Surface cyclogenesis in middle latitudes is preceded by the arrival of a pre-existing upper-tropospheric disturbance. Observational studies indicate that the preferred regions for the development of these upper-level troughs are characterized by weak low-level baroclinicity, large surface roughness and enhanced low-level stability. Linear instability calculations confirm that the development of baroclinic waves with maximum amplitude near the tropopause is favored when the low-level vertical shear is weak, while Ekman dissipation and low-level static stability are large. Conversely, when the low-level vertical shear is strong, while Ekman dissipation and low-level static stability are weak, the most unstable waves are surface concentrated. / It is hypothesized that surface cyclogenesis in the Northern hemisphere storm track regions can be described by the structural modification of baroclinic wave packets traversing a zonally varying flow field. This hypothesis is tested using a linear, quasi-geostrophic model with zonal variation in the basic state and the Ekman layer. The basic state consists of a region of strong low-level baroclinicity and weak Ekman dissipation, flanked by regions of weak low-level baroclinicity, strong Ekman dissipation, and enhanced low-level stability. Model calculations show that an isolated disturbance upstream of the mid-channel baroclinic zone evolves rapidly into a wave packet with maximum amplitude near the tropopause. Disturbances within the wave packet undergo a structural modification so that they have maximum amplitude at the surface within a few days of entering the mid channel baroclinic zone. The growth rate of an individual surface disturbance can exceed the growth rates of both the most unstable eigenmode of the zonally varying basic state and the most unstable eigenmode of a zonally homogeneous basic state characteristic of the mid-channel baroclinic zone. The surface cyclogenesis is due to the constructive interference between the several most unstable eigenmodes of the zonally varying basic state. The addition of a simple parameterization of latent heat release in the mid-channel baroclinic zone does not significantly alter the initiation of surface cyclones, but results in cyclones of smaller scale which undergo a longer period of rapid development. / Source: Dissertation Abstracts International, Volume: 51-12, Section: B, page: 5925. / Major Professor: Albert I. Barcilon. / Thesis (Ph.D.)--The Florida State University, 1990.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_78407 |
| Contributors | Whitaker, Jeffrey Stuart., Florida State University |
| Source Sets | Florida State University |
| Language | English |
| Detected Language | English |
| Type | Text |
| Format | 121 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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