Gauge and RadarRadarGauge

PaoPao--Liang ChangChangLiang

Central Weather Bureau, TaiwanCentral Taiwan

A Training Course on Quantitative Estimation/Forecasting (QPE/QPF) Crowne Plaza Manila Galleria, Quezon City, Philippines 27-30 March 2012 OutlineOutline

and Gauge Network in TaiwanTaiwanRadar

 Radar Data QC using Reflectivity andandRadar Rainfall ClimatologyClimatologyRainfall

 Radar QPE and GaugeGaugeRadar --corrected QPEcorrectedQPE

 OutlookOutlook

2 Operational Radar Network in TaiwanTaiwanOperational

RCWFRCWF

RCCKRCCK RCHLRCHL RCMKRCMK RCCGRCCG

RCKTRCKT

CWB: RCWF, RCHL, RCKT, RCCG (Doppler, wavelength: 10cm)10cm)CWB: Air Force: RCCK, RCMK (dual(dualAir --polarization, wavelength: 5cm)5cm)polarization, Taiwan operational radar network basic information

RCWF RCHL RCCG RCKT RCCK RCMK

Observation Range (km) 460,230 460,230 460,230 460,230 460,160 460,160 (Z,Vr)

Gematronik Gematronik Gematronik Gematronik Gematronik Type WSR-88D 1500S 1500S 1500S 1500C 1500C

Height (m) 766 63 38 42 203 48

Wavelength (cm) 10 10 10 10 5 5

Polarization Single Single Single Single Dual Dual

Max. Unambiguous 26.55 21.15 21.15 49.5 49.5 49.5 Velocity (m/s) Gauge StationsStationsGauge in TaiwaninTaiwan

Data from CWB and Gov. agencies (WRA, SWCB,TPC,..)

•All Gauge stations ~570 stations •Overland ~560 stations Mean Gauge SpacingSpacingMean from CWB Sites (data in 2007)2007)from

Number of Gauges Concept of Reflectivity ClimatologyClimatologyConcept in Constructing Radar Hybrid ScansScansinConstructing

 TheThe hybridhybrid scanscan ofof aa radarradar includesincludes thethe lowestlowest radarradar binsbins thatthat dodo notnot havehave significantsignificant blockagesblockages oror clutterclutter contaminationscontaminations..

 TheThe radarradar reflectivityreflectivity climatologyclimatology isis defineddefined asas thethe frequencyfrequency ofof occurrenceoccurrence ofof reflectivityreflectivity (FOR)(FOR) thatthat isis higherhigher thanthan aa certaincertain threshold,threshold, andand itit isis calculatedcalculated onon aa pixelpixel--byby--pixelpixel basisbasis inin thethe radarradar (spherical)(spherical) coordinatescoordinates..

 TheThe valuesvalues ofof FORFOR rangerange fromfrom 00 toto 11,, withwith 11 representingrepresenting echoesechoes thatthat areare detecteddetected allall thethe timetime (clutters)(clutters) andand 00 indicatingindicating thatthat nono echoesechoes higherhigher thanthan thethe thresholdthreshold areare everever detecteddetected (blockages)(blockages)..

 TheThe reflectivityreflectivity climatologyclimatology atat anyany givengiven locationlocation isis relatedrelated toto whetherwhether therethere isis rainrain oror clutterclutter atat thethe locationlocation.. IfIf allall thethe echoesechoes detecteddetected atat thethe locationlocation areare ,rain, thenthen thethe expectedexpected rangerange ofof FORFOR valuesvalues shouldshould bebe closeclose toto thosethose ofof thethe frequencyfrequency ofof occurrenceoccurrence ofof gaugegauge rainfallrainfall (FOG)(FOG)

Chang, P. L., P. F. Lin, B. J. -D. Jou, and J. Zhang, 2009:An application of reflectivity climatology in constructing radar hybrid scans over complex terrains. J. Atmos. Oceanic Technol. 26, 1315-1327. Radar data quality controlcontrolRadar

Radar ScanScanRadar StrategyStrategy

 Terrain HeightHeightTerrain

 Ref. ClimatologyClimatologyRef.

Gauge RainfallRainfallGauge ClimatologyClimatology Frequency of occurrence (%) ofofFrequency ≧ 00--dBZdBZ reflectivity at 0.5 degrees elevationelevationreflectivity

RCWF RCHL

RCCG RCKT Frequency of occurrence (%) ofofFrequency ≧ 1010--dBZdBZ reflectivity at 2.4 degrees elevationelevationreflectivity

RCWF RCHL

RCCG RCKT Frequency of occurrence of reflectivityreflectivityFrequency at 0.5 degrees elevation for four seasonsseasonsat

Spring Summer

Fall Winter Gauge rainfall frequency ofofGauge occurrence during 20052005occurrence --20072007 spring summer

fall winter Hybrid scan tables determined from terrain,terrain,Hybrid scan strategy, and radar climatologyclimatologyscan MosaickedMosaicked Hybrid Height (four )radars)Hybrid

RCCKRCCK

RCMKRCMK

Severe blockage Frequency of occurrence (%) ofofFrequency reflectivitiesreflectivities ≥ 15 dBZdBZ with hybrid scan tables before and after QCQCwith summer summer before After (terrain only) (Terrain + Climo.

winter winter Summary of ReflectivitySummary Reflectivity and Gauge Rainfall ClimatologyClimatologyand

 ByBy comparingcomparing thethe reflectivity climatologyclimatology withwith gaugegauge observations,observations, itit waswas foundfound thatthat 1515 dBZdBZ waswas aa goodgood approximationapproximation forfor rain/norain/no--rainrain segregationsegregation inin coolcool seasonsseasons andand 2020 dBZdBZ workedworked wellwell inin warmwarm seasonsseasons..

 ComparisonsComparisons betweenbetween thethe standardstandard andand nonstandardnonstandard hybridhybrid scanscan FORsFORs showedshowed thatthat thethe formerformer diddid notnot accuratelyaccurately reflectreflect thethe clutterclutter andand blockageblockage distributionsdistributions inin thethe realreal atmosphereatmosphere..

 TheThe applicationapplication ofof thethe reflectivity climatologyclimatology waswas shownshown toto significantlysignificantly reducereduce thethe impactsimpacts ofof clutterclutter andand blockagesblockages andand providedprovided improvedimproved radarradar QPEsQPEs overover thethe complexcomplex terrainterrain.. RadarRadar ReflectivtyReflectivty QPEQPE

Localized Z (reflectivity)(reflectivity)Localized -- R (rain rate) relationshipR(rain relationship Hybrid reflectivity Hourly rain rate

1- and 3-h acc

6- to 72-h acc Rainfall information over the area without rain gaugegaugeRainfall Convective/Stratiform SegregationConvective/StratiformSegregation

 dBZdBZ > 50 in any bin or,or,>50

 dBZdBZ > 30 at temperatures <<>30 --10 C or,10Cor,

 1 lightning flashflash1lightning

non-tropical precipitation non-tropical precipitation

tropical precipitation tropical precipitation ZZ--R relationRrelation

Z= 10 log dBZ Z  D6 Z   N (D) D 6 dD  R  N(D) D3w(d)dD 3 6  t R  D

Z= ? R Depends on N(D) ! There are various Z-R relationships applicated over the world.

Z=200R1.6 Marshall and Palmer(1948) Z=140R1.5 drizzle Z=500R1.5 Z=300R1.4 NEXRAD雷達 ……… Z=32.5R1.65 QPESUMS ZZ--R relationshipsRrelationships

Precipitation a b Type convective 300.0 1.4

300.0 1.4

stratiform 200.0 1.6

tropical 32.5 1.65

75.0 2.0 Steps of Gauge Corrected Radar QPEQPESteps

 1) Computing gaugegauge1) --radar biases at each gauge stations usingusingradar hourly rainfalls from gauge observations and from radar estimateshourly rainfalls from gauge observations and from radar estimates at coatco--located grid cells.cells.located ~560

 2) Interpolating the gaugegauge2) --radarradar biases from gauge stations ontoontobiases the HRQ analysis grid.grid.the

 3) Applying the gridded gaugegauge3) --radar biasesbiasesradar to the radarradarto --based QPE.QPE.based

 4) Replacing the final LGC QPE at all grid cells thatthat4) coco--locate with a gauge station with the gauge observed values.locate with a gauge station with the gauge observed values.

 5) Applying a land mask to the LGC QPE field and cutting off the5) Applying a land mask to the LGC QPE field and cutting off the data over the ocean because no gauge correction is available indata over the ocean because no gauge correction is available in the ocean area.area.the corrected radar QPEQPERain

00--24 hrs QPE+gaugeQPE+gauge24hrs 00--24 hrs QPEQPE24hrs

0-24 hrs gauge obs Finer and more reasonable QPE over landlandFiner Difference between the local gaugegaugeDifference corrected radar QPE and a gauge analysisanalysiscorrected a b

Radar QPE GAUGE

c

LGC QPE LGC QPE - Gauge LGC QPE EvaluationEvaluationLGC  Select a different number of rain gauges for the calculation ofSelect a different number of rain gauges for the calculation of LGC QPE, the rest gauges are used for verifications.LGC verifications.

 Interpret the selected gauge rainfall to Cartesian grid.grid.Interpret

 Calculate the correlations between LGC QPE and rest gauges,Calculate the correlations between LGC QPE and rest gauges, as well as gauge rainfall in Cartesian.Cartesian.as   50 gauge 250 gauge stations selected stations selected

Total ~400 in 2005 Gauge Corrected QPE Southwest flow caseSouthwest case

50 gauge stations selected

Guage

250 gauge stations selected Gauge Corrected QPE TyphoonTyphoon HaitangHaitang (2005)(2005)

50 gauge stations selected

Guage

250 gaugeGauge stations Corrected selected QPE 2005 0612~061620050612~0616 –– 50 stations selectedselected50stations 2005 0612~061620050612~0616 –– 250 stations250stations selectedselected Southwest Flow/TyphoonFlow/TyphoonSouthwest HaitangHaitang casescases

Local Gauge Corrected QPE

Correlations Coefficient R (%)

Gauges Only (interpolated)

350 300 250 200 150 100

Number of Gauges used Comparisons between gaugegaugeComparisons and gauge corrected QPEQPEand

Gauge Gauge corrected QPE

+ + + + + + ++ + + + + +

＋:Gauge station

Typhoon Megi (2010/1018~22) 96 hours rainfall accumulation TyphoonTyphoon FanapiFanapi (2010/0918~21)(2010/0918~21) 72 hours rainfall accumulationaccumulation72

Gauge Gauge corrected QPE Summary of Gauge Corrected Radar QPEQPESummary

TheThe gaugegauge datadata improvedimproved thethe rainfallrainfall intensityintensity andand filledfilled inin somesome gapsgaps inin radarradar coveragecoverage..

GaugeGauge correctedcorrected QPEQPE providesprovides moremore reasonablereasonable rainfallrainfall amountamount betterbetter thanthan gauge,gauge, especiallyespecially forfor thethe areaarea withwith coarsecoarse gaugegauge spacingspacing..

AnAn appropriateappropriate integrationintegration ofof thethe radarradar QPEQPE andand rainrain gaugegauge observationobservation isis highlyhighly helpfulhelpful forfor thethe detectiondetection ofof extremeextreme rainfallrainfall amountamount andand forfor thethe monitoringmonitoring ofof rainfallrainfall patternspatterns generatedgenerated byby severesevere weatherweather systemssystems.. OutlookOutlook

 Continually improve the radar data QCQCContinually

 Improve the QPE quality using dualdualImprove -- polarization data.polarizationdata.

 Ingest new radars to improve thetheIngest coverage, especially in mountainous area.area.coverage,

 Cooperate with the adjacent countries totoCooperate extend the radar network.network.extend Operational Dual Polarized RadarsRadarsOperational

•Reflectivity •Doppler velocity RCCKRCCK c •Spectrum width •Differential phase RCMKRCMK •Specific differential phase •Differential reflectivity •Correlation coefficient Reflectivity

Differential phase Specific differential phase Differential reflectivity Correlation coefficient DualDual polarimetricpolarimetric radar algorithmsalgorithmsradar for rainfall estimation (Synthetic QPE)for QPE)

(Brandes et al. 2002; Chang et al. 2009) (Friedrich et al. 2007)

•R(Z,ZDR): Robust at different rain rates but sensitive to calibration error, attenuation, beam blockage, and Drop Size Distribution (DSD)

•R(KDP): Immune to calibration error, attenuation, DSD, and beam blockage but it is noisy at light rain and sensitive to Drop Shape Relation (DSR) PerformancePerformance EvaluationEvaluation 24 hours Accumulation TyphoonTyphoon24 morakotmorakot 0000 UTC ~ 2400 UTC 9 August 200920090000 4 S-band radars 4 S-band + 2 C-band radars

BIAS: 1.251.25BIAS: BIAS: 1.201.20BIAS: C.C.: 0.590.59C.C.: C.C.: 0.860.86C.C.: RMSE (mm): 151.64151.64RMSE RMSE (mm): 69.39RMSE 69.39 Ingest New Radars to Improve the CoverageCoverageIngest

Six radars

RCCKRCCK

RCMKRCMK Four radars Future RadarRadarFuture Network ??Network

CWB/FSL/NSSL Project ReviewCWB/FSL/NSSLProjectReview Thanks for youryourThanks AttentionAttention !!!!