Research Fellows Directory
Sir Brian Hoskins CBE FRS
University of Reading
Blocking in the atmosphere, the occurrence of a slow moving and persistent high pressure system, is an important phenomena in climate, particularly that of Europe. For example, blocking events led to the extreme summer heat of 2003 and the extreme winter cold of 2009/10. In weather forecasting the prediction of the onset and decay of blocking has in the past been a problem but the situation is improving in last few years. However climate models are still in general poor at representing blocking, and there is currently no reliable information on how the frequency, intensity and nature of blocking may change with global warming. Consequently for Europe the likely future occurrence of extreme winter cold or summer heat is not known and so the basis for planning adaptation strategies in Europe is very shaky.
Inspired by modern theoretical ideas, we have developed and used a new way of looking at atmospheric data to increase understanding of blocking and its role in different parts of the world. The diagnostics have enabled us to see the different character of blocking in the different regions.
Using the same ideas we have developed a new way of looking at the North Atlantic Oscillation (NAO), which describes how the flow in the N Atlantic/European region varies. The negative phase of the NAO is associated with recurrent blocking in the Greenland region and the positive phase with the absence of this blocking phenomenon.
We have shown that the near-surface westerly winds over the N Atlantic in winter tend to be largest in one of 3 latitudes. The southernmost maximum is associated with NAO- and the other two peaks with the two phases of another well-know pattern. This has led to a simple description of weather regimes in the N Atlantic region.