Laserfiche WebLink
<br />1772 <br /> <br />JOURNAL OF APPLIED METEOROLOGY <br /> <br />VOLUME 17 <br /> <br />TABLE 3. Crest group statistics for the seven projects studied. <br /> <br /> Pyramid San ta <br /> Bridger Climax San Juan CENSARE Jemez Lake Barbara <br />Total cases 135 420 306 118 173 96 111 <br />Mean no-seed precipitation*[mm(6 h)-l] 1.61 1.20 3.18 3.93 1.75 3.40 1.71 <br />Mean seed precipitation [mm(6 h)-l] 1.31 1.76 3.13 6.39 1.68 3,70 1.87 <br />Ratio 0.81 1.47 0.98 1.63 0,96 1.09 1.10 <br />Test statistic -1.840 3.642 0.440 3.649 0.461 0.411 1. 620 <br />P value 0.066 <0.001 0,660 <0.001 0,646 0,682 0.108 <br /> <br />* Mean seed and no-seed precipitation obtained from crest group gage data within project areas, The "test statistic" is computed <br />using the Wilcoxon nonparametric two-sample test, "P value" is the probability by chance alone of having a test statistic value more ex- <br />treme in either direction than the actually observed test statistic value. <br /> <br />lowest average cloud-base moisture values since they <br />are the farthest north and highest in elevation, re- <br />spectively, In addition, they appear to be the most <br />stable. Bridger shows the largest average negative BTI <br />and consequently the highest "blow-over" potential. <br />This is due to the narrow barrier and relatively high <br />average wind speed. CENSARE, Pyramid Lake and <br />Santa Barbara show the most unstable, moist conditions. <br />Table 3 gives the precipitation statistics of the crest <br />group for each of the seven projects. It is noted that an <br />increase in precipitation occurred for CENSARE and <br />Climax at the 1 % level. A decrease for Bridger occurred <br />at less than the 10% level. The other projects showed <br />small positive and negative effects, but none were <br />statistically significant at less than the 10% level, <br />although Santa Barbara was very close. The average <br /> <br />4 <br /> <br />.. <br />.&; <br />10 <br />.... 3 <br />E <br />E <br /> <br />w <br />u <br />~ 2 <br />cr <br />W <br />IJ.. <br />IJ.. <br />o <br />Z <br />o <br />.... <br /><( <br />.... <br /> <br />, <br /> <br />no-seed precipitation is least for Bridger and Climax <br />and the greatest for CENSARE and Pyramid Lake. <br />Single-variable stratifications were then performed <br />by project and groups of projects to determine seed/no- <br />seed ratios and P values which indicated whether <br />seeding caused a change in precipitation. Each of the <br />variables was stratified to optimize positive and negative <br />seeding effects. Basic agreement with reported results <br />(Elliott et at, 1971, 1976; Grant and Kahan, 1974, <br />Keyes et at., 1973, 1974; Mielke et at., 1971; Rowland' <br />et al., 1973; Squires, 1977; Super et al., 1972) was found <br />in most cases, but disagreement among projects con- <br />tinued to exist. Certain single-variable stratifications <br />showed clear demarcation of seeding effects for one <br />project while conflicting with results from another. <br />For example, in Fig. 2, Climax and San Juan indi- <br /> <br />~.-- <br />, .-- <br />· .-..., CENSARE <br />/ <br /> <br />, <br /> <br />/ <br /> <br />. <br /> <br />---.-.-----.----/ <br /> <br />SAN )( JEMEZ <br />..... ---"'" JUAN I <br />..... ...... "...- ............\ 0 PYRAMID <br />. ..".... d 00000 LAKE <br />.' '."....' .\ ~., 00000 x <br />.' - ........ '. / '.\ 000.0. L <br />.....- . . . 00000 <br />.. - .~,...... 00' 0 ___ - CLIMAX <br />:. .."" 000.0000 ".\ ,..- x <br />.'- <br /> <br /> <br />-30 -25 -20 <br />LCTT! (.C) <br /> <br />FIG. 2, Seed/no-seed difference as a function of LCTTI. Precipitation difference was plotted over a running mean of SoC. <br /> <br />ll.. <br /> <br />u 0 <br />w <br />cr <br />ll.. <br />Z <br />I <br />fn -I <br /> <br /> <br />-45 <br /> <br />~ <br /> <br />x <br /> <br />-15 <br /> <br />-10 <br /> <br />-5 <br />