A numerical study of the nonlinear interaction of Hurricane Camille with the Gulf of Mexico Loop Current

A three-dimensional, primitive equation, ocean general circulation model is used to study the response of the Gulf of Mexico to Hurricane Camille (1969). The free-surface dynamics and the mixed-layer features are included in the model. The numerical model incorporates the realistic coastline and bottom topography. The sigma coordinate model bas eighteen levels in the vertical and 0.2° x 0.2° horizontal resolution for the entire gulf. The study focuses on nonlinear interaction between hurricane induced currents and the Loop Current. The numerical simulations show that there is a strong nonlinear interaction between the hurricane and the Loop Current in the southern and central parts of the eastern gulf. The surface currents due to nonlinear interaction obtain a maximum of over 1 m s·1 in the southern gulf. The numerical results also show that the hurricane interaction with the Loop Current strongly affects current, mixed-layer depth, and elevation fields. There is a strong current response to Hurricane Camille in the surface layer on the shelf with a peak velocity approximately 2.2 m s-1• There is a definite right band bias in the mixed-layer depth field with a maximum of about 90 m.Navy Ocean Modeling and Prediction Program (NOMP) of the Office of Naval Research (ONR)Department of Oceanography, Naval Postgraduate SchoolNOAA Great Lakes Environmental Research LabsOceanweather, IncResearch Triangle InstituteNavy Ocean Modeling and Prediction Program (NOMP) of the Office of Naval Research (ONR)Department of Oceanography, Naval Postgraduate SchoolNOAA Great Lakes Environmental Research LabsOceanweather, IncResearch Triangle Institut

A Numerical Model of the Atmospheric Boundary Layer Over a Marginal Ice Zone

A two-dimensional, multilevel model for simulating changes in the atmospheric boundary layer across a marginal ice zone is described and applied to off-ice, on-ice, and along-ice edge wind conditions. The model incorporates a second-moment closure for parameterizing the intensification and suppression of turbulent mixing in the boundary layer due to stratification effects. For off-ice winds, as the atmospheric boundary layer passes from cold smooth ice onto warm open water, the onset of intense convection raises the inversion. Over the transition zone of rough rafted ice with open leads, the shear stress on the ice cover increases significantly before dropping down to the downstream values over water. Such nonmonotonic surface stress could be the cause of divergence of sea ice near the ice edge in a marginal ice zone. These results are in agreement with the one-layer model simulations of off-ice winds by Overland et al. (1983). For on-ice wind conditions, as the warm flow in the boundary layer encounters the cold ice conditions, the resulting stable stratification could rapidly suppress the turbulence in the boundary layer, leading to the development of a shallow inversion and an associated jet. When the wind is predominantly along the ice edge, the temperature contrast between the open water and the ice could produce a thermal front at the ice edge in the boundary layer with strong associated turbulence. More observations are needed to verify these model predictions. Nevertheless, these model results suggest that it is important to account for the changes in the characteristics of the atmospheric boundary layer across the marginal ice zone in our attempts to understand the behavior of the ice cover in these regions. 1

A two dimensional coupled ice-ocean model of the Bering Sea

A two-dimensional coupled ice-ocean model has been formulated and applied to the wintertime Bering Sea marginal ice zone. The oceanic component is a multilevel model that incorporates second-moment closure for turbulent mixing in the water column. The ice cover is modeled as a viscous-plastic continuum. Melting at the ice-ocean interface is computed using well-known lawof-the-wall concepts in a turbulent boundary layer, with particular attention to the disparate momentum and scalar transfer resistance coefficients over rough walls. The thermodynamic and dynamical interactions between the ocean and the ice cover and the energy balances at the air-ice and air-sea interfaces are modeled according to the companion paper (Mellor and Kantha, this issue). The model incorporates barotropic tides, both diurnal and semidiurnal, for application to the Bering Shelf. Double-diffusive fluxes across the interface between the colder, fresher layer beneath the melting ice and the warmer, more saline water underneath are prescribed from laboratory data on double-diffusive convection. During winter, sea ice in the central Bering Sea is transported toward the shelf break by off-ice winds, where it encounters northward flowing warmer north Pacific waters and melts. It is this situation to which the two-dimensional model has been applied by neglecting all variations in the along-ice-edge direction. The water conditions downstream of the ice edge, the ice conditions upstream, and the wind stress are the primary inputs to the model. The model simulates transition from ice-covered to open ocean conditions and the associated ice edge front and the two-layer circulation underneath the ice cover. Sensitivity studies indicate that the density structure and the circulation beneath the ice and the position of the ice edge are rather sensitive to the parameters affecting the dynamics and the thermodynamics of the coupled ice-ocean system. Even small changes in the relevant parameters can cause a substantial retreat or advance of the ice edge, which may help explain why marginal ice zones are such dynamically active regions. 1

Power law decay in model predictability skill

Geophysical Research Letters, American Geophysical Union, 29 (15), 10.1029/2002GLO14891.The article of record as published may be located at http://dx.doi.org/10.1029/2002GL014891Ocean predictability skill is investigated using a Gulf of Mexico nowcast/forecast model. Power law scaling is found in the mean square error of displacement between drifting buoy and model trajectories (both at 50 m depth). The probability density function of the model valid prediction period (VPP) is asymmetric with a long and broad tail on the higher value side, which suggests longterm predictability. The calculations demonstrate that the long-term (extreme long such as 50–60 day) predictability is not an "outlier" and shares the same statistical properties as the short-term predictions

Geotechnical properties of stabilised Indian red earth

Locally available soils amended with sufficient bentonite are generally used for construction of liners for water and waste retention facilities. The amount of bentonite required to keep the hydraulic conductivity low varies with the nature of the local soil. Many studies have shown that bentonite content higher than 20% by weight is not usually required. This is also the case with Indian red earth containing predominantly quartz and kaolinite minerals. Incorporating bentonite, though keeps the hydraulic conductivity of soil low, increases the swelling and shrinkage potential; increases the loss of strength due to reduction in cohesion. This paper aims to improve the geotechnical properties of red earth and bentonite mixture with lime or cement. The studies reveal that the geotechnical properties of red earth with 20% by weight bentonite stabilised with 1% by weight of lime or cement are greatly enhanced, particularly after curing for 28 days. it has been shown that the early gain in strength is better with cement whereas its long-term strength gain is better with lime