The Role of Stationary Eddies in Shaping Midlatitude Storm Tracks
Transient and stationary eddies shape the extratropical climate through their transport of heat, moisture, and momentum. In the zonal mean, the transports by transient eddies dominate over those by stationary eddies, but this is not necessarily the case locally. In particular, in storm-track entrance and exit regions during winter, stationary eddies and their interactions with the mean flow dominate the atmospheric energy transport. Here it is shown that stationary eddies can shape storm tracks and control where they terminate by modifying local baroclinicity. Simulations with an idealized aquaplanet GCM show that zonally localized surface heating alone (e.g., ocean heat flux convergence) gives rise to storm tracks, which have a well-defined length scale that is similar to that of Earth's storm tracks. The storm tracks terminate downstream of the surface heating even in the absence of continents, at a distance controlled by the stationary Rossby wavelength scale. Stationary eddies play a dual role: within about half a Rossby wavelength downstream of the heating region, stationary eddy energy fluxes increase the baroclinicity and therefore contribute to energizing the storm track; farther downstream, enhanced poleward and upward energy transport by stationary eddies reduces the baroclinicity by reducing the meridional temperature gradients and enhancing the static stability. Transports both of sensible and latent heat (water vapor) play important roles in determining where storm tracks terminate.
© 2013 American Meteorological Society. Manuscript received 7 March 2012, in final form 28 February 2013. This research has been supported by the NOAA Climate and Global Change Postdoctoral Fellowship administered by the University Corporation for Atmospheric Research, by a David and Lucile Packard Fellowship, by NSF Grant AGS-1019211, and by a Marie Curie Career Integration Grant CIG-304202. We thank Simona Bordoni, Xavier Levine, Tim Merlis, and Adam Sobel for very helpful discussions during the preparation of this manuscript. The simulations were performed on Caltech's Division of Geological and Planetary Sciences Dell cluster.
Published - jas-d-12-082.1.pdf