Elliptical diagnostics of stratospheric polar vortices

• Published in: Quarterly Journal of the Royal Meteorological Society
• Main Author: Waugh, Darry N. W.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1997
• Subjects: Antarc*; Antarctic
• Online Access: http://dx.doi.org/10.1002/qj.49712354213; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fqj.49712354213; https://onlinelibrary.wiley.com/doi/pdf/10.1002/qj.49712354213; https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/qj.49712354213

Abstract Diagnostics based on the spatial moments of isopleths of a long‐lived tracer, or of potential vorticity, are presented that enable the structure and evolution of stratospheric polar vortices to be concisely summarized and quantified. The area, centre, aspect ratio and orientation of the ‘equivalent ellipse’ of the vortex, on an isentropic surface, are defined using the second‐ and lower‐order spatial moments of contours within the vortex‐edge region. By examining the variations of these ‘elliptical’ diagnostics with time and altitude, the temporal evolution and vertical structure of the polar vortices can be quantified. The usefulness of the diagnostics is assessed by examining nitrous oxide data from the Geophysical Fluid Dynamics Laboratory ‘SKYHI’ general‐circulation model. The diagnostics show, and quantify, several differences between the Arctic and Antarctic vortices in the SKYHI model. The Arctic vortex moves further off the pole, is generally more elongated, and has a more complicated vertical structure than the Antarctic vortex (with larger variations of both the vortex centre and elongation with height). The elliptical diagnostics also identify the occurrence of large‐scale Rossby‐wave breaking events, both at the vortex edge and in the subtropics, in the model.