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- Author or Editor: Hans-Rainer Schneider x
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Abstract
A numerical transport scheme that avoids the problem of spurious generation of negative mixing ratios has been developed. The scheme is computationally simple in any number of spatial dimensions can be used with nonperiodic boundary condition and preserves shapes reasonably well. It is based on the idea of formulating a quadratically conservative finite-difference advection equation and then advecting the square root of the concentration instead of the concentration itself. The requirement of step-by-step quadratic conservation in time places restrictions on the time-differencing method. A modified Lax-Wendroff procedure is shown to be suitable under this constraint and is used here. The transport scheme has properties comparable to fourth- order centered spatial differencing combined with leapfrog time-stepping and filliing.
Abstract
A numerical transport scheme that avoids the problem of spurious generation of negative mixing ratios has been developed. The scheme is computationally simple in any number of spatial dimensions can be used with nonperiodic boundary condition and preserves shapes reasonably well. It is based on the idea of formulating a quadratically conservative finite-difference advection equation and then advecting the square root of the concentration instead of the concentration itself. The requirement of step-by-step quadratic conservation in time places restrictions on the time-differencing method. A modified Lax-Wendroff procedure is shown to be suitable under this constraint and is used here. The transport scheme has properties comparable to fourth- order centered spatial differencing combined with leapfrog time-stepping and filliing.
Abstract
Use of the residual circulation for stratospheric tracer transport has been compared to a fully three-dimensional calculation. The wind fields used in this study were obtained from a global, semispectral, primitive equation model, extending from 10 to 100 km in altitude. Comparisons were done with a passive tracer and an ozone-like substance over a two-month period corresponding to a Northern Hemisphere winter. It was found that the use of the residual circulation can lead to errors in the tracer concentrations of about a factor of 2. The error is made up of two components. One is fluctuating with a period of approximately one month and reflect directly the wave transience that occurs on that time-scale. The second part is increasing steadily over the integration period and results from an overestimate of the vertical transport by the residual circulation. Furthermore, the equatorward and upward mixing that occurs with transport by the three-dimensional circulation at low latitudes is not well reproduced when the residual circulation is used.
Abstract
Use of the residual circulation for stratospheric tracer transport has been compared to a fully three-dimensional calculation. The wind fields used in this study were obtained from a global, semispectral, primitive equation model, extending from 10 to 100 km in altitude. Comparisons were done with a passive tracer and an ozone-like substance over a two-month period corresponding to a Northern Hemisphere winter. It was found that the use of the residual circulation can lead to errors in the tracer concentrations of about a factor of 2. The error is made up of two components. One is fluctuating with a period of approximately one month and reflect directly the wave transience that occurs on that time-scale. The second part is increasing steadily over the integration period and results from an overestimate of the vertical transport by the residual circulation. Furthermore, the equatorward and upward mixing that occurs with transport by the three-dimensional circulation at low latitudes is not well reproduced when the residual circulation is used.
