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Abstract
A coupled one-dimensional ice-ocean model is used for studies of Arctic phenomena. The ice-snow system is represented by the simplified thermodynamic ice model of Semtner and a dynamic approximation that neglects the internal stresses. The ocean is represented by the Mellor–Yamada level-2 turbulence mixed-layer model together with a prescribed geostrophic velocity.
The thermodynamic coupling considers an ice front and a salinity flux generated by the freezing or melting of ice. The dynamic coupling occurs via the turbulent stress that exists in the mixed layer beneath the ice. Various boundary conditions for ice-ocean coupling are examined including an analytical representation of the constant flux layer.
Two test cases are used for model validation and scientific studies. One is the standard climatological test used by Semtner and others. The other test case is with the AIDJEX data.
The ice-ocean model is compared to Semtner's ice model to determine the effects of a variable-depth mixed layer as opposed to an isothermal, fixed-depth mixed layer. In the variable-depth mixed layer model, a warm spot develops in the surface layers of the mean during open water periods. When the ocean refreezes some heat remains in the warm spot and gradually diminishes as the ice continues to grow. This heat is released from the upper ocean through the mixing process. Its release significantly affects the heat budget and the growth rate of ice. Open water occurs nearly every year, in climatology simulations, as opposed to once every six years in the case Semtner examined.
Simulations of the AIDJEX Experiment predicted the general trends of the temperature and salinity measurements. Specific discrepancies may be due primarily to the omission of advection.
Abstract
A coupled one-dimensional ice-ocean model is used for studies of Arctic phenomena. The ice-snow system is represented by the simplified thermodynamic ice model of Semtner and a dynamic approximation that neglects the internal stresses. The ocean is represented by the Mellor–Yamada level-2 turbulence mixed-layer model together with a prescribed geostrophic velocity.
The thermodynamic coupling considers an ice front and a salinity flux generated by the freezing or melting of ice. The dynamic coupling occurs via the turbulent stress that exists in the mixed layer beneath the ice. Various boundary conditions for ice-ocean coupling are examined including an analytical representation of the constant flux layer.
Two test cases are used for model validation and scientific studies. One is the standard climatological test used by Semtner and others. The other test case is with the AIDJEX data.
The ice-ocean model is compared to Semtner's ice model to determine the effects of a variable-depth mixed layer as opposed to an isothermal, fixed-depth mixed layer. In the variable-depth mixed layer model, a warm spot develops in the surface layers of the mean during open water periods. When the ocean refreezes some heat remains in the warm spot and gradually diminishes as the ice continues to grow. This heat is released from the upper ocean through the mixing process. Its release significantly affects the heat budget and the growth rate of ice. Open water occurs nearly every year, in climatology simulations, as opposed to once every six years in the case Semtner examined.
Simulations of the AIDJEX Experiment predicted the general trends of the temperature and salinity measurements. Specific discrepancies may be due primarily to the omission of advection.
Abstract
Using a hydrocast survey of the Iceland-Faroe Front (IFF) from October 1992, quasigeostrophic forecasts are studied to validate their efficacy and to diagnose the physical processes involved in the rapid growth of a cold tongue intrusion. Explorations of 1) the choice of initial objective analysis parameters, 2) the depth of the unknown level of no motion, 3) the effects of surrounding mesoscale activity, 4) variations in the boundary conditions, and 5) simple assimilation of newly acquired data into the forecasts are carried out.
Using a feature validation technique, which incorporates a 1) validating hydrocast survey, 2) satellite SST images, and 3) surface drifter observations, most of the forecasts are found to perform well in capturing the key events of the validation strategy, particularly the development of the cold tongue intrusion (though it tends to develop somewhat more weakly and slightly farther downstream than observed). Sharp resolution of frontal structure (to capture seed anomalies in the IFF, which later can grow to large amplitude) and smooth representation of far-field boundary conditions (to eliminate spurious persistent inflow/outflow at the boundaries, which can corrupt developing interior flows) are found to be crucial in generating good forecasts.
An analysis of the potential and kinetic energy equations in the region of the developing cold tongue intrusion reveals a clear signature of baroclinic instability. Topography has little influence on this particular instability event because it tends to be surface intensified and occurs rapidly over a timescale of 3–5 days.
Abstract
Using a hydrocast survey of the Iceland-Faroe Front (IFF) from October 1992, quasigeostrophic forecasts are studied to validate their efficacy and to diagnose the physical processes involved in the rapid growth of a cold tongue intrusion. Explorations of 1) the choice of initial objective analysis parameters, 2) the depth of the unknown level of no motion, 3) the effects of surrounding mesoscale activity, 4) variations in the boundary conditions, and 5) simple assimilation of newly acquired data into the forecasts are carried out.
Using a feature validation technique, which incorporates a 1) validating hydrocast survey, 2) satellite SST images, and 3) surface drifter observations, most of the forecasts are found to perform well in capturing the key events of the validation strategy, particularly the development of the cold tongue intrusion (though it tends to develop somewhat more weakly and slightly farther downstream than observed). Sharp resolution of frontal structure (to capture seed anomalies in the IFF, which later can grow to large amplitude) and smooth representation of far-field boundary conditions (to eliminate spurious persistent inflow/outflow at the boundaries, which can corrupt developing interior flows) are found to be crucial in generating good forecasts.
An analysis of the potential and kinetic energy equations in the region of the developing cold tongue intrusion reveals a clear signature of baroclinic instability. Topography has little influence on this particular instability event because it tends to be surface intensified and occurs rapidly over a timescale of 3–5 days.
