Estimation of gravity‐wave parameters to alleviate the delay in the Antarctic vortex breakup in general circulation models

• Published in: Quarterly Journal of the Royal Meteorological Society
• Main Authors: Scheffler, Guillermo, Pulido, Manuel
• Other Authors: Agencia Nacional de Promoción Científica y Tecnológica, Consejo Nacional de Investigaciones Científicas y Técnicas
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2017
• Subjects: Antarctic; The Antarctic; Antarc*
• Online Access: http://dx.doi.org/10.1002/qj.3074; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fqj.3074; https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/qj.3074

The impact of optimal parameters in a non‐orographic gravity‐wave drag parametrization on the middle atmosphere circulation of the Southern Hemisphere is examined. Optimal parameters are estimated using a data assimilation technique. The proposed technique aims to reduce the delay in the winter vortex breakdown of the Southern Hemisphere found in general circulation models, which may be associated with a poor representation of gravity‐wave activity. We introduce two different implementations of the parameter estimation method: an offline estimation method and a sequential estimation method. The delay in the zonal‐mean zonal‐wind transition is largely alleviated by the optimal gravity‐wave parameters. The sequential method diminishes the model biases during winter vortex evolution, through gravity‐wave drag alone. On the other hand, the offline method accounts better for unresolved–resolved wave interactions and the zonal‐wind transition. We show that the final warmings in the lower mesosphere are driven mainly by planetary‐wave breaking. These are affected by changes in the gravity‐wave drag that are responsible for stratospheric preconditioning. Parameter estimation during the vortex breakdown is a challenging task that requires the use of sophisticated estimation techniques, because there are strong interactions between unresolved gravity‐wave drag and planetary waves.