QPE/QPF of JMA

Application of Radar Data

Masashi KUNITSUGUHead, National Typhoon Center Japan Meteorological Agency

TYPHOON COMMITTEE Integrated Workshop on Urban Flood Risk Management in a Changing Climate: Sustainable and Adaptation Challenges Macao, China 06-10 September 2010

Purpose of QPE/QPFlocal meteorological office, local government , mass media, weather companiesJMAWeather Information Products of QPE/QPFHigh resolution data (spatial, time, intensity)Observation data

Products of QPE/QPF of JMA*Composite of echo intensity (every 30 min) *Composite of echo top height (every 30 min) * Radar/Raingauge-Analyzed Precipitation (every 30 min) *Very-Short-Range-Forecast(VSRF) of precipitation (every 30 min)

Application *Analyzed 10-min precipitation (every 5 min) *Precipitation Nowcasts (every 10 min) * Soil Water Index * Runoff Index

Digitalized radar(automatic rejection of ground clutter)Raingaugenetwork Communication network with rapid transmissionHigh performance computer NWP model with high resolutionTechnical base of QPE/QPF

Precipitation observation equipmentRaingaugesRadar

RaingaugesRadar AdvantagesCan measure actual amounts of precipitation.Can observe large areas with higher spatial resolution than the raingauge network.Dis-advantagesCan observe precipitation at single points only.May produce readings different from precipitation observed on the ground, as it measures the amount of rain overhead.

Calibrate radar estimate with raingauge dataprecipitationRaingauge dataRadar estimateRadar/Raingauge-Analyzed Precipitation

Analyzed precipitationCalibration factorCalibrated radar estimate with raingauge data are more accurateprecipitationRaingauge data Radar estimateRadar/Raingauge-Analyzed Precipitation

Qualification of radar data*remove false echo like ground clutterprocess Calibration over the entire radar detection range Calibration over land*modification of calibration factorComposition *using maximum value method *replace with raingauge dataRadar/Raingauge-Analyzed precipitationRadar/Raingauge-Analyzed Precipitation

Conditions in calibration1calibration factor is a function of beam height and is calculated for each radar every time2analyzed precipitation estimates of each radar in the area where multiple radars overlap should be equal3 analyzed precipitation estimates should be equal to the raingauge precipitationCalibration over the entire radar detection range

Calibration over the entire radar detection range (1)F1(x,y)= Fa(x,y)1+Fx(x,y)H(x,y)2E1(x,y)=F1(x,y)E0(x,y)calculation of Fx

Calibration over the entire radar detection range (2)calculation of FaF1(x,y)= Fa(x,y)1+Fx(x,y)H(x,y)2E1(x,y)=F1(x,y)E0(x,y)

modify calibrated estimates on raingauge gridsR(i) = C2(i)E1(i)R(i) raingauge precip.E1(i) calibrated estimatesC2(i) factor to modify estimatesraingauge gridfor all the raingauge grids of the radarCalibration over land (modification)

Determine factors of all grids over landInterpolate factors of raingauge grids to a target grid with weights. weightW1 (i) for distanceW2 (i) for rain intensity and beam attenuationW(i)=W1(i)W2(i) factor of a target grid W(i)C2(i)i : raingauge numbertarget gridCalibration over land (modification)

raingauge precipitation1-hour radar precipitationRadar/Raingauge-Analyzed Precipitation

Calibrated precipitationRadar precipitationRadar/Raingauge-Analyzed Precipitation

Radar/Raingauge-Analyzed PrecipitationComposite calibrated radar data

Extrapolation of precipitation with orographic effect(EX6)processMerge EX6 and MSM(MRG)VSRF of precipitationup to 6 hours, spatial resolution 1km Flowchart of VSRF

Extrapolation methodEX6Extrapolation method is effective up to ~ 3 forecast hoursbefore 1 hournow after 1 hour extrapolationMove it with the same speed and the same direction as it moved.Non-linear extrapolation was introduced in 2006.

Outputs of Numerical Weather PredictionData used for making VSRF*MSM(mesoscale model) operation:8 times a day*wind700900hPa *temperature(900hPa)*relative humidity(900hPa) *precipitation(surface) Topography data

Precipitation enhanced by orographic effectEstimate precipitation due to updraft along a mountainseeder-feeder model BrowningandHill1981MSM(900hPatemperature, windAnalyzed precipitationStationary part of precipitation over mountains caused by *cold air outbreak across the sea *low pressure

Enhancement and dissipation of precipitation by orographic effect

Enhancement and dissipation of precipitation by orographic effect(1) EnhancementPrecipitable amount by orographic effectWithout orographic effectWith orographic effectDifference caused by orographic effect

Without orographic effectWith orographic effectDifference caused by orographic effectEnhancement and dissipation of precipitation by orographic effect(2) Dissipation

MRGCompare the accuracy of EX6/MSM using pattern distanceMerging ratio considering timeMerge every 10 minute up to 6 hours Merging methodMerging ratio considering spaceIncrease the ratio of MSM as forecast time goes

Calculate the reliability r of MSM indicate the merging ratioMRGCompare the accuracy of EX6/MSM using pattern distanceCalculate the merging ratio R(t) using reliability r and weight function C(t)Merge every 10 minute up to 6 hours Merging method

RAMSMEX6Radar/raingauge precipitaion analysis at initial timeupper leftEX6 FT=3 of the initial time 3 hours beforelower rightlatest MSMlower leftcalculate the reliability of MSM comparing the similarity

ratio of merge considering timeratio of EX6 at forecast time

the larger the r of MSM, the smaller the ratio of EX6red line : lower limit of the ratio of EX6 : C(t)Ratio of MSM = r {1 C(t)}reliability of MSMreliability of MSM0.5FT

Examples of VSRF(Merging method)Top left R-A, top right MSM, bottom left EX6, and bottom right MRG at 11JST 31 May 2000 (6-hour forecast). MRG could predict the extending western rain systems.Same as the left figure, at 15JST 31 May 2000(6-hour forecast). MRG could predict isolated convective rain systems.

initial = 0730JST 06 June 2004 Disseminate within 3 minutes of observation timePrevious calibration factors (10 min before) are used.Use the movement derived by VSRFOnly dissipation by orographic effect is introduced.10minutes rainfallPrecipitation Nowcastsres.=1km, forecast every 10minForecast 10 minute precipitation amount up to 60 minutes every 10 minute with extrapolation method

Thank you for your attention!

The basic types of equipment for observing precipitation are raingauges and radar. An advantage of raingauges is that they measure actual amounts of precipitation, while a disadvantage is that they can observe precipitation only at single points. An advantage of radar is that it observes large areas at a higher spatial resolution than the raingauge network, and a disadvantage is that it may produce readings different from those of rainfall observed on the ground because radar does not measure the amount of rainfall directly.

**I will show you some of its algorithm.The calibration factor F1 consists of 2 part, Fa and Fx. At the beginning, we calculate the Beam height H related factor Fx. In the common detection region, radar precipitations E0a and E0b should coincides. Usually they do not. Fx is a factor to make the ratio of them to be constant. At this stage, we require only/ ratio to be constant. Iterating these processes 3 times, ratio of them gradually converges. For Fa, we use a statistical value as a first guess.*Next step is a determination of Fa. At the former stage, the ratio of adjacent radar precipitations became nearly constant. At this step, we use raingauge data distribution(doted line in green) and determine the calibration factor Fa for each radar site.

After this calculation, we proceed to modification stage of these calibration factors on the land/ using raingauge data and some interpolation schemes.

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