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A Study of Frontal Cyclone Surface and 300-hPa Geostrophic Kinetic Energy Distribution and Scale Change

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  • 1 Atmospheric Science Program, Department of Land, Air, and Water Resources, University of California, Davis, Davis, California
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Abstract

An earlier article deduced a doubling of the scale of the sea level pressure pattern for lows as they developed in the North Pacific. Scale here refers to horizontal extent of the low. This study uses a different technique to estimate scale change in the upper troposphere. The prior study used wavelets; here circular averaging is used on several fields, with primary emphasis on the geostrophic kinetic energy (gKE) field.

The technique herein confirms the earlier result that sea level pressure (SLP) scale increases. When applied to the 300-hPa level, the trough extent does not change scale significantly. The average scale has radius of about 1200 km at sea level and 1700 km at 300 hPa. During development the average radius of maximum gKE changes little at the surface but decreases at upper levels. The maximum gKE is typically located 600–1100 km from the 300-hPa low center, 450–650 km from the SLP low center. Composite maps of gKE are shown during different stages in cyclone development at both levels. Consistency between the results presented here and the conventional view of jet streak migration around an upper low is mentioned. Some implications for theoretical work are mentioned.

Corresponding author address: Prof. Richard Grotjahn, Atmospheric Science Program, University of California, Davis, Hoagland Hall, One Shields Avenue, Davis, CA 95616-8627.

Email: grotjahn@ucdavis.edu

Abstract

An earlier article deduced a doubling of the scale of the sea level pressure pattern for lows as they developed in the North Pacific. Scale here refers to horizontal extent of the low. This study uses a different technique to estimate scale change in the upper troposphere. The prior study used wavelets; here circular averaging is used on several fields, with primary emphasis on the geostrophic kinetic energy (gKE) field.

The technique herein confirms the earlier result that sea level pressure (SLP) scale increases. When applied to the 300-hPa level, the trough extent does not change scale significantly. The average scale has radius of about 1200 km at sea level and 1700 km at 300 hPa. During development the average radius of maximum gKE changes little at the surface but decreases at upper levels. The maximum gKE is typically located 600–1100 km from the 300-hPa low center, 450–650 km from the SLP low center. Composite maps of gKE are shown during different stages in cyclone development at both levels. Consistency between the results presented here and the conventional view of jet streak migration around an upper low is mentioned. Some implications for theoretical work are mentioned.

Corresponding author address: Prof. Richard Grotjahn, Atmospheric Science Program, University of California, Davis, Hoagland Hall, One Shields Avenue, Davis, CA 95616-8627.

Email: grotjahn@ucdavis.edu

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