Jet stream

The polar front jet stream is a belt of westerlies in the upper troposphere, with wind speeds up to 200mph. It sits at a around 10km, the height at which aeroplanes fly. Trans-Atlantic pilots make use of the jet stream to minimise flight times.

The jet stream is found where the poleward surface temperature gradient is strongest, ie above the polar front (Figure 1); a common location for the formation and intensification of depressions.

Depressions on average follow the same path as the jet stream. This creates a clustering of the tracks followed by depressions known as the ‘storm track’ at the surface. The developing depression interacts with the jet creating continental-scale waves along its path.

Figure 1: The jet stream is found above where cold and warm air meets at the ground

Figure 2: The position of the jet stream in a normal summer.

Figure 3: The position of the jet stream the summer of 2012.

Figure 4 shows the position of a jet stream in the winter of 2013/14. It indicates that the storms were approaching the UK from further south over the Atlantic, bringing relatively warm air and plenty of energy with them, contributing to the destruction they caused.

Figure 4: The position of the jet stream in the winter of 2013/14