Boundary-layer observations in the Pilbara coastal region

Abstract

The seasonal mean of a climate variable is affected by processes with timescales from less than seasonal to interannual or longer. In this paper, the seasonal mean is conceptualised as consisting of intraseasonal and slowly varying (longer than a season) components. The slow component of the seasonal mean is related to slowly varying internal and external processes which are potentially predictable, and is therefore itself regarded as potentially predictable. An analysis of variance method, which separates the interannual variance of the seasonal mean of these components, is applied to Australian surface maximum and minimum temperature. The potential predictability is defined as the percentage of the interannual variance of the seasonal mean that is due to the slow component. Using data from the Australian Water Availability Project dataset for the period 1958–2007, it is found that there is high estimated potential predictability (over 50 per cent) for surface maximum and minimum temperature for northern Australia (north of 25°S) in most of the 12 three-month seasons. In contrast, there are regions of southern Australia (south of 25°S) with low estimated potential predictability (under 30 per cent) in many seasons. The results given here provide guidance for where and when longrange forecasts of seasonal mean temperature variables are most likely to be skilful.