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<br />. <br /> <br />... <br /> <br />. <br /> <br />. <br /> <br />~/'...... <br /> <br />tiH. "G../.;r~~L t\;o'a ~~.., p;l..:r r.."....,je.:~ Cu"",r.../.e",j...r:;: EV"'/..,AI,..... I("',,/,~,,-T" <br />""'p'~ll;~tr '17..'-'. SJ.ol (I,.r; 11,c..,..u-t 4:$ J.r. HA"'''lIf..,-..I ./~7~ <br />.... J <br /> <br />h7 <br /> <br />6. SUHMARY DISCUSSION M"D RECO:-!:'IH"TIATIO:-;'S <br /> <br />The princ.ipal conclusions arrrlved at <:':1 the basis of the overall evaluation <br /> <br />are: <br /> <br />" <br /> <br />1) There vas no stgnific8n~ difference in the net target area precipitation <br />on seeded experimental days and that on nor-s'~ec~d experimental days. This null <br />effect vas apparently due to the.mixinR of positive and negative seeding effects. <br />Negative effects occurred when seeding vas conducted during out-of-bounds condi- <br />tions and positive effects occurred vhen seeding vas conducted during in-bounds <br />conditions. The findings discussed in ite~s 2 through 8 below are based upon <br />diagnostic analyses (see Chapter 5) of six-hour block precipitation data rather <br />than on the 24-hour experimental day data. This permitted the sorting out of <br />the various effects of seeding. <br />2) During the 147 experimental days, stable orographic clouds prevai~~. <br />about 52% of the time and accounted for about 33% of the experimental day pre~ <br />cipitation (at K03) covered by the diagnostic analysis. This stable orographic <br />cloud category includes cases witb shalloy unstable layers no thieker than 75 mb. <br />Excluding the stable ones, cases range ~ost1y from neurrally stable stratifo~ <br />clouds to ones containing embedded shalloy cumuli or stratocumulus. During 37% <br />of the time, or about 10% of the diagnostic analysis experimental day precipita- <br />tion, warm top stable clouds occurred. ~~en these were seeded, substantial pre- <br />cipitation increases occurred in the target area and on the dovnyind flank. <br />During .15% of the time, or about 23% of the experimental day precipitation, <br />stable orographic clouds whose tops ~ere colder than -29C occurred. ~~en these <br />vere seeded, decre~scs in precipitation occurred. The decreases vere marked <br />when the cloud level Yind component normal to the barrier was strong and the. <br />cloud deep. If the Yind component norm;\l to the barrier "'as weak and the cloud <br />shallow, then increases occurred in the cold top category. This latter effect <br />had not been anticipated from earlier cloud ;~eding tests. <br />J) Durin~ approximately 48Z of th~ ti~e, and accounting for about 67% of <br />the experimental day precipitation, the air ~ss had sufficient thermodynamic <br />instability to be considered outside of the stable orogr<Jphic category. Le., <br />deep convection was present. Seeding under these conditions may have resulted <br />in an increase in precipitation on downwind slopes, particularly "'hen the normal <br />....ind component ....:150 low. It probably res\11tcc in dccre.1ses on the 1.lp...,ind slope.s. <br /> <br />f,-j <br /> <br />'/ <br /> <br />~if. <br />J <br />jx . <br />,~, ' <br />,1'14, <br />. I.. ' <br />, <br /> <br />) -~.. . <br />IF. <br /> <br />i~ . <br />j/"' <br />;"" <br /> <br />, <br /> <br />A-ll-S <br />