Moist baroclinic eddies as features of the dry and moist isentropic circulations in a warming climate

Pauluis et al. (2008, Science) have recently shown that the zonal mean circulations on moist and dry isentropes differ significantly in the midlatitudes. The total mass transport on moist isentropes in the current climate was observed to be about twice as important as on dry isentropes. This difference has been interpreted as originating from low-level moist subtropical air rising to the upper troposphere through the storm tracks. We used IPCC AR4 model outputs to investigate the variability of these isentropic circulations under the sresa1b global warming scenario. Comparison between models have highlighted important modeling differences across the data as well as robust evolutions under the warming scenario.

Some of the results that will be presented include an observed increase of the moist circulation relatively to the dry circulation in the midlatitudes, specially in the winter hemisphere. These changes indicate the augmented influence moist processes will have on the midlatitudes of a warmer world. It is hypothesized that these moist processes are primarily moist baroclinic eddies, thus indicating essential modifications of the storm track.

Using dynamical arguments substantiated with life-cycle numerical experiments, we will argue that these modifications are driving an intensification in moist baroclinic activity as well as a displacement of its latitude of its maximal intensity. These results ultimately propose novel ways of thinking about the global overturning circulation of a warming climate.