Watts Up With That?

UPDATE: The SWPC press conference audio is now available, hear it here

Shortly after SWPC dropped on their website their still invisible “press conference” ( I have yet to get the link to audio, even though requested twice from Doug Biesecker) Leif Svalgaard remarked that the 10.7 cm radio flux graph produced by SWPC in that announcement on their web page was “just wrong”.

After spending months as a regular supporting commenter, Leif asked if he could write a guest post about it. After several microseconds of uncertainty, I said “yes”. So for the first time ever on WUWT, I present Dr. Leif Svalgaard as guest author, rather than commenter. – Anthony

Since 1947 we have routinely measured the flux of microwaves from the Sun at wavelengths between 3 and 30 cm [frequencies between 10 and 1 GHz]. This emission comes from high in the Chromosphere and low in the Corona and has two different sources [although there is debate about their relative importance]: thermal bremsstrahlung [due to electrons radiating when changing direction by being deflected by other charged particles] and ‘gyro’-radiation [due to electrons radiating when changing direction by gyrating around magnetic field lines]. These mechanisms give rise to enhanced radiation when the temperature, density, and magnetic field are enhanced, so the microwave radiation is a good ‘measure’ of ‘general’ solar activity. As strong magnetic fields are located in specific regions that can live for weeks and often reoccur at or near the same location for months [perhaps even years], there is a strong rotational signal in the emission superposed on a solar cycle variation of a ‘background’ activity level. At solar minimum, especially a ‘deep’ one as we now experiencing, the effect of active regions largely disappears and we observe a sort of solar ‘ground state’.

As the radio flux measurements [as opposed to the sunspot number] are unaffected by changes of [human] observers and their observing techniques and instrumental and atmospheric differences they may be a ‘truer’ and more objective measure of solar activity [to the extent that we can reduce this complex concept to a single number per day] and the many decades-long flux record could throw light on the important issue of the long-term variation of solar activity. The solar microwave flux is nominally an absolute flux, one solar flux unit defined as [the very small amount of] 10^-22 Watt per square meter per Hertz. Making an absolute measurement is always difficult and considerable uncertainty and debate surrounded these measurements early on, before being settled by international cooperative work in the late 1960s [Tanaka et al., Solar Phys. 29 (1973) p. 243-262; http://www.leif.org/research/Tanaka-Calibration-F107.pdf]. By observing the radio flux from supernova remnants [Cassiopeia-A, Cygnus-A, and Virgo-A] one can verify the constancy of the calibration. Read the rest of this entry »