Effect of Ageostrophic Vorticity and Temperature Advection on Lower-Tropospheric Vertical Motions in a Strong Extratropical Cyclone

Abstract

The impact of ageostrophic vorticity and temperature advection on vertical motions in a strong extratropical cyclone is studied by comparing the contribution of the two advection terms in the generalized omega equation to the contribution obtained when these terms are evaluated by using the geostrophic assumption. The differences in ? are substantial especially in the lower troposphere, where ageostrophic advections make both the rising and sinking motion weaker but the latter is affected much more drastically than the former. Two main factors are found to explain these results. First, the subgeostrophy of the along-contour wind component acts to make the temperature and vorticity advections weaker, thereby weakening both the rising and sinking motions. Second, the low-level anticyclonic vorticity advection associated with the strong inflow toward the center of the low induces widespread rising motion, thus creating asymmetry between the uplift and subsidence areas.