Monday, March 28, 2011

Sunday, March 20, 2011

Wavelet Coherence Analysis!

I've started using a cool Matlab program that generates a 4-dimensional power spectra for any time series. A normal power spectra is averaged over an entire dataset, but this technique, called Wavelet Coherence Analysis using a sliding "window" to examine power spectra continuously over the entire series. Of course, for longer and longer wavelengths, the sliding window necessarily becomes larger and larger, until wavelengths can no longer be measured on the data. The dark black hemicurve on this diagram shows that limit, and the data greyed out beyond that line is edge-affected power spectra.

The data I chose for this analysis were the maximum daily temperatures for Chapel Hill, North Carolina, in 2010. There are 365 days along the X axis, and various wavelengths ranging from 4 to 64 days along the Y axis. Colors indicate "power" at a given wavelength, for a given time of the year. Significant areas within the hemicurve are circled with a black line.

This analysis shows that there were some 6-day cycles in springtime (near DOY 150) that were statistically significant. Beyond that, not much jumps out: the signal does now have high periodicity. Now I'm looking for better-behaving data.

Friday, March 11, 2011

Sunspots, Space Weather, and the Earth

Prikryl et al 2009: Solar magnetic sector boundary passage (SBP) and vorticity area index (VAI), by weather reconstruction ERA-40 dataset back to 1963-2002, confirmed the "Wilcox effect". The interplanetary magnetic field and associated "space weather" directly effect Earth's weather.

News from Dr. Leif Svalgaard at Stanford:
Wolf was right...we can use magnetic field strength to calibrate solar irradiance. The correlation between solar far-UV radiation and geomagnetic force on the Earth's surface is extremely good;
now we have an objective calibration for sunspot number.
The conclusion? Leif 2007 finds no long-term trend in solar irradience from at least 1600. through the present.

Risk Assessment

Nuclear and chemical technologies (except for medicines) have been stigmatized by being perceived as entailing unnaturally great risks.

R. Gregory, J. Flynn, and P. Slovic, ‘‘Technological Stigma,’’ American Scientist 83, 220–223 (1995).

The social problem is compounded by the fact that we tend to manage our risks within an adversarial legal system that pits expert against expert, contradicting each other’s risk assessments and further destroying the public trust. The young science of risk assessment is too fragile, too indirect, to prevail in such a hostile atmosphere. Scientic analysis of risks cannot allay
our fears of low-probability catastrophes or delayed cancers unless we trust the system. In the absence of trust, science (and risk assessment) can only feed public concerns, by uncovering more bad news. A single study demonstrating an association between exposure to chemicals or radiation and some adverse health effect cannot easily be offset by numerous studies failing to and such an association.