High Resolution air-sea coupling for downstream storm prediction

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The structure of the storm-track is one of the key determinants of weather in the midlatitudes. Its climatological state depends on a complex non-linear balance between the upper level jet, turbulent baroclinic eddies and their associated eddy fluxes of heat and momentum, and forcing and dissipative processes. Getting the full structure of the storm track right in models is still one of the big challenges of weather and climate models. Recent work by the supervisor and collaborators has shown that northward heat fluxes due to weather systems over the Atlantic provide a strong steer to the downstream development and direction of the storm track. For example, high upstream heat fluxes are associated with a northward tilt of the storm track, a northward shift of the low level jet stream over our longitudes, and reduced periods between recurring storms. Independent theoretical support for most of the ingredients in this link have been published in the literature. This work is supported by a NERC project, and takes place in the context of several other research projects globally, such as WGNE-Drag, T-NAWDEX, and Primavera. Some preliminary work in the Primavera project at the University of Reading has also shown how very high resolution climate runs improve the upstream heat flux characteristics, the tilt of the storm track, and the statistical properties of the downstream storm tracks. In the present PhD project we will be examining the effects of high resolution coupling between the ocean and the atmosphere in the W. Atlantic region on the meridional heat fluxes in the atmosphere and the attendant effects on the storm track. For this work we will tie in with the second phase of UK Environmental Prediction programme, which aims to develop a high resolution (1km or less) coupled prediction model for the UK. Part of this programme is to assess the new science that such high resolution coupled models can address. In particular, heat exchange between the oceans and the atmosphere occurs at relatively small scales which are hard to resolve, but it is expected to contribute to the overall heat transport generated by the cyclone and by implication the expected downstream structure of the storm track. This project aims to use data from high resolution runs to establish the link between the ocean and the atmosphere at a wide range of scales and establish links to the downstream storm-track structure. We will be examining both statistical properties as well as specific time periods (case studies). The aim would be whether high resolution modelling of the coupling can improve our prediction of these atmospheric heat fluxes, and whether the hoped for improvement leads to a concomitant improvement of storm forecasts over the UK. The project will also make use of a newly developed technique to map the phase space of storm track development, where the interaction between upstream baroclinic growth rate and storm track activity can be followed in a dynamically consistent way.