Abstract
The classic partitioning between slow-moving, low-wavenumber planetary waves and fast-moving, high-wavenumber synoptic waves is systematically extended by means of a wavenumber/phase speed spectral decomposition to characterize the day-to-day evolution of Rossby wave activity in the upper troposphere. This technique is employed to study the origin and the propagation of circumglobal Rossby wave patterns (CRWPs), amplified Rossby waves stretching across the Northern Hemisphere in the zonal direction and characterized by few, dominant wavenumbers. Principal component analysis of daily anomalies in spectral power allows for two CRWPs to emerge as dominant variability modes in the spectral domain during boreal winter. These modes correspond to the baroclinic propagation of amplified Rossby waves from the Pacific to the Atlantic storm track in a hemispheric flow configuration displaying enhanced meridional gradients of geopotential height over midlatitudes. The first CRWP is forced by tropical convection anomalies over the Indian Ocean and features the propagation of amplified Rossby wave packets over northern midlatitudes, while the second one propagates rapidly over latitudes between 35° N and 55° N and appears to have extratropical origin. Propagation of Rossby waves from the Atlantic eddy-driven jet to the African subtropical jet occurs for both CRWPs following anticyclonic wave breaking.
Highlights
Most of the weather affecting northern midlatitudes has its dynamical origin in the Atlantic and Pacific storm track regions, 15 located to the east of the main continental landmasses and characterized by a strong meridional temperature gradient (e.g., Chang et al, 2002; Hakim, 2003)
We show that hemispheric-scale Rossby wave patterns dominated by few, 70 selected wavenumber/phase speed harmonics appear as basic modes of variability in the spectral domain, allowing circumglobal Rossby wave patterns (CRWPs) to emerge and their evolution to be characterized
We compiled a climatology of the spectral signatures of midlatitude Rossby waves and let CRWPs emerge from it as variability patterns with a prominent, well-defined signal in the spectral domain
Summary
Most of the weather affecting northern midlatitudes has its dynamical origin in the Atlantic and Pacific storm track regions, 15 located to the east of the main continental landmasses and characterized by a strong meridional temperature gradient (e.g., Chang et al, 2002; Hakim, 2003). Recent research work (Wirth, 2020; Wirth and Polster, 2021) discussed the limitations of the Rossby wave ray tracing approach (cf Hoskins and Karoly, 1981; Hoskins and Ambrizzi, 1993), 55 based on the Wentzel-Kramers-Brillouin (WKB) approximation, when applied to evaluate Rossby wave "waveguidability" at the hemispheric scale and pointed out the need of alternative frameworks to study Rossby wave characteristics in the context of extreme events This piece of work proposes wavenumber/frequency spectral analysis as an alternative, versatile tool to describe the variability in shape and stationarity of the midlatitude flow, without having to make a-priori assumptions about the existence of a. 75 of space/time spectral analysis in the context of climate dynamics
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