Application of DualPolarization Weather Doppler Radar

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Application of Dual-Polarization Weather Doppler
Radar

• Michihiro Teshiba
• SEC Rm 1458
• teshiba_at_ou.edu

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Objective of my study

• Examine the detailed structure of gust front by
  using a wind profiler
• Typical gust front
• Downdraft caused by evaporative cooling and
  precipitation drag
• Dense air (downdraft) spreads out along the
  ground
• A gust front causes at the leading edge of the
  outflow
• Problems are

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Cont. Objective

• Does a gust front have such a simple structure?
• Are simple arrows enough to explain the
  structure?
• Dont we know the detailed structure due to the
  insufficient data resolutions (observation
  simulation)?
• A wind profiler has good range and time
  resolutions rather than a weather Doppler radar
• To compare the data between a wind profiler and
  KOUN weather Doppler radar

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As an Introduction of my study

• Introduction of myself (within 1 min.)
• Introduction of dual-polarization weather Doppler
  radar
• Technical terms
• Meteorological terms
• Preliminary results about a cold front
• KOUN Doppler radar

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Introduce myself

• I had studied on meso-scale convective systems
  observed with a wind profiler
• Near a Baiu-Meiyu front (MC)
• Typhoon-Tropical Cyclone (BC, Ph.D)
• I have some licenses in Japan of
• Weather forecaster
• Driver licenses of track, bus, trailer (no
  limitation)
• I often played baseball and softball
• I love cats and fighting fish (betta) !

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What a Dual-pol Radar can examine?

• By parameters obtained by a dual-pol radar
• Size and shapes of hydrometeors
• Distributions of rain, hail, graupel, etc

• Distributions of rain rates and amounts
• Forecasting of lightning (in future)
• position, frequency, and strength

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Equilibrium shapes of rain particles
Bringi et al. (2003) How a rain particle in 5mm
diameter oscillate.

• To define rain shape
• Surface tension
• Hydrostatic pressure
• Aerodynamic pressure
• Internal circulation
• Electric stress
• If particles cant and orient, the radar-observed
  parameters are changed.

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Parameter of Dual-polarization Radar

• Reflectivity Z (Horizontal polarization)
• Doppler velocity v
• Spectrum width s
• Differential reflectivity Zdr
• Cross-correlation coefficient ?hv
• Differential phase fdp
• Specific differential propagation phase Kdp

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Observation with Dual-Pol Radar

• Simultaneous transmission and reception with
  horizontal and vertical polarizations
• Powers in the horizontal (Ph) and vertical (Pv)
• Differential reflectivity ZDR
• How hydrometeor (rain, hail, graupel, etc.)
  shapes in the horizontal and vertical axis

2mm sphere 2mm oblate spheroid
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Observation Parameters

• Copolar cross correlation function Rco
• Cross correlation coefficient ?hv
• (complex conjugate, mtime series)
• If em has large fluctuations, ?hv should be small.

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Observation Parameters

• Differential phase fdp
• Specific differential phase Kdp
• Canting angle and orientation of hydrometeors
• Electrical charged particles
• Kdp should be obtained by fdp as a slope of a
  least squares fit

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Parameter of KOUN Radar
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Map of Observation Sites
KOKC Upper-soundings
KTLX
KOUN
Purcell Wind Profiler
Sulphur Upper-soundings
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Animations of KOUN Imageries

• 12-19 UTC on May 27, 2005
• 0.5 deg. Elevation (every 1 min.)
• Reflectivity Zh (filtered many clutters)
• Doppler velocity v
• Differential Reflectivity Zdr
• Kdp

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Example of cold front
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Example of a cold front
May 27, 2005, 1721 UTC Positive away the
radar Negative toward the radar

• A cold front passed over the profiler site
• Strong Zh observed NE and SW of Purcell
• NE parameters except Zh are weak small rains
• SW all parameters are strongLarge rain
  particles
• Small difference of Doppler velocity across a
  front
• Large difference perpendicular to the beam
  direction

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Summary

• Dual-polarization Doppler radar can obtain
• Distribution of hydrometeors (density, shape,
  angle, and type)
• Distribution of rain rate and rain amount
• Roughly, movement of precipitating clouds and
  clear air disturbances

• Forecasting of thunderstorms, lightning, etc.

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If you want to study more

• Dual-polarization radar and rainfall estimation
• Bringi et al., 2003 JAS, 60, 354-365.
• Ryzhkov et al., 2002 JTECH, 19, 340-354.
• Ryzhkov et al., 2005 JAM, 44, 502-515.
• KOUN radar
• Brown et al., 2005 Wea. Forecast., 20, 3-14.
• JPOLE Web page http//cimms.ou.edu/schuur/jpole/
  
• Rain shapes
• Beard and Chuang, 1987 JAS, 44, 1509-1524.
• E-mail me! teshiba_at_ou.edu
• See web site http//kyodai.metr.ou.edu/teshiba/

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Large Reflectivity means

• Strong turbulances
• Large slopes of temperature and humidity
• (by the radar equation)
• Large echo is observed along a gust front

But

• The KOUN radar uses the frequency of S-band
• Large reflectivity if there are rain particles in
  the radar beam
• Observed Doppler velocity should be the sum of
  the movement of the air and rain particles