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-yr, 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; i.e., 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.