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Meso‐β‐scale circulations in realistic fronts. I: Steady basic state
Author(s) -
Fischer Claude,
Lalaurette François
Publication year - 1995
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 - 10.1002/qj.49712152605
Subject(s) - instability , mesoscale meteorology , kinetic energy , vorticity , perturbation (astronomy) , potential vorticity , hydrostatic equilibrium , troposphere , mechanics , physics , growth rate , vortex , meteorology , classical mechanics , mathematics , geometry , quantum mechanics
This paper investigates the occurrence of conditional symmetric instability during MFDP/Fronts87IOP2. A saturated negative equivalent‐potential‐vorticity area is detected by the mesoscale analysis in the upper troposphere, and this is confirmed by dropsounding data. Two‐dimensional hydrostatic simulations are performed with the Météo‐France PERIDOT model which give rise to the onset of symmetric instability. A complete life cycle is obtained as well as the growth rate of the perturbation (about 2.5 × 10 −5 s −1 ≈ (11 hours) −1 ). Particular emphasis is put on the meanings and results of the kinetic‐energy conversions. Most of the perturbation energy comes from the basic state through vertical momentum fluxes, which is consistent with previous theoretical or numerical works. the decay of the perturbation is also shown to be due to its own dynamics, the symmetric rolls advecting positive equivalent potential vorticity into the unstable region. Deformations of equivalent potential temperature (θ e ) surfaces and m‐surfaces give an insight into the parcel trajectories: the ascending parcels follow θ e ‐surfaces. leading to a buckling of the m‐surfaces, and the descending parcels follow θ‐surfaces. the small value of the growth rate is stressed as well as of the maximum intensity (w ≈ 5 cm s −1 ). Thus, interactions with the frontogenetical forcing are expected owing to the small growth rate obtained. This is the subject of Part II of this paper.