Tropical cyclone energy dispersion under vertical shears

Abstract

[1] Tropical cyclone Rossby wave energy dispersion under easterly and westerly vertical shears is investigated in a baroclinic model. In a resting environment, the model simulates a Rossby wave train that has a baroclinic structure with alternating cyclonic-anticyclonic-cyclonic (anticyclonic-cyclonic-anticyclonic) circulations in the lower (upper) troposphere. A significant asymmetry appears in the wave train development under easterly and westerly vertical shears, that is, an easterly (westerly) shear confines the maximum amplitude of the wave train primarily to the lower (upper) level. It is proposed that the vertical wind shear may impact the Rossby wave train development through both the barotropic-baroclinic mode coupling and the modulation of the group velocity by the mean flow through a “Doppler shift effect”. Additional experiments with uniform westerly and easterly mean flows confirm the hypothesis. The enhancement of the Rossby wave train in the lower level by the easterly shear may have an important implication for understanding the tropical cyclogenesis and the origin of the synoptic wave trains in the western North Pacific.