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<br />simple three-layer numerical model. Uc:cillini has related initiation <br />of severe convective stoms to apparent gravity wave triggering. He <br />found that the lifting induced by gravity wave passage occurs in a <br />short enough time interval to produce the observed explosive develop- <br />ment of convective stoms. Other numey'ical experiments of cloud- <br />envi ronmental interact ion (Matthews, 1974) have shown that indivi dual <br />soundings can be quite sensitive to loc:al vertical motions of 5 to <br />20 cm s-l. An experiment using summer soundings from Montana and <br />Colorado showed that significant change!s in middle and lower tropo- <br />spheric stability were caused by mesosc:ale lifting ranging from <br />180 to 720 m over a I-hour period. Significant changes in the <br />available convective potential energy r'esult in dramatic changes in <br />cloud development diagnosed by a mesocumulus model (MESOCU) deve,loped <br />by Kreitzberg and Perkey (1973). Using! this model on a sample of <br />120 soundings, Matthews (l978) has shown that cloud growth predicted <br />is dramatically changed by 1 ifting of the same order magnitude as <br />that produced by gravity waves. The magnitude, height, and signifi- <br />cance of sounding modification induced by lifting were shown to be a <br />function of individual sounding stability and moisture. These <br />changes have added importance because grravity waves which produce <br />similar magnitudes of lifting have been found to occur frequently <br />over wide areas. <br /> <br />9 <br />