Date of this Version
Quarterly Journal of the Royal Meteorological Society. 137: 179–198, January 2011 Part A
The influence of precipitation near the surface warm front on precipitation downstream is evaluated. A two-way nested simulation is computed for two selected cases: 13–15 February 2003 and 3–5 January 2005. The results of the simulation are compared with output from the North American Regional Reanalysis dataset, which is used as a high-resolution proxy for true atmospheric conditions. The relevant physical processes in the generation and maintenance of precipitation poleward of other precipitation areas are analysed, along with perturbation potential vorticity (PV) fields. Piecewise PV inversion is used to determine height and wind fields associated with the perturbation PV. These height and flow fields are used to compute derived quantities such as balanced deformation, balanced temperature perturbation, and balanced moisture flux. Both cases illustrate that the role of rainfall near surface warm fronts on precipitation downstream is complex, and is associated with more than just moisture flux. The strength, depth and orientation of diabatically generated PV anomalies within these areas of rainfall are associated with mesoscale processes relevant to the maintenance of downstream precipitation. Lastly, this work presents a methodology for analysing the role of precipitation in individual events.