An observational and numerical study of a surface high wind event related to stratospheric potential vorticity streamers and gravity wave breaking

The 18 January 2007 windstorm in the British Isles is examined using meteorological analyses, satellite data, rawinsondes, and numerical simulations. The storm is associated with strong curvilinear features in the potential vorticity (PV) field in the upper troposphere. Mechanisms of downward transport of momentum are investigated in detail, and include subsidence in the stratospheric dry intrusion, induced convection and convective outflow, and stratospheric gravity wave breaking. Turbulence at the boundary layer inversion and evolving mixed layer structures are found to mix momentum to the surface. High-resolution simulations with the University of Wisconsin Nonhydrostatic Modeling System enable quantification of processes contributing to downward momentum transfer. The local circulations around PV streams are also investigated.