The diurnal evolution of cold fronts in the Australian subtropics

Gerald Thomsen, Michael John Reeder, Roger K Smith

Research output: Contribution to journalArticleResearchpeer-review

Abstract

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 coil vergence, 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.
Original languageEnglish
Pages (from-to)395 - 411
Number of pages17
JournalQuarterly Journal of the Royal Meteorological Society
Volume135
Issue number639
Publication statusPublished - 2009

Cite this

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title = "The diurnal evolution of cold fronts in the Australian subtropics",
abstract = "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 coil vergence, 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.",
author = "Gerald Thomsen and Reeder, {Michael John} and Smith, {Roger K}",
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pages = "395 -- 411",
journal = "Quarterly Journal of the Royal Meteorological Society",
issn = "0035-9009",
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The diurnal evolution of cold fronts in the Australian subtropics. / Thomsen, Gerald; Reeder, Michael John; Smith, Roger K.

In: Quarterly Journal of the Royal Meteorological Society, Vol. 135, No. 639, 2009, p. 395 - 411.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - The diurnal evolution of cold fronts in the Australian subtropics

AU - Thomsen, Gerald

AU - Reeder, Michael John

AU - Smith, Roger K

PY - 2009

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N2 - 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 coil vergence, 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.

AB - 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 coil vergence, 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.

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JO - Quarterly Journal of the Royal Meteorological Society

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