Estimates of the Natural Variability of Time-Averaged Sea-Level Pressure

Estimates of the natural variability of monthly-mean sea-level pressure are made based on a 74-year, grid-point data set. The natural variability of monthly means is defined as those interannual fluctuations that can be ascribed to the effects of statistical sampling alone. That is, the natural variability of monthly means is that variability resulting from the variance and autocorrelation associated with daily weather fluctuations. The natural variability does not reflect a “climate change,” but rather it is the variability within an “unchanging climate.” As such it is a measure of the “climatic noise.” Comparisons between natural and actual interannual variability are discussed in the context of potential long-range predictability. A characteristic time between independent estimates is determined.