ABSTRACT
The global circulations are evident after averaging the fluctuating winds that are actually measured. This chapter discusses some of the detail which was overlooked in focusing on year-long averages over the whole globe. It considers winds on the scale of a thousand kilometres or so – the ‘synoptic scale’ – and look at day-by-day snapshots instead of long-term patterns. Isobars at middle and high latitudes show the direction and strength of the geostrophic winds. The winds are shown blowing anticlockwise around the high-pressure regions and clockwise around the lows, in accordance with Buys-Ballot’s Rule. Synoptic-scale winds can be thought of as distinct streams of air, which may emerge from large regions of uniform air temperature, humidity, stability, wind speed and direction. A tropical cyclone is an especially intense low-pressure system at low latitudes, away from any front, including a ring of particularly strong winds around the centre.
