Radar Interpretation Problems

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

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

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

15. Sources of Error - Radar Dome Wetting

16. 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

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

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

19. Melting layer signature:- Z

20. Melting layer signature:- ρHV Bright Band Ring

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

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

25. 0.3 Degree PPI 0.3 Degree PPI PPI and CAPPI 4.0 km CAPPI 1.5km CAPPI

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

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

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

31. Cross section to the southwest

32. 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?

33. 3.5 Degree Doppler Z PPI scan Echoes at higher altitude precede precipitation at low Levels – virga?

34. What the radar misses close in

36. 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.

37. June 16th 2008- 1900Z

38. June 16th 2008- 1900Z

39. 1 1 2 June 16th 2008- 1900Z 2

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

41. Echo Tops

42. Partial Beam Filling

43. 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

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

45. Partial Beam Filling

46. One storm 2 radars with different beamwidths

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