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

2. Meteorological Sensors
Two types of two types of sensors:
Remote vs. In-situ
Active vs. Passive
Our passive eyes can only see features of the storm
In order to see the inner workings of a thunderstorm, and to understand it better, we need an active remote sensor – weather radar
Radar will allow us to interrogate information about the storm by detecting precipitation and wind information within
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

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

4. 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
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

5. 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
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

6. ESAS 1115 Severe and Unusual Weather
Reflectivity
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 1mm6/m3
Doubling of power results in a linear increase of 3dBZ
Z is proportional to D6
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

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

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

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

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

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

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

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

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

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

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

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

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

19. ESAS 1115 Severe and Unusual Weather
Using the Zero Isodop
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?
00 = 100% - Parallel
150 = 97%
300 = 87%
450 = 71%
600 = 50%
750 = 26%
900 = 0% - Perpendicular
When the wind velocity is parallel to the radial, the full component of the wind is measured
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

20. 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
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

21. 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)
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

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

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

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

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

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

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

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

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

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

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

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

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

34. ESAS 1115 Severe and Unusual Weather
TVS
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

35. Azimuth Resolution Considerations
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 10 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 3
Weak inbound, weak outbound
Rotation too small to be resolved
Azimuth 2
Strong inbound, strong outbound
Azimuth 1
Stronger inbound than outbound
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

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

37. SRV vs. Base Velocity with Subtle Rotation
Storm 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.
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

38. 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
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

39. 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
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

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

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

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

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

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

45. 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
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

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

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

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

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

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