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- Author or Editor: Robert A. Pearson x
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Abstract
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Abstract
A simple model of the sea breeze is integrated numerically. If the total beat input into the air is kept constant, the speed of the sea breeze front is found to be independent of the vertical distribution of the temperature change, the stability of the atmosphere, and the Coriolis parameter. The speed V of the front is shown to increase as the square root of the vertically integrated change in the buoyancy of the air. This is a type of Froude-number relationship with V 2=k∫o h g(θ′/θ0)dz. After about a half-pendulum day, this front decreases in intensity and becomes slower. The addition of drag and diffusion significantly alters the velocity and temperature structure of the sea breeze but only decreases slightly the speed of the front.
Abstract
A simple model of the sea breeze is integrated numerically. If the total beat input into the air is kept constant, the speed of the sea breeze front is found to be independent of the vertical distribution of the temperature change, the stability of the atmosphere, and the Coriolis parameter. The speed V of the front is shown to increase as the square root of the vertically integrated change in the buoyancy of the air. This is a type of Froude-number relationship with V 2=k∫o h g(θ′/θ0)dz. After about a half-pendulum day, this front decreases in intensity and becomes slower. The addition of drag and diffusion significantly alters the velocity and temperature structure of the sea breeze but only decreases slightly the speed of the front.
Abstract
In numerical computation it is often necessary to truncate the region of interest and formulate appropriate boundary conditions. A way of using the Sommerfeld radiation boundary condition for a certain class of initial value problems in dispersive systems is derived. The details of this analysis are given for a continuously stratified fluid in a rotating reference frame.
Abstract
In numerical computation it is often necessary to truncate the region of interest and formulate appropriate boundary conditions. A way of using the Sommerfeld radiation boundary condition for a certain class of initial value problems in dispersive systems is derived. The details of this analysis are given for a continuously stratified fluid in a rotating reference frame.
Abstract
Errors in the numerical analog to a simple convection model can lead to an instability, even though existing methods of analysis predict that the scheme is stable.
The solutions obtained from a number of finite difference schemes and different resolutions are compared. This shows that increasing the resolution does not significantly improve the results, also that increasing the order of the finite difference scheme can lead to greater errors. The mechanism of the instability is discussed.
Abstract
Errors in the numerical analog to a simple convection model can lead to an instability, even though existing methods of analysis predict that the scheme is stable.
The solutions obtained from a number of finite difference schemes and different resolutions are compared. This shows that increasing the resolution does not significantly improve the results, also that increasing the order of the finite difference scheme can lead to greater errors. The mechanism of the instability is discussed.
Abstract
Numerical models of thermals usually introduce a closed box within which convection occurs. A boundary condition which allows inflow and outflow through the edges of the computational domain is discussed. The results of numerical experiments using this boundary condition are then compared and contrasted with those obtained when a rigid boundary is assumed. It is found that the flow development is especially sensitive to the choice of the upper boundary condition even before warm fluid reaches the top of the computational domain.
Abstract
Numerical models of thermals usually introduce a closed box within which convection occurs. A boundary condition which allows inflow and outflow through the edges of the computational domain is discussed. The results of numerical experiments using this boundary condition are then compared and contrasted with those obtained when a rigid boundary is assumed. It is found that the flow development is especially sensitive to the choice of the upper boundary condition even before warm fluid reaches the top of the computational domain.
Abstract
The Penn State/NCAR mesoscale model is initialized with calm winds, a barotropic temperature pattern, and a uniform surface pressure in studies of the response of the marine atmospheric boundary layer (MABL) to realistic differential fluxes of heal and moisture at the sea surface in the vicinity of the Gulf Stream. A maritime sounding from the GALE data region during Intensive Observation Period 2 (IOP 2) is used to define the initial vertical structure of the temperature and humidity fields. The sensitivity of the MABL to two sea surface temperature (SST) patterns is tested. One is a relatively smooth analysis that is typical of those used by research and operational models applied on the synoptic scale and mesoscale. The other is based on the experimental 14 km high-resolution analysis of NOAA. In addition, other simulations are used to determine the sensitivity of the MABL response to physical factors such as surface moisture fluxes, latent heating, and the sea-surface roughness. These studies have two purposes: one is to provide a better understanding of the three- dimensional MABL response to a realistic SST pattern; the other is to isolate the mesoscale circulations produced by this differential thermal forcing so that their interaction with other processes, such as cyclogenesis, can be inferred in real-data simulations.
The results of simulations using the two SST analyses are quite different. For example, the MABL front that develops near the north wall of the Gulf Stream is much stronger with the high-resolution analysis. Horizontal temperature gradients below 950 mb are 2–3 times larger, horizontal velocities near the surface are in excess of 7 m s−1 instead of ∼2 m s−1, and the vertical velocity patterns showed significantly different spatial characteristics and amplitudes. In both simulations, responses to the surface forcing extended upward to about 800 mb. In the experiment with the high-resolution SST analysis, a moderately strong mesoscale circulation was produced in the MABL within 12 h. Additional factors found to be important contributors to the MABL response are latent heat release in the lower atmosphere and sea-surface fluxes of moisture. The enhancement of the heat and moisture fluxes associated with the higher winds in the vicinity of the MABL front also significantly contributes to the amplitude of the circulation.
Abstract
The Penn State/NCAR mesoscale model is initialized with calm winds, a barotropic temperature pattern, and a uniform surface pressure in studies of the response of the marine atmospheric boundary layer (MABL) to realistic differential fluxes of heal and moisture at the sea surface in the vicinity of the Gulf Stream. A maritime sounding from the GALE data region during Intensive Observation Period 2 (IOP 2) is used to define the initial vertical structure of the temperature and humidity fields. The sensitivity of the MABL to two sea surface temperature (SST) patterns is tested. One is a relatively smooth analysis that is typical of those used by research and operational models applied on the synoptic scale and mesoscale. The other is based on the experimental 14 km high-resolution analysis of NOAA. In addition, other simulations are used to determine the sensitivity of the MABL response to physical factors such as surface moisture fluxes, latent heating, and the sea-surface roughness. These studies have two purposes: one is to provide a better understanding of the three- dimensional MABL response to a realistic SST pattern; the other is to isolate the mesoscale circulations produced by this differential thermal forcing so that their interaction with other processes, such as cyclogenesis, can be inferred in real-data simulations.
The results of simulations using the two SST analyses are quite different. For example, the MABL front that develops near the north wall of the Gulf Stream is much stronger with the high-resolution analysis. Horizontal temperature gradients below 950 mb are 2–3 times larger, horizontal velocities near the surface are in excess of 7 m s−1 instead of ∼2 m s−1, and the vertical velocity patterns showed significantly different spatial characteristics and amplitudes. In both simulations, responses to the surface forcing extended upward to about 800 mb. In the experiment with the high-resolution SST analysis, a moderately strong mesoscale circulation was produced in the MABL within 12 h. Additional factors found to be important contributors to the MABL response are latent heat release in the lower atmosphere and sea-surface fluxes of moisture. The enhancement of the heat and moisture fluxes associated with the higher winds in the vicinity of the MABL front also significantly contributes to the amplitude of the circulation.
