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3 rd Conference on QPE /QPF and Hydrology. World Meteorological Organization, Nanjing, China, Oct.18-­‐22,2010. temporal (1min) and spatial (60m) resolution. Two orographicVPR slopes are derived, One is the west coast orographic VPRslope generated from CZC, and the other is the Sierra slopederived from ATA. For the central valley, the VPR slope is setto zero below bright band, meaning no orographicenhancement to the precipitation in the region.2.2 Parameterize apparent VPREach single tilt AVPR is parameterized with a linearmodel (Fig.2), and the linear model is described by apparentbright band top, peak, and bottom heights and piece-wiselinear segments with different slopes (α, β, γ and η). Three ηslopes for three different areas (west coast η coast , central valleyη valley and east mountain η sierra ) as shown in Fig.2. η coast(1.87dBZ/km) and η sierra (3.5dBZ/km) are average valueobtained from CZC and ATA respectively. For η valley , we stillset it zero because no profiler data can be obtained from thecentral valley.2.3 Apply apparent VPRThe VPR correction is applied to the observed reflectivityfield to obtain an estimated reflectivity near the ground,assuming a horizontally invariant vertical reflectivitystructure. The correction is applied to each individual tilt andis only applied to areas with potential bright bandcontamination and with radar sampling in the ice region.Specifically, the areas for correction must meet the followingcriteria: 1) Height of the reflectivity bin is above the apparentBB bottom. 2) VIL20dBZ orcomposite reflectivity >30dBZ in the bright band region; 4)Reflectivity >5dBZ or composite reflectivity >30dBZ in theice region.Fig.3 Hybrid scan reflectivity field at 12Z Oct. 14, 2009 before (a) and after (b) the VPR correction. The bias ratio field betweenradar estimated and gauge observed 48-hr rainfalls before (c) and after (d) the correction are also shown. The dash purplelines indicate the bright band area, and the dash yellow lines indicate the area where radar was sampling in the ice region.-448-

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