Doppler Radar

Analysis & Diagnosis 1Radar Palette Home Doppler

Doppler Radar

• The Doppler Effect• The Doppler Dilemma• Etc – other topics• Doppler Analysis and Diagnosis (Important New

and Original Material linked to slide 80)


The Doppler effect

• Classically, the Doppler effect is a frequency shift • The change in frequency of a signal returned from a target owing to

its radial motion relative to an observer• With radar, this is measured as a shift in phase between the

transmitted pulse and the backscattered microwave radiation• Average radial velocity of the target is calculated from this phase

shift


The Radar Waveform


Velocity Spectrum

-VN 0 +VN

GC

WX

Stationary

WXMoves


Phase Shift Ambiguity

A shift of ¼ wavelength is ambiguous.

You don’t know if your are coming or going?


Velocity folding – Phase Shift Ambiguity

• Target radial velocities producing phase shifts greater than one-half wavelength (or p radians) results in velocity folding

• Maximum unambiguous radial velocity Vmax (Nyquist velocity) =

• (PRF X Wavelength) / 4• This range is not adequate to describe all

horizontal velocities

Nyquist velocity=1200 X 5cm/4 = 1500cm/sec=15m/s=30knotsIs a Nyquist velocity of 30knots enough?


The velocities with this storm are HUGE !!!!

Quick, increase the PRF and give me a sector scan on the storm cell !

Vmax (Nyquist velocity) =

(PRF X Wavelength) / 4

By increasing the PRF, velocity foldng starts at a higher radial velocity


Before Helen’s DemandAfter PRF increased

Folded Doppler quickly reaches the maximum colour range and cycles to opposite colours = noisy, complicated fields Interpretation is challenging!

?

?

Helen was right!


Doppler Dilemma

• Maximum unambiguous range: • Rmax = c / 2PRF

• What is this for PRF = 1200 ?

• VmaxRmax = c/8

• Vmax and Rmax are inversely proportional to each other, but we want to maximize both

• That’s the Doppler dilemma

125 km


How can we increase Vmax ?


Velocity Unfolding

• Use two PRF’s and take the difference in the Doppler velocities !

• The difference turns out to be a unique function of the actual velocity out to much higher velocities!!

• So V and one of the velocity measurements can be used to unambiguously calculate the actual radial velocity, perhaps up to 48 m/s (almost 100 knots).


Whoa. Now that’s fast!!


Dual PRF Unfolding


Now we can see the whole storm, Bill !

That’s great, Jo. Now if only Dorothy and pigs would fly !


Example: Radial Velocity Product with Vr to 48 m/s

SELY low level winds

WLY upper level windsKatabatic

ColdFront?

N-S WarmFront?


Doppler Patterns


Doppler wind interpretation

You can determine wind direction vs. height away from radar in two different directions

• Go out along zero line

• Draw line back to radar

• Wind is perpendicular to this line, towards the red echoes


Doppler wind interpretation

For any height you can attempt to determine the wind in 4 locations

• Determine the two zero line winds

• Look roughly 90° away for the max wind, which should be all directed along a radial

In this way you can see areas of non-uniform flow

• confluence, diffluence


Doppler Uniform30 m/s wind everywhere


Doppler Display - Uniform Wind Shear

Vertical Wind Shear of 13 knots per kilometre = Speed Shear only


Doppler with Directional Shear and Jet

20

20

Directional Shear and Wind Maximum


Doppler with Wind Shear - Speed and Directional

Direction veering with heightDirection veering with height

Speed increasing with heightSpeed increasing with height


The Doppler Vortex


Doppler Practice

Westerly Winds with only Speed shear


Doppler Practice

Westerly Winds with Low Level Jet


Doppler Practice

Veering Winds with no Speed shear


Doppler Practice

Backing Winds with no Speed shear


Doppler Practice

Low Level Veering under High Level Backing Winds - no Speed shear

Changes in Stability?


Doppler Practice

Wind shift line


Doppler Practice

Large Scale Convergence


Doppler Practice

Divergence

Radar

Site


Doppler Practice

Cyclonic Vortex

Radar

Site


Doppler Practice

NNELY

SWLY

LLJ

QS Horizontal LLJ

Marginal winds Backing with Height - Cold Air AdvectionMaybe a Cold Conveyor Belt ahead of a synoptic system…


Doppler Displays


Velocity Azimuth Display - VAD

• Doppler radial velocity data used to construct a wind profile in the vertical

• Direction, speed (m/s) and reflectivity (dBZ) displayed as a function of height (km)

• Note: Velocity scale is fixed in range 0-20 m/s ( i.e. most of the unfolded velocities are not used )


Velocity Azimuth Display - VAD• At a given height (h), then the radial velocity is: • For a uniform flow field and assume Vw (Vertical Velocity) approximately = 0

then• Best fit of a sine curve to the observations around the circle.


Velocity Azimuth Display - VAD• Accuracy of VAD decreases

with elevation angle and height. The desired horizontal wind component becomes a smaller part of the radial wind component actually measure.

• Errors in the radial component has a bigger impact on the accuracy of the horizontal wind


VAD Example


A new Velocity Azimuth Display

LOLAA sees winds far from radar

3.5° scan sees winds closer in to radar – behaves most like a “profiler”


Doppler Spectra Width

• Spread of the Doppler Power Spectrum

• the spread, range of terminal fall speeds of the scatterers (more pronounced for rain than for snow) spectra for rain spectra for snow

• turbulence of the air (upper levels in severe convection)

• vertical wind shear (e.g., along a gust front)

• antenna motion

Rain

Snow


Doppler Image Characteristics

Small Spectral Width

Large Spectral Width


Spectral Width and “Doppler Display Texture”

RainTexture

SnowTexture


The Doppler Precipitation Spectral Width

Doppler Precipitation Texture

Example


The Doppler Twist Signature - Example

•The white dashed line separates different wind regimes in the vertical.

•It also separates regimes of differing Doppler texture.

•Above the dashed line the Doppler texture is uniform and characteristic of snow.

•Below the dashed line the texture is lumpy like oatmeal and characteristic of rain.

•This is also an example of the Virga Hole Signature

The dashed line is likely the warm front. The layer immediately below is where the snow is melting into rain.


Filtering using Doppler and Processing


Second Trip Echo – Extending the Range of the Doppler Scan

Random Phase Processing extends the Doppler Range

Dual PRF’s extends the Nyquist Velocity


Second Trip Echoes


Second Trip Echo

The velocity signatures of second trip echoes are very noisy.These still contribute to the reflectivity signal where they should not.


Second Trip Processing


Second Trip Processing

Conventional CAPPI

Doppler ReflectivityDoppler Reflectivity with

Second Trip Echoes

Doppler Reflectivity with

Processed Second Trip Echoes


Long Range Z


Long Range Radial Velocity


Doppler Wind Shifts

A

B

The angle of viewing is very important and determines whatone sees!


Operational Applications


Doppler Wind Shift


Doppler Wind Shift 30 minutes later

Cold Front


• Reflectivity Z is empirically related to rain rate R in the form :

Z = aRb

• In Canada we use Marshall-Palmer (stratiform rain) :

Z = 200RZ = 200R1.61.6

• U.S. NEXRAD :

Z = 300RZ = 300R1.4 1.4

• For snow we use :

Z = 1780SZ = 1780S2.212.21

Rain rate vs. Snow rate

But these are not valid in all situations


Rain Rate vs Snow RateSnow being depicted using the Rain Z-R

RelationshipSnow depicted using the Snow Z-R Relationship

Normal CAPPI height is 1.5 km - precipitation intensities are given in a mm/hr scale

Cold season (snow expected) CAPPI height is lowered to 1.0 km better look at low level features that are significant in winter storms and may be missed at 1.5 km

Normal CAPPI height is 1.5 km - precipitation intensities are given in a mm/hr scale

Cold season (snow expected) CAPPI height is lowered to 1.0 km better look at low level features that are significant in winter storms and may be missed at 1.5 km


Bird Migration and Radar


Radar Detection of a Lake Breeze


“Clear” Air Radar Returns


“Clear” Air Radar Returns and Lake Breeze


“Clear” Air Thunderstorm Outflow Gust


Severe Weather Signatures on Radar


The spikes signature is associated with hail or heavy rain. It results from the radar beam being reflected from the hail or rain in the thunderstorm, then reflecting from the surface then back to the thunderstorm and then back to the radar… a longer path...

Radar Observation of Hail

or

Very Heavy Precipitation


”Hail spikes" from the

Carvel Radar near Edmonton

Radar Palette Home Doppler

Hail Spikes & Side Lobe

MAXR Echo Top


Hail Hazards Map


0.5 Doppler Velocity 1.5 Doppler Velocity

3.5 Doppler Velocity

1.3km 4km

11kmRotating Downbursts on Descent

Cyclonic rotationCyclonic rotationCyclonic rotationCyclonic rotation


A December Squall Line with Rear Inflow Jet


Severe Thunderstorm Processes


Mesocyclone on Reflectivity Display0.5 Degree PPI Reflectivity Display

0.5 Degree PPI Doppler Velocity

3.5 Degree PPI Doppler Velocity

3.5 Degree Doppler Close-up View


0.5 and 3.5 Degree PPI Doppler


Doppler Analysis and Diagnosis Strategies

An operational guide to getting the most information from Doppler radar:

• Determining the actual wind direction• Determining wind backing and veering• Diagnosing spatial versus vertical wind

variations• The Screaming Eagle and Bird Patterns


Diagnosis of the Conveyor Belts

• Wind direction and speed diagnosis should be completed independently in each conveyor belt

• Given the nature of isentropic flow, this is a prudent mode of diagnosis. Isentropic flows stay relatively separate and maintain their distinctive properties.

• The Doppler characteristics depicted in the CCB are separate from those in the WCB. When added, instructive patterns are revealed.


Range Ring versus Radial Zero Velocity Doppler Lines

A

B

C

Range Ring Zero Lines

•A is the radar site•Zero Doppler Velocity line that follows a range ring like BC depicts velocity vectors that are:

•All at the same elevation•Depictions of horizontal wind differences – primarily directional wind shear

•Range Ring Zero Lines thus depict spatial wind difference (primarily directional shear)

A B C

Radial Zero Lines

•A is the radar site•Zero Doppler Velocity line that follows a radial from the radar like BC depicts velocity vectors that are:

•At ever increasing heights•Depictions of vertical speed shear wind differences (no directional shear)

•Radial Zero Lines thus depict vertical wind difference/shear

The real Doppler data is a combination of these two patterns


Diagnosis of Wind Direction – Using the Zero Line

A

•A is the radar site•BC the zero line•Everywhere along the zero line the radial component of the real wind detected by Doppler must be zero – meaning the total wind must be perpendicular to the radar radial – or actually zero which is unlikely.

B

C

•Draw a radial line from the radar site to the zero line

•The wind must be either zero or the wind direction must be exactly perpendicular to the radial line

•The wind direction can be determined as blowing from the toward colours (blue) to the away colours (red) perpendicular to the radial

•Click now

Zero Line

In Doppler wind analysis always establish the layers where the zero line veers (turns clockwise with range/height) and layers where the zero line backs (turns counterclockwise with range/height. These are the thermal advection layers. The point of inflection between backing and veering separates these important analytical layers.


Diagnosis of Vertical Windshear – Using the Zero line

AB

C

D

•Determine the wind at B. Draw a radial line from the radar site to the zero line at B. Click

•Determine the wind at C. Click

•The wind backs from B to C

•Determine the wind at D. Click

•The wind veers from C to D

Summary - Generalizations

Thermal Advection Intensity•The larger the angle subtended by the arc, the stronger the thermal advections.•The smaller the angle subtended by the arc, the weaker the advections.•This angle is independent of range from the radarThermal Advection Type•If the arc rotates cyclonically with height (increasing range) the arc is associated with warm advection.•If the arc rotates anticyclonically with height, the arc is associated with cold advection.

Note that the directional wind shear increases with the angle subtended by the arc – This angle does not change with range from the radar (directional shear).The angle subtended by the zero line arc is the directional wind shear component of the velocity vector shear.


Diagnosis of Vertical Windshear – Using the Zero line

AB

C

D

The angle subtended by the counter-clockwise arc BC would be the same regardless of the exact location of C anywhere along the radial AC from the Doppler radar. The amount of backing with height is also independent of the location of C along the radial AC. The amount of wind shear (cold advection) is dependent only on the subtended angle and not the orientation of the arc.

AB

C

D

The angle subtended by the clockwise arc CD would be the same regardless of the exact location of D anywhere along the radial AD from the Doppler radar. The amount of veering with height is also independent of the location of D along the radial AD. The amount of wind shear (warm advection) is dependent only on the subtended angle and not the orientation of the arc. The thermal VWS is thus the angle subtended by the arc divided by the elevation change that this thermal advection occurred over. The following slide illustrates these concepts.


Thermal Advections and Vertical Wind Shear

AB

C

AB

C

AB

C

•The angle subtended by the counter-clockwise arc BC is identical in 1, 2 and 3.•In 1, the backing winds occur over a short radial range and thus a short height interval.•The radial range difference increases for case 2 and is even more for case 3. The height interval for the Thermal VWS increases with the length of the radial AC from case 1 to case 3.•The Thermal VWS determined by dividing the direction shear (subtended angle dependent) by the height interval (difference between AC and AB=AD) that it occurs over, is strongest for 1 and weakest for 3. •As detailed, Thermal VWS is a combination of the size of the subtended angle and the radial range (AC-AB=AD) which when combined, is inversely proportional to the area CBD. •This could feasibly be automatically calculated in URP. I sincerely doubt if it is.

1.

2.

3.

D

D

D


Thermal Advections and Vertical Wind Shear

•Which has the strongest Thermal VWS?•The smaller the area CBD, the more intense the Thermal VWS and thus the more intense the thermal advections.

AB

C

1.

D

AB

C

2.

D

AB

C

3.

D

For a given subtended angle:•the strongest Thermal VWS occurs with a Doppler Zero Line closely following the range rings•the weakest Thermal VWS occurs with a Doppler Zero Line closely following the radar radial lines

Similarly for a given height interval CD radial:•the strongest Thermal VWS occurs with the largest subtended angle•the weakest Thermal VWS occurs with the smallest subtended angle


Diagnosis of Stability Trends

• Stability increases with:• Cold advection decreasing with height:

– Angle of Doppler arc backing counterclockwise decreasing (rate of cooling decreases) with height (range) increasing (Area CBD increasing),

• Warm advection increasing with height:– Angle of Doppler arc veering clockwise increasing

(rate of warming increases) with height (range) decreasing (Area CBD decreasing),

• Warm advection over cold advection:– Doppler arc veering clockwise with height (range)

over Doppler arc backing counterclockwise with height (range).


Doppler Examples for Increasing Stability

AB

C1.

D

Stronger cold advection BCLevel C

Weaker cold advection CDStabilization

Level D

Level B

A

B C

2. D

Weaker warm advection BCLevel C

Stronger warm advection CDStabilization

Level D

Level B

AB

C

3. D

(Weak) Cold advection BCLevel C

(Strong) Warm advection CDStabilization

Level D

Level B

Note: Angles kept constant.Changing the Thermal Advection Intensity by changing the depth of the directional wind shear.


Diagnosis of Stability Trends

• Stability decreases (Destabilization) with:• Cold advection increasing with height:

– Angle of Doppler arc backing counterclockwise decreasing (rate of cooling increases) with height (range)

• Warm advection decreasing with height:– Doppler arc veering clockwise with height (range)

under Doppler arc backing counterclockwise with height (range).

– Angle of of Doppler zero arc veering clockwise increasing (rate of warming decreases) with height (range),

• Warm advection under cold advection:


Doppler Examples for Increasing Instability

AB

C2.

D

Stronger warm advection BCLevel C

Weaker warm advection BCDestabilization

Level D

Level B

A

B C

3.

D

(Strong) Warm advection BCLevel C

(Weak) Cold advection CDDestabilization

Level D

Level BNote: Angles kept constant.Changing the Thermal Advection Intensity by changing the depth of the directional wind shear.

AB

C

1.

D

Weaker cold advection BCLevel C

Stronger cold advection CDDestabilization

Level D

Level B


Changing Stability by Changing the Angle of the Vertical Wind Shear

• As the angle subtended by the zero line increases, the amount of directional wind shear also increases.

• The directional wind shear must be divided by the height over which this shear occurs in able to determine the magnitude of the thermal advections.

• Generally, as the angle increases, so does the thermal advections. The angle of the zero line relative to the range rings is essential to use this technique in an operational setting.


Doppler Examples for Increasing Stability

Note: VWS Depth kept constant. Changing the Thermal Advection Intensity by changing the subtended angle (amount) of the directional wind shear. Increasing the angle, decreases the enclosed area.

AB

C

1.

D

Stronger cold advection BCLevel C

Weaker cold advection CDStabilization

Level D

Level B

A

B C

2.

D

Weaker warm advection BCLevel C

Stronger warm advection CDStabilization

Level D

Level B

o o

Cold AdvectionDecreasing with Height

Stabilization

Warm AdvectionIncreasing with Height

StabilizationThe angles that the zero line makes with the range rings is the operational approach to employ.

CAA angle increasing with range/height.

WAA angle decreasing with range/height.


Doppler Examples for Increasing Instability

AB

C

1.

D

Note: VWS Depth kept constant. Changing the Thermal Advection Intensity by changing the subtended angle (amount) of the directional wind shear. Increasing the angle, decreases the enclosed area.

Weaker cold advection BCLevel C

Stronger cold advection CDDestabilization

Level D

Level B

A

B

C2.

D

Stronger warm advection BCLevel C

Weaker warm advection CDDestabilization

Level D

Level B

o o

Cold AdvectionIncreasing with Height

Destabilization

Warm AdvectionDecreasing with Height

DestabilizationThe angles that the zero line makes with the range rings is the operational approach to employ.

CAA angle decreasing with range/height.

WAA angle increasing with range/height.


Example of Increasing Instability – Differential Warm Advection in the Vertical

A

B

The VirgaHole

C

D

E

F

•Southeast of the radar Arc CD subtends a veering, clockwise angle with range/height. This is warm advection.

•As detailed the warm advection CE is stronger than that from ED.

•The air mass is strongly destabilizing southeast of the radar.

•Applying the same principles to AB, AF and FB, the air mass northwest of the radar is also destabilizing but not as much.


• Consider the angle between the veering or backing arc and the radar range ring.

• If this angle increases (in time) from previous values then the rate of wind shear with height is decreasing, since height is a function of radial range. This must imply that for a given arc, the thermal advections have decreased.

• If this angle decreases (in space) along the arc then the rate of wind shear with height is increasing, since height is a function of radial range. This must imply that for a given arc, the thermal advections have increased.

• Track the angle the arc makes with the radar rings with both time (between scans) and in space along the trace of the arc… if the angle increases, then the associated thermal advections are decreasing.

Doppler Rate of Thermal Advections with Height

o



• For example:• A clockwise, veering arc associated with warm

advection vertical wind shear:• Indicates that the layer is becoming more stable

if the angle with the range rings decreases with range. (warm advection increasing with height)

• Indicates that the layer is becoming more unstable if the angle with the range rings increases with range. (warm advection decreasing with height)



• For example:• A counterclockwise, backing arc associated with

cold advection vertical wind shear:• Indicates that the layer is becoming more stable

if the angle with the range rings increases with range. (cold advection decreasing with height)

• Indicates that the layer is becoming more unstable if the angle with the range rings decreases with range. (cold advection increasing with height)


The Doppler Twist Signature


The Doppler Twist Signature - Example

A

B

The VirgaHole

Veerin

g Lid

Twist

Sign

atur

e

C

D

E

F

•The white vectors match the colours from below the mixing level to above the mixing level.

•The direction of rotation indicates the type of thermal advection associated with the Doppler Twist.

•The length of the vectors indicate the magnitude of the thermal advection.

•This is also an example of the Virga Hole Signature


Conveyor Belt Conceptual Models

This information is repeated in links within the Conveyor Belt Conceptual

Model


Doppler and the Conveyor Belt Conceptual Model

North of the Surface Warm Front Conceptual Models

RCL

R = Right of the ColC = Centered on the ColL = Left of the Col


Vertical Deformation Zone Distribution and the CBMSimplified Summary

C

C

WC

B

DCB

CCB

DCB

C

The WCB overrides the warm frontThe CCB undercuts the warm frontThe frontal surface overlies the mixing layerWind shear in the CCB is variable

Looking along the WCB flow:•In WCB to the right of the Col expect veering winds with height – Katabatic warm front•In WCB approach to the Col expect maximum divergence – the eagle pattern with ascent and increasing pcpn•In WCB to the left of the Col expect backing winds with height – Anabatic warm front


CCB Doppler Diagnosis – CCB Conceptual Models

A

B

C

The Beaked Eagle

•A is the radar site•AB is backing with height indicative of cold advection where really there should be veering as a result of the Ekman Spiral•BC is veering with height indicative of warm advection•B is the front with the mixing layer hidden in the cold advection•This is a strong cold advection•The warm front will be slow moving or stationary

A

B

C

The Headless Eagle

•A is the radar site•ABC is all veering with height indicative of warm advection. Layer AB is apt to be partially the result of the Ekman Spiral•BC is veering with height indicative of warm advection•Where is the front and the mixing layer?•The cold advection is not apparent and the warm front will advance

The CCB Conceptual Model is independent of that in the WCB. Like Mr. Potato Head, one can mix and match conceptual models in the distinctly different conveyor belts.


Vertical Deformation Zone Distribution and the CBMSimplified Flows in the Vertical

C

C

WC

B

DCB

CCB

DCB

CXrXcXl

Warm Sector: Winds veer withHeight and distance from Xr

Above frontal surface: Winds veer withHeight and distance from Xr

Below frontal surface: Winds could veer or back

Warm Sector: Winds back withHeight and distance from Xl

Above frontal surface: Winds back withHeight and distance from Xl

Below frontal surface: Winds could veer or back but likely veer

No

VW

S


WCB to the Right of the Col

o

C

Warm frontal surface

Mixing layer

Cold CB

Warm CB

Within the WCB:•East of radar veering, warm advection•West of radar nil VWS

Within the CCB:•Probable Ekman spiral nearest surface•Probable cold advection above Ekman spiral

The Warm Right Wing Stoop CM

The eagles right wing is folded in as if it is about to swoop down.The left wing is still fully extended to catch the lift of the WCB.

Right W

ingLe

ft W

ing

Signature ofWarm Frontal surfaceWarm

advection


Inactive or Katabatic Warm Front


WCB Approaching the Col

o

C


Mixing layer

Cold CB

Warm CB

Within the WCB:•East of radar veering, warm advection – katabatic warm front.•West of radar backing, cold advection – anabatic warm front.


The Warm Screaming Eagle CM

Both wings are fully extended to catch the lift of the WCB. This is a divergent signature.

Right W

ingLe

ft W

ing

Signature ofWarm Frontal surface

discontinuity


BCAD

E

F

G

H

Need to emphasizeThe PPI nature of theDoppler scan- The cone

The Warm Screaming Eagle Conceptual Model


Inactive or Katabatic Warm Front

Active or Anabatic Warm FrontApproaching the Col the Warm Front should have characteristics intermediate between the Anabatic Warm Front to the Left of the Col and the Katabatic Warm Front to the Right of the Col


WCB to the Left of the Col

C


Mixing layer

Cold CB

Warm CB

Within the WCB:•West of radar backing, cold advection•East of radar nil VWS


o

The Warm Left Wing Stoop CM

The eagles left wing is folded in as if it is about to swoop down.The right wing is still fully extended to catch the lift of the WCB.

Right Wing

Le

ft W

ing

Signature ofWarm Frontal surfaceWarm

advection

Signature ofWarm Frontal surface… odd?


ABC

D

F

G


Active or Anabatic Warm Front


WCB Doppler Diagnosis – Diagnosis of the Eagle Wing

A

The Right Eagle Wing

•A is the radar site•BC is backing with height indicative of cold advection. •CD is veering with height indicative of warm advection•Larger angles subtended by the arcs BC and CD by the radar site A, are associated with strong thermal advections•A broad wing in the eagle is associated with strong advections

B

C

D B

C

D

A

The Left Eagle Wing

•A is the radar site•BC is veering with height indicative of warm advection. •CD is backing with height indicative of cold advection•Larger angles subtended by the arcs BC and CD by the radar site A, are associated with strong thermal advections•A broad wing in the eagle is associated with strong advections


WCB Doppler Diagnosis – Diagnosis on the Gull Wing

A

The Right Eagle Wing

•A is the radar site•BC is backing with height indicative of cold advection. •CD is veering with height indicative of warm advection•Larger angles subtended by the arcs BC and CD by the radar site A, are associated with strong thermal advections•A narrow wing in the gull is associated with weak advections

B

CD B

C

DA

The Left Eagle Wing

•A is the radar site•BC is veering with height indicative of warm advection. •CD is backing with height indicative of cold advection•Larger angles subtended by the arcs BC and CD by the radar site A, are associated with strong thermal advections•A narrow wing in the gull is associated with weak advections

The Gull Conceptual Model - weaker thermal advections



Within the Warm Sector Conceptual Models

RCL

R = Right of the ColC = Centered on the ColL = Left of the Col


Radar Data and the Warm Sector Portion of the Warm Conveyor Belt

• Precipitation returns will be limited in extent if they exist at all

• Radar data will be largely unavailable and unreliable

• This results in a very incomplete display of the Doppler wind field in particular


Within the Warm Sector Conceptual Models

These conceptual models will be virtually identical to those associated with the three locations north of the warm front with the exceptions that:

• There will be and cannot be any evidence of the cold conveyor belt

• The veering and backing with height signatures will be less pronounced

• The reduced extent of warm sector precipitation will be an issue

• Gulls are found in the warm sector, more so than eagles…


Right of the WCB in the Warm Sector

o

C

Within the WCB:•East of radar veering, warm advection•West of radar nil VWS

Within the PBL:•Probable Ekman spiral near surface resulting in slight veering with range

The Headless Right Wing Stoop CM

The headless gull’s right wing is folded in as if it is about to swoop down.The left wing is still fully extended to catch the lift of the WCB.

Right W

ing

Left

Wing

Signature ofEkman Spiral


The Headless Right Wing Stoop CMThis slide is reserved for an actual radar example.

o Right W

ing

Left

Wing


Within the WCB:•East of radar veering, weak warm advection – veering winds possible•West of radar backing, cold advection – backing winds possible

Under the WCB in the Warm Sector

o

Within the PBL:•Probable Ekman spiral near surface resulting in slight veering with range

The Headless Gull CM

Both wings are fully extended to catch the lift of the WCB. This is a straight line uniform wind field but could be a slightly divergent signature.

Right WingLeft Wing

Note that headless gulls can’t scream…The advections in the warm sector do not warrant this being called an eagle pattern.


The Headless Gull CMThe southwesterly WCB is essentially a straight flow but there are hints of the upper level divergence depicted in the conceptual model. o Right WingLeft W

ing


Left of the WCB in the Warm Sector

Within the WCB:•West of radar backing, cold advection•East of radar nil VWS

Within the PBL:•Probable Ekman spiral near surface resulting in slight veering with range o

The Headless Left Wing Stoop CM

The headless gull’s left wing is folded in as if it is about to swoop down.The right wing is still fully extended to catch the lift of the WCB.

Right Wing

Left

Win

g

C


The Headless Left Wing Stoop CMThis slide is reserved for an actual radar example. o

Right Wing

Left

Win

g



Behind the Cold Front Conceptual Models

RC

LR = Right of the ColC = Centered on the ColL = Left of the Col


Radar Data and the Cold Front

• Precipitation returns will be limited in extent• Precipitation will tend to be very cellular • This results in an incomplete display of the

Doppler wind field in particular


DCB

Cold Frontal Cross-section along Poleward Branch of the Dry Conveyor Belt (DCB)

Cold air in Cold Conveyor Belt (CCB) deep and moist

Warm Conveyor Belt (WCB) is deep, warm and moist

CCB backs with height consistent with cold advection

Mixing Zone

SurfaceCold Front

Frontal slope is steeper than the typical 1:50

WCB oriented for

less frontal lift

Common area for deep instability

A

B

A B

WCB just ahead of cold front also typically veers with height

WCBCCB

Backing winds above the frontal zone indicative of anabatic cold front

Behind the Cold Front Conceptual ModelsLeft of the Col looking along the flow.

The same backing winds make the warm front anabatic and active as well.


DCB to the Left of the ColC

Cold frontal surface

Mixing layer

Dry CB

Within the DCB:•West of radar backing, cold advection, Anabatic cold front•East of radar nil VWS or possibly weaker backing

Within the CCB – Cold Advection:•Cold advection probably overpowers the Ekman spiral signature

The Cold Left Wing Climb CM

The eagles left wing is folded backward having just caught more air for a climb.This portion of the DCB in the dry slot is typically ascending.The right wing is still fully extended to catch the lift of the WCB.

oRight Wing

Left

Win

g

The steeper frontal slope of the cold front will be very evident. Notice that the frontal area outlined is an oval skewed to the cold side of the front.


The Cold Left Wing Climb CMThis cold front is oriented NE-SW.

Right Wing

Left

Win

g o


Cross Section of Active Cold Front


Active or Anabatic Cold front


DCB

Cold Frontal Cross-section along Poleward Branch of the Dry Conveyor Belt (DCB)

Cold air in Cold Conveyor Belt (CCB) becoming less deep and less moist compared to the left of the flow

Warm Conveyor Belt (WCB) is still probably deep, warm and moist

CCB nearly a straight flow with weakening cold advection

Mixing Zone

SurfaceCold Front

Frontal slope is near the typical 1:50

WCB oriented for

less frontal lift

Common area for deep instability

A

B

A B


WCBCCB

Winds nearly straight above the frontal zone indicative of a cold front which is neither anabatic or katabatic

Behind the Cold Front Conceptual ModelsCentered on the Col looking along the flow.


DCB Centred on the ColC


Mixing layer

Dry CB

Within the DCB:•Nil VWS


The Cold Screaming Eagle CM

Both of the eagle’s wings are fully extended.

oRight WingLeft Wing


A B


The Cold Screaming Eagle CMThis is a placeholder for a real example. o

Right WingLeft Wing


DCB

Cold Frontal Cross-section along Equatorward Branch of the Dry Conveyor Belt (DCB)

Cold air in Cold Conveyor Belt (CCB) shallow and dry. Precipitation will be lacking for radar coverage.

Warm Conveyor Belt (WCB) is shallow, warm and moderately moist

CCB probably veers backs with height consistent with warm advection … I know this seems odd.

Mixing Zone

SurfaceCold Front

Frontal slope is more shallow than the typical 1:50

WCB oriented for

less frontal lift

Common area for deep instability A

B

A B


WCBCCB

Veering winds above the frontal zone indicative of katabatic cold front

Behind the Cold Front Conceptual ModelsRight of the Col looking along the flow.


DCB Centred on the ColC


Mixing layer

Dry CB

Within the DCB:•Winds veer with range/height to the west•Katabatic cold front


The Cold Left Wing Dive CMThe eagles left wing is folded forward as if it is about to turn to the right and swoop down. That is what this part of the DCB does.The right wing is still fully extended to catch the lift of the WCB.

oRight WingLeft Wing


AB


The Cold Left Wing Dive CMThis is a placeholder for a real example. o

Right WingLeft Wing


Cross Section of Inactive Cold Front


Inactive or Katabatic Cold Front



Preliminary Dry Conveyor Belt Conceptual Models

RC

LR = Right of the ColC = Centered on the ColL = Left of the Col


Radar Data and the Preliminary Dry Conveyor Belt

• Precipitation returns will be very limited in extent if they exist at all

• Radar data will be largely unavailable and unreliable

• This results in a very incomplete display of the Doppler wind field in particular


Within the Preliminary Dry Conveyor Belt Conceptual Models

These conceptual models should be similar to those associated with the dry conveyor belt that trails the cold front. Typically, any frontal zone in this region of the conveyor belt conceptual model will be weak and ill defined and probably not worth finding.

• Further investigation especially using isentropic surfaces is required – very required!


Illustrative Cross-section


Vertical Deformation Zone Distribution and the CBMSummary

C

C

C

C

C

WC

B

DCB

CCB

DCB

C


Note to Whom it May Concern

• These conceptual models were constructed largely using the Conveyor Belt Conceptual Model to estimate what the Doppler radar should be seeing.

• This use of Doppler radar and in particular, the increased use of the 3.5 degree scan, are largely unprecedented.

• This is a first attempt at expanding the science and as a result, will likely require further refinements as we learn more.

Doppler Radar

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