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Life‐cycle simulations of shallow frontal waves and the impact of deformation strain
Author(s) -
Dacre H. F.,
Gray S. L.
Publication year - 2006
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1256/qj.05.238
Subject(s) - deformation (meteorology) , strain (injury) , strain rate , geology , hydrostatic equilibrium , mechanics , materials science , physics , composite material , medicine , quantum mechanics , oceanography
The life cycle of shallow frontal waves and the impact of deformation strain on their development is investigated using the idealized version of the Met Office non‐hydrostatic Unified Model which includes the same physics and dynamics as the operational forecast model. Frontal‐wave development occurs in two stages: first, a deformation strain is applied to a front and a positive potential‐vorticity (PV) strip forms, generated by latent‐heat release in the frontal updraught; second, as the deformation strain is reduced the PV strip breaks up into individual anomalies. The circulations associated with the PV anomalies cause shallow frontal waves to form. The structure of the simulated frontal waves is consistent with the conceptual model of a frontal cyclone. Deeper frontal waves are simulated if the stability of the atmosphere is reduced. Deformation strain rates of different strengths are applied to the PV strip to determine whether a deformation strain threshold exists above which frontal‐wave development is suppressed. An objective method of frontal‐wave activity is defined and frontal‐wave development was found to be suppressed by deformation strain rates ≥0.4×10 −5 s −1 . This value compares well with observed deformation strain‐rate thresholds and the analytical solution for the minimum deformation strain rate needed to suppress barotropic frontal‐wave development. The deformation strain‐rate threshold is dependent on the strength of the PV strip with strong PV strips able to overcome stronger deformation strain rates (leading to frontal‐wave development) than weaker PV strips. Copyright © 2006 Royal Meteorological Society