1 An expansive upwards, polewards flow of air. As a mid-latitude depression develops, a warm conveyor belt rises at c.20 cm s^–1, ahead of the cold front, and a reciprocal cold conveyor belt descends from medium/upper levels, below the warm conveyor, well ahead of the surface warm front; see Pomroy and Thorpe (2000) Monthly Weather Rev. 128, for a useful diagram. Schultz (2001) Monthly Weather Rev. 129 suggests that cyclones with well-defined warm fronts show a sharp break between the cyclonic and anticyclonic paths of the cold conveyor belt, while cyclones with weaker warm fronts have a broad transition zone between the two.

2 In the oceans of the world, a global system of currents. The Atlantic conveyor is a vast ocean current, which is part of the global ocean circulation. Warm water travels northwards close to the surface of the ocean. Beneath it there is a slow, deep-water flow carrying cold dense Arctic waters to Antarctica along the ocean bottom. As it travels north, water in the upper current becomes colder and denser. Winter sea ice forming in the Arctic Ocean leaves salt in the water making it denser still. At certain places in the North Atlantic the dense water sinks down towards the sea floor and begins to flow south. In this way the circulation ‘overturns’ to form the loop in the conveyor belt between the warm shallow current and the cold deep current (PEEP, What Drives the Atlantic Conveyor?). Broecker et al. (1985) Nature 315, 21 were the first to suggest a link between the Atlantic conveyor belt and possible climate change, and Alley (2007) Ann. Rev. Earth & Plan. Scis 35: 241 gives an impressive review of the acceptance of this link.

http://www.peep.ac.uk/content/1873.0.html Website of Physics & Ethics Education Project (PEEP).