Predictability of weather regime transitions

The atmospheric circulation is not completely random. Certain circulation patterns will occur more often than others. The preferred patterns of the atmosphere on time scales of one week to one or more months are called weather regimes. The weather in Europe is for a large part determined by the occurrence of two weather regimes, a blocking regime (a high) and a strong zonal flow regime (a westerly wind). The atmospheric circulation will alternate between these regimes, with transitional intervals in between.

The transition of one regime to the other can occur very fast, within a couple of days, and is very difficult to predict. In this thesis, the sensitivity in the initial conditions for changes in the regimes a few days later are studied. It appears that the sensitivity fluctuates each day. Flows with a high sensitivity, and a low predictability, are characterized by a strong jetstream to the west of a diffluent flow.