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Dual-Polarization Radar Variables

Dual-Polarization Radar Variables . Differential Reflectivity ( Zdr ). Ratio of returned power in the horizontal to returned power in the vertical Can also be thought of as difference between horizontal reflectivity factor and vertical reflectivity factor

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Dual-Polarization Radar Variables

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  1. Dual-Polarization Radar Variables

  2. Differential Reflectivity (Zdr) • Ratio of returned power in the horizontal to returned power in the vertical • Can also be thought of as difference between horizontal reflectivity factor and vertical reflectivity factor • Meteorologists typically look at reflectivity factors (dBZ) • Allows for determination of particle shape • Spherical (drizzle or tumbling hail) or teardrop shape (rain) • Near zero Zdr spherical • Positive Zdr values  more teardrop shaped • Larger values with larger raindrops • Negative  vertically oriented ice crystals • Can locate thunderstorm updrafts • Zdr columns

  3. Differential Reflectivity (Zdr) • Use in concert with reflectivity (at least) • High reflectivity, near zero Zdr hail • Low reflectivity, near zero Zdr  drizzle or dry snow • High reflectivity, positive Zdr  rain

  4. Differential Reflectivity (Zdr) Hail Large rain drops Small rain drops and drizzle

  5. Differential Reflectivity (Zdr) • Zdr Column (location of updraft) • Higher positive values (rain) embedded in near zero values (dry snowor graupel)

  6. Correlation Coefficient (ρhv) • How similar the precipitation particles are in a given volume • Values near 1  all particles are similar • All rain or all snow in the volume • Values between .8 and .97  mixed precipitation, hail, wet snow • Values less than .8  birds, buildings, tornadic debris • Use in concert with reflectivity and other dual-pol variables

  7. Correlation Coefficient (ρhv) • Very useful for determining: • Winter precip, melting layers (bright banding) • Non-meteorological objects (i.e. bugs) • Large hail • Tornadic debris signature (TDS)

  8. Correlation Coefficient (ρhv) Melting layer/bright banding

  9. Correlation Coefficient (ρhv) Snow Mix Rain Clutter • Be careful when using operationally! • Only tells you precip type at height of radar beam

  10. Correlation Coefficient (ρhv) • Tornado Debris Signature • High reflectivity, low correlation coefficient, and velocity couplet

  11. Specific Differential Phase (KDP) • Differential phase • Difference between horizontal and vertical phase shifts • Depends on horizontal and vertical cross sections of precip particle • Positive for rain drops, near 0 for drizzle and hail • Specific differential phase is just the change in differential phase with distance • Useful for distinguishing between liquid (rain) and ice (hail, snow, etc.) • Good for rainfall estimation • Positive  rain drops • Near zero  ice particles • Negative  vertically oriented ice particles

  12. Specific Differential Phase (KDP)

  13. Specific Differential Phase (KDP) Heaviest rain

  14. What is the Precip Type? Reflectivity Differential Reflectivity (Zdr)

  15. What is the Precip Type? Reflectivity Correlation Coefficient (CC)

  16. What is the Precip Type? Reflectivity Zdr CC

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