Daily-Scale Planetary Wave Patterns and the Modulation of Cold Season Weather in the Northern Extratropics
The study systematically and objectively delineates and characterizes day-to-day variations in the planetary scale wave field during the Northern Hemispheric cool season along with their relation to regional U.S. weather extremes.
The research provides a novel framework for characterizing daily variability in the planetary scale flow and its relation to U.S. weather extremes.
Daily variability in wavenumbers 1-5 of 500 hPa geopotential height (Z500) is isolated for 1950-2005 via a hierarchical cluster analysis. Six distinct boreal-cold-season planetary wave patterns are identified: The first, second and sixth patterns exhibit a zonal wavenumber 1 structure, while the fourth and fifth patterns resemble the negative and positive phases of northern annular mode, respectively. Extreme cold waves over the U.S. are frequent during episodes of the fourth and sixth patterns while the first pattern favors above normal rainfall over much of the continental U.S.