D6 Diagnosis of Waves and Circulation

Topic

Wave and circulation diagnostics apply analytical techniques to the three-dimensional wind, temperature, and pressure fields—derived from reanalyses, numerical weather prediction models, or radiosondes—to identify, quantify, and predict large-scale flow patterns and the atmospheric wave activity propagating within them. One such technique, Wheeler-Kiladis space-time spectral analysis, decomposes these convective and dynamic fields based on the spatial scale and temporal period of their constituent components; this decomposition allows for the separation of distinct equatorial wave modes—Kelvin waves, Rossby waves, and mixed waves—within the same field.

Another technique, Eliassen-Palm vectors, serves as the standard diagnostic for tracking the transport and dissipation of Rossby and gravity waves across the latitude-height plane. The divergence of these Eliassen-Palm vectors measures the extent to which these waves accelerate or decelerate the mean zonal flow transporting them—a measurement critical to understanding three distinct phenomena: sudden stratospheric warming, the Brewer-Dobson circulation, and the formation of the polar jet stream.

A third technique, quasi-geostrophic potential vorticity inversion, enables the reconstruction of wind and temperature fields from a single field—potential vorticity—while simultaneously separating the background flow's dynamic equilibrium from the wave perturbations propagating upon it.

A fourth technique, the omega diagnostic, addresses a different problem: vertical atmospheric motion, expressed in pressure coordinates, is not a variable that most observations can measure directly. Consequently, the omega diagnostic employs an equation relating this vertical motion to the directly observed wind and temperature fields, inferring the vertical motion that was not measured directly by radiosondes or satellites. Thus, the four techniques for diagnosing waves and circulation—Wheeler-Kiladis space-time spectral analysis, Eliassen-Palm vectors, quasi-geostrophic potential vorticity inversion, and omega diagnosis—all originate from the same three-dimensional wind, temperature, and pressure fields, and all aim for the same result: identifying the dynamic structures that control weather and climate, whether at the scale of a synoptic system lasting a few days or at the planetary scale spanning weeks and months.

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