On 02/12/2012 10:33 PM, Mauro Lacy wrote:
I'll perform a power spectral density analysis of sunspot number/solar
activity data. If there's a 5.52 year cycle in solar activity,
it'll show up, along with the main 11 year cycle. I don't think
something that big can be easily overlooked,
but nevertheless... it bodes well with my modest attempts at statistical
signal processing :-)
More about this later, probably.
Well, here are the graphs:
http://maurol.com.ar/solar_cycle
The data was obtained from http://solarscience.msfc.nasa.gov/greenwch. I
used the daily sunspot area as an indicator of solar activity.
The method used is an estimate of power spectral density by the Welch
(1967) periodogram/FFT method, which is readily available, by example in
octave or Matlab. I had to do some manual preprocessing of the data, and
after fiddling for a relatively long time with the scales, I finally
began to obtain some meaningful values.
As can be seen in http://maurol.com.ar/solar_cycle/daily_area-PSD3.png,
there are two peaks near Eta Carinae's period (5.539 years) of dimming
X-ray activity , at 5.51 and 5.3 years. They are both much less
significant than the main period of the solar cycle (which by the way,
seems to be actually near 10.6 years, not 11.04 years as usually
stated), and there's is not a period of exactly 5.539 years, but they
are close nevertheless. That is, there are (secondary) periods of the
solar system not in, but closer, to 5.539.
I obtained 5.539 years from the literature. This site in particular was
very helpful: http://etacar.umn.edu/
Regarding these results, I suppose you take it or leave it. I mean, they
really aren't *that* significant. But if you take it, there are some
interesting things to try:
1) smooth/consolidate the periodograms, to try to obtain less noise, and
higher peaks.
2) look for north hemisphere vs. south hemisphere cycles. As Eta Car is
south, maybe the periods in the south hemisphere are closer to Eta Car's
period. I'll do this next.
3) look for phase, not only frequency, correlations. I have yet to learn
how to do statistical phase analysis.
I hope you enjoy the pictures! If there are some people interested, I
can publish the scripts and techniques I used to obtain the graphs. It
really wasn't that difficult.
Best regards,
Mauro
