This is the second paper in Yi Ming’s study of the role of aerosols in altering major atmospheric circulation features. The first paper is discussed in my post
The second paper is
Yi Ming and V. Ramaswamy and Gang Chen, 2011. A Model Investigation of Aerosol-induced Changes in Boreal Winter Extratropical Circulation. J of Climate (in press).
The abstract read (emphasis added)
“We examine the key characteristics of the boreal winter extratropical circulation changes in response to anthropogenic aerosols, simulated with a coupled atmosphere-slab ocean general circulation model. The zonal-mean response [to aerosols] features a pronounced equatorward shift of the Northern Hemisphere subtropical jet owing to the mid-latitude aerosol cooling. The circulation changes also show strong zonal asymmetry. In particular, the cooling is more concentrated over the North Pacific than over the North Atlantic despite similar regional forcings. With the help of an idealized model, we demonstrate that the zonally asymmetrical response is linked tightly to the stationary Rossby waves excited by the anomalous diabatic heating over the tropical East Pacific. The altered wave pattern leads to a southeastward shift of the Aleutian low (and associated changes in winds and precipitation), while leaving the North Atlantic circulation relatively unchanged. Despite the rich circulation changes, the variations in the extratropical meridional latent heat transport are controlled strongly by the dependence of atmospheric moisture content on temperature. This suggests that one can project reliably the changes in extratropical zonal mean precipitation solely from the global-mean temperature change, even without a good knowledge of the detailed circulation changes caused by aerosols. On the other hand, such knowledge is indispensable for understanding zonally asymmetrical (regional) precipitation changes.”
Excerpts from the conclusions reads
“Maximum aerosol forcing is centered over the NH low and mid-latitudes. During the boreal winter, the strong local aerosol forcing influences many of the key characteristics of the vigorous extratropical circulation by causing local cooling mainly over the source regions. Such a cooling enhances the meridional temperature gradient equatorward of the NH subtropical jet, but weakens it poleward. The end result is an equatorward shift of the jet.”
“….the detailed spatial pattern of the aerosol-induced tropical circulation change….. plays a critical role in determining the extratropical response by altering stationary Rossby waves.”