The dynamics of coastal troughs and coastal fronts

Økland, Hans

doi:10.1034/j.1600-0870.1990.t01-3-00004.x

Cited by 5 publications

(4 citation statements)

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“…The best known example, the New England coastal front, was documented by Bosart et al (1972). Similar mesoscale features have been identified farther south in the Carolinas (Lapenta and Seaman 1990) and Texas (Bosart 1984), along the coast of Norway (Okland 1990), and along the southeast coast of China (Huang 1993). Numerical simulations presented by Garner (1986, hereafter G86) indicate that the topography in most of these regions can fully block a layer of surface air in certain types of idealized onshore flow.…”

Section: Introductionsupporting

confidence: 55%

Blocking and Frontogenesis by Two-Dimensional Terrain in Baroclinic Flow. Part I: Numerical Experiments

Garner

1999

J. Atmos. Sci.

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The shallow atmospheric fronts that develop in the early winter along the east coast of North America have been attributed, in various modeling and observational studies, to the land-sea contrasts in both surface heating and friction. However, typical synoptic conditions are such that these ''coastal'' fronts could also be a type of upstream influence by the Appalachian Mountain chain. Generalized models have suggested that relatively cold air can become trapped on the windward side of a mountain range during episodes of warm advection without a local contribution from differential surface fluxes. Such a process was proposed decades ago in a study of observations along the coast of Norway. Could coastal frontogenesis be primarily a consequence of a mountain circulation acting on the large-scale temperature gradient?A two-dimensional, terrain-following numerical model is used to find conditions under which orography may be sufficient to cause blocking and upstream frontogenesis in a baroclinic environment. The idealized basic flow is taken to have constant vertical shear parallel to a topographic ridge and a constant perpendicular wind that advects warm or cold temperatures toward the ridge. Land-sea contrasts are omitted. In the observed cases, the mountain is ''narrow'' in the sense that the Rossby number is large. This by itself increases the barrier effect, but the experiments show that large-scale warm advection is still crucial for blocking. For realistic choices of ambient static stability and baroclinicity, the flow can be blocked by a range like the northern Appalachians if the undisturbed incident wind speed is around 10 m s Ϫ1 . Cold advection weakens the barrier effect.The long-term behavior of the front in strongly blocked cases is described and compared to observations. Because of the background rotation and large-scale temperature advection, blocked solutions cannot become steady in the assumed environment. However, the interface between blocked and unblocked fluid can settle into a balanced configuration in some cases. A simple argument suggests that, in the absence of dissipation, the frontal slope should be similar to that of the ambient ''absolute momentum'' surfaces.

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Section: Introductionsupporting

confidence: 55%

Blocking and Frontogenesis by Two-Dimensional Terrain in Baroclinic Flow. Part I: Numerical Experiments

Garner

1999

J. Atmos. Sci.

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“…These results are consistent with observations of barrier jets (Parish 1982) and cold-air damming (Bell and Bosart 1988;Xu 1990) during steady-state flow. More typically, the orographic response is complicated because of its dependence on a combination of effects including variations in topography; temporal and spatial variations in the incident flow; diabatic, especially latent, heating; and viscous effects (e.g., Okland 1990). Most work on stormterrain interactions involves orographic modification of fronts, particularly by the Alps, and includes theoretical (Blumen 1992;Gross 1994), modeling (Williams et al 1992), and observational studies (Hoinka et al 1990).…”

Section: Scientific Issuesmentioning

confidence: 99%

The Coastal Observation and Simulation with Topography (COAST) Experiment

Bond¹,

Mass²,

Smull³

et al. 1997

Bull. Amer. Meteor. Soc.

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The Coastal Observation and Simulation with Topography (COAST) program has examined the interaction of both steady-state and transient cool-season synoptic features, such as fronts and cyclones, with the coastal terrain of western North America. Its objectives include better understanding and forecasting of landfalling weather systems and, in particular, the modification and creation of mesoscale structures by coastal orography. In addition, COAST has placed considerable emphasis on the evaluation of mesoscale models in coastal terrain. These goals have been addressed through case studies of storm and frontal landfall along the Pacific Northwest coast using special field observations from a National Oceanic and Atmospheric Administration WP-3D research aircraft and simulations from high-resolution numerical models. The field work was conducted during December 1993 and December 1995. Active weather conditions encompassing a variety of synoptic situations were sampled. This article presents an overview of the program as well as highlights from a sample of completed and ongoing case studies.

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“…The large-scale easterly wind in the area had where C H is the transfer coefficient, assumed here to be 0.0014 (Fujitani, 1975). Based on the obser-increased somewhat during the previous day, and had veered towards northeast, in accordance with vations, we have chosen V s to be 25 ms−1 and the temperature difference to be 12 K. Then H turns a pressure drop in the area between Bear Island and the coast of Norway.…”

Section: Introductionmentioning

confidence: 99%

Modification of frontal circulations by surface heat flux

Økland¹

1998

Tellus A

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Based on Arnt Eliassen's papers on the transverse circulation at baroclinic zones, we study the influence of heat fluxes from the ocean. The paper first examines a particular weather situation over the Arctic Ocean, where a front separates very cold air over the ice cover from warmer air over the open water. The paper aims at showing that an observed increase of the wind force might be caused by the intense heating of the cold air over the water. For this purpose, we devise an analytical solution of the Eliassen equation. The fortunate location of the front in relation to the observations permits a comparison between the observed wind and the wind estimated from the equation. It is suggested that many tragic shipwrecks along the border of the ice may be explained in this way.

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The dynamics of coastal troughs and coastal fronts

Cited by 5 publications

References 0 publications

Blocking and Frontogenesis by Two-Dimensional Terrain in Baroclinic Flow. Part I: Numerical Experiments

Blocking and Frontogenesis by Two-Dimensional Terrain in Baroclinic Flow. Part I: Numerical Experiments

The Coastal Observation and Simulation with Topography (COAST) Experiment

Modification of frontal circulations by surface heat flux

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