Lagrangian vortices in developing tropical cyclones
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Authors
Rutherford, B.
Dunkerton, T.J.
Montgomery, M.T.
Subjects
Vortex identification
Lagrangian coherent structures
Tropical cyclogenesis
Lagrangian coherent structures
Tropical cyclogenesis
Advisors
Date of Issue
2015-10
Date
Publisher
Royal Meteorological Society
Language
Abstract
Tracking pre-genesis tropical cyclones is important for earlier detection of developing systems as
well as targeting potential locations for dropsondes in field experiments. The use of a reference
frame moving with the disturbance gives a more accurate depiction of streamlines and closed
circulation than the Earth-relative frame. However, identification of recirculating regions does
not require a choice of reference frame when marked by the Galilean invariant Eulerian Okubo– Weiss
(OW) parameter. While the Eulerian OW parameter is generally effective at identifying vortex cores
at a given place and a given time, it has its limitations in weak disturbances and in
time-dependent flows. Integrating the eigenvalue of the velocity gradient tensor along particle
trajectories provides a time- smoothing of the Eulerian OW parameter, and provides earlier
detection with fewer false alarms. We refer to this integration along trajectories as the
Lagrangian OW parameter. When mapped to a horizontal grid it becomes a Lagrangian OW field.
The Lagrangian OW field has advantages over the Eulerian OW field in the detail of additional flow
structures that it identifies. The Lagrangian OW field shows the Lagrangian boundaries that are
present as a disturbance develops from an easterly wave, and a shear sheath that forms when a
disturbance becomes self-sustaining, typically at tropical storm strength. Since all of these
structures are Lagrangian, they are advected with the flow field, and display the continuous
evolution of coherent flow features as the fluid evolves.
Examples of the use of the Lagrangian OW field are given for ECMWF forecast data from the 2014
Atlantic hurricane season. All of the Lagrangian coherent structures that can be identified by this
field are shown for developing disturbances and mature cyclones. The Lagrangian OW field also shows
additional details of vortex mergers, and is used to identify a stable crystal lattice
configuration in which vorticity does not aggregate.
Type
Article
Description
The article of record as published may be found at http://dx.doi.org/10.1002/qj.2616
Series/Report No
Department
Meteorology
Organization
Naval Postgraduate School (U.S.)
Identifiers
NPS Report Number
Sponsors
National Science Foundation
NASA
Naval Postgraduate School
NASA
Naval Postgraduate School
Funder
Grant AGS-1439283 (NSF)
Grant AGS-1313948 (NSF)
Grant NNG11PK021 (NASA)
Grant AGS-1313948 (NSF)
Grant NNG11PK021 (NASA)
Format
11 p.
Citation
B. Rutherford, T.J. Dunkerton, M.T. Montgomery, "Lagrangian vortices in developing tropical cyclones," Quarterly Journal of the Royal Meteorological Society, v. 141, no.693, (October 2015), Pt. B, pp. 3344-3354.
Distribution Statement
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.