Filamentation time diagnosis of thinning troughs and cutoff lows
Journal
Monthly Weather Review
Journal Volume
138
Journal Issue
6
Pages
2327-2335
Date Issued
2010
Author(s)
Abstract
This paper analyzes synoptic-scale trough-thinning processes using a filamentation time diagnostic. The filamentation time diagnostic is derived from the potential vorticity equation expressed in spherical coordinates in the horizontal plane and the isentropic coordinate in the vertical direction. The diagnostic is an accurate measure of stirring processes under the condition of "slowly varying velocity gradients." Troughthinning processes are analyzed for one tropical example and two midlatitude examples. The results indicate that the filamentation time for the tropical trough-thinning event is generally longer than those for the midlatitude trough events. In addition to the effects of stretching and shearing deformation, the filamentation time diagnostic contains the effects of divergence. For the calculation of filamentation time on isentropic surfaces in spherical coordinates, it is acceptable to ignore the curvature effects in the tropics; however, in both the midlatitudes and the tropics, isentropic divergence effects should be retained for improved accuracy. Combining an analysis of cross potential vorticity contour flows on isentropic surfaces with the filamentation time analysis gives a more complete description of the dynamics. The results show that the filamentation time diagnostic can serve as a useful aid in the analysis and prediction of trough thinning and cutoff-low formation. © 2010 American Meteorological Society.
Subjects
Atmospheric circulation; Dynamics; Mesoscale processes; Potential vorticity; Synoptic-scale processes
SDGs
Other Subjects
Atmospheric circulation; Curvature effect; Cut-off low; Filamentation; Horizontal planes; Isentropic; Isentropic surfaces; Mesoscale; Midlatitudes; Potential vorticity; Shearing deformation; Spherical coordinates; Thinning process; Time analysis; Velocity gradients; Vertical direction; Climatology; Vorticity; Tropics; atmospheric circulation; atmospheric dynamics; climate prediction; mesoscale meteorology; midlatitude environment; potential vorticity; synoptic meteorology; tropical environment
Type
journal article