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<br />I <br />The validity of these estimates can be checked by comparison with the <br />radar-estimated rainfall in cases where the radar can vjew the +10 oc <br />level. Significant discrepancies will make the use of AER suspect, <br />while reasonable agreement will be evidence supporting the use of AER <br />at ranges where the radar cannot view melted hydrometeors. <br /> <br />H. Precipitation Response Variables Estimated From Radar Measurements <br /> <br />Ground-based radar can provide reasonable estimates of rainfall if <br />the beam is largely or fully filled with liquid hydrometeors. <br />Measurements made during the Miles City HIPLEX Program have indi- v <br />cated that frozen or partially melted hydrometeors are commonly found <br />at the +5 Oc level. They occur much less frequently at'the +10 oc <br />level, and considerably more confidence can be placed in estimates of ~ <br />rain based on the radar data collected at the +10 oc level than at <br />higher (colder) levels. The range at which the +10 oc level inter- <br />sects the center of the lowest tilt (0.70) radar beam will be deter- <br />mined prior to each HIPLEX-1 mission. Every effort will be made to <br />select potential candiates that are expected to .stay within this <br />radar range (about 85 km) for 40 minutes after treatment. Cases will <br />be selected at further ranges only when suitable cases cannot be <br />found closer to the Miles City SWR-75 radar. <br /> <br />The following response variables will be determined fro~ the SWR-75 <br />radar: <br /> <br />1. Time to initial precipitation at the +10 oc level (TIPR), <br />defined as the first appearance of a 15-dBZ echo on the Miles City <br />SWR-75 radar. <br /> <br />2. Radar-estimated rainfall at the +10 oc level (RERA) based on <br />separate Z-R relationships calculated for the seeded and the <br />un seeded cases. The two relationships will be developed from <br />measurements of precipitation spectra obtained at the +10 oc level <br />by the King Air aircraft and will be tested after each season and <br />after the end of the experiment to determine whether they are <br />statistically different. If they are found to be different, the <br />values of RERA for the seeded and unseeded experimental units will <br />be calculated from their respective Z-R relationships using the <br />SWR-75 radar data. The change in precipitation spectra will be <br />acknowledged as another effect of seeding. If they are not found <br />to be different, the data for the seeded and un seeded experimental- <br />unit populations will be pooled and a single Z-R relationship will <br />be determined for calculating the values of RERA. <br /> <br />3. Radar-estimated rainfall at the +10 oc level (RERC) based on a <br />single Z-R relationship (Z = 520R1.35) determined from radar and <br />cloud-base precipitation spectra obtained as part of the HIPLEX-1 <br />background studies in the Miles City area. <br /> <br />$ <br /> <br />22 <br />