 1991 IPS commenced work on a major upgrade to the instrument to replace electronics which were obsolete and had degraded badly in performance. The new Radiospectrograph was brought back into operation in May 1992 and has been performing its role effectively since that time.

The figure 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 on June 4, 1992. The vertical axis is radio frequency spanning a range of 18 MHz up to 180 MHz (in August 1992 the frequency range was expanded up to 1800 MHz). The large dark areas in the figure show a radio burst originating from the sun. The particularly interesting, and important for forecasters, event is the slanted one 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 IPS make an estimate of the speed at which this cloud of material is travelling outwards from the sun - important information in making terrestrial forecasts.

Further spectrograph images, including a higher resolution version of this image, can be found in the Culgoora section.

Material Prepared by Richard Thompson. © Copyright IPS - Radio and Space Services.