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- Author or Editor: Leonard M. Druyan x
- Journal of Applied Meteorology and Climatology x
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Abstract
A computer procedure, described in an earlier study, uses the wind speed field near the ocean surface in combination with a small number of observations of pressure and wind velocity to specify the maritime sea-level pressure field. An improved version was used to analyze the pressure distribution over the North Pacific Ocean for eleven synoptic times in February 1967. Independent knowledge of the central pressures of lows is shown to reduce the analysis errors for very sparse data coverage. The application of planned remote sensing of sea-level wind speeds is shown to make a significant contribution to the quality of the analysis especially in the high gradient mid-latitudes and for sparse coverage of conventional observations (such as over Southern Hemisphere oceans). Uniform distribution of the available observations of sea-level pressure and wind velocity yields results far superior to those derived from a random distribution. A generalization of the results indicates that the average lower limit for analysis errors is between 2 and 2.5 mb based on the perfect specification of the magnitude of the sea-level pressure gradient from a known verification analysis, and 15 uniformly distributed, high-quality buoy, weather ship or island observations of the pressure and wind velocity. (A less than perfect specification will derive from wind-pressure relationships applied to satellite-observed wind speeds.) Analysis errors computed using poorly defined wind fields indicate the procedure's potential for sparse data analysis even without supplementary satellite data.
Abstract
A computer procedure, described in an earlier study, uses the wind speed field near the ocean surface in combination with a small number of observations of pressure and wind velocity to specify the maritime sea-level pressure field. An improved version was used to analyze the pressure distribution over the North Pacific Ocean for eleven synoptic times in February 1967. Independent knowledge of the central pressures of lows is shown to reduce the analysis errors for very sparse data coverage. The application of planned remote sensing of sea-level wind speeds is shown to make a significant contribution to the quality of the analysis especially in the high gradient mid-latitudes and for sparse coverage of conventional observations (such as over Southern Hemisphere oceans). Uniform distribution of the available observations of sea-level pressure and wind velocity yields results far superior to those derived from a random distribution. A generalization of the results indicates that the average lower limit for analysis errors is between 2 and 2.5 mb based on the perfect specification of the magnitude of the sea-level pressure gradient from a known verification analysis, and 15 uniformly distributed, high-quality buoy, weather ship or island observations of the pressure and wind velocity. (A less than perfect specification will derive from wind-pressure relationships applied to satellite-observed wind speeds.) Analysis errors computed using poorly defined wind fields indicate the procedure's potential for sparse data analysis even without supplementary satellite data.
Abstract
A computer-based procedure is developed that combines a field of simulated satellite-derived wind speeds with a limited amount of conventional surface data so as to recover the surface pressure field and the vector wind field over the North Pacific Ocean. Wind speeds are determined from an objective analysis of high spatial density ship observations in order to simulate the anticipated output of a proposed satellite-mounted radar-radiometer system. The conventional surface data consist of sparse observations from ocean-going vessels, observations from several tropical stations, and boundary pressures from analyses over coastal areas.
The simulated speeds are combined with the conventional network for various spatial distributions of ship data. The average rms departure of sea-level pressure fields analyzed by deleting from 75–94% of the available ship observations from the maximum data analysis is from 3.0–4.0 mb. Comparison of the wind components implied by the isobaric patterns to those of the withheld ship observations yields average rms differences of from 8.7–9.4 kt for a range of 75–94% data deletion.
Abstract
A computer-based procedure is developed that combines a field of simulated satellite-derived wind speeds with a limited amount of conventional surface data so as to recover the surface pressure field and the vector wind field over the North Pacific Ocean. Wind speeds are determined from an objective analysis of high spatial density ship observations in order to simulate the anticipated output of a proposed satellite-mounted radar-radiometer system. The conventional surface data consist of sparse observations from ocean-going vessels, observations from several tropical stations, and boundary pressures from analyses over coastal areas.
The simulated speeds are combined with the conventional network for various spatial distributions of ship data. The average rms departure of sea-level pressure fields analyzed by deleting from 75–94% of the available ship observations from the maximum data analysis is from 3.0–4.0 mb. Comparison of the wind components implied by the isobaric patterns to those of the withheld ship observations yields average rms differences of from 8.7–9.4 kt for a range of 75–94% data deletion.
Abstract
Throughout the month of June 1965 tetroons ballasted for 150–300 m altitude were released and radar-tracked in New York City and environs. The study evaluates the skill with which data from both a dense mesoscale network of surface wind observations and a less dense network of balloon-derived wind observations in the planetary boundary layer can be used to reconstruct the tetroon trajectories.
Root-mean-square errors in predicting 2- and 4-hr tetroon positions from surface-wind-derived trajectories are reduced by the addition of a vector correction to account for vertical wind shear; this correction also randomizes the direction of the errors. Corrected surface wind trajectories, when compared with the tetroon trajectories, are slightly better than those computed from the balloon-derived winds.
The best results obtained yield rms 2-hr prediction errors of 15 km; the median error of this distribution expressed as a percentage of the range of each tetroon flight was 36%.
Abstract
Throughout the month of June 1965 tetroons ballasted for 150–300 m altitude were released and radar-tracked in New York City and environs. The study evaluates the skill with which data from both a dense mesoscale network of surface wind observations and a less dense network of balloon-derived wind observations in the planetary boundary layer can be used to reconstruct the tetroon trajectories.
Root-mean-square errors in predicting 2- and 4-hr tetroon positions from surface-wind-derived trajectories are reduced by the addition of a vector correction to account for vertical wind shear; this correction also randomizes the direction of the errors. Corrected surface wind trajectories, when compared with the tetroon trajectories, are slightly better than those computed from the balloon-derived winds.
The best results obtained yield rms 2-hr prediction errors of 15 km; the median error of this distribution expressed as a percentage of the range of each tetroon flight was 36%.
Abstract
Ensembles of three simulations each, forced by June–September 1987 and 1988 sea surface temperatures, respectively, were made with a new version of the general circulation model of the National Aeronautics and Space Administration/Goddard Institute for Space Studies. Time series of 6-h meridional winds at about 780 mb over West Africa were spectrally analyzed to detect African wave disturbances, whose properties for the two ensembles are compared and contrasted. The realistically simulated, stronger 1988 tropical easterly jet and the associated stronger upper-tropospheric divergence are components of interannual differences in the SST-forced planetary circulation, which correspond to higher amplitudes of African wave activity and concomitant excesses in 1988 Sahel rainfall rates. Results do not show, however, that most of the heavier precipitation was spatially organized by African wave structures. The excess rainfall is associated with stronger mean southerly circulation in the lower troposphere, which carried more moisture into the Sahel. Nevertheless, because waves modulate winds, convergence, humidity, and precipitation, the study suggests that they serve as a teleconnection mechanism, whereby extreme Pacific Ocean SST anomalies are able to influence climate variability in Africa's Sahel.
Abstract
Ensembles of three simulations each, forced by June–September 1987 and 1988 sea surface temperatures, respectively, were made with a new version of the general circulation model of the National Aeronautics and Space Administration/Goddard Institute for Space Studies. Time series of 6-h meridional winds at about 780 mb over West Africa were spectrally analyzed to detect African wave disturbances, whose properties for the two ensembles are compared and contrasted. The realistically simulated, stronger 1988 tropical easterly jet and the associated stronger upper-tropospheric divergence are components of interannual differences in the SST-forced planetary circulation, which correspond to higher amplitudes of African wave activity and concomitant excesses in 1988 Sahel rainfall rates. Results do not show, however, that most of the heavier precipitation was spatially organized by African wave structures. The excess rainfall is associated with stronger mean southerly circulation in the lower troposphere, which carried more moisture into the Sahel. Nevertheless, because waves modulate winds, convergence, humidity, and precipitation, the study suggests that they serve as a teleconnection mechanism, whereby extreme Pacific Ocean SST anomalies are able to influence climate variability in Africa's Sahel.
