Epoch-based Sea Surface Temperature for Climate System Analysis

Taking the principle that climate is what one expects, I suggest and illustrate with Sea Surface Temperature (SST) that it is desirable to represent the climatology as linear in time with the first few (3, it turns out) harmonics of the annual cycle. In many regions of the globe the trend is physically and statistically significant. We also expect the seasonal cycle to continue, though amplitude and phase of the harmonics do change — themselves matters of direct interest in climatology. In representing the SST climatology this way, rather than the common average over each month or for each day independently, the approach is similar to how slowly varying terms in astronomy, such as the earth’s eccentricity, are represented by an Epoch (date for time 0) and adjustments for secular changes while moving away in time.  

The Epoch-based climatology approach is shown in comparison to the traditional by developing a 30 year climatology for each and examining the departure from each climatology of the next 10 years observations. The Epoch climatology has markedly reduced anomalies compared to the traditional. A further comparison is to examine the autocorrelation of the anomalies in time. The traditional climatology has inflated times, including excess autocorrelation at annual time scale, meaning that there were things we could and should expect but which are not captured by that approach.