Biases in the calculation of Southern Hemisphere mean baroclinic eddy growth rate
Article first published online: 13 JAN 2009
Copyright 2009 by the American Geophysical Union.
Geophysical Research Letters
Volume 36, Issue 1, January 2009
How to Cite
2009), Biases in the calculation of Southern Hemisphere mean baroclinic eddy growth rate, Geophys. Res. Lett., 36, L01707, doi:10.1029/2008GL036320., and (
- Issue published online: 13 JAN 2009
- Article first published online: 13 JAN 2009
- Manuscript Accepted: 2 DEC 2008
- Manuscript Revised: 13 NOV 2008
- Manuscript Received: 13 OCT 2008
- Eady growth rate;
- Southern Hemisphere extratropical cyclones
 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.