Weekly Notes from the Yohkoh Soft X-Ray Telescope
(Week 19, 2002)
Science Nugget: May 10, 2002
Complicated radio waves from an X-class flare
The remarkable flare that we introduced in the
April 19 science nugget will continue to amaze and astound us,
partly because the
"Max Millennium" organizational machinery worked splendidly, so
that many of the world's observatories were looking at the right place
at the right time.
In this nugget we present complicated data from ground-based observatories
in China and Japan.
The purpose here is mainly to give a feeling for the range of data people
need to consider while they work out explanations for these things.
The intention is to return to this flare again with future nuggets, and
no doubt this well-observed phenomenon will be the subject of an actual
workshop in which people meet physically, rather than through the ether
as we are doing now.
Radio time profiles
The plot below shows a sample of three time profiles at radio frequencies
of 1, 17, and 34 GHz, from the
Nobeyama solar radio observatory.
Many complicated things can be seen in this plot:
At 1 GHz (red) a huge flux, due (we think) to a plasma emission
mechanism capable of making the apparent temperature (hence radio flux)
far greater than its natural thermal temperature;
At 17 GHz (purple) the gyrosynchrotron spectrum, also inherently
non-thermal, produced by fast electrons gyrating in coronal magnetic
At 34 GHz (yellow), barely detected because of drifting background
levels, the thermal signal - bremsstrahlung or free-free radiation are other
terms for this - that is the low-frequency tail of what we see in
Even more complicated, almost to the point of inexplicability, one has
various kinds of radio spectra, such as the following from
This represents a narrow range (1.2 GHz) of frequencies not far from the red
line in the plot above), over a short time interval (about 3 minutes).
It contains a myriad of drifting structures.
Radio events with drifting fine structure occur, and in principle their
occurrences tells us many things.
Because of the frequencies we know that the sources of these emissions
do not lie far up in the corona, but rather in the dense core of the
flaring active region.
So probably we would learn about flare dynamics directly if only we
could understand them.
But, this will require a new instrument: a
Frequency Agile Solar Radiotelescope
capable of true imaging spectroscopy, with high resolution in all parameters.
No conclusions, really, except to remind data analyzers of the great
complexity of the radio spectrum of a solar flare.
This complexity is unfortunate, but of course it points to complex
knowledge that will be gained once the phenomena are understood.
index] -o- [Chronological
May 10, 2002
Hugh Hudson and David McKenzie(email@example.com)