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.
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