1. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Severe and Unusual Weather ESAS 1115 Severe and Unusual Weather ESAS 1115 Spotter Training and Radar Meteorology Part 2 – Introduction to Radar Meteorology

2. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Radio Detection and Ranging NEXRAD – Next Generation Radar WSR-88D – Weather Surveillance Radar, 1988 Doppler NEXRAD – Next Generation Radar WSR-88D – Weather Surveillance Radar, 1988 Doppler

3. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Important Angles  The azimuth angle is the compass angle from north (360°)  Targets are indicated by A/R (Azimuth/Range)  Birds eye view is displayed on a PPI (Planned Position Indicator)  A cross sectional display is an RHI (Range Height Indicator)  Volume scan

4. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Gate Size  Reflectivity Information is displayed in pixel- like units of area called “gates”  Gate size is determined by pulse length and angular beam width

5. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather ReflectivityReflectivity  dBm = 10log(power returned/1milliwatt)  Z is reflectivity  dBZ is a logarithmic scale similar to dBm  1dBZ is the power returned by a sphere of 1mm 6 /m 3  Doubling of power results in a linear increase of 3dBZ  Z is proportional to D 6

6. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Clear Air Mode Range from -28 to 28 dBZ 16 4dBz increments Range from -28 to 28 dBZ 16 4dBz increments

7. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Precipitation Mode Range from 5 to 75 dBZ 16 5dBz increments Range from 5 to 75 dBZ 16 5dBz increments

8. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather The Significance of Clear Air Mode During Snowfall

9. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather NIDS - Nexrad Information Dissemination Service Base Reflectivity – Various Elevation Angles

10. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather NIDS - Nexrad Information Dissemination Service Base (or Storm Relative) Velocity – Various Elevation Angles

11. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather NIDS - Nexrad Information Dissemination Service 1 Hour Precipitation

12. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather NIDS - Nexrad Information Dissemination Service Storm Total Precipitation

13. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather NIDS - Nexrad Information Dissemination Service VIL – Vertically Integrated Liquid

14. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather NIDS - Nexrad Information Dissemination Service Echo Tops

15. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather NIDS - Nexrad Information Dissemination Service VAD – Velocity Azimuth Display VWP – VAD Wind Profile

16. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather NIDS - Nexrad Information Dissemination Service Composite Reflectivity

17. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Interpreting Doppler Radar Radial Velocity is the velocity toward or away from a radar

18. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather When the wind velocity is parallel to the radial, the full component of the wind is measured When the radial is perpendicular to the the wind, the radar displays zero velocity - This “zero zone” is called the “Zero Isodop”. What percentage of actual wind will the radar detect? 0 0 = 100% - Parallel 15 0 = 97% 30 0 = 87% 45 0 = 71% 60 0 = 50% 75 0 = 26% 90 0 = 0% - Perpendicular Using the Zero Isodop

19. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Interpreting Doppler Radar  Winds will flow perpendicular to the zero isodop from green to red  Veering wind profile is denoted by an “S” on the overall winds display  Veering winds with height indicate warm air advection and hence rising air

20. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Interpreting Doppler Radar  Backing wind profile is denoted by a backwards “S” on the overall winds display  Backing winds with height indicate cold air advection and hence sinking air (subsidence)

21. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather What Does this Represent?

22. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Veering Winds on VWP Velocity Azimuth Display (VAD) Wind Profile

23. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Hurricane Katrina

24. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather DivergenceDivergence Divergence is indicated by radial shear (along the radius)

25. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather RotationRotation Cyclonic rotation is indicated by azimuthal shear (from one azimuth to another)

26. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Low-level Rotation and Storm Top Divergence

27. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Rotation or Convergence?

28. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Automated Detection of Meteorological Phenomena  Algorithms help detect significant features MDA – Mesocyclone Detection AlgorithmMDA – Mesocyclone Detection Algorithm Meso - “donut” Meso - “donut” Persistent, strong and detected over a large depth of the storm Persistent, strong and detected over a large depth of the storm TDA – Tornado Detection AlgorithmTDA – Tornado Detection Algorithm TVS – Tornado Vortex Signature TVS – Tornado Vortex Signature Strong gate to gate shear Strong gate to gate shear HDA – Hail Detection AlgorithmHDA – Hail Detection Algorithm  SCIT - Storm Cell Identification and Tracking

29. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Composite Reflectivity with Storm Attribute Table

30. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Composite Reflectivity with Symbols

31. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Gate to Gate Shear (TVS)

32. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather TVSTVS

33. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather TVSTVS

34. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Weak inbound, weak outbound Rotation too small to be resolved Stronger inbound than outbound Strong inbound, strong outbound Azimuth 3 Azimuth 2 Azimuth 1 Rotational couplet identification can be affected by azimuth resolution. As the diagram shows, the closer a rotation is to the radar the more likely it will be identified correctly. If the rotation is smaller than the 1 0 beam width (possible at long ranges) then the rotation will be diluted or averaged by all the velocities in that sample volume. This may cause the couplet to go unidentified until it gets closer to the radar. Azimuth Resolution Considerations

35. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Strong TVS

36. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather SRV vs. Base Velocity with Subtle Rotation Base VelocityStorm Relative When diagnosing straight line winds use base velocity. The strength of an advancing line of storms producing straight line winds is the sum of the winds produced by the storms, plus the movement of the storms. When diagnosing rotation, use storm relative velocity. SRV subtracts out the motion of a storm to display pure rotational characteristics of that storm.

37. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather FAR vs. POD  FAR (False Alarm Ratio) – An event is warned for but does not occur results in a false alarm  POD (Probability of Detection) – An event that occurs and has been warned for results in a 100% POD  A high POD is achieved at the expense of an increased FAR

38. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Doppler Dilemma  Radial velocity and range is limited by PRF  High PRF’s result in short unambiguous ranges and vice versa  Low PRF’s result in velocity aliasing and vice versa  Given a PRF, the radar can determine the radial velocity within some range, + or – some velocity, called the velocity interval  Any velocity beyond that range will “fold over” into the incorrect value  Bad data must be “dealiased”  The Doppler Dilemma: There is no single PRF that maximizes both Rmax and Vmax

39. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Velocity Aliasing and Dealiasing

40. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Three-Body Scatter Spike (TBSS)  The “flare” appears further than the main core along the same radial as the highest core  The added distance the beam makes from stone to ground to stone (3 bodies) results in a display further than reality

41. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather TBSS Examples

42. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Same Storm, Different Radar

43. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather TBSS in Velocity Data

44. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Anomalous Propagation (AP) In the wake of this line of thunderstorms, a low-level inversion created by the cold pool results in superrefraction and thus AP

45. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather AP and Ground Clutter Cooling in the evening hours results in a low-level nocturnal inversion and AP AP is enhanced by strong returns from buildings (ground clutter)

46. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Sunset Spike

47. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Sunset Spikes Sunset spikes

48. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Sunset Spike

49. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather What the Heck Is This?