1. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 1 Radar Interpretation Problems Reflectivity

2. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 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. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 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 Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 4 Radar Sources of Error Attenuation

5. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 5 Attenuation: What lies beyond?

6. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Attenuation The All time best Canadian Example

7. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Foreground Storm Wedge of attenuation Example of Attenuation in Precipitation

8. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Attenuation Warm Frontal Supercell

9. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Attenuation north end of derecho?

10. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 10 Correcting Attenuation Polarimetric Radar

11. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 11

12. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 12

13. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 13 Heavy Rain QPE (cont’d) Rain Accumulation (Z)

14. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 14 Heavy Rain QPE (cont’d) Rain Accumulation (Z CORR )

15. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 15 Sources of Error - Radar Dome Wetting

16. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 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. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Bright band shows up as ring (or partial ring) of high Z centred on the radar Bright band

18. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Bright Band Freezing Level ~2.5km AGL Either associated with Rain or Freezing Rain Melting of Snow Flakes starts at 2.5 km height

19. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 19 Melting layer signature:- Z

20. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 20 Melting layer signature:- ρ HV Bright Band Ring

21. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 21

22. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 22 Vertical Bright Band over WKR January 21 st, 2006 rain snow 0°C0°C

23. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 23

24. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 24 Radar Beam Overshooting What real weather the radar can miss

25. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 25 PPI and CAPPI 1.5km CAPPI 4.0 km CAPPI 0.3 Degree PPI

26. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 26

27. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 27

28. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts North East South West North Approximate current lowest beam location BALD Approximate proposed lowest beam location LOALA

29. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 29 Radar Beam Undershooting Weather that’s not hitting the ground

30. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 30 Sources of Error - Virga Typical of strong overrunning WCB with equally strong and dry CCB

31. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 31 Cross section to the southwest

32. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 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. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 33 3.5 Degree Doppler Z PPI scan Echoes at higher altitude precede precipitation at low Levels – virga?

34. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 34 What the radar misses close in

35. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 35

36. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 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. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 37 June 16 th 2008- 1900Z

38. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 38 June 16 th 2008- 1900Z

39. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 39 June 16 th 2008- 1900Z 150.25/3.25161/5.75 Z51.1655.72 Zcorr49.5252.47 Zdr2.522.67 Zdrcorr2.170.53 Rhohv0.980.76 21 1 2

40. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 40 Sources of Error - ECHO TOP - Beamwidth and Beamfilling

41. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 41 Echo Tops

42. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 42 Partial Beam Filling

43. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 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. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 44 Beam Spreading At 240 km 3 km diameter Radar beam At 30 km 0.5 km diameter Radar beam

45. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 45 Partial Beam Filling

46. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 46 One storm 2 radars with different beamwidths

47. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 47

48. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 48

49. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 49

50. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Second Trip Echoes to a distant target... first pulse returning first pulse second pulse

51. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Second Trip Echo actual position of echo beyond range Echo within range mapped position of 2nd trip echo Pulse One Pulse Two

52. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Second Trip Echo Elongated Radial Weaker Far Away Randon Doppler Changing the PRF changes Location Check the Satellite

53. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 53 Purple Haze

54. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 54 Reflectivity…Rain Rates and Snow Rates Snow being depicted using the Rain Z-R Relationship Snow depicted using the Snow Z-S Relationship

55. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 55 Snow Reflectivity & Snowfall Rate Value of a depends on –whether the snow is dry or rimed –snowflake size distribution y-intercept constant Large N 0 => large number of small flakes compared to large –radar dark matter ?? Small N 0 => small number of small flakes compared to large –snowflake terminal velocity dense flakes fall twice as fast

56. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 56 Snow Reflectivity & Snowfall Rate For a typical range of values of N 0, and dry snow falling at 100 cm/s and wet snow falling at 200 cm/s –Here is a graph of Z vs. S in mm/h Dry airy snow falling slowly; 0.75 mm/h Rimed dense snow falling rapidly; 3 mm/h Factor of 4 difference in snow rate for same Z !!

57. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 57 Snow Reflectivity & Snowfall Rate Plot these empirical Z-S relationships on the theoretical graph … Z = 3300S 1.7 Spatial dendrites Z = 3300S 1.7 Z = 1780S 2.21 Standard Z = 1780S 2.21 Z = 400S 1.6 Plates & columns Z = 400S 1.6 Standard eq’n underestimates almost all high snow rate situations

58. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 58 Snow Reflectivity & Snowfall Rate

59. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 59

60. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 60 Another hypothesis Z DR vs Z scatter plots and observed precipitation (snow) Red squares –Radar estimate close Green –Radar estimate slightly underdone Purple triangles –Radar low by factor of 2-3.

61. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 61 Z and Rainrate

62. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 62 Reflectivity Z is empirically related to rain rate R in the form : Z = a R b In Canada we use Marshall-Palmer (stratiform rain) : Z = 200R 1.6 U.S. NEXRAD : Z = 300R 1.4 U.S. Tropical : Z = 250R 1.2 Empirical Z-R Equations

63. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 63 Z proportional to drop diameter to 6 th power. If more big drops than standard DSD radar overestimates rainfall –Attenuation often cancels this out. If more small drops Z underestimates rainfall.

64. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 64 Observed precipitation

65. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 65 Radar Accumulations

66. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 66 Conclusions Radar returns are not always what they seem. Before making conclusions think about –-How high the beam is above the ground –How wide is it where you are looking. –What other echoes did it have to go through to get to the storm you are interested in. –What are the chances the drop size (snowflake) distribution is different from the “standard” –Does the beam go through a melting layer –Could there be second trip echoes. Despite all the above radar does quite a remarkable job of detecting weather.

67. Radar Palet e Home Radar Artifacts Radar Palet e Home Radar Artifacts Analysis & Diagnosis 67 THE END