Random Calculation: Calculation details
The timeseries you get is a randomly calculated "red noise" timeseries. In this case, the solution is calculated from the integrated stochastic differential equation
dx/dt = (-1/T)x + whitenoise.
1/T is set to -1/3 months or -.333 for all cases. x(0) is determined using a changing seed value and the white noise is obtained by sampling from a gaussian distribution. Values are set for all 12 months of 1958-1999 and seasonal values are calculated from that. Code was graciously provided by Cecile Penland of CDC. Other definitions of a random timeseries could have been used.
The intention is to demonstrate how spatial patterns that look "reasonable" will arise during correlation analysis even if the index timeseries has no physical basis. Please do not try to do Monte Carlo tests by repeatedly running the web-page.