Low-frequency waves and traveling storm tracks. Part II: three- dimensional structure

Abstract

The following are the main characteristics of the Northern Hemisphere midlatitude planetary-scale low-frequency waves (zonal wavenumber m = 1, 2, 3, and 4,) in winter: (i) The amplitude of the planetary scale low-frequency waves is nearly constant with the zonal wavenumber m, and has a maximum at 300 mb for geopotential height and at 850 mb for temperature; (ii) All low-frequency waves have a nearly equivalent barotropic structure (much more so than the stationary waves); (iii) The instantenous zonal phase speed of an individual low-frequency wave is nearly independent of height and latitude. The traveling storm tracks, defined as the local maxima on the rms map of the phase-shifted high-frequency eddies, are identifable from both geopotential height and temperature data throughout the troposphere. The mutual dependence between the low-frequency flow and their attendant traveling storm tracks dynamically resembles that between the climatological stationary waves and the climatological storm tracks. Therefore, our observational study seems to lend support for the local instability theory that accounts for the existence of the stationary/traveling storm tracks as the consequence of the zonal inhomogeneity of the climatological mean/low-frequency flow. -from Authors