A Brief Summary and the Important Conceptual Models
of Doppler Radar Analysis and Diagnosis
The Radar Mantra
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Look for something odd
Look UP… use the high elevation angle scans
Doppler measures backscattered power, mean radial velocity, spectral width
Rain Doppler spectral width is large 2-12 m/sec - grainy
Snow Doppler spectral width is small 1-2 m/sec - smooth
Errors in radial component increase with elevation angle and range
Max/Min/null Horizontal Wind Determination for uniform flows
Zero Isodop Horizontal Wind Determination for all flow patterns
Vertical discontinuities follow a range ring
Horizontal discontinuities do not follow a range ringe
Something that is difficult to find is probably not worth finding
Dynamic Features are Puzzle Pieces – only fit one way
Analyze and Diagnose the Real Atmosphere
Ground Truth the Numerical Atmosphere
Humans have a skill set that can improve on the Numerical Atmosphere
Have fun and continue to learn!
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Thermal Advection Intensity
The larger the angle subtended by the arc, the larger the wind shift and
stronger the thermal advections.
This wind shift/angle independent of range from radar
Thermal Advection Type – Relative to Radar Site
If isodop turns counter-clockwise with height (increasing range), arc
associated with cold advection… winds back with height.
If isodop turns clockwise with height (increasing range), arc associated
with warm advection… winds veer with height.
The VWS inflection at the limiting radial marks the range/height
separating backing and veering portions of the isodop.
The amount of wind shear is dependent only on the subtended angle and
not the orientation of the arc.
Thermal VWS is the angle subtended by the isodop divided by the
elevation change that this thermal advection occurred over.
Important Generalization for the orientation of the isodop:
For Stabilization isodop veers with height/range
Veering with Height = Warming with Height = Stabilization (Red = Stop)
Isodop veering relative to its starting orientation for stabilization
Important Generalization for the orientation of the isodop:
For Destabilization isodop backs with height/range
Backing with Height = Cooling with Height = Destabilization (Green = Go)
Isodop backing relative to its starting orientation for destabilization
SUMMARY
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Conventional Analysis and Diagnosis - Steps
Not so focused
Lots of possible interpretations for features both in space and height and
time
Must employ the conceptual models of the many artefacts and many
meteorological features
Situational awareness is critical for success
Process takes less than 5 minutes
Repeat as required
Add water and stir briskly…
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Think 3D
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Doppler Analysis and Diagnosis - Steps
Find the origin – home base
Follow one isodop branch out and up (depends on elevation angle)
Oddity = change in angle with respect to the range rings (second order
oddity) larger angle = larger significance/larger oddity
Oddity = inflection point marking change of direction (first order oddity)
Repeat for other isodop branch
Match oddities in height
Infer spatial slopes
Invoke conceptual models
Determine the four winds (max in, max out, two normal zero isodops)
Process takes less than 5 minutes
Situational Awareness
Repeat as required
Add water and stir briskly…
Think 3D!
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Use your Innate Human Skills
Pattern recognition skills
Animated real data
Conceptual Models (Satellite/Radar Palettes)
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What gets rewarded, gets done…
Important Note: The following analysis and diagnosis of anabatic and katabatic
fronts applies equally well to cold fronts.
Phil Chadwick
November 2008