17.4 Deducing changes in the extratropical storm tracks in response to idealized SST forcings using Lagrangian diagnostics

Friday, 21 June 2013: 9:30 AM
Viking Salons ABC (The Hotel Viking)
Lise Seland Graff, University of Oslo, Norway, Oslo, Norway; and J. H. LaCasce

Studies of the past and future climates reveal that the extratropical storm tracks are shifting meridionally. The mechanism behind this shift however remains unclear. We investigate the effect of changes in the surface ocean temperatures (SST) on the storm-track position and cyclone characteristics. The ocean affects the storm tracks via latent heating but also by altering the low-level atmospheric baroclinicity. We examine the storm track-response to altered SST in an atmospheric general circulation model. Specifically, the SSTs were augmented or decreased by 2K in various latitude bands.

We studied the storm tracks from a Lagrangian perspective, tracking cyclones using the TRACK routine of Hodges (1995, 1999) on relative vorticity at 850-hPa. We studied cyclones in both the Southern and Northern Hemispheres, during their respective summer and winter seasons.

The results show that the storm tracks shift in response to the altered SST consistent with previous studies. But the SST also impacts the storm characteristics, particularly with regards to their strength and propagation. For instance, with warmer SSTs at low latitudes, mid-latitude cyclones travel further, both meridionally and zonally, and are more intense. The changes in strength and propagation moreover are related, consistent with models of vortex self-advection in the presence of a mean PV gradient.

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