AbstractsPhysics

This thesis was funded by the Natural Environment Research Council (NERC) and is presented in an alternative thesis format. The thesis consists of three separate journal articles which form a coherent research project.Paper 1 investigates the development of strong winds in a dry, idealised extratropical cyclone using the horizontal momentum equation. In particular, the southwest wind maximum that develops was found to contain air parcels from three airstreams. The development of the horizontal along-flow forces around the cyclone and along trajectories entering the southwest wind maximum were analysed. An attempt to extend this methodology to a moist, idealised extratropical cyclone was made. However, the effect of adding moisture to the initial condition was found to be negligible. The reasons for this are explored in Paper 2, which documents this finding: that the effect of moisture on the development of an idealised, baroclinic wave is sensitive to the choice of initial condition. Paper 3 applies the horizontal momentum equation diagnostics to an intense, marine extratropical cyclone that brought strong winds to Ireland and the United Kingdom on 12 February 2014. The development of strong winds in Cyclone Tini was investigated by turning off latent heat release and surface fluxes. In the absence of latent heat release a weaker wind maximum developed. However, the simulation without surface fluxes had a very similar vertical structure of the horizontal wind to the full-physics simulation, but a weaker surface wind maximum. The reason for this weaker wind maximum was analysed using the quasigeostrophic omega equation. This analysis demonstrated a maximum in forcing for descent southwest of the low both in the full-physics simulation and in the simulation without surface fluxes, however strong winds were prevented from reaching the surface in the simulation without surface fluxes because of a more stable boundary layer around the bent-back front.