Half Year Cyclic Variaition in RSS,UAH and GISS Anomaly
Posted by Jeff Condon on October 26, 2008
From my previous post we looked at the FFT of the three main temp metrics from which Tamino noticed a strong 1 year signal in the UAH weather. From Leif Svalgaard’s comments on my other post, the solar heating effect is compensated for on a monthly basis by some function. This creates a few problems, scientists need to know the response of the earth climate to solar forcing, the difference in albedo between the hemispheres, the phase angle lag created by the thermal mass of the climate system and any feedback mechanisms associated with the response to make an accurate correction.
The phase of the one year trend I found in my last post means that (not surprisingly) the AGW guys have underestimated the annual response to solar heating in all three anomaly metrics. In their defense, they may have simply estimated the lag incorrectly. e.g. The differrence between two slightly out of phase sine waves is a sine wave.
There is also a half year signal present in all three metrics. This kind of variation could be caused by seasonal effects or corrections between the hemispheres. Below are the three Fourier transforms I did of the three metrics.
Because of the sampling rate of the R fft function, I don’t have better resolution on the peak. I may need to write my own function again but in the meantime, this is the best resolution I have.
All three measurements show a strong half year variation in temp. I ran my correlation analysis again, checking the phase correlation of a half year wavelength sine wave and again found interesting results.
The peak of each best correlation to about 1 week resolution was
RSS – 1.68 months and 7.68 months after Jan 1
Giss – 1.44 months and 7.44 months after Jan 1
UAH – 1.68 months and 7.68 months after Jan 1
The FFT signal of all three was around 0.1 degrees C in amplitude. All three measurements have a very similar underlying half year trend.
Now I wonder what the temp anomalies look like with the 1 year and half year variation removed.