Cyclone surface pressure fields and frontogenesis from NASA scatterometer (NSCAT) winds

Abstract

Two extratropical marine cyclones and their associated frontal features are examined by computing surface pressure fields from NASA scatterometer (NSCAT) winds. A variational method solves for a new surface pressure field by blending high‐resolution (25 km) relative vorticity computed along the satellite track with an initial geostrophic vorticity field. Employing this method with each successive pass of the satellite over the study area allows this surface pressure field to evolve as dictated by the relative vorticity patterns computed from NSCAT winds. The result is a high‐resolution surface pressure field that captures features such as fronts and low‐pressure centers in more detail than National Centers for Environmental Prediction (NCEP) reanalyses. While using the actual relative vorticity to adjust the geostrophic vorticity ignores the ageostrophy of surface winds, which can be significant in the vicinity of fronts and jet streaks, it is a necessary approximation given that the technique uses only surface data. The NSCAT surface pressure fields prove to be nearly as accurate as NCEP reanalyses when compared to ship and buoy observations, which is an encouraging result given that NCEP reanalyses incorporate a myriad of data sources and the NSCAT fields rely primarily on one source. In addition, the high‐resolution relative vorticity fields computed from NSCAT winds reveal the location of surface fronts in great detail. These fronts are verified using NCEP analyses, in situ data, and satellite imagery.