Jet-Stream Structure over the Central United States Determined from Aircraft Observations

R. M. Endlich Stanford Research Institute, Menlo Park, Calif.

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G. S. McLean Air Force Cambridge Research Laboratories, Bedfort, Mass.

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Abstract

Aircraft observations over the central United States are used to construct empirical models of jet streams that agree well with models based on data from other regions of the mid-latitudes. Individual jet streams conform to speeds of the model within certain limits. These limits are represented by a percentage variability that is larger to the north of the jet core than to the south. On the other hand, variations in the structure of the average speed field with season and with position in the upper flow appear to be rather small so that a single model describes the jet stream adequately. The field of average transverse wind component indicates appreciable motion toward high pressure in a layer beneath the jet-stream core. Average mesoscale vertical motion as large as −0.4 m sec−1 occurs below and slightly north of the core. Turbulence has a minimum frequency of occurrence at the maximum wind level immediately south of the jet core. Vertical wind shear has appreciably larger magnitudes than thermal wind shear in two shallow layers separated by the maximum wind level. The vorticity field corresponding to the wind and temperature fields is described. Several unexplained features of jet streams are mentioned briefly.

Abstract

Aircraft observations over the central United States are used to construct empirical models of jet streams that agree well with models based on data from other regions of the mid-latitudes. Individual jet streams conform to speeds of the model within certain limits. These limits are represented by a percentage variability that is larger to the north of the jet core than to the south. On the other hand, variations in the structure of the average speed field with season and with position in the upper flow appear to be rather small so that a single model describes the jet stream adequately. The field of average transverse wind component indicates appreciable motion toward high pressure in a layer beneath the jet-stream core. Average mesoscale vertical motion as large as −0.4 m sec−1 occurs below and slightly north of the core. Turbulence has a minimum frequency of occurrence at the maximum wind level immediately south of the jet core. Vertical wind shear has appreciably larger magnitudes than thermal wind shear in two shallow layers separated by the maximum wind level. The vorticity field corresponding to the wind and temperature fields is described. Several unexplained features of jet streams are mentioned briefly.

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