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- Author or Editor: Steven E. Koch x
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Abstract
An objective analysis scheme based on the Barnes technique and designed for use on an interactive computer is described. In order to meet the specific needs of the research meteorologist, the interactive Barnes scheme allows real-time assessments both of the quality of the resulting analyses and of the impact of satellite-derived data upon various meteorological data sets. Display of a number of statistical and mapped analysis quality control indicators aid the impact assessments. Simple means for taking account of the spatially clustered nature typical of satellite data are included in the internal computations of the relative weights of data at grid point locations.
An analyst is allowed the capability of modifying values of certain input parameters to the interactive Barnes scheme within internally set limits. These constraints were objectively determined and tested in a number of different situations prior to implementation. The following constraints are employed: 1) calculation of the weights as a function of a data spacing representative of the data distribution; 2) automatic elimination of detail at wavelengths smaller than twice the representative data spacing; 3) placement of bounds upon the grid spacing by the data spacing; and 4) setting of a fixed limit on the number of passes through the data to achieve rapid and sufficient convergence of the analyzed values to the observed ones. A mathematical analysis of the convergence properties of the Barnes technique is presented to support the validity of the latter constraint.
Despite these constraints, the interactive Barnes scheme remains versatile because it accepts limited inputs to the data and grid display areas, to the data and grid spacings, and to the rate of convergence of the analysis to the observations. Input parameter values are entered through a series of questions displayed on a computer video terminal and by manipulation of display function devices. The analyst immediately sees a plot of the data, the contoured grid values, superimposed in various colors if desired, and the effects of choice of analysis options. Examples of both meteorological and satellite data analyses are presented to demonstrate the objectivity, versatility and practicality of the interactive Barnes scheme.
Abstract
An objective analysis scheme based on the Barnes technique and designed for use on an interactive computer is described. In order to meet the specific needs of the research meteorologist, the interactive Barnes scheme allows real-time assessments both of the quality of the resulting analyses and of the impact of satellite-derived data upon various meteorological data sets. Display of a number of statistical and mapped analysis quality control indicators aid the impact assessments. Simple means for taking account of the spatially clustered nature typical of satellite data are included in the internal computations of the relative weights of data at grid point locations.
An analyst is allowed the capability of modifying values of certain input parameters to the interactive Barnes scheme within internally set limits. These constraints were objectively determined and tested in a number of different situations prior to implementation. The following constraints are employed: 1) calculation of the weights as a function of a data spacing representative of the data distribution; 2) automatic elimination of detail at wavelengths smaller than twice the representative data spacing; 3) placement of bounds upon the grid spacing by the data spacing; and 4) setting of a fixed limit on the number of passes through the data to achieve rapid and sufficient convergence of the analyzed values to the observed ones. A mathematical analysis of the convergence properties of the Barnes technique is presented to support the validity of the latter constraint.
Despite these constraints, the interactive Barnes scheme remains versatile because it accepts limited inputs to the data and grid display areas, to the data and grid spacings, and to the rate of convergence of the analysis to the observations. Input parameter values are entered through a series of questions displayed on a computer video terminal and by manipulation of display function devices. The analyst immediately sees a plot of the data, the contoured grid values, superimposed in various colors if desired, and the effects of choice of analysis options. Examples of both meteorological and satellite data analyses are presented to demonstrate the objectivity, versatility and practicality of the interactive Barnes scheme.
Abstract
The impact of satellite-derived cloud motion vectors (CMVs) on analysts of winds measured by rawinsondes during the 1979 SESAME Experiment is studied in two case studies (10 April and 9 May 1979). Cloud motion vectors are both arbitrarily assigned and vertically interpolated to typical “low” levels of 825 mb and &sigma = 0.9 before being combined with the rawinsonde-measured winds at these levels. Magnitudes of vector differences between the combined winds and rawinsonde-measured winds are computed to show the effect of single-level assignment of CMVs on the rawinsonde-measured wind fields. The impact of the existence of horizontal and vertical gradients of wind and moisture on these results is also examined. In addition, divergence and relative vorticity fields are derived to determine whether the addition of CMVs increase the amount of useful information to the kinematic computations.
The results show that the standard method of arbitrarily assigning wind vectors to a “low-level” coordinate surface yields systematic differences between the rawinsonde-measured winds and combined wind fields. Arbitrary assignment of cloud motions to the 0.9 sigma surface produces smaller magnitudes of vector differences than assignment to the 825-mb pressure surface. Additionally, systematic differences in the wind occur near moisture discontinuities and in regions of horizontal and vertical wind shears. If forced to make arbitrary assignments, the use of the terrain-following sigma surface yields more consistent results than arbitrary assignment to a pressure surface in the lower troposphere. The differences between the combined and rawinsonde-measured wind fields are reduced by vertical interpolation to either a pressure or sigma surface. However, the accuracy of these interpolated fields depends to a large extent on the methods used to determine cloud-base levels and the vertical wind shear.
Abstract
The impact of satellite-derived cloud motion vectors (CMVs) on analysts of winds measured by rawinsondes during the 1979 SESAME Experiment is studied in two case studies (10 April and 9 May 1979). Cloud motion vectors are both arbitrarily assigned and vertically interpolated to typical “low” levels of 825 mb and &sigma = 0.9 before being combined with the rawinsonde-measured winds at these levels. Magnitudes of vector differences between the combined winds and rawinsonde-measured winds are computed to show the effect of single-level assignment of CMVs on the rawinsonde-measured wind fields. The impact of the existence of horizontal and vertical gradients of wind and moisture on these results is also examined. In addition, divergence and relative vorticity fields are derived to determine whether the addition of CMVs increase the amount of useful information to the kinematic computations.
The results show that the standard method of arbitrarily assigning wind vectors to a “low-level” coordinate surface yields systematic differences between the rawinsonde-measured winds and combined wind fields. Arbitrary assignment of cloud motions to the 0.9 sigma surface produces smaller magnitudes of vector differences than assignment to the 825-mb pressure surface. Additionally, systematic differences in the wind occur near moisture discontinuities and in regions of horizontal and vertical wind shears. If forced to make arbitrary assignments, the use of the terrain-following sigma surface yields more consistent results than arbitrary assignment to a pressure surface in the lower troposphere. The differences between the combined and rawinsonde-measured wind fields are reduced by vertical interpolation to either a pressure or sigma surface. However, the accuracy of these interpolated fields depends to a large extent on the methods used to determine cloud-base levels and the vertical wind shear.
