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The diurnal evolution of cold fronts in the Australian subtropics
Author(s) -
Thomsen Gerald L.,
Reeder Michael J.,
Smith Roger K.
Publication year - 2009
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.387
Subject(s) - mesoscale meteorology , frontogenesis , mm5 , climatology , cold front , diurnal cycle , boundary layer , atmospheric sciences , convection , morning , geology , daytime , front (military) , meteorology , mechanics , geography , physics , astronomy
The effect of the diurnal cycle on the evolution of cold fronts in the Australian subtropics is investigated in two high‐resolution numerical simulations. The simulations are made using the Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model (MM5) with the initial and boundary conditions taken from the operational analyses of the European Centre for Medium‐range Weather Forecasts. These simulations are compared with the observations of two cold fronts taken during the Central Australian Fronts Experiment in 1991. The simulations show a number of features that have been suspected, but never confirmed or quantified: (i) although the wind field in the boundary layer is frontogenetic, daytime turbulent mixing is strongly frontolytic, which accounts for the weakening and deceleration of the fronts during the late morning and afternoon when convective mixing in the boundary layer is most vigorous; (ii) when the mixing subsides in the early evening, the low‐level winds increase along with the deformation and convergence, leading to a strengthening and acceleration of the fronts; (iii) bore‐like disturbances are generated during the early hours of the morning as the nocturnal inversion strengthens. These bores propagate ahead of the front, developing a series of large‐amplitude waves at their leading edge. Copyright © 2009 Royal Meteorological Society