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<br />4. TOPICS IN PREVIOUS ANNUAL REPORTS <br /> <br />A number of important topics related to the SAA have been discussed in detail in the first two annual <br />reports (Super and Holroyd, 1996; Super and Holroyd, 1997a). Their level of detail will not be repeated <br />here. The equation coefficients quoted in the following abstracts from those reports have been changed <br />as a result of further analyses. <br /> <br />4.1 The First Annual Report Abstract (Super and Holroyd, 1996) <br /> <br />Reclamation provided a Research Report to the OSF, R-96-04, dated June 1996. The 133 page report is <br />titled, "Snow Accumula~ion Algorithm for the WSR-88D Radar, Version 1." It was written by the <br />authors ofthis report except for Appendix A which was written by Prof. James A. Heimbach ofthe <br />University of North Carolina at Asheville. For general information, the report's abstract is noted below, <br />but the values of the constants have since been revised. <br /> <br />Abstract <br /> <br />This annual Bureau of Reclamation report describes the initial year of a 3-year effort to develop a Snow <br />Accumulation Algorithm for the new network ofWSR-88D (NEXRAD) radars. Snowfall measurements <br />were made during the 1995-96 winter/spring within range of WSR-88Ds at Albany, NY, Cleveland, OH, <br />and Denver, CO. Observations of S (snow water equivalent) from the latter two locations were related to <br />Ze (effective reflectivity factor) measurements to determine "best fit" a and P coefficients for the <br />commonly-used equation Ze = aSp. Recommended a and p values are 318 and 1.5 for Cleveland and 155 <br />and 1.6 for Denver. <br /> <br />Observations near Lake Erie revealed a significant range effect. The Cleveland radar underestimated <br />snowfall beyond about 60 km. Radar-estimated snowfall accumulations were about 85, 61, 31, and <br />22 percent of gage observations at 61,87, 115, and 146 km, respectively. A scheme should be developed <br />to use the vertical profile of Ze to adjust for mid- and far-range snowfall underestimates by WSR-88Ds. <br /> <br />Initial Snow Accumulation Algorithm code is described and presented. The code development borrows <br />from the current NEXRAD rainfall algorithm but makes several important modifications, including an <br />advection scheme, because snowflakes can be transported tens of kilometers from the lowest tilt radar <br />beam to the ground. <br /> <br />4.2 The Second Annual Report Abstract (Super and Holroyd, 1997a) <br /> <br />Reclamation provided a Research Report to the OSF, R-97-05, dated June 1997. The 79 page report is <br />titled, "Snow Accumulation Algorithm for the WSR-88D Radar: Second Annual Report." It was also <br />written by the authors of this report. For general information, the report's abstract is noted below: <br /> <br />Abstract <br /> <br />This Bureau of Reclamation report describes the second year ofSAA (snow accumulation algorithm) <br />development for the NEXRAD radar. An optimization technique applied to 1995-96 winter observations <br />determined reflectivity-snowfall relationships for Albany, Cleveland and Denver. These relationships <br /> <br />8 <br />