Prediction and Monitoring of Clear-Air Turbulence: An Evaluation of the Applicability of the Rawinsonde System

John L. Keller University of Dayton, Research Institute, Dayton, OH 45469

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Abstract

The ability to sense turbulent layers in the free atmosphere is a fundamental requirement necessary for further progress in the area of clear air turbulence (CAT) prediction. Results from an investigation of the applicability of rawinsonde (RW) profiles for the detection of CAT are discussed. Previous studies have determined that the most significant factor for the existence of turbulent layers is the magnitude of the vertical shear. Certain shear-layer criteria, obtained from theoretically consistent statistics of detailed vertical wind profiles, are applied to statistical comparisons of conjuctive rawinsonde and Jimsphere/Jimsonde (J/J) vertical profiles made between 1 and 15 km. It was found that a loose relationship exists between J/J and RW shears. That is, the cross-correlation coefficient comparing their respective shears at the same levels is quite small. This seems to indicate that no general statement can be made in consideration of critical shear criteria with respect to RW shears. It is suggested that reasons for such a loose empirical relationship include the mesoscale nature of the apparent CAT mechanism.

Abstract

The ability to sense turbulent layers in the free atmosphere is a fundamental requirement necessary for further progress in the area of clear air turbulence (CAT) prediction. Results from an investigation of the applicability of rawinsonde (RW) profiles for the detection of CAT are discussed. Previous studies have determined that the most significant factor for the existence of turbulent layers is the magnitude of the vertical shear. Certain shear-layer criteria, obtained from theoretically consistent statistics of detailed vertical wind profiles, are applied to statistical comparisons of conjuctive rawinsonde and Jimsphere/Jimsonde (J/J) vertical profiles made between 1 and 15 km. It was found that a loose relationship exists between J/J and RW shears. That is, the cross-correlation coefficient comparing their respective shears at the same levels is quite small. This seems to indicate that no general statement can be made in consideration of critical shear criteria with respect to RW shears. It is suggested that reasons for such a loose empirical relationship include the mesoscale nature of the apparent CAT mechanism.

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