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<br />Oliver (1974) has shown that nearly all convective activity in the <br /> <br />tropics forms along a preexisting line., Where two lines interSE!ct <br />or where a thunderstorml s arc 1 i ne i ntE!rSects another 1 i nes he found <br /> <br />new shower and thunderstorm activity. <br /> <br />A two-dimensional conceptual model of the mesohigh and arc line <br /> <br />intersection between two thunderstorms is shown in figure 7. The <br /> <br />colds dense air of the mesohigh is fonned by evaporation of cloud <br /> <br />and rainwaters as cold air sinks to produce a moist downdraft within <br /> <br />the cloud and subcloud as shown. Aloft between thunderstorms <br /> <br />compensating sinking or subsidence occurs to maintain continuity of <br />the envi ronment-thunderstorm system. Thi s subs idence may creatE! a <br /> <br />clear rel at ively stabl e 1 ayer surrounding the thunderstorm. ThE! <br />discontinuity of density between the cold dome and the warmer air <br /> <br />above it may also provide a media for \lIave propagation. The inter- <br />section of the two cold domes forms a line of intense convergenc:e <br /> <br />which mechanically lifts the air. This lifting may provide sufficient <br />energy to trigger additional convectiVE! development. <br /> <br />VI. Relationships Between Gravity Waves and Intense Convective <br />Development <br /> <br />Uccillini (1973) has reported that gravity waves having properties <br />observed by satell ites can produce vertical motion of 30 cm s-l <br /> <br />associated with an upward displacement of 790 m and a downward <br />displacement of 90 m (-6 cm s-l). These results were based upon a <br /> <br />8 <br />