. Compendium of meteorology. Meteorology. CUMULUS CONVECTION AND ENTRAINMENT 699 shape since they indicate that the cloud mass continues to increase with height. These graphs should be in- terpreted as rciJreseuting, at any elevation, the fraction of the cloud air which has originated at a lower eleva- tion. For example, in the case 7» = 9 X 10~^C cm"' and H = in Fig. 5, the air at 2 km above the cloud base contains one part of air which originated at the base and five parts of air which have come from the environment. However, this may not necessarily mean that the mass of the cloud
. Compendium of meteorology. Meteorology. CUMULUS CONVECTION AND ENTRAINMENT 699 shape since they indicate that the cloud mass continues to increase with height. These graphs should be in- terpreted as rciJreseuting, at any elevation, the fraction of the cloud air which has originated at a lower eleva- tion. For example, in the case 7» = 9 X 10~^C cm"' and H = in Fig. 5, the air at 2 km above the cloud base contains one part of air which originated at the base and five parts of air which have come from the environment. However, this may not necessarily mean that the mass of the cloud at 2 km is six times as great as the mass at the base. In fact, it is probable that not all of the air which reaches a particular level continues to ascend. Data on Convective Showers In view of the eddy diffusion to which a cloud is subject, it seems probable that the ideal conditions for the persistence of a cumulus cloud are a high liquid- water content and large horizontal extent. For the development of the vertical accelerations to force the cloud upward it seems desirable that there be a steep lapse rate of temperature. The analysis, as summarized in Table I, indicates that it is not possible to satisfy all three conditions; for example, a condition which gives rise to a high liquid-water content does not appear to favor the development of vertical accelerations. Therefore, it should not be expected that a steep lapse rate of temperature in the environment is necessarily the most favorable condition for cumulus growth. Con- sequently, attempts have been made to obtain some empirical data on cumulus clouds which would give an insight into the mixing process. Austin [1] studied the occurrence of convective showers in the vicinity of three radiosonde stations in the eastern United States. It was found that the relative humidity of the environment was as important a con- sideration for the development of showers as the vertical stability of the air. Chalker [7] confirmed th
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