Using a joint isentropic analysis, a theory of the meridional overturning circulation is developed. Our method is based on a careful treatment of the mass flux joint distribution, a quantity that records meridional mass fluxes according to their potential temperature and their equivalent potential temperature simultaneously. This approach reveals mass fluxes that would otherwise be impossible to retrieve with previously available methods. Moreover, it creates as a by-product a completely new diagnostic for the vertical profile of equivalent potential temperature in midlatitudes. These vertical profiles are unusual in that they represent the atmospheric state that is experienced by poleward and equatorward fluxes independently. While poleward fluxes are subjected to a moist atmosphere with slanted moist isentropes, equatorward fluxes experience a dry atmosphere with moist isentropes confounded with dry isentropes. Using these diagnostics, we unify the circulation on dry isentropes with the circulation on moist isentropes by identifying the mass fluxes related to midlatitudes moist ascents. In the process of unifying the two, we propose a moist theory of lower tropospheric dynamic that, when viewed in the context of strong moist ascents, gives an explanation for the midlatitudes moist stratification.
This theory is applied to the study of moist baroclinic eddies using idealized moist life-cycle experiments. We compute the cumulative mass flux joint distribution for a series of individual eddies and use it to describe transports of mass and heat. We relate the moist circulation strength to the amount of available moisture and show that by increasing the depth or relative humidity of a surface moist layer we are increasing the mass fluxes associated with moist ascents. It is further shown that these added mass fluxes correspond to an increase in eddy kinetic energy in the breaking region of the underlying long wave.
Based on these observations, we apply similar diagnostics to model outputs of the A1B global warming scenario. We describe effects of surface warming on the isentropic circulations and conclude that winter mass fluxes associated with moist ascents could strengthen so much that they could overcome the weakening of the dry circulation during the northern winter.
|Advisor:||Pauluis, Olivier M.|
|Commitee:||Gerber, Edwin P., Polvani, Lorenzo m., Shaw, Tiffany A., Tabak, Esteban G.|
|School:||New York University|
|School Location:||United States -- New York|
|Source:||DAI-B 72/06, Dissertation Abstracts International|
|Subjects:||Applied Mathematics, Climate Change, Atmospheric sciences|
|Keywords:||Climate change, Large-scale circulation, Meridional overturning circulation, Moist thermodynamics|
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