Biases in the calculation of Southern Hemisphere mean baroclinic eddy growth rate
AuthorSIMMONDS, IAN; LIM, EUN-PA
Source TitleGeophysical Research Letters
PublisherAmerican Geophysical Union
University of Melbourne Author/sSimmonds, Ian
AffiliationScience - Earth Sciences
Document TypeJournal Article
CitationsSimmonds, I. & Lim, E. (2009). Biases in the calculation of Southern Hemisphere mean baroclinic eddy growth rate. Geophysical Research Letters, 36, doi:10.1029/2008GL036320.
Access StatusOpen Access
© 2009 American Geophysical Union
The maximum Eady growth rate measure of baroclinic instability is very commonly used in the literature. Its average is usually calculated directly from the time-mean flow. It is suggested here that this approach is not entirely suitable, but rather one should obtain the Eady growth rates at all relevant synoptic times and average these. It is found at the 850 hPa level in the Southern Hemisphere that the time-mean of the instantaneous rates exceed those calculated from the time-mean field over much of the mid and high latitudes, and the difference is even more marked at 500 hPa. At both levels the axes of the maxima Eady growth rates are displaced to the south. Some implications are discussed, including the need for caution when diagnosing changes in cyclone properties from changes in Eady growth rate calculated directly from the time-mean flow in climate change model simulations.
KeywordsEady growth rate; baroclinicity; Southern Hemisphere extratropical cyclones
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