Mesoscale Generation of Available Potential Energy in the Warm Sector of an Extratropical Cyclone

Henry E. Fuelberg Department of Earth and Atmospheric Sciences, Saint Louis University, St. Louis, MO 63103

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Mark G. Ruminski Department of Earth and Atmospheric Sciences, Saint Louis University, St. Louis, MO 63103

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David O'C. Starr Department of Earth and Atmospheric Sciences, Saint Louis University, St. Louis, MO 63103

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Abstract

Generation of available potential energy (APE) is computed for the warm sector of an extratropical cyclone containing intense convection. Three hourly mesoscale rawinsonde data from the 10–11 April day of AVESESAME 1979 are used to evaluate generation by five diabatic components. Convective latent heat release is found to be the dominant diabatic term during times of intense convection, whereas stable latent heating provides a relatively small contribution. Sensible heat transfer is important near the surface during the afternoon. Solar and infrared radiative processes are quite significant in regions of low-level stratus and convective activity. Solar absorption during midday is observed to be much greater than at the standard rawinsonde observation times. The use of subjectively specified cloud data and sophisticated radiative transfer models permit more detailed resolution of cloud effects thin possible in earlier studies of this type.

Negative generation of APE is dominant during the 24 h period because convective latent heating is superimposed on areas of negative efficiency. The only consistent positive generation is due to infrared cooling. Sensible heating is the third largest generating component, while stable heating and solar absorption are least significant. Results document rapid temporal variations in generation as well as contrasts between energetics of the warm sector and those of entire cyclones.

Abstract

Generation of available potential energy (APE) is computed for the warm sector of an extratropical cyclone containing intense convection. Three hourly mesoscale rawinsonde data from the 10–11 April day of AVESESAME 1979 are used to evaluate generation by five diabatic components. Convective latent heat release is found to be the dominant diabatic term during times of intense convection, whereas stable latent heating provides a relatively small contribution. Sensible heat transfer is important near the surface during the afternoon. Solar and infrared radiative processes are quite significant in regions of low-level stratus and convective activity. Solar absorption during midday is observed to be much greater than at the standard rawinsonde observation times. The use of subjectively specified cloud data and sophisticated radiative transfer models permit more detailed resolution of cloud effects thin possible in earlier studies of this type.

Negative generation of APE is dominant during the 24 h period because convective latent heating is superimposed on areas of negative efficiency. The only consistent positive generation is due to infrared cooling. Sensible heating is the third largest generating component, while stable heating and solar absorption are least significant. Results document rapid temporal variations in generation as well as contrasts between energetics of the warm sector and those of entire cyclones.

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