ABSTRACT
This chapter deals with observed variations of the large-scale wind circulation, variant patterns that differ in greater or less degree from the simple zonal circulation model (with its well-developed circumpolar vortex, long waves of no great amplitude in the upper westerlies and at the surface general westerly winds in middle latitudes balanced by polar and tropical easterlies) described in Chapter 3. We are not in the first place concerned here with the duration of an anomaly, nor with any tendency for regular periodicity or otherwise, but with identification of modes of behaviour and, where possible, characteristic successions and their time-scales. Full understanding and confidence in prediction demand knowledge of the physical processes at work.
