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Uncertainty in Scatterometer-Derived Vorticity

Title: Uncertainty in Scatterometer-Derived Vorticity.
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Name(s): Ford, Kelly Mcbeth, author
Bourassa, Mark, professor directing thesis
Reasor, Paul, committee member
Cunningham, Philip, committee member
Department of Earth, Ocean and Atmospheric Sciences, degree granting department
Florida State University, degree granting institution
Type of Resource: text
Genre: text
Issuance: monographic
Date Issued: 2008
Publisher: Florida State University
Place of Publication: Tallahassee, Florida
Physical Form: computer
Physical Form: online resource
Extent: 1 online resource
Language(s): English
Abstract/Description: A more versatile and robust technique is developed for determining area averaged surface vorticity based on vector winds from the SeaWinds scatterometer on the QuikSCAT satellite. This improved technique is discussed in detail and compared to two previous studies by Sharp et al. (2002) and Gierach et al. (2007) that focused on early development of tropical systems. The error characteristics of the technique are examined in detail. Specifically, three independent sources of error are explored: random observational error, truncation error and representation error. Observational errors are due to random errors in the wind observations, and determined as a worst-case estimate as a function of averaging spatial scale. The observational uncertainty in vorticity averaged for a roughly circular shape with a 100 km diameter, expressed as one standard deviation, is approximately 0.5 x 10 -5 s-1 for the methodology described herein. Truncation error is associated with the assumption of linear changes between wind vectors. For accurate results, it must be estimated on a case-by-case basis. An attempt is made to determine a lower bound of truncation errors through the use of composites of tropical disturbances. This lower bound is calculated as 10-7 s-1 for the composites, which is relatively small compared to the tropical disturbance detection threshold set at 5 x 10-5 s-1, used in an earlier study. However, in more realistic conditions, uncertainty related to truncation errors is much larger than observational uncertainty. The third type of error discussed is due to the size of the area being averaged. If the wind vectors associated with a vorticity maximum are inside the perimeter of this area (away from the edges), it will be missed. This type of error is analogous to over-smoothing. Tropical and sub-tropical low pressure systems from three months of QuikSCAT observations are used to examine this error. This error results in a bias of approximately 1.5 x 10-5 s-1 for area averaged vorticity calculated on a 100 km scale compared to vorticity calculated on a 25 km scale. The discussion of these errors will benefit future projects of this nature as well as future satellite missions.
Identifier: FSU_migr_etd-4422 (IID)
Submitted Note: A Thesis submitted to the Department of Meteorology in partial fulfillment of the requirements for the degree of Master of Science.
Degree Awarded: Fall Semester, 2008.
Date of Defense: August 14, 2008.
Keywords: Vorticity, Scatterometer, Cyclone Genesis, Rrror Analysis, Tropical Storm
Bibliography Note: Includes bibliographical references.
Advisory Committee: Mark Bourassa, Professor Directing Thesis; Paul Reasor, Committee Member; Philip Cunningham, Committee Member.
Subject(s): Meteorology
Persistent Link to This Record: http://purl.flvc.org/fsu/fd/FSU_migr_etd-4422
Owner Institution: FSU