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  • 1
    Online Resource
    Online Resource
    Coastal Atmospheric Circulation around an Idealized Cape during Wind-Driven Upwelling Studied from a Coupled Ocean–Atmosphere Model
    American Meteorological Society ; 2011
    In:  Monthly Weather Review Vol. 139, No. 3 ( 2011-03-01), p. 809-829
    Details
    In: Monthly Weather Review, American Meteorological Society, Vol. 139, No. 3 ( 2011-03-01), p. 809-829
    Abstract: The study analyzes atmospheric circulation around an idealized coastal cape during summertime upwelling-favorable wind conditions simulated by a mesoscale coupled ocean–atmosphere model. The domain resembles an eastern ocean boundary with a single cape protruding into the ocean in the center of a coastline. The model predicts the formation of an orographic wind intensification area on the lee side of the cape, extending a few hundred kilometers downstream and seaward. Imposed initial conditions do not contain a low-level temperature inversion, which nevertheless forms on the lee side of the cape during the simulation, and which is accompanied by high Froude numbers diagnosed in that area, suggesting the presence of the supercritical flow. Formation of such an inversion is likely caused by average easterly winds resulting on the lee side that bring warm air masses originating over land, as well as by air warming during adiabatic descent on the lee side of the topographic obstacle. Mountain leeside dynamics modulated by differential diurnal heating is thus suggested to dominate the wind regime in the studied case. The location of this wind feature and its strong diurnal variations correlate well with the development and evolution of the localized lee side trough over the coastal ocean. The vertical extent of the leeside trough is limited by the subsidence inversion aloft. Diurnal modulations of the ocean sea surface temperatures (SSTs) and surface depth-averaged ocean current on the lee side of the cape are found to strongly correlate with wind stress variations over the same area. Wind-driven coastal upwelling develops during the simulation and extends offshore about 50 km upwind of the cape. It widens twice as much on the lee side of the cape, where the coldest nearshore SSTs are found. The average wind stress–SST coupling in the 100-km coastal zone is strong for the region upwind of the cape, but is notably weaker for the downwind region, estimated from the 10-day-average fields. The study findings demonstrate that orographic and diurnal modulations of the near-surface atmospheric flow on the lee side of the cape notably affect the air–sea coupling on various temporal scales: weaker wind stress–SST coupling results for the long-term averages, while strong correlations are found on the diurnal scale.
    Type of Medium: Online Resource
    ISSN: 1520-0493 , 0027-0644
    URL: Article
    DOI: 10.1175/2010MWR3372.1
    RVK:
    RA 1000
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2011
    detail.hit.zdb_id: 2033056-X
    detail.hit.zdb_id: 202616-8
    SSG: 14
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  • 2
    Online Resource
    Online Resource
    Baroclinic Frontal Instabilities and Turbulent Mixing in the Surface Boundary Layer. Part I: Unforced Simulations
    American Meteorological Society ; 2012
    In:  Journal of Physical Oceanography Vol. 42, No. 10 ( 2012-10-01), p. 1701-1716
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 42, No. 10 ( 2012-10-01), p. 1701-1716
    Abstract: Interaction between mixed layer baroclinic eddies and small-scale turbulence is studied using a nonhydrostatic large-eddy simulation (LES) model. Free, unforced flow evolution is considered, for a standard initialization consisting of an 80-m-deep mixed layer with a superposed warm filament and two frontal interfaces in geostrophic balance, on a model domain roughly 5 km × 10 km × 120 m, with an isotropic 3-m computational grid. Results from these unforced experiments suggest that shear generated in narrow frontal zones can support weak three-dimensional turbulence that is directly linked to the larger-scale baroclinic waves. Two separate but closely related issues are addressed: 1) the possible development of enhanced turbulent mixing associated with the baroclinic wave activity and 2) the existence of a downscale transfer of energy from the baroclinic wave scale to the turbulent dissipation scale. The simulations show enhanced turbulence associated with the baroclinic waves and enhanced turbulent heat flux across the isotherms of the imposed frontal boundary, relative to background levels. This turbulence develops on isolated small-scale frontal features that form as the result of frontogenetic processes operating on the baroclinic wave scale and not as the result of a continuous, inertial forward cascade through the intermediate scales. Analysis of the spectrally decomposed kinetic energy budget indicates that large-scale baroclinic eddy energy is directly transferred to small-scale turbulence, with weaker forcing at intermediate scales. For fronts with significant baroclinic wave activity, cross-frontal eddy fluxes computed from correlations of fluctuations from means along the large-scale frontal axis generally agreed with simple theoretical estimates.
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    DOI: 10.1175/JPO-D-10-05016.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2012
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 3
    Online Resource
    Online Resource
    Modeling the Atmospheric Boundary Layer Wind Response to Mesoscale Sea Surface Temperature Perturbations
    American Meteorological Society ; 2014
    In:  Monthly Weather Review Vol. 142, No. 11 ( 2014-11-01), p. 4284-4307
    Details
    In: Monthly Weather Review, American Meteorological Society, Vol. 142, No. 11 ( 2014-11-01), p. 4284-4307
    Abstract: The wind speed response to mesoscale SST variability is investigated over the Agulhas Return Current region of the Southern Ocean using the Weather Research and Forecasting (WRF) Model and the U.S. Navy Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) atmospheric model. The SST-induced wind response is assessed from eight simulations with different subgrid-scale vertical mixing parameterizations, validated using Quick Scatterometer (QuikSCAT) winds and satellite-based sea surface temperature (SST) observations on 0.25° grids. The satellite data produce a coupling coefficient of sU = 0.42 m s−1 °C−1 for wind to mesoscale SST perturbations. The eight model configurations produce coupling coefficients varying from 0.31 to 0.56 m s−1 °C−1. Most closely matching QuikSCAT are a WRF simulation with the Grenier–Bretherton–McCaa (GBM) boundary layer mixing scheme (sU = 0.40 m s−1 °C−1), and a COAMPS simulation with a form of Mellor–Yamada parameterization (sU = 0.38 m s−1 °C−1). Model rankings based on coupling coefficients for wind stress, or for curl and divergence of vector winds and wind stress, are similar to that based on sU. In all simulations, the atmospheric potential temperature response to local SST variations decreases gradually with height throughout the boundary layer (0–1.5 km). In contrast, the wind speed response to local SST perturbations decreases rapidly with height to near zero at 150–300 m. The simulated wind speed coupling coefficient is found to correlate well with the height-averaged turbulent eddy viscosity coefficient. The details of the vertical structure of the eddy viscosity depend on both the absolute magnitude of local SST perturbations, and the orientation of the surface wind to the SST gradient.
    Type of Medium: Online Resource
    ISSN: 0027-0644 , 1520-0493
    URL: Article
    DOI: 10.1175/MWR-D-13-00332.1
    RVK:
    RA 1000
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2014
    detail.hit.zdb_id: 2033056-X
    detail.hit.zdb_id: 202616-8
    SSG: 14
    Location Call Number Limitation Availability
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  • 4
    Online Resource
    Online Resource
    Effects of Inversion Height and Surface Heat Flux on Downslope Windstorms
    American Meteorological Society ; 2011
    In:  Monthly Weather Review Vol. 139, No. 12 ( 2011-12-01), p. 3750-3764
    Details
    In: Monthly Weather Review, American Meteorological Society, Vol. 139, No. 12 ( 2011-12-01), p. 3750-3764
    Abstract: Simulations are presented focusing on the role of temperature inversions in controlling the formation and strength of downslope wind storms. Three mechanisms are examined depending on the relative height of the inversion with respect to the mountain and the stability of vertically propagating mountain waves. For low-level inversions, flows are generated that closely resemble a reduced gravity shallow water hydraulic response with a large vertical displacement of the inversion on the lee side of the mountain. For higher-level inversion cases, simulated flows more closely followed a stratified hydraulic behavior with the inversion acting as a rigid reflective lid. In the third mechanism, downslope winds were forced by a self-induced critical layer located below the inversion height. The presence of the inversion in this case had little effect on the resulting downslope winds. Observations made on the Falkland Islands show that downslope windstorms may preferentially occur in early morning even without synoptic-scale changes in atmospheric structure. Most windstorms on the Falkland Islands generally have a short jet length; rare, longer jet length storms typically occur in conjunction with a strong low-level inversion. Idealized numerical experiments tend to produce a similar response depending on the presence of strong low-level inversion and surface cooling. Results suggest that surface heating can have significant control on the flow response by reducing the low-level inversion strength, or by changing the stratification and wind velocity below the inversion, thereby preventing a strong downslope windstorm.
    Type of Medium: Online Resource
    ISSN: 0027-0644 , 1520-0493
    URL: Article
    DOI: 10.1175/2011MWR3619.1
    RVK:
    RA 1000
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2011
    detail.hit.zdb_id: 2033056-X
    detail.hit.zdb_id: 202616-8
    SSG: 14
    Location Call Number Limitation Availability
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    Online Resource
  • 5
    Online Resource
    Online Resource
    Observations and numerical simulations of large‐eddy circulation in the ocean surface mixed layer
    American Geophysical Union (AGU) ; 2014
    In:  Geophysical Research Letters Vol. 41, No. 21 ( 2014-11-16), p. 7584-7590
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 41, No. 21 ( 2014-11-16), p. 7584-7590
    Abstract: Ocean dye releases were mapped using scanning, depth‐resolving airborne lidar Dye evolved into rolls aligned with the wind and/or near‐surface current Large‐eddy simulations showed similar features without Stokes drift forcing
    Type of Medium: Online Resource
    ISSN: 0094-8276 , 1944-8007
    URL: Issue
    URL: Article
    DOI: 10.1002/grl.v41.21
    DOI: 10.1002/2014GL061637
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2014
    detail.hit.zdb_id: 2021599-X
    detail.hit.zdb_id: 7403-2
    SSG: 16,13
    Location Call Number Limitation Availability
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