Experience with a Network of Micro-Rain Radars

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13-14 th September 2007. RAINMAP: Oxford, UK. Experience with a Network of Micro-Rain Radars. Dr Chris Kidd Catherine Muller School of Geography, Earth and Environmental Sciences The University of Birmingham. Rain… why we're here. 13-14 th September 2007. RAINMAP: Oxford, UK.
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13-14th September 2007RAINMAP: Oxford, UKExperience with a Network of Micro-Rain RadarsDr Chris KiddCatherine MullerSchool of Geography, Earth and Environmental SciencesThe University of BirminghamRain… why we're here13-14th September 2007RAINMAP: Oxford, UKA few basic calculations1 mm of rainfall over 1 m2 = 1000000 mm31000000 mm3 = 1000 cm3 = 1 litre = 1 kg of water1 mm or rainfall over 1km2 = 1000000 kg or 1000 t 100 mm of rainfall – as in the July 20th event will produce 100,000 tonnes of water every 1 km2 over the Severn-Trent region, 2.16 billion tonnes of water!13-14th September 2007RAINMAP: Oxford, UKConventional measurementsThe physical measurement of rainfall is still the 'truth'
  • Standard gauge: still used and the 'standard'
  • Tipping bucket gauges (TBRs): fixed quantitative tip, limited by accuracy of tip (e.g. amount) and timing resolution (e.g. actual tips, 15 mins etc).
  • Tilting siphon: Graphical – difficult to automate & losses when siphoning.
  • All reasonable at measuring time-integrated rainfall, but not necessarily rain intensity.
  • Scanning radars okay, but suffer from range of calibration issues: DSD's, range effects, clutter etc.
  • But – how reliable are they?13-14th September 2007RAINMAP: Oxford, UKTBR data – 1 minute resolution13-14th September 2007RAINMAP: Oxford, UKComparison of 8 TBRs + 4 MRR13-14th September 2007RAINMAP: Oxford, UK13-14th September 2007RAINMAP: Oxford, UK13-14th September 2007RAINMAP: Oxford, UK13-14th September 2007RAINMAP: Oxford, UK13-14th September 2007RAINMAP: Oxford, UKMRR characteristicshigh sensitivity to light rainfall10-200 m typically, with 31range gates: 310-6200 musually integrated over 1 minup to ~12 ms-1Doppler – measures frequency of backscatter13-14th September 2007RAINMAP: Oxford, UKThe Micro Rain RadarSmall backscatterTransmit signalReceive signal13-14th September 2007RAINMAP: Oxford, UKBackground:Rain dropletFrequency13-14th September 2007RAINMAP: Oxford, UKRain dropletsLarger backscatterTransmit signalReceive signalFrequency13-14th September 2007RAINMAP: Oxford, UKFalling rain dropletsLarger backscatterTransmit signalReceive signalFrequency13-14th September 2007RAINMAP: Oxford, UKMixed-sized falling rain dropletsLarger backscatterTransmit signalReceive signalFrequencysmall drops=slower=less shiftlarge drops=faster=more shift13-14th September 2007RAINMAP: Oxford, UKMixed-sized falling rain dropletsLarger backscatterTransmit signalReceive signalFrequencyin reality a "continuous"spectrum of return signals13-14th September 2007RAINMAP: Oxford, UKWhat information do you get?
  • Reflectivity
  • Rain intensity
  • Fall velocity
  • Liquid water content
  • Drop size distribution (in 64 steps)
  • …for each of the 31 range gates13-14th September 2007RAINMAP: Oxford, UKBirmingham facilityCalibration phase:
  • 4 micro rain radars
  • 8 calibration gauges (2/radar)
  • 1 active rain sampler
  • 2 passive rain samplers
  • 13-14th September 2007RAINMAP: Oxford, UK5th October 2006: Warm front13-14th September 2007RAINMAP: Oxford, UKMRR time-series 07-10 February 200713-14th September 2007RAINMAP: Oxford, UKComparison of reflectivitiesGood rain/no-rain agreement; reasonable reflectivity13-14th September 2007RAINMAP: Oxford, UKComparison of rainratesGood rain/no-rain agreement; reasonable intensities13-14th September 2007RAINMAP: Oxford, UKComparison of rainratesGood rain/no-rain agreement; reasonable intensities13-14th September 2007RAINMAP: Oxford, UKScatterplots: reflectivities & rainratesReflectivity5th October 2006RainratesLow-end reflectivity scatter: high-end rain-rate scatter13-14th September 2007RAINMAP: Oxford, UKRainfall occurrence (Bham)Light rainfall is dominant – although rain-rates -> 150mmh-1< 1 mmh-11 minute rain rates derived from Doppler radar (10 months data)13-14th September 2007RAINMAP: Oxford, UKRainfall occurrence1 minute rain rates derived from 4 Doppler radars (4x10 months data)13-14th September 2007RAINMAP: Oxford, UKRainfall accumulation1 minute rain rates derived from 4 Doppler radars (4x10 months data)13-14th September 2007RAINMAP: Oxford, UKMRR derived storm height12957> 3km30613rain eventsmmh-130% of events have storm heights < 1km; 50% <1.8km; 70% < 3km13-14th September 2007RAINMAP: Oxford, UKCurrent deployment4 MRRs deployed in and around Birmingham:
  • Urban site: University of Birmingham: Edgbaston
  • Downwind site: Tamworth
  • Upwind (SW) site: Droitwich Spa
  • Upwind (W) site: Wombourne
  • Purpose: to measure changes in precipitation characteristics over an urban area: does DSD distribution vary – anthropogenic aerosols?Chemical composition of rainwater13-14th September 2007RAINMAP: Oxford, UKBirmingham MRRsTamworthWombourneUniversity10 kmDroitwichprevailingwind13-14th September 2007RAINMAP: Oxford, UKTypical MRR setupDroitwich: Back garden (!) – connected to mini-ITX based PC (1.2GHz, 1Gb RAM, 40Gb HD, WinXP)13-14th September 2007RAINMAP: Oxford, UKAnalysis of June 2007 stormsUK Met.Office Nimrod radar composite20 July 2007Clee Hill radar (2km, 200x200km)13-14th September 2007RAINMAP: Oxford, UKRegional rainfall totalsRadar suggest bulk of rain west of M5, over Herefordshire13-14th September 2007RAINMAP: Oxford, UKEA TBR gauge measurements13-14th September 2007RAINMAP: Oxford, UKReflectivity: 20th July 2007TamworthxBirminghamxxDroitwich2km Clee Hill13-14th September 2007RAINMAP: Oxford, UKFall velocity: 20th July 2007TamworthxBirminghamxxDroitwich2km Clee Hill13-14th September 2007RAINMAP: Oxford, UK1 minute MRR vs GaugeDemonstrates the problems associated with tip measurements (can be worked around)Scale: mm/min13-14th September 2007RAINMAP: Oxford, UK5 minute MRR vs GaugeAgain, demonstrates the problems associated with tip measurements (can be worked around)Scale: mm/5-min13-14th September 2007RAINMAP: Oxford, UK15 minute MRR vs GaugeReasonable agreement overallScale: mm/15-minFor July:Gauge – 179mmMRR level 1 – 161mmMRR level 2 – 149mm13-14th September 2007RAINMAP: Oxford, UKRainfall accumulationGauge-corrected MRRDifferences between accumulations over time to be investigated13-14th September 2007RAINMAP: Oxford, UKOverall conclusions
  • MRR's provide an additional means of observing and measurement rainfall
  • Useful for extraction of other parameters, e.g. DSD
  • Measurements over a number of levels – providing profiles of hydrometeors
  • Can measure frozen precipitation (i.e. hail, snow) where gauges might have difficulty
  • However
  • Generally, they tend to underestimate rainfall with respect to gauge
  • They do not replace conventional gauges.
  • 13-14th September 2007RAINMAP: Oxford, UKFuture ideas
  • GPM – 2013+
  • Global constellation of passive microwave sensorsGV element: organisation and co-ordination of sensors and observations (radar, gauges, observations, aircraft etc)Improved observation, monitoring and measurement of global precipitationGreater understanding of precipitation processes:occurrence, accumulation etc;measurement accuracy;anthropogenic influences;climate change
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