Interpretations of the EOLE Experiment I. Temporal Variation of Eulerian Quantities

Peter J. Webster Dept. of Meteorology, University of California, Los Angeles 90024

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David G. Curtin Dept. of Meteorology, University of California, Los Angeles 90024

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Abstract

The recent EOLE constant density balloon experiment, conducted between August 1971 and July 1972 in the upper troposphere of the Southern Hemisphere, produced large quantities of highly accurate Lagrangian data. The question of the inference of Eulerian mean quantities from Lagrangian information is considered, and, in the absence of an exact and general transformation between the two data forms, an approximate method is developed. It is shown that unless sufficient care is taken in this transformation, large errors can occur in the inferred Eulerian estimates by the introduction of a Lagrangian temporal bias into the means. It is suggested that earlier GHOST estimates of the momentum flux by Solot and Angell were abnormally small by a factor of 4 for this reason.

After the elimination of the Lagrangian bias and character, the “Eulerian” data are used to study the temporal variation of various measured and derived quantities which is used to infer the dynamic structure of the hemisphere during the EOLE year. Comparisons are made with estimates derived from conventional data sources and earlier balloon experiments. Large differences are found in regions where the EOLE data are maximum and unbiased longitudinally. It is concluded that many of these differences, for example the Southern Hemisphere double jet stream, may be attributed to the introduction into the conventional data sets of a Eulerian spatial bias due to the longitudinal clustering of the Eulerian sensors.

Finally, the viability of a balloon system to produce meaningful hemispheric data is discussed. It is concluded that while the system seems to represent mid-latitude motion adequately, there is some doubt as to how representative the derived mean tropical atmosphere is for a population of balloons whose maximum density is at higher latitudes.

Abstract

The recent EOLE constant density balloon experiment, conducted between August 1971 and July 1972 in the upper troposphere of the Southern Hemisphere, produced large quantities of highly accurate Lagrangian data. The question of the inference of Eulerian mean quantities from Lagrangian information is considered, and, in the absence of an exact and general transformation between the two data forms, an approximate method is developed. It is shown that unless sufficient care is taken in this transformation, large errors can occur in the inferred Eulerian estimates by the introduction of a Lagrangian temporal bias into the means. It is suggested that earlier GHOST estimates of the momentum flux by Solot and Angell were abnormally small by a factor of 4 for this reason.

After the elimination of the Lagrangian bias and character, the “Eulerian” data are used to study the temporal variation of various measured and derived quantities which is used to infer the dynamic structure of the hemisphere during the EOLE year. Comparisons are made with estimates derived from conventional data sources and earlier balloon experiments. Large differences are found in regions where the EOLE data are maximum and unbiased longitudinally. It is concluded that many of these differences, for example the Southern Hemisphere double jet stream, may be attributed to the introduction into the conventional data sets of a Eulerian spatial bias due to the longitudinal clustering of the Eulerian sensors.

Finally, the viability of a balloon system to produce meaningful hemispheric data is discussed. It is concluded that while the system seems to represent mid-latitude motion adequately, there is some doubt as to how representative the derived mean tropical atmosphere is for a population of balloons whose maximum density is at higher latitudes.

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