Large scale forcing of the North Atlantic storm track

• Main Author: Brayshaw, David James
• Published: University of Reading 2006
• Subjects: 551.645
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440074

The North Atlantic storm track is a key component of the climate system and dominates the weather and climate of north western Europe. Its unique characteristics are thought to be controlled by a combination of surface features including orography, land-sea contrast and sea surface temperature anomalies, although a consistent understanding of the individual and collective roles of these forcings and their feedbacks remains elusive. Such an understanding is vital for confident predictions of climate change in Europe. This thesis presents a comprehensive approach using a state-of-the-art atmospheric general circulation model, HadAM3, to perform a series of simulations with both idealised and semi-realistic boundary conditions. This hierarchy enables the behaviour of the more complex simulations to be interpreted in terms of simpler configurations. In this manner, the effects of the idealised northern hemisphere continents, South America, the Rocky mountains and the sea surface temperature anomalies associated with the Gulf Stream and the North Atlantic Drift are investigated both in isolation and in various combinations. Each of the features is found to be capable of influencing the North Atlantic storm track. In particular, the deflection of the flow caused by the Rocky mountains is important in generating the southwest -northeast tilt of the track. The storm track is suppressed over continental land masses and over the oceans it is highly sensitive to changes in the midlatitude SST gradients on the poleward side of the subtropical jet, with the Gulf Stream enhancing and the North Atlantic Drift suppressing storm activity. Physical mechanisms for these signals are discussed. Finally, the atmospheric response to the sea surface temperature patterns of the North East Atlantic ocean are discussed in the context of the ocean's thermohaline circulation, both in terms of the impacts on Europe and the potential feedbacks on the ocean.