Superposition Effects in Rapid Cyclogenesis.
NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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The effects of the zonal and meridional superposition of finite amplitude upper and lower level perturbations are investigated using a two-level analytical model and the Navy Operational Regional Atmospheric Prediction System NORAPS. The initial along stream phase difference is crucial to the subsequent intensification of the low level perturbation. A westward tilt with height of slightly less than a quarter wavelength is most favorable. The initial meridional superposition only modifies the growth rate established by the optimum zonal phase difference. The strength and location of the low-level baroclinity and upper level shear vorticity, which depend on the structure of the mean flow, are important factors in determining the most favorable cross track tilt. In the jet streak case with strong upper level forcing, the lower perturbation quickly moves to the most favored meridional position under the left front quadrant. An east coast cyclogenesis event during 19-21 January 1986 is used to illustrate the effects of superposition. Despite strong upper-level forcing, rapid cyclogenesis did not occur, because the optimum superposition between the upper-level vorticity center and the surface cyclone was not achieved.
- Atmospheric Physics