## Observing the minimum through Solar Flux

Published July 12, 2009 by Sean

According to this blog there are no signs of a new cycle although there has recently been a sunspot which all seem to agree does count as a real spot worthy of a number, region 1024, lasting 8 days before rotating out of view – photo timeseries.
With reference to the solar flux at 10.7cm, it is understood that sunspot activity gives rise to an increase of flux at the times when sunspots are present. As the sun’s regular cycle which varies around 11 years in duration progresses, the underlying flux level also increases, and the sun becomes generally more active (although only by a small fraction). According to Dr Svalgaard, F10.7 is a good proxy for sunspot activity, and if I have understood, is representative of several underlying processes taking place within the sun.
At each minimum F10.7 drops to about the same level, this is the sun’s idle state, corresponding to about 1360 W/m^2 of the total energy received from the sun. At the peak of solar cycle activity, this goes up by 1 W/m^2, so the changes are small compared with the background noise. Data for the above plot is taken from noaa

In order to construct this chart, I took the approach used when measuring the noise figure of sensitive radio amplifiers. I assume that the measured value is the sum of two input sources, the background level, which here i assume to be 67.0 (this happens to be the lowest monthly observation in my time-series).
I then construct an inferred cycle activity value which is the amount i have to add to the background in order to reach the observed value. Since we are adding powers of un-correlated signals (really two noise sources) the summation is done a the sum of squares. (The reasoning being that if we convert to voltages, voltages add linearly).
I took an arbitrary decision to draw the two sides of the minimum as being 100% contributed by the fading cycle 23 and the emerging cycle 24, but hopefully it is clear that if I wanted to decompose the 3.6 flux units in Nov08 into cycle 23 and 24 evenly (each giving 2.6 units) and then subtracted the same cycle 24 value from Oct08, I would get the following split for Oct08

• Background 67
• Cycle 23: 10.1 (rather than the 10.3 shown)
• Cycle 24: 2.6
• Now, the period of increasing flux is short, but the rate of increase is not wildly different to the decrease. What I have shown here is a better method of analysing the small variation in the measurement, rather than making any attempt to explain the underlying physics or make predictions. Just because the curve appears to be almost flat and quite noisy doesn’t mean that there is no information to be gained from it.

###### Update 13July

In order to confirm that the ramp is not very differnet from the start of Cycle 23, I have overlaid the same decomposition of old and new cycle for the previous minimum. I took an arbitary start point for the alignment, and plotted the end of cycle 22, and the start of cycle 23. in order to aportion flux between the two cycles, at an arbitary point I replaced the cycle 22 values with a simple straight line (as indicated in the dotted section) and subtracted this from the total, leaving a nominal strength for cycle 23. Both of the tail ends of old cycles show a consistent form, it is too early to tell how the new cycle compares with the start of cycle 23, but it is looking good so far. Filed under Solar