Planetary Waves

Planetary Waves

By Sandro Lubis

updated: January 2017

Planetary waves can be defined as large-scale atmospheric perturbations or disturbances having zonal wavelengths in the scale of the earth’s radius. Planetary waves have significant influence on the circulation, temperature, and distribution of ozone. Planetary waves are responsible for the prevailing variability in the stratosphere, such as QBO, SSW, and the vacillation of the mean flow at the extratropical latitudes, and also play an important role for the MLT dynamics (Salby 1984, Pogoreltsev et al., 2007, Forbes et al. 2004). Planetary waves are generated by orographic and diabatic heating in the troposphere and also possible forced by irregular thermal or mechanical forcing in the lower atmosphere (Holton 2004, Andrews et al., 1987, Fedulina 2004).


Planetary waves also can be distinguished into two types.  (1) Stationary Planetary Waves (SPWs) are waves whose surfaces of constant phase and amplitude are fixed with respect to the equator and (2) Travelling Planetary Waves (TPWs) are waves that propagate in time and space having incoherent progressive and retrogressive components. The progressive and retrogressive terms arise from the separation technique in space time-frequency domain analysis purposed by Hayashi (1971, 1979). The other types of planetary waves such as quasi-two-day wave and quasi-stationary wave are also exist in the atmosphere. These waves are commonly generated by baroclinic instability or by deposition of zonally asymmetric momentum onto the mean flow.


Figure 1.  Polar stereographic projection of geopotential heights associated with the a westward propagating of 16 -day wave, k=1 for (left) SPWs and right (TPWs) [Part of my master report for the  “middle atmosphere” course from Prof. Ch. Jacobi].

SPWs with zonal wave number 1 and 2 are striking features of the winter middle atmosphere dynamics (Fedulina 2004, Fröhlich 2005, Pancheva et al., 2007). The most prominent traveling waves observed in the atmosphere are traveling Rossby waves or global normal mode with s=1 which is 5-day wave (Andrews, 1987). Traveling planetary waves predominantly propagates westwards. In the middle atmosphere they have zonal wave number between 1 and 4 with periods between 2 days and 16 days (Fröhlich 2005). Many of them are able to propagate upwards through the winter hemisphere into the MLT region. The 5-day waves with zonal wave number 1appears also in the summer hemisphere (Fröhlich 2005, Pogoreltsev et al., 2007).


~ by sandrolubis on September 19, 2012.

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