The evolution of a long-lived mesovortex and its transformation into a tropical storm are studied by a three dimensional mesoscale model. The major aspects of the work are: (1) to demonstrate the mesoscale predictability of a long-lived mesoscale convective system (MCS) from a mid-level vortex over land to a tropical storm over ocean, (2) to understand the processes involved in the transformation of a mid-level continental vortex into a tropical storm, and (3) to perform sensitivity experiments to assess the impact of model physics on an idealized simulation. / The major conclusions are: The 90-h real-data simulation shows that the mesoscale model reproduces very well much of the meso-beta-structures and the evolution of the long-lived MCS. These include the development and dissipation of the continental mesovortex, the initiation of a new MCS both in time and in space, the genesis of a surface mesolow over the warm Gulf Stream water, the track and the deepening of the surface cyclone into a "tropical storm", the maintenance of a mid-level mesovortex system, and the propagation of a large-scale cold front with respect to the surface cyclone. / The simulation also shows that the mid-level mesovortex provides persistent convergence at its southern periphery for the continued convective development, whereas the convectively enhanced low-level flow increases surface energy fluxes over the warm water causing further conditional instability. Such feedback processes lead to the rapid deepening of the "tropical storm". / An idealized simulation was performed to eliminate the possible influence of the cold frontal system on the genesis of the tropical storm. The initial conditions resemble the basic structure of the subtropical high in the real-data case, but without the embedded frontal system. The simulation reproduces almost all of the essential features in the real-data simulation. In particular, the eye-like warm core structure of the tropical storm is well simulated. By decomposing the vertical relative vorticity into the curvature vorticity and the shear vorticity, it is shown that the amplification of a low-level vortex after 36 h arises mainly from the increase of curvature vorticity. The quasi-Lagrangian theta budget calculation shows that the descending motion in the center of the surface cyclone contributes to the formation of the warm core at 800 hPa. / The results of sensitivity experiments demonstrate the impact of model physics on the idealized simulation. Using the Betts-Miller scheme, we showed that the model fails to simulate the multiple-episodes of convective activity which are present in observational studies of tropical cyclogenesis and in the simulation using the Kain-Fritsch scheme. We further found that the surface latent heat fluxes represent a dominant factor in the production of CAPE to maintain the persistent convection. Finally, we discussed the cumulative cooling effect by long-wave radiation on the destabilization of the environment of the storm.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.35567 |
| Date | January 1999 |
| Creators | Bao, Ning, 1961- |
| Contributors | Yau, M. K. (advisor), Zhang, Da-Lin (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Atmospheric and Oceanic Sciences.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001744937, proquestno: NQ64506, Theses scanned by UMI/ProQuest. |
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