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.

OSP

Real-Time Correction:

1-hr accumulation

Uncorrected

OSP:12 CAPPIs are corrected

“One-shot” :one map is corrected

BB Convection

Uncorrected

ConvectionBB

(a)

“One-shot” :one map is corrected

(b)

OSP:12 CAPPIs are corrected

(c)

Climatological: 12 CAPPIs are corrected

(d)

Climatological Vertical Profiles (250 hrs)

1-hr Accumulations: 0300 GMT 21-Nov-2004

Unc C1

OSP Clim

0000 Z to 2400 Z 21-Nov-2004

Unc C1

OSP Clim

R/G:3.86 %AD:291 Corr:0.77 R/G:1.42 %AD:75 Corr:0.78

R/G:1.19 %AD:48 Corr:0.76 R/G:2.05 %AD:1.18 Corr:0.86

0000 Z to 2400 Z 21-Nov-2004

0000 Z to 2400 Z 28-Nov-2004

Unc C1

OSP Clim

R/G:1.72 %AD:94 Corr:0.55 R/G:0.94 %AD:38 Corr:0.66

R/G:1.17 %AD:48 Corr:0.74 R/G:1.30 %AD:48 Corr:0.79

0000 Z to 2400 Z 28-Nov-2004

2400Z 1-Dec-2004

Unc C1

OSP Clim

R/G:1.20 %AD:47 Corr:0.48 R/G:2.06 %AD:119 Corr:0.55

R/G:0.89 %AD:35 Corr:0.47 R/G:1.02 %AD:31 Corr:0.53

2400Z 1-Dec-2004

0000 Z to 2400 Z 24-Nov-2004

Unc C1

OSP Clim

R/G:0.74 %AD:36 Corr:0.71 R/G:0.56 %AD:50 Corr:0.61

R/G:0.68 %AD:38 Corr:0.77 R/G:0.46 %AD:56 Corr:0.80

0000 Z to 2400 Z 24-Nov-2004

0000 Z to 2400 Z 16-Oct-2004

Unc C1

OSP Clim

R/G:1.19 %AD:32 Corr:0.42 R/G:0.80 %AD:25 Corr:0.52

R/G:0.93 %AD:20 Corr:0.54 R/G:0.73 %AD:30 Corr:0.64

0000 Z to 2400 Z 16-Oct-2004

24-hr Accumulation 2200Z 9-Sep-2004

Unc C1

OSP ClimR/G:0.69 %AD:32 Corr:0.73 R/G:0.66 %AD:34 Corr:0.65

R/G:0.66 %AD:34 Corr:0.82 R/G:0.64 %AD:36 Corr:0.81

24-hr Accumulation 2200Z 9-Sep-2004

0000 Z – 2400 Z 1-Jun-2004

Climatological correctionmap not available

R/G:1.28 %AD:33 Corr:0.70

R/G:0.86 %AD:23 Corr:0.64

R/G:0.97 %AD:13 Corr:0.81

R/G:0.92 %AD:13 Corr:0.86

Projection of near range VPRs into far ranges

250 hr of data,

21 events

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.

Unc

Real-Time Correction:

24-hr accumulation

Uncorrected

“One-shot” correction of 24 1-hr acc. maps

OSP: 24 x 12 CAPPIs are corrected

C1

FRANKTOWN Radar: 21-hr Accumulation 0900Z 15-Jun-2004

• No Climatological Accumulation

Unc C1

OSP

0000 Z – 2400 Z 3-Aug-2004

Unc C1

OSP ClimR/G:1.94 %AD:94 Corr:0.89 R/G:1.77 %AD:78 Corr:0.89

R/G:1.69 %AD:74 Corr:0.89 R/G:1.76 %AD:80 Corr:0.88