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Radar Interpretation Problems

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  1. Radar Interpretation Problems Reflectivity

  2. Acknowledgments • Phil Chadwick’s Radar Palette Course • MetEd courses- stole a few slides • Polarimetric presentation- staff at King City • Dave Patrick.. Radar and snow rates. • K-stream

  3. Outline Radar Interpretation Problems-Reflectivity • Attenuation • By Intervening Precipitation • Wet Radome • Radar Beam filled or not filled • Low topped precip • Drizzle • Virga • Bright Band • The sometimes invalid assumptions of the z-r relationship • Second Trip Echoes

  4. Radar Sources of Error Attenuation

  5. Attenuation: What lies beyond?

  6. Attenuation • The All time best Canadian Example

  7. Example of Attenuation in Precipitation Wedge of attenuation Foreground Storm

  8. Attenuation Warm Frontal Supercell

  9. Attenuation • north • end • of • derecho?

  10. Correcting Attenuation Polarimetric Radar

  11. Heavy Rain QPE (cont’d) Rain Accumulation (Z)

  12. Heavy Rain QPE (cont’d) Rain Accumulation (ZCORR)

  13. Sources of Error - Radar Dome Wetting

  14. Bright Band • Melting snowflakes are large bright radar targets • Reflectivity from melting snow is larger than that of the rain below or the snow above as falling snow passes through the melting layer • Huge impact on quantitative precipitation estimates

  15. Bright band shows up as ring (or partial ring) of high Z centred on the radar Bright band

  16. Melting of Snow Flakes starts at 2.5 km height Bright Band • Freezing Level ~2.5km AGL • Either associated with Rain or Freezing Rain

  17. Melting layer signature:- Z

  18. Melting layer signature:- ρHV Bright Band Ring

  19. Vertical Bright Band over WKR January 21st, 2006 0°C rain snow

  20. Radar Beam Overshooting What real weather the radar can miss

  21. 0.3 Degree PPI 0.3 Degree PPI PPI and CAPPI 4.0 km CAPPI 1.5km CAPPI

  22. Approximate current lowest beam location BALD North East South West North Approximate proposed lowest beam location LOALA North East South West North

  23. Radar Beam Undershooting Weather that’s not hitting the ground

  24. Sources of Error - Virga Typical of strong overrunning WCB with equally strong and dry CCB

  25. Cross section to the southwest

  26. Low-elevation angle Doppler Z PPI scan Let’s look at the same case observed by the Doppler scans Low level reflectivities to the west of the radar – rain?

  27. 3.5 Degree Doppler Z PPI scan Echoes at higher altitude precede precipitation at low Levels – virga?

  28. What the radar misses close in

  29. Algorithms that fail very close to Radar…Hail • As you approach the cone of silence the top part of the storm is above the highest scan angle of the radar. • Height of MAXR and VIL values are unrealistically low. • URP hail algorithm fails.

  30. June 16th 2008- 1900Z

  31. June 16th 2008- 1900Z

  32. 1 1 2 June 16th 2008- 1900Z 2

  33. Sources of Error - ECHO TOP - Beamwidth and Beamfilling

  34. Echo Tops

  35. Partial Beam Filling

  36. Radar beam widths and sensitivity • Not all radars are equal • In Canada • Many are retrofitted Enterprise radars with 1.1° beam width and 4 m dishes • Some (10) are Andrews radars with 0.65° beam width and 6 m dishes • Many have obvious issues • differences in sensitivity between each other • But many have less obvious, but significant problems that only become apparent with long-term precipitation accumulations

  37. At 240 km 3 km diameter Radar beam At 30 km 0.5 km diameter Radar beam Beam Spreading

  38. Partial Beam Filling

  39. One storm 2 radars with different beamwidths

  40. to a distant target... first pulse second pulse returning first pulse Second Trip Echoes