WEATHER AND CLIMATE

Fluid dynamics is at the heart of our climate system, governing the motion of the atmosphere, oceans, and ice sheets. Indeed, as will be described here, the equations of motion for a fluid on a rotating sphere form the core of the numerical climate models used to predict future change. The spherical shape of the Earth leads to different approximations being appropriate within and outside the tropical regions. Aspects of weather phenomena such as mid-latitude winter storms and the tropical monsoons can be understood in this way. The Pacific and Atlantic Oceans are bounded in longitude by the continents, whereas the Southern Ocean is not. This leads to the dominance of different physical processes and hence different circulation patterns. Some processes, such as those associated with the El Niño Southern Oscillation, can only be understood in terms of the coupled dynamics of the atmosphere and ocean. In both the atmosphere and the oceans, global-scale overturning circulations transport heat as well as chemical species around the Earth. The physical mechanisms responsible for these aspects of the climate system are reviewed, and their potential for change with increased atmospheric greenhouse gas concentrations is discussed.