The School of Earth and Atmospheric Sciences Presents Dr. Peter Webster: Emeritus Professor, GA Tech

Global Climate Synergies and Synchronization:A Potential Vorticity Substance Perspective

For decades, it has been thought that the tropics and the extratropics were relatively independent. If there was a connection it was thought, incorrectly, to be through some form of a zonally symmetric Hadley Circulation. Further, the two hemispheres, vastly different in geography, one mainly ocean, the other with a far greater landmass, have been assumed to be relatively independent. Yet, total annual rainfall rate or volume in each hemisphere is the same within 2%.

The annually averaged top of the atmosphere radiation budget is also nearly identical. Reponses to asymmetric forcing (one hemisphere greater than another) appears to produce a near-identical interhemispheric response. The question then becomes how can this synchronization take place? Is there an overriding physical constraint?

It evolves that these global structures can be best understood in terms of the conservation of potential vorticity substance that is conserved even in the presence of diabatic heating and dissipation (as distinct from potential vorticity that may not be conserved). This understanding allows the “impermeability theorem” of Haynes and McIntyre (1987) to a wide range of problems such as: the communication between the extratropics and the tropics, communication of signals between hemispheres and the synchronization of the response.

The possible relevance of these ideas to dynamic meteorology, climate dynamics and climate change (including paleoclimate), and perhaps planetary atmospheres, will be discussed.

This work comes from joint research with Drs. V. Toma and S. Ortega.