Zonal wavenumber

In meteorological applications, a zonal wavenumber or hemispheric wavenumber is the dimensionless number of wavelengths fitting within a full circle around the globe at a given latitude.[1]

500mb geopotential height averaged between October 9–21, 2010 illustrating Rossby wave pattern with the zonal wavenumber 4. DOE AMIP reanalysis data.

where λ is the wavelength, r is the Earth's radius, and is the latitude.

Zonal wavenumbers are typically counted on the upper level (say 500-millibar) geopotential maps by identifying troughs and ridges of the waves. Wavenumber 1 has one trough and one ridge, i.e. one wavelength fits degrees. Wavenumber 2 has two ridges and two troughs around 360 degrees.

Wavenumber 0 corresponds to zonal (symmetric) flow. Wavenumbers 1–3 are called long waves and often synonymous in meteorological literature with the mid-latitude planetary Rossby waves, while wavenumbers 4-10 are often referred to as "synoptic" waves.[2] In the Northern Hemisphere, wavenumbers 1 and 2 are important for the time-mean circulation due to topography (Tibetan Plateau and Rocky Mountains),[3][4] whereas in the Southern Hemisphere, tropical convection is responsible for the presence of mainly zonal wavenumber 3.[5]

See alsoEdit


  1. ^ "AMS Glossary". Glossary.ametsoc.org. 2015-07-28. Retrieved 2016-12-01.
  2. ^ Vallis, Geoffrey K (2006). Atmospheric and Oceanic Fluid Dynamics - Fundamentals and Large-scale Circulation. Cambridge, UK: Cambridge University Press. ISBN 9780521849692.
  3. ^ Held, I; Ting, M; Wang, H (2002). "Northern winter stationary waves: Theory and modeling". Journal of Climate. 15 (16): 2125–2144. doi:10.1175/1520-0442(2002)015<2125:NWSWTA>2.0.CO;2.
  4. ^ Garfinkel, C; White, I; Gerber, E; Jucker, M; Erez, M (2020). "The building blocks of Northern Hemisphere wintertime stationary waves". Journal of Climate. 33 (13): 5611–5633. doi:10.1175/JCLI-D-19-0181.1.
  5. ^ Goyal, Rishav; Jucker, Martin; Sen Gupta, Alex; Hendon, Harry; England, Matthew (2021). "Zonal wave 3 pattern in the Southern Hemisphere generated by tropical convection". Nature Geoscience. doi:10.1038/s41561-021-00811-3.