The persistence of the hemispheric averages of mean monthly surface temperature anomalies

Abstract

The hemispheric averages of detrended mean monthly surface temperature anomalies are more highly persistent in summer than in winter. This property of the season is strikingly evident in the Northern Hemisphere, where summer months correlate highly with each other, and positively with the same summer months in the following year, while winter months have low correlations with all months, falling to zero, for the same months in the following year. The month to month variability in the persistence of temperature is presented as evidence to suggest that Northern Hemisphere summers are likely to exhibit stable properties while Northern Hemisphere winters may occasionally exhibit chaotic flow behaviour. The longer term persistence of summer temperature anomalies from one summer to the following summer may be explained by the fact that summers retain their memory for several years due to the heat capacity of the oceans, but this memory is temporarily destroyed in winter by the chaos induced by baroclinic instability of the upper level westerly flow.