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Last modified
7/28/2009 2:40:56 PM
Creation date
4/24/2008 2:56:27 PM
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Template:
Weather Modification
Title
Snow Accumulation Algorithm for the WSR-80D Radar: Supplemental Report
Date
11/1/1999
Weather Modification - Doc Type
Report
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<br />4.3 Sierra Nevada, California <br /> <br />Our work has revealed that the KBBX, Beale AFB radar site, at an elevation of 61 m, is poor with respect <br />to viewing precipitation development over the Sierra Nevada range. The lowest elevation scan and even <br />some of the second and third elevation scans are blocked over the mountainous terrain. <br /> <br />All seven hourly ETI gages listed in table 1 were operated by the California Department of Water <br />Resources. They had load sensors with 0.04 inch (1 mm) resolution. Our best (number of hours of <br />unmelted snow) gage site was at La Porte, yet the gage was far below the lowest unblocked beam. A <br />snowboard was observed about 0.5 km away from the La Porte site by Pete and Jim Burkholder, who <br />provided occasional air temperatures and remarks about the storms. <br /> <br />Analyses from all gages yielded small alpha values (as shown in table 1), indicative of having the radar <br />beam examine light snow far above the growth zone and even farther above the surface gages. That table <br />lists the occultation correction (Corr.), correlation coefficient (R2) for the relation between the SAA - S <br />and gage values, the number of data points (n), and the clearance between the radar beam center and the <br />gage elevation. <br /> <br />.. <br /> <br />For our analyses, wet snow or rain events were <br />excluded. It appears that the clearance between <br />the radar beam center and the gage elevation <br />strongly affects the value of alpha, as shown in <br />figure. 2. All seven gages are plotted, with the <br />left-most point (smallest alpha) probably being <br />offset from the apparent linear relation by poor <br />data resolution in the calculation of alpha. As the <br />ground clearance increases, alpha decreases. <br />That indicates a strong vertical gradient in <br />reflectivity. In areas with strong orographic <br />uplift, such as the Sierra Nevadas, the greatest <br />growth in precipitation is in the layers of the <br />atmosphere close to the surface. There is, <br />therefore, a strong decrease in reflectivity with <br />altitude. <br /> <br />10000 <br /> <br />. <br /> <br />. <br /> <br />E <br />a 1000 <br />~ <br /> <br />. <br /> <br />. <br /> <br />100 <br /> <br />0.1 <br /> <br />10 <br /> <br />100 <br /> <br />A1pho <br /> <br />Figure 2.-A nearly linear relation exists between the <br />logarithms of alpha and ground clearance of the radar <br />beam. <br /> <br />4.4 Chicago, Illinois <br /> <br />Work by Arlin Super on the KLOT, Chicago, <br />Illinois, data set was not completed before his <br />retirement. He learned that most of the 25 gages in the area were not adequately shielded against wind <br />effects. The main siting priority was to minimize vandalism damage to the gages, to the extent that gages <br />were sometimes put on top of buildings. Due to the poor quality of gage data, no comparisons with radar <br />data could be made. <br /> <br />4.5 Medford, Oregon <br /> <br />Through a different project, Hartzell and Super (2000) compared reflectivity data from the KMAX, <br />Medford, Oregon, radar to gage data. The Medford radar is sited at high elevation (2300 m) and, <br />therefore, overlooks low elevation precipitation. All six gages in the study are located at elevations <br /> <br />6 <br />
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