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<br />cloud-base heights) were averaged to provide a mean mixing ratio repre- <br /> <br />sentative of a well-mixed PBl (planetary boundary layer). Hence, the <br /> <br />mixed CCl would better represent a convective airmass environment during <br /> <br />the summer. <br /> <br />The model determination of CCl assumes that the surface convective tempera- <br /> <br />: <br />1 <br /> <br />ture will be reached, thus producing sufficient heating to form a cloud at <br /> <br />that level. In order to minimize errors in cloud diagnosis, checks were <br /> <br />added so cases that required heating in excess of the climatological <br /> <br />extreme were rejected. Excessive heating was required in nearly 10 percent <br /> <br />of all cases. <br /> <br />A sample of days when cloud physics aircraft observations at cloud base <br />and cloud top were available was used to determine the model's ability to <br />correctly diagnose observed cloud development. The sample consisted of <br /> <br />26 morni ng and afternoon rawi nsondes observed on 13 days dur ing May, June, <br /> <br />and July of 1977 at Miles City, Montana. The model was initialized with <br />six cloud updr~ft radii (0.5, 1.0, 1.5,2.0,3.0, and 10.0 km). <br /> <br />. The comparison between model and. observed cloud properties is presented in <br />table 3 for 13 cases having simultaneous cloud-base and cloud-top observa- <br />tions. In general, for all rawinsonde data, the model was able to <br /> <br />di agnose the observed convect ive cloud development reasonab ly we 11 con- <br /> <br />sidering prob 1 ems of soundi ng representat ivenessand the 1 imitat ions of a <br />one-dimensional, steady-state model. The correlation coefficients for <br /> <br />cloud-base height (0.78), cloud-top height (0.86 for a cloud model updraft <br />radius of 3.0 km) with a relatively small rms error and bias for the <br /> <br />afternoon soundings indicate that the model is able to diagnose important <br /> <br />14 <br />