Diagnosis of Anafronts and Katafronts

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  • 1 St. Louis University, Department of Earth and Atmospheric Sciences, St. Louis, Missouri
  • | 2 Air Weather Service, U.S. Air Force, March AFB, California
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Abstract

Diagnostic techniques are presented that aid in determining whether a cold front is of the anafront (upslope flow) or katafront (downslope flow) type, as well as in measuring the intensity of the vertical motions in the vicinity of the frontal zone. Anafronts are characterized by postfrontal cloudiness and precipitation, while katafronts typically have precipitation in a band along or ahead of the cold front.

The techniques described include: 1) examination of the vertical profile of front-normal and front-parallel winds, 2) construction of an isentropic cross-section normal to the front including front-normal wind components, 3) computation of vertical motion using either the Bellamy triangle approach or adiabatic vertical motion on isentropic surfaces, and 4) analysis of cold air soundings for inversions, relative humidity profiles, and the degree of backing of winds in the vertical.

Case studies are then shown in which we apply the above techniques and prove their efficacy in classifying, anafronts and katafronts. Each technique is then discussed in terms of how useful it might be to an operational forecaster who typically has limited time for diagnosis.

Abstract

Diagnostic techniques are presented that aid in determining whether a cold front is of the anafront (upslope flow) or katafront (downslope flow) type, as well as in measuring the intensity of the vertical motions in the vicinity of the frontal zone. Anafronts are characterized by postfrontal cloudiness and precipitation, while katafronts typically have precipitation in a band along or ahead of the cold front.

The techniques described include: 1) examination of the vertical profile of front-normal and front-parallel winds, 2) construction of an isentropic cross-section normal to the front including front-normal wind components, 3) computation of vertical motion using either the Bellamy triangle approach or adiabatic vertical motion on isentropic surfaces, and 4) analysis of cold air soundings for inversions, relative humidity profiles, and the degree of backing of winds in the vertical.

Case studies are then shown in which we apply the above techniques and prove their efficacy in classifying, anafronts and katafronts. Each technique is then discussed in terms of how useful it might be to an operational forecaster who typically has limited time for diagnosis.

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