Real-Time Comparisons of Radar Corrected Rainfall Estimates with MESONET Gauges - Correction is essential in Low Bright Band Cases - Real-time accumulations produced by RAPID: 1- Uncorrected (C0) 2- VPR correct the 1-hr C0 accums (C1) 3- VPR correct every “lowest” CAPPI map, then accumulate (C2) (Use observed and simulated VPR in #2 and #3) 4- Climatological Correction (C3) (applied to every “lowest” CAPPI map)
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Real-Time Comparisons of Radar Corrected Rainfall Estimates with MESONET Gauges
Real-Time Comparisons of Radar Corrected Rainfall Estimates with MESONET Gauges. Correction is essential in Low Bright Band Cases Real-time accumulations produced by RAPID: 1- Uncorrected (C0) 2- VPR correct the 1-hr C0 accums (C1) 3- VPR correct every “lowest” CAPPI map, - PowerPoint PPT Presentation
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Real-Time Comparisons of Radar Corrected Rainfall Estimates with MESONET Gauges
- Correction is essential in Low Bright Band Cases- Real-time accumulations produced by RAPID:
1- Uncorrected (C0)2- VPR correct the 1-hr C0 accums
(C1)3- VPR correct every “lowest” CAPPI map, then accumulate (C2)(Use observed and simulated VPR in #2 and #3)
4- Climatological Correction (C3)(applied to every “lowest” CAPPI map)
Mesonet Gauge Locations
120 km
1. Accumulations based on CAPPIs at a pre-defined height (1.5 to 2.5 km) (Correction applied to the 1-h accumulations as a function of range)
a) dBZ = VPR[ CAPPI height ] - VPR[ Ref. height ] (For each of the 5 VPRs)
(Ref. Ht: 0.2 to 0.4 km above visibility height, or at BB top if contaminated by low BB)
b) Beyond 110 km, apply Gaussian smoother (vertical) to last VPR dBZ = VPRG [ H(range) ] – VPRLast[ Ref. height ]
c) Interpolate dBZ at every km and convert it into a rainfall rate factor
d) Multiply uncorrected 1-h accumulations and integrate for total rainfall
UNCORRECTED C1 CORRECTED
2. Accumulations based on OSP maps (C3)(Optimum Surface Precipitation)
(Correction performed at every radar cycle and for every pixel)
a) Lowest pixel (~1.3 km) up to 90 km. 2nd elevation angle afterwards
- dBZ is obtained from VPR as in (1) to modify reflectivity at selected height
b) Automatic VPR identification and correction
- Should we avoid rather than correct for bright band ? (CORRECT) c) No dBZ adjustment for convective pixels ( > 32 dBZ 2 km above BB height)
UVIL (above 3.5 km) > 1 or 2 kg/m2
- Separate Z-R for stratiform and convective pixels
d) Knowledge of 0º isotherm from model forecasts prevents correction in cases of low bright band. Reflectivity at BB top is used as reference
- Identifies low level growth due to warm rain or snow. (Add extra dBZ) - Evaporation: Set to 0 if dBZ < 20, otherwise subtract 5 dBZ
When observedat a farther range
ERRORS DUE TO EXTRAPOLATION FROM HEIGHT OF MEASUREMENT TO GROUNDERRORS DUE TO EXTRAPOLATION FROM HEIGHT OF MEASUREMENT TO GROUND
BW=0.2 0.5
1.72.0
To determine the errors,values at the measurementheight are compared with the low level ground truth
Real-Time Correction (CAPPIs)
Uncorrected C2 Corrected
The reflectivity at pixels affected by the bright band is reduced while estimates at far ranges (in the snow) are increased.
Total Error Summary: Stratified by BB height(Data from 0.50 elevation for r>100km and from 1.5 km CAPPI for r<100km)
Representativeness of VPRRepresentativeness of VPR
Increased NRMS errors for 1-hr accumulations generated with VPR correctionfactors that are appropriate for a different time interval (in order to simulatea different VPR at farther ranges). The uncorrected NRMS and that from theclimatological correction are provided as reference. (At the “lowest default height” and at 10-km resolution).
Snowfall Accumulation
In snow, it is necessary to correct for the increase in reflectivity of snow as it falls tothe surface. The VPR display (Vertical Profile of Reflectivity) helps to quantify thisvertical gradient. In general, the VPR is essential for a proper estimate of surface precipitation,particularly under stratiform rainfall conditions.