Former Graduate Student of Leipzig Institute for Meteorology, University of Leipzig, Germany
Planetary waves can be defined as large-scale perturbations or disturbances of the atmospheric dynamical structure having zonal wavelengths of the scale of the earth’s radius. These waves have significant influence on the wind speeds, temperature, distribution of ozone, and other characteristics of the middle atmosphere structure. Planetary waves (PW) are responsible for the longer-period variability in the stratospheric dynamic such as QBO, SSW, and vacillation of the mean flow at extratropical latitudes and also play an important role in the dynamic of MLT (Salby 1984, Pogoreltsev et al., 2007, Forbes et al. 2004). These 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. Stationary Planetary Waves (SPWs) are waves whose surfaces of constant phase and amplitude are fixed with respect to the equator and Travelling Planetary Waves (TPWs) are waves that propagate in time and space having incoherent progressive and retrogressive component. Terms of progressive and retrogressive component 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 instability activity and zonally asymmetric momentum deposition, respectively.
[CLICK THE ANIMATIONS BELLOW!!]
Figure 1. Polar Stereographic Projection of Geopotential Height associated to the westward propagating of 16 DW, S=1, NH (TPWs and SPWs) [Sandro Wellyanto Lubis, 2012].
Several researches have been expanded to investigate and analyze planetary waves activity. General investigation results show that SPWs with zonal wave number 1 and 2 are striking features of the winter middle atmosphere (Fedulina 2004, Fröhlich 2005, Pancheva et al., 2007). The most prominent traveling waves observed in the atmosphere is traveling Rossby waves or global normal mode with s=1 which is 5-day wave (Andrews, 1987). Traveling planetary waves or Rossby 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, however 5 days waves with zonal wave number 1 appears also in the summer hemisphere (Fröhlich 2005, Pogoreltsev et al., 2007).