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Quarterly Journal of the Royal Meteorological Society Q. J. R. Meteorol. Soc. 136: 15061513, July 2010 Part B Instability of surface-temperature filaments in strain and shear
 

Summary: Quarterly Journal of the Royal Meteorological Society Q. J. R. Meteorol. Soc. 136: 15061513, July 2010 Part B
Instability of surface-temperature filaments in strain and shear
B. J. Harvey* and M. H. P. Ambaum
University of Reading, Reading, UK
*Correspondence to: B. J. Harvey, Department of Meteorology, University of Reading, PO Box 243, Reading, RG6 6BB,
UK. E-mail: b.j.harvey@reading.ac.uk
The effects of uniform straining and shearing on the stability of a surface quasi-
geostrophic temperature filament are investigated. Straining is shown to stabilize
perturbations for wide filaments but only for a finite time until the filament thins
to a critical width, after which some perturbations can grow. No filament can be
stabilized in practice, since there are perturbations that can grow large for any strain
rate. The optimally growing perturbations, defined as solutions that reach a certain
threshold amplitude first, are found numerically for a wide range of parameter
values. The radii of the vortices formed through nonlinear roll-up are found to be
proportional to /s, where is the temperature anomaly of the filament and s the
strain rate, and are not dependent on the initial size of the filament.
Shearing is shown to reduce the normal-mode growth rates, but it cannot stabilize
them completely when there are temperature discontinuities in the basic state;
smooth filaments can be stabilized completely by shearing and a simple scaling
argument provides the shear rate required. Copyright c 2010 Royal Meteorological

  

Source: Ambaum, Maarten - Department of Meteorology, University of Reading

 

Collections: Geosciences