Editorial Type:
Article
Article Type:
Research Article

Diabatic Effects on Late-Winter Cold Front Evolution: Conceptual and Numerical Model Evaluations

William A. Gallus Jr. Department of Geological and Atmospheric Science, Iowa State University, Ames, Iowa

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Moti Segal Department of Agronomy, Iowa State University, Ames, Iowa

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Print Publication:
01 Jul 1999
DOI:
https://doi.org/10.1175/1520-0493(1999)127<1518:DEOLWC>2.0.CO;2
Page(s):
1518–1537
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Abstract

The impact of diabatic heating on late winter frontogenesis is evaluated both through conceptual scaling and the use of high-resolution Eta Model simulations of a strong but relatively dry cold surface front that occurred during the Storm-scale Operational Research Meteorology Fronts Experiment Systems Test (STORMFEST) project. Although skies were clear ahead of the front, it was trailed by an extensive area of cloud cover that influenced frontal strength during the daylight hours by reducing solar insolation and sensible heat flux.

An Eta control simulation of the event agreed reasonably well with observations and indicated intensification of the frontal temperature gradient during the daytime with a weakening at night. Additional simulations have been done to investigate sensitivity to several diabatic processes. These tests include the role of cloud shading on surface sensible heat flux, the role of soil moisture in the warm sector, and the role of evaporative cooling of precipitation in the light precipitation area behind the cold front. All of these diabatic processes have a measurable impact on the front, although soil moisture and cloud shading appear to play the most important roles. The moisture and static stability of the frontal environment were unfavorable for precipitation along the front, and the increase in frontal strength due to reduced surface sensible heat flux from extensive cloud shading behind the front did not significantly influence near-front precipitation for this event.

Corresponding author address: Dr. William A. Gallus, Department of Geological and Atmospheric Science, Iowa State University, 3025 Agronomy Hall, Ames, IA 50011.

Email: wgallus@iastate.edu

Abstract

The impact of diabatic heating on late winter frontogenesis is evaluated both through conceptual scaling and the use of high-resolution Eta Model simulations of a strong but relatively dry cold surface front that occurred during the Storm-scale Operational Research Meteorology Fronts Experiment Systems Test (STORMFEST) project. Although skies were clear ahead of the front, it was trailed by an extensive area of cloud cover that influenced frontal strength during the daylight hours by reducing solar insolation and sensible heat flux.

An Eta control simulation of the event agreed reasonably well with observations and indicated intensification of the frontal temperature gradient during the daytime with a weakening at night. Additional simulations have been done to investigate sensitivity to several diabatic processes. These tests include the role of cloud shading on surface sensible heat flux, the role of soil moisture in the warm sector, and the role of evaporative cooling of precipitation in the light precipitation area behind the cold front. All of these diabatic processes have a measurable impact on the front, although soil moisture and cloud shading appear to play the most important roles. The moisture and static stability of the frontal environment were unfavorable for precipitation along the front, and the increase in frontal strength due to reduced surface sensible heat flux from extensive cloud shading behind the front did not significantly influence near-front precipitation for this event.

Corresponding author address: Dr. William A. Gallus, Department of Geological and Atmospheric Science, Iowa State University, 3025 Agronomy Hall, Ames, IA 50011.

Email: wgallus@iastate.edu

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