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<br />'"',....".--.,---~.. <br /> <br />.~. . <br /> <br />....';. <br /> <br />". <br /> <br />;;~~,~{'~.' ~'., <br />,:,', ,:.;, ~ <br />",t, <br /> <br />;, <br />" <br />" ' <br />,r;-.}("t::', <br /> <br />~tA..., <br /> <br />ti,~ "Cu/.;rn<tG I\;..u L3.4>... P.141t'" ;..;.-....je.:r c.u.,..,.",..,I.eI'1~'''~ Ev,.,lvAI,~,. ..."''''/,J..-r'' <br />I\,D,tEIUf.tf-;R..w. $1.4'/~..;fI.(..J'.Jrt ~ J..F. 1111"" "f.-...J ~ 197" <br /> <br />"1 <br /> <br />6. SUMIIARY DISCUSSION AND RECOf~IE~'DATlO~S <br /> <br />The principal conclusions arrrived at ~n the basis of the overall evaluation <br /> <br />are: <br /> <br />1)' There vas no .{gnilic.at difference in the net target area'precipitation <br />on seeded experimental days and chat 00 llot-s~eded experimental days~;. This "null <br />effe~t waa apparently due to the.ftiKing of positive and negative seeding eff.~ts. <br />Negativ. effects occurred when seeding vas conducted during out-of-bounds condi- <br />. .'.' tlone and 'positive effects occurred, when seeding was conducted durins in-bound. <br />eOnd1tl~n.. > The f1ndinp discussed in items 2 through 6 below are based upon;,:'.' <br />. ", ,~." d~in08C1c' .:naIyses (aee Chapter', 5) of six-hour block precipitation' data, rath;~: . > . <br />..,,- <br />. "than' on the. 2~-hour uper1mental day data. This pemitted the Borting out 'of'-"7.:."'::. <br />the various effects of 'seeding.: . -"'.: -. <br />~~) During the 147'experimental days. stable orographic clouds prevai~ed:' <br />about 52% of the time and accounted for about 33% of the experimental day'pre- <br />cipitation (at K(3) covered by the' diagnostic analys1s.' nais stable orographic <br />cloud category includes eases vith shallow unstable layers no th1cker.than 75 mb. <br />Excluding the stable ones, cases range ~ostly from neutrally stable.strat1fo~ <br />clouds to ones containing embedded shalloy cumuli or stratocumulus. During 31% <br />of the time, or about 10% of the diagnostic analysis experimental day precipita- <br />tion, Warm top stable clouds occurred. ~~n these were seeded, substantial pre- <br />cipitation increases occurred in the target area and ort the downwind flank. <br />During ~S% of the time, or about 23% of the experimental day precipitation, <br />atable orosraphic clouds whose topa were colder than -29C occurred. When these <br />were seeded, decre~ses in precipitation oceurred. The decreases were marked <br />when the cloud level wind component normal to the barrier was strong and the. <br />cloud deep. If the wind component normal to the barrier ".as weak and the cloud <br />shallow. then increases occurred in the cold top category. This latter effect <br />bad not been anticipated from earlier cloud ;~ed1ng tests. <br />3) During approximately 48% of the tiDe, and accounting for about 67% of <br />the experimental day precipitation, the air ~8SS had sufficient thermodynamic <br />instability to be considered outside of the srahle orographic category. 1.e.. <br />deep convection was present. Seeding under these conditions may have resulted' <br />in an increase in precipitation on dovnwind slopes. particularly when the norm~t <br />\llnd component W:lS 10\01'. It ['robably rcslIltcc in decreases on the upwind slopes. <br /> <br />.-, <br /> <br />1": <br /> <br />{.-J <br /> <br />:~ <br />" <br /> <br />i <br /> <br />A-ll-S <br />