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Mesoscale Budgets of Heat and Moisture in a Convective System over the Central United States

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  • 1 National Center for Atmospheric Research, Boulder, Co 80307
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Abstract

The effect midlatitude organized onvection on its environment is diagnosed through the calculation of mesoscale heat and moisture budgets over a region during the 10–11 April 1979 AYE-SESAME case. The noise level or error at individual points is about 5°C day−1 for the heat budget and 2 g kg−1 day−1 for the moisture budget, consistent with the sensitivity tests discussed by Kuo and Anthes in a related paper. However, when averaged over an area bigger than the observational scale, the noise level is considerably reduced. The general agreement between the observed rainfall rate and the vertically integrated apparent heat sources and moisture sinks, together with the temporal continuity shown by the budgets at the nine analysis times, supports the credibility of the area-averaged budget results. The vertical structure of convective heating diagnosed from this organized midlatitude convection shows significant differences from those structures diagnosed in the tropics on much larger temporal and spatial scales; in particular, the maximum at about 350 mb is greater, little heating occurs below 650 mb, and strong cooling is diagnosed in the upper troposphere. High correlation exists between large-scale moisture convergence and observed rainfall rate. However, there is a time lag of several hours between the moisture convergence and the rainfall rate. Their phase relationship is similar to that observed in previous studies on the easterly waves, and suggests a strong relationship between the large-scale and the convective systems.

Abstract

The effect midlatitude organized onvection on its environment is diagnosed through the calculation of mesoscale heat and moisture budgets over a region during the 10–11 April 1979 AYE-SESAME case. The noise level or error at individual points is about 5°C day−1 for the heat budget and 2 g kg−1 day−1 for the moisture budget, consistent with the sensitivity tests discussed by Kuo and Anthes in a related paper. However, when averaged over an area bigger than the observational scale, the noise level is considerably reduced. The general agreement between the observed rainfall rate and the vertically integrated apparent heat sources and moisture sinks, together with the temporal continuity shown by the budgets at the nine analysis times, supports the credibility of the area-averaged budget results. The vertical structure of convective heating diagnosed from this organized midlatitude convection shows significant differences from those structures diagnosed in the tropics on much larger temporal and spatial scales; in particular, the maximum at about 350 mb is greater, little heating occurs below 650 mb, and strong cooling is diagnosed in the upper troposphere. High correlation exists between large-scale moisture convergence and observed rainfall rate. However, there is a time lag of several hours between the moisture convergence and the rainfall rate. Their phase relationship is similar to that observed in previous studies on the easterly waves, and suggests a strong relationship between the large-scale and the convective systems.

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