PhD Thesis Defence
Christopher T. Fogarty
Department of Oceanography
Degrees
- BSc (Physics), Dalhousie University, 1996
- Diploma in Meteorology, Dalhousie University, 1997
- MSc (Synoptic Meteorology), McGill University, 1999
Title of Thesis:
- Numerical Modeling of Atlantic Hurricanes Moving Into The Middle Latitudes
Time/Date:
- 9:00 am , Friday, March 3, 2006
Place:
- Lord Dalhousie Room, Main floor, Henry Hicks Academic and Administration Building
Examining Committee:
- Dr. Kerry Emanuel, Program in Atmospheres, Oceans and Climate, Massachusetts Institute of Technology (External Examiner)
- Dr. Harold Ritchie, Department of Oceanography, Dalhousie University (Reader)
- Dr. Jinyu Sheng, Department of Oceanography, Dalhousie University (Reader)
- Dr. Tom Duck, Department of Physics and Atmospheric Science, Dalhousie University (Reader)
- Dr. Richard Greatbatch, Department of Oceanography, Dalhousie University (Supervisor)
- Dr. Daniel Kelley, Department of Oceanography, Dalhousie University (Departmental Representative)
Chair:
- Dr. Richard Singer, PhD Defence Panel, Faculty of Graduate Studies
Abstract
Hurricanes that form over the Atlantic Ocean very frequently migrate into the middle latitudes where they encounter much different oceanic and atmospheric conditions than in the tropics. Cool sea surface temperatures (SSTs) cause these storms to weaken and become thermodynamically decoupled from the ocean, while baroclinic atmospheric environments often cause them to transform into extratropical storms - a process known as extratropical transition (ET). The changing structure of these storms in the middle latitudes presents many unique forecasting challenges related to the increasing asymmetry in moisture and wind fields, and their potentially destructive nature.
An examination of three such events over Eastern Canada - using a combination of observations and a numerical model - forms the foundation of this work, with an emphasis on applying the research to weather forecasting. The case studies include Hurricane Michael (2000), Hurricane Karen (2001) and Hurricane Juan (2003). Hurricane Michael intensified in a strongly-baroclinc environment and evolved into an intense extratropical storm over Newfoundland. Karen also underwent ET, but weakened quickly during its approach to Nova Scotia, while Hurricane Juan struck the province as a category-two hurricane, experiencing only marginal weakening over anomalously warm SSTs. In essence, these cases represent a cross section of the behavior of many tropical cyclones in this part of the world.
Hindcast simulations are conducted for each event using the Canadian Mesoscale Compressible Community (MC2) model with a synthetic, observationally-consistent hurricane vortex used in the model's initial conditions. Sensitivity experiments are run for each case by modifying initial specifications of the vortex, model physics parameterizations, and surface boundary conditions like SST. In the case of Hurricane Juan, it is determined that the anomalously-warm SSTs played a significant role in the landfall intensity, while Hurricane Michael was not particularly sensitive to small anomalies of the SSTs. Experiments conducted on Hurricane Karen reveal that the storm's landfalling intensity is not particularly sensitive to its intensity prior to traversing the cool waters south of Nova Scotia. Significant improvements in the representation of the moisture and mass fields are observed in all three cases compared with numerical forecast models that did not employ vortex insertion in the initial atmospheric fields.
