Brian J. Hoskins, I. N. James · 2014
The acceleration of the cross-front flow is negligible and the along-front wind is approximately in geostrophic balance. This chapter shows the Eady model demonstrates frontogenesis in the manner of the shear mechanism. The mechanism for the frontal formation is similar to the idealized frontogenesis described in the chapter: secondary circulations that develop to maintain balance distort as the gradients become stronger. This leads to the formation of discontinuities in a finite time. It focuses on frontogenesis near the surface. The cross-frontal circulation equation is quite generally valid and if the geostrophic motion over a deep layer which includes the tropopause is such as to increase horizontal temperature gradients. The confluence model can be extended to include two regions, a uniform potential vorticity troposphere with a uniform higher potential vorticity stratosphere above it. Solutions have to be determined numerically with matching across the ‘tropopause’ separating the two regions.
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Lance F. Bosart, Cosmo J. Vaudo, John H. Helsdon · Journal of applied meteorology · 1972
Detailed synoptic analyses are made of mesoscale frontogenesis situations along the southeastern New England coast. Temperature gradients of 5–10C over 5–10 km along a line separating light northerly or northwesterly flow from stronger easterly flow are common. The coastal thermal contrast may follow 6–12 hr after the establishment of a cold anticyclone to the north of New England and persist for 12 hr. Dissipation takes place when in offshore cyclonic circulation reaches the latitude of southern New England such that coastal winds back to northerly. The whole process is called coastal frontogenesis. A persistent tendency for coastal fronts to stagnate along a Boston to Providence line is noted. Precipitation appears to be enhanced along and just on the cold side of the frontal zone. Arguments are presented in favor of the importance of surface friction, orography, coastal configuration, and land-sea thermal contrast on the life cycle of coastal fronts. An inspection of eight years of data suggests that coastal frontogenesis is a maximum in late fall and early winter when land-sea temperature contrasts are greatest. Evidence is presented in one case of a coastal front, acting as a channel for a developing secondary wave disturbance, with latent heat release associated with the precipitation maximum proving to be important for development.
Cited by 51Open access
McDougall, Catherine M. · Calhoun: The Naval Postgraduate School Institutional Archive (Naval Postgraduate School) · 2001
Numerical experiments are conducted with a hydrostatic primitive equation model initialized in a baroclinically unstable slate to simulate the passage of cold fronts over the ocean. The model includes K-theory planetary boundary layer (PBL) parameterization with implicitly defined diffusion coefficients. An adiabatic and inviscid simulation provided the control for these experiments. The PBL simulations are integrated: (1) with Z(sub o) held constant at 0.4 m and no heat flux; (2) with sea surface temperature (SST) set equal to theta 1 at t = 0 h; (3) with a 5 deg warmer SST; (4) with diffusion coefficients set equal to 1. Horizontal resolution is increased to achieve smaller scale fronts in the inviscid and ocean simulations. The frontogenetic effects of shear, tilting, convergence, and the PBL on isentropic surfaces are evaluated. Relative to the inviscid simulation, the PBL simulations produce reduced frontogenesis. Surface heat and momentum fluxes combined with turbulent mixing of heat promote the development of a deep, well-mixed layer whose depth is dependent on the air-sea temperature difference. The rate of frontogenesis is extremely dependent on the parameterization of the PBL, specifically surface roughness lengths. Smaller scale fronts were produced during the ocean simulations than the PBL land case. Forcing in all simulations is due primarily to shearing deformation initially. As the wave grows in amplitude, convergence contributes more to frontogenesis than shear. Other terms in the frontogenetic equation become important in the PBL simulations.
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Oxford University Press eBooks · 2023
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W. Rockwell Geyer, David K. Ralston · Journal of Physical Oceanography · 2014
Abstract Model studies and observations in the Hudson River estuary indicate that frontogenesis occurs as a result of topographic forcing. Bottom fronts form just downstream of lateral constrictions, where the width of the estuary increases in the down-estuary (i.e., seaward) direction. The front forms during the last several hours of the ebb, when the combination of adverse pressure gradient in the expansion and baroclinicity cause a stagnation of near-bottom velocity. Frontogenesis is observed in two dynamical regimes: one in which the front develops at a transition from subcritical to supercritical flow and the other in which the flow is everywhere supercritical. The supercritical front formation appears to be associated with lateral flow separation. Both types of fronts are three-dimensional, with strong lateral gradients along the flanks of the channel. During spring tide conditions, the fronts dissipate during the flood, whereas during neap tides the fronts are advected landward during the flood. The zone of enhanced density gradient initiates frontogenesis at multiple constrictions along the estuary as it propagates landward more than 60 km during several days of neap tides. Frontogenesis and frontal propagation may thus be essential elements of the spring-to-neap transition to stratified conditions in partially mixed estuaries.
Cited by 41Open access
Reeder., Michael John · Monash University · 2021
This thesis was scanned from the print manuscript for digital preservation and is copyright the author. Researchers can access this thesis by asking their local university, institution or public library to make a request on their behalf. Monash staff and postgraduate students can use the link in the References field.
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W. R. Peltier, G. W. K. Moore, Saroja Polavarapu · Tellus A Dynamic Meteorology and Oceanography · 1990
Detailed linear analysis of the stability of realistic atmospheric frontal structures using the full hydrostatic primitive equations has demonstrated that such localized baroclinic zones support instability at two distinct and well-separated length scales, even when the frontal mean states have uniform potential vorticity. The first scale is associated with the well-known Charney-Eady mode of baroclinic instability with a wavelength of 3000–4000 km that is responsible for the generation of observed mid-tropospheric long waves. The second scale is defined by an apparently new mode of baroclinic instability, that we have previously called the “cyclone mode”, which has a wavelength near 1000 km and is boundary confined rather than being troposphere filling as is the case of the Chamey-Eady mode. The most important characteristic of the cyclone mode is that it is completely filtered by both the quasi-geostrophic and semi-geostrophic approximations to the equations of motion. In this paper, we demonstrate explicitly through the analysis of a specific case of polar low development that this new mode is an important actor in at least one recurrent atmospheric dynamical process. Besides reviewing and extending these linear stability analyses, we describe a number of rather interesting results that we have obtained from a new series of f-plane analyses of the nonlinear life cycles of frontal baroclinic waves. These have already provided considerable new insight into the detailed dynamics of the processes through which frontal waves “break”.
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David M. Schultz · Encyclopedia of Atmospheric Sciences · 2014
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Reeder., Michael John · Figshare · 2021
This thesis was scanned from the print manuscript for digital preservation and is copyright the author. Researchers can access this thesis by asking their local university, institution or public library to make a request on their behalf. Monash staff and postgraduate students can use the link in the References field.
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Jonathan E. Martin · Elsevier eBooks · 2024
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R. T. Williams, Jon Plotkin · Journal of the Atmospheric Sciences · 1968
An exact solution to the quasi-geostrophic equations is derived for an initial horizontal wind field which contains deformation. The variation in the initial temperature field is confined to a band which is oriented normal to the axis of contraction of the deformation field. In the solution, a frontal zone forms and the temperature at two boundary points becomes discontinuous as the time approaches infinity. The solution is very similar to Stone's solution and it generalizes his work. Some aspects of the solution are not realistic.
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Brian J. Hoskins · American Meteorological Society eBooks · 2003
It is a great pleasure for me to contribute to this symposium and volume in honor of Dick Reed. My Ph.D. research on frontogenesis owed much to the papers by Dick and his collaborators. Since then I have always found scientific meetings with him to be exhilarating, and my wife and I have found social meetings with Joan and him to be very enjoyable. I suspect that my main contribution to Dick’s life is that I guided him in the art of driving around roundabouts in England!
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H. Arakawa · Journal of the Meteorological Society of Japan Ser II · 1948
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Bishop, Craig H. · Monash University · 2021
This thesis was scanned from the print manuscript for digital preservation and is copyright the author. Researchers can access this thesis by asking their local university, institution or public library to make a request on their behalf. Monash staff and postgraduate students can use the link in the References field.
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Craig H. Bishop · Figshare · 2021
This thesis was scanned from the print manuscript for digital preservation and is copyright the author. Researchers can access this thesis by asking their local university, institution or public library to make a request on their behalf. Monash staff and postgraduate students can use the link in the References field.
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Leif N. Thomas, C. M. Lee · 2004
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G. HARTJENSTEIN, Joseph Egger · Tellus A Dynamic Meteorology and Oceanography · 1990
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Christopher N. K. Mooers · 1978
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E.‐Y. Hsie · 1983
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Vern Ostdiek, William Blumen · Journal of the Atmospheric Sciences · 1995
A low-level deformation frontogenesis event that occurred during the Stormscale Operational and Research Meteorology-Fronts Experiment Systems Test (STORM-FEST) field program is analyzed in the context of semigeostrophic theory. The observed evolution and vertical structure of the potential temperature and alongfront wind fields are compared to that predicted by both numerical and analytical solutions of the semigeostrophic equations initialized at the onset of the deformation frontogenesis. The model solutions provide relatively accurate predictions of the surface potential temperature distribution 5 h later, when the frontogenesis ended. The point along the front with the steepest potential temperature gradient is observed to move closer to the point with the highest relative vorticity by an amount that is in rough agreement with the model prediction. Vertical profiles of potential temperature from soundings show a nearly mixed layer below ∼400 m that cannot be predicted by the inviscid solutions, but there is good agreement with inviscid theory above this level. The observed profiles of alongfront wind are characterized by a low-level jet with maximum speed at the level of the inversion, and the vertical shear below the jet maximum is opposite that predicted by the thermal wind equation. The semigeostrophic model does appear to depict this frontogenesis event in the upper layer, while the lower layer is dominated by surface drag and shear-induced turbulent mixing.
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