Detection of planetary wave breaking events

 

The wave breaking detection method was developed by Torben Kunz as part of his doctoral thesis (Kunz et al., 2009).

Wave breaking events are detected in global fields of potential vorticity and wind components on theta (potential temperature) levels, separately for the northern and the southern hemisphere. They are specified by the calculated stretching deformation factor.

At a given longitude the isentropic potential vorticity (ipv) absolute minimum and the poleward located absolute maximum are detected. The ipv reversal magnitude (abs max - abs min) has to be greater than a given threshold for the event to be considered. The stretching deformation for the position of the absolute maximum ipv is calculated of the wind components. By means of the stretching deformation the event is classified as cyclonal/anticyclonal.
The westward and eastward expansion is checked, also the tracking in time.

After the wave breaking detection, composites of ipv are calculated separately for anticyclonic (ab) and cyclonic (cb) events for a number of days (choosen by parameter), the temporal center is the day of detection.

The wave breaking detection program needs global fields of potential vorticity and wind components on theta (potential temperature) levels. A program (by Torben Kunz) to calculate these from temperature, wind components and vorticity on pressure levels is also available.

Find here some more information on isentropic potential vorticity dynamics.

Example:

The wave breaking detection was carried out for NCEP data, months May to August for 3 years (2008 to 2010). These are plots for which programs are available ...

Tool:

A program package for calculation and plotting is available together with a detailed description. Please contact Silke Schubert.

Requirements:

Iinput data in SERVICE format (can be obtained from netCDF easily using CDOs)gfortran, CDO, GrADS, R, awk

References:

  • Kunz, T., K. Fraedrich, and F. Lunkeit (2009) Impact of synoptic scale wave breaking on the NAO and its connection with the stratosphere in the ERA-40 reanalysis. J. Climate, 22, 5464-5480, doi: 10.1175/2009JCLI2750.1
  • Peltret, D. (2011) Diploma Thesis: A Rossby wave breaking climatology: Present day climate and greenhouse warming in ECHAM5. (available as pdf, please contact Silke Schubert)