Transcritical Flows in the Coastal Marine Atmospheric Boundary Layer*

Rogerson, A. M.

doi:10.1175/1520-0469(1999)056<2761:tfitcm>2.0.co;2

Cited by 55 publications

(52 citation statements)

References 28 publications

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“…To test this several runs with a more accurate numerical model with no explicit lateral dissipation were made using the fourth-order in space, third-order in time ENO scheme described in Rogerson (1999). That model, which could not be used in cases that developed layer depths near zero, gave shock speeds and amplitudes that were slightly larger (3-5% in the worst cases) than the results from our numerical model.…”

Section: )mentioning

confidence: 97%

Nonlinear Rossby adjustment in a channel

1999

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The Rossby adjustment problem for a homogeneous fluid in a channel is solved for large values of the initial depth discontinuity. We begin by analysing the classical dam break problem in which the depth on one side of the discontinuity is zero. An approximate solution for this case can be constructed by assuming semigeostrophic dynamics and using the method of characteristics. This theory is supplemented by numerical solutions to the full shallow water equations. The development of the flow and the final, equilibrium volume transport are governed by the ratio of the Rossby radius of deformation to the channel width, the only non-dimensional parameter. After the dam is destroyed the rotating fluid spills down the dry section of the channel forming a rarefying intrusion which, for northern hemisphere rotation, is banked against the right-hand wall (facing downstream). As the channel width is increased the speed of the leading edge (along the right-hand wall) exceeds the intrusion speed for the non-rotating case, reaching the limiting value of 3.80 times the linear Kelvin wave speed in the upstream basin. On the left side of the channel fluid separates from the sidewall at a point whose speed decreases to zero as the channel width approaches infinity. Numerical computations of the evolving flow show good agreement with the semigeostrophic theory for widths less than about a deformation radius. For larger widths cross-channel accelerations, absent in the semigeostrophic approximation, reduce the agreement. The final equilibrium transport down the channel is determined from the semigeostrophic theory and found to depart from the non-rotating result for channels widths greater than about one deformation radius. Rotation limits the transport to a constant maximum value for channel widths greater than about four deformation radii.The case in which the initial fluid depth downstream of the dam is non-zero is then examined numerically. The leading rarefying intrusion is now replaced by a Kelvin shock, or bore, whose speed is substantially less than the zero-depth intrusion speed. The shock is either straight across the channel or attached only to the righthand wall depending on the channel width and the additional parameter, the initial depth difference. The shock speeds and amplitudes on the right-hand wall, for fixed downstream depth, increase above the non-rotating values with increasing channel width. However, rotation reduces the speed of a shock of given amplitude below the non-rotating case. We also find evidence of resonant generation of Poincaré waves by the bore. Shock characteristics are compared to theories of rotating shocks and qualitative agreement is found except for the change in potential vorticity across the shock, which is very sensitive to the model dissipation. Behind the leading shock the flow evolves in much the same way as described by linear theory except for the generation of strongly nonlinear transverse oscillations and rapid advection down the 188 K. R. Helfrich, A. C. Kuo and L. J. Pratt rig...

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Section: )mentioning

confidence: 97%

Nonlinear Rossby adjustment in a channel

1999

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“…Most studies about CLLJ published in the literature are based on field campaigns during the summer (Beardsley et al, 1987;Zemba and Friehe, 1987;Winant et al, 1988, Sundararajan andTjernstro¨m, 1999), and on modelling and theoretical efforts (Cui et al, 1998;Rogerson, 1999). These studies have focused mainly on the California and ChileÁPeru coastal jets, with some exceptions on the SomaliÁOman jet (Findlater, 1969;Ardanui, 1979) and more recently on the Benguela jet (Nicholson, 2010).…”

Section: Introductionmentioning

confidence: 99%

Climatology of the Iberia coastal low-level wind jet: weather research forecasting model high-resolution results

Soares

Cardoso²,

Semedo

et al. 2014

Tellus A: Dynamic Meteorology and Oceanography

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A B S T R A C T Coastal low-level jets (CLLJ) are a low-tropospheric wind feature driven by the pressure gradient produced by a sharp contrast between high temperatures over land and lower temperatures over the sea. This contrast between the cold ocean and the warm land in the summer is intensified by the impact of the coastal parallel winds on the ocean generating upwelling currents, sharpening the temperature gradient close to the coast and giving rise to strong baroclinic structures at the coast. During summertime, the Iberian Peninsula is often under the effect of the Azores High and of a thermal low pressure system inland, leading to a seasonal wind, in the west coast, called the Nortada (northerly wind). This study presents a regional climatology of the CLLJ off the west coast of the Iberian Peninsula, based on a 9 km resolution downscaling dataset, produced using the Weather Research and Forecasting (WRF) mesoscale model, forced by 19 years of ERA-Interim reanalysis (1989Á2007). The simulation results show that the jet hourly frequency of occurrence in the summer is above 30% and decreases to about 10% during spring and autumn. The monthly frequencies of occurrence can reach higher values, around 40% in summer months, and reveal large inter-annual variability in all three seasons. In the summer, at a daily base, the CLLJ is present in almost 70% of the days. The CLLJ wind direction is mostly from north-northeasterly and occurs more persistently in three areas where the interaction of the jet flow with local capes and headlands is more pronounced. The coastal jets in this area occur at heights between 300 and 400 m, and its speed has a mean around 15 m/s, reaching maximum speeds of 25 m/s.

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“…Rogerson (1999) explored the dynamic characteristics of hydraulically transcritical flows adjacent to a spatially varying coastline; that is, flows having localized supercritical (Fr>1) regions embedded within a domain that generally is subcritical (Fr < 1). While CTD's are able to propagate northward in the subcritical region of the base flow, they can be severely attenuated, or halted altogether, upon encountering a supercritical region.…”

Section: Shock Feature Interaction With the Ctd And Eddy Roll-upmentioning

confidence: 99%

“…Rogerson (1999) used a shallow water model to investigate the interaction of an artificially created CTD with transcritical flow in the vicinity of coastal topographic bends.…”

Section: Introductionmentioning

confidence: 99%