doppler 1 doppler patterns - outline doppler basics doppler signatures –basic signatures wind...

Doppler 1

Doppler Patterns - Outline• Doppler Basics• Doppler Signatures

– Basic Signatures• Wind Analysis (Convection,

Synoptic Flows)

– Advanced Signatures• Atmospheric Diagnosis

(VWS, Stability, Trends)

• Conveyor Belt Conceptual Model (CBCM)

• Summary

Many of the following signatures will only be evident in Doppler –

Clouds obscures the low level, precipitating signatures in Satellite

Imagery.

Doppler 2

Doppler Patterns

Analysis and Diagnosis for All SeasonsThe Doppler Mantra

‘Look for Something “Odd”’“Look UP ”

Doppler 3

What You Know from Part 1 of the Radar Course• The Doppler Effect and Shift• Doppler Weather Radar• Velocity Determination

– Signal Processing

– Limitations

– More on Velocity Aliasing

– Solving the Doppler Dilemma

• PPI Displays of Raw Doppler Data of Radial Wind – Determining Wind Direction

• Wind Profiles – Vertical Profiles

– Broadscale Flows

– Mesoscale Flows

Doppler 4

Doppler Radar Quantities – The Data• Backscattered power (R)

– equivalent reflectivity factor and

– estimates of the precipitation rate

• Mean radial velocity (V)• Spectral width of radial velocity of

targets within the sample volume (W)

Integral of S(v) over V

R=

Mean Radial V

Spectral Width

Doppler 5

Spectral Width and “Doppler Display Texture”

Rain DopplerTexture

Snow DopplerTexture

Doppler 6

Velocity Azimuth Display - VAD• At a given height (h), then the radial velocity is: Vr• For a uniform flow field, assume Vw (Vertical Velocity) approximately = 0• Best fit of a sine curve to the observations around the circle.

Maximum Inbound

Maximum Inbound

Maximum Outbound

Maximum Outbound

No Radial

Doppler 7

Velocity Azimuth Display - VAD• VAD accuracy decreases with elevation

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

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

• Variation in the Doppler velocity are pronounced at the higher elevation angles – shooting through the precipitation?

Doppler 8

Doppler Wind Shifts – Viewing Angles

A

B

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

Doppler 9

Doppler Radar Analysis and Diagnosis Quantities• Determining the

Horizontal Winds– Curvature

– Convergence

– Wind Shear

– VWS Trends

– Thermal Advections

• Stability– Stability Trends

• Doppler Texture and Spectral Width– Precip Phase

• Doppler Data and Viewing Angle– Limitiations

Know the limitations of the data…

Doppler 10

Horizontal Wind Determination

Max/Min Method

Comes in … Goes out

Caution:•Not all flows are uniform•Important flows not uniform

Doppler 11

Horizontal Wind Determination

Zero Isodop Method

Caution:•Think the pattern through•Deduces important non-

uniform flows

The Purple VectorsHave ZERO radialComponent – Not measured.

Com

es in

… G

oes

out

Doppler 12

Doppler Wind Signatures

Constant Directionand Speed

Constant DirectionBut Speed IncreasesWith Height (Range)



Doppler 13


Constant DirectionBut Speed MaximumHorizontal Flow

Constant DirectionBut Ascending Speed Maximum


Comes in …Goes out

Doppler 14


Divergence

Convergence

Continuity requires ascent from below

Continuity requires descent to below

Doppler 15


BackingCounter-clockwiseIsodop

VeeringClockwiseIsodop

Cold Advection

Warm Advection

With Height

With Height

Doppler 16

Doppler Wind Signatures - Doppler Vortex

‘Look for Something “Odd”’

Broad

Sca

le F

low

Doppler 17


Doppler Radial Divergence

Doppler Radial Convergence…

Doppler Wind Signatures - Doppler Downburst

Doppler 18

Doppler Wind Shear

Zero Isodop Method

Bac

kB

ack

Winds Back with height = VWS = Cold advection

Isodop Arc backs or is counter-clockwise with height/rangeCold VWSCold Advection

Doppler 19

Doppler Wind Shear•“look for something odd”

Winds Veer with height = VWS = Warm advection

Vee

rV

eer

Isodop Arc veers or is clockwise with height/range Warm VWSWarm Advection

Think in 3-D

Doppler 20

Vertical Discontinuities“look for something odd”

SW -

Leve

l

SE - Level

SW -

Leve

l

follow a range ring for vertical discontinuities

Doppler 21

Horizontal Discontinuities “look for something odd” follow a radial looking for discontinuities that

do NOT follow along a range ring…

SW -

Leve

l

?

NW – Level ?

Doppler 22

Doppler Practice

Low Level Veering

What are the implications for vertical stability?

“look for something odd”W

arm

ing

Co

oli

ng

Black range ring separates Veering Isodop from Backing Isodop

Under High Level Backing

Doppler 23

Doppler Practice

NNELY

SWLY

LLJ

QS Horizontal LLJ

Winds Backing with Height - Cold Air AdvectionCold Conveyor Belt ahead of a synoptic system…Horizontal or Vertical Discontinuity?Cold front with surface discontinuity to the southeast.


Ver

tical

March 93 – the storm of the century! Snow!

Doppler 24

Doppler Wind Analysis – More Practice

Isodop Wind Analysis

• Follow isodop outward

• Draw line back to radar

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

Doppler 25

Doppler Wind Analysis – More Practice

For any height you can determine the wind in four locations• Determine the two isodop winds• For the maximum winds look roughly 90° away from the isodop winds•The wind maxs are where the winds align along a radial•Full wind toward radar •Full wind away from radarAnalyze areas of non-uniform flow• curvature from direction• confluence from speed

At 5.3 km … Anticyclonic Ridge with mass convergenceSubsidence below. Nil pcpn above.What’s your short range forecast?

Doppler 26

Doppler Wind Analysis – Even More Practice

Below Discontinuity •NLY winds veering 30o with height•Warm advection •Max wind rising a lot•ACYC curvature•No sig convergence ….23kts in 23kts out….

Synoptic Situation … Zonal frontal zone with stable wavesWarm front slanted toward the NNW. Subsidence below.but strong Cold Conveyor Belt – nil motion

Discontinuity Slope •2.4 km SE rising to 2.8km NW•2.7 km S steady to 2.7 N

Above Discontinuity •SLY winds nil directional shear•Nil thermal advections •ACYC curvature•Mass convergence …60kts in only 45kts out..

23

23

Range Ring Discontinuity - Difference in the Vertical

Isodop Discontinuity•Veers clockwise•Warm front

Doppler 27

AB

C

D

•Determine the wind at B. Draw a radial line from the radar site A to the isodop at B.

•Determine the wind at C.

•The wind backs from B to C. Relative to A the isodop backs or turns counter-clockwise as well.

•Determine the wind at D.

•The wind veers from C to D. The isodop veers or turns clockwise as well.

Summary

Diagnosis of VWS – Isodop Method= VWS Inflection

Thermal Advection Intensity•The larger the angle subtended by the arc, the larger the wind shift and stronger the thermal advections.•This angle is independent of range from the radar Thermal Advection Type•If the isodop turns counter-clockwise with height (increasing range), the arc is associated with cold advection… winds back with height.•If the isodop turns clockwise with height (increasing range) the arc is 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.

Doppler 29

Thermal Advections and VWS

AB

C

AB

C

AB

C

•The angle subtended by the counter-clockwise isodop BC is identical in 1, 2 and 3.•In 1, winds back over a short radial range•Radial range & height difference increases for 2•Radial range difference is even more for 3•Height interval for the Thermal VWS increases with the length of the radial DC from case 1 to 3•Thermal VWS determined by dividing the directional shear (isodop angle) by the height interval (Difference between AC and AD=DC):

•Strongest for 1•Moderate for 2•Weakest for 3.

•Thermal VWS is proportional to the size of the subtended angle divided by the radial range (AC-AD=DC) which is inversely proportional to area BCD

1.

2.

3.

D

D

D

VWS = WS

Depth

Isodop Angle

Radial Height Change =

1

Isodop Area (BCD) ~

~1/Small Area~1/Medium Area~1/Large Area

Isodop

Range Ring

Radial

Doppler 32

Doppler Isodops for Increasing ?

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.

Backing Wind Turning Along the Radial

Veering Wind Turning Along the Rings

Stability

Doppler 33

Isodop Diagnosis of Stabilization Trends

Stability increases with:• Cold advection decreasing with height:

– Angle of backing Doppler isodop veers to become more aligned along a radial,

• Warm advection increasing with height:– Angle of veering Doppler isodop veers to

become more aligned along the range rings,

• Cold advection under warm advection:– Doppler isodop backing counterclockwise with

height (range) under Doppler isodop veering clockwise with height (range).

• Following the Isodop – for Stabilization

AB

C

A

B C

D

AB

C

D

Cold Advection - Backing Veers

Warm Advection - Veering Veers

Important Generalization: For Stabilization Isodop veers with height/range

Remember:Veering with Height =Warming with Height =Stabilization (Red = Stop)

Doppler 35

Isodop Diagnosis of Destabilization Trends

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

– Angle of backing Doppler isodop backs to become more aligned along the range rings

• Warm advection decreasing with height:– Angle of veering Doppler isodop backing to

become more aligned along a radial,

• Warm advection under cold advection:– Doppler isodop veering clockwise with height

(range) under Doppler isodop backing counterclockwise with height (range).

• Following the Isodop – for Destabilization

A

BC

D

A

B C

D

AB

C

D

Cold Advection - Backing backs

Warm Advection - Veering backs

Important Generalization: For Destabilization Isodop backs with height/range

Remember:Backing with Height =Cooling with Height =Destabilization (Green = GO)

Doppler 39

Doppler Example Isodops for Increasing Instability – Differential Warm Advection in the Vertical

A

B

The VirgaHole

C

D

E

F

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

•Warm advection CE is stronger than that for ED.

•The air mass is strongly destabilizing southeast of the radar. Isodop backs with height/range.

•For AB, AF and FB, the air mass northwest of the radar is also destabilizing

•even more…larger angle in about the same height interval.

Isodop Backs with height (relative to the range rings)Destabilization

Stronger Destabilization

Weaker Destabilization

•Larger angle•Along range ring

•Smaller angle•Along range ring

Isod

op B

acks

Doppler 40

An operational guide to getting the most information from Doppler radar:• Look for Something “Odd”• Determining the actual Wind Direction and Speed – Blue towards Red Away

Curvature from direction & Mass Convergence from speed• Determining VWS - Wind backing & veering with height

for Thermal AdvectionsAngle subtended by Isodop veers for Warm AdvectionAngle subtended by Isodop backs for Cold Advection

• Determine Trends in the VWS - Angle between the Isodop and Range RingsIf angle (area) increases (in time) then vertical wind shear/thermal advection is decreasingIf angle (area) decreases (in time) then vertical wind shear/thermal advection is increasing

• Determining Stability Trends -Isodop backing & veering with height relative to range ringsFor Stabilization Isodop veers with height/rangeFor Destabilization Isodop backs with height/range

Stabilization/Destabilization rate stronger for longer legs… • Diagnosing Vertical versus Spatial wind discrepancies

Along a Range Ring versus along Radial

… some of this is probably new to you … I made it up :>)

StrongerDestabilization

Doppler Analysis & Diagnosis Strategies

IncreasingDecreasing

StrongerDestabilization

Discontinuities in theVertical

Follow the range rings

Discontinuities in theHorizontal

Tend to be lines

Doppler 41

The Doppler Twist Signature - Example

The VirgaHole

•White vectors match the colours from one level to a higher level – difficult to do.

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

•Length of the vectors indicate the relative magnitude of the thermal advection.

•An example of the Virga Hole Signature

Doppler 42


The VirgaHole

260o

210

o

260o

Higher

Lower

Virg

a

Virga

•White vectors match the colours from one level to a higher level – difficult to do.

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

•Length of the vectors indicate the relative magnitude of the thermal advection.

•An example of the Virga Hole Signature

Doppler 43


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

•It also separates regimes of differing Doppler texture.

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

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

•There is Virga – no rain to the ground.

•Consider the dashed line.

The white line is the warm front. The layer immediately below is where the snow is melting into rain. See the Doppler Texture…

Is the dashed line a better analysis for the warm front! Were we analyzing the melting layer before … Typically cold air gets deeper & warm front gets higher to the north.

Keep an open mind & get all the data you can!

Doppler 44

12Z March 10, 2009

Doppler adds a lot of information to the surface map…

R-R

Virga

Winds veer from SE at the surfaceto SSW in 2.6 kmAny chance of ZR-?

Nil chance of ZR-due veering, warm

advection under the warm front –

no below freezing layer at ground. NO

ZR-

Doppler 46

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

End

Doppler 47

The Conveyor Belt Conceptual Model

End

SL

Y F

low

s R

isin

g Is

entr

op

ical

ly

NL

Y F

low

s S

inkin

g Isen

trop

ically

Think in 3-D

Doppler 48

Vertical Deformation Zone Distribution & CBMSimplified Summary

C

C

WC

B

DCB

CCB

DCB

C

WCB overrides the warm frontCCB undercuts the warm front

Frontal surface overlies mixing layer

Looking along the WCB flow:•In WCB right of the Col expect veering winds with height – Katabatic (red for stop) 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 (green for Go) warm front

Vee

rin

g

Nil

Bac

kin

gCCB wind shear variable

End

Doppler 49

CCB Doppler Diagnosis – 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.

End

Doppler 50

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

End

Doppler 51

WCB

CCB

Warm Frontal Cross-section along Leading Branch of the Warm Conveyor

Belt (WCB)

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

Moist portion of Warm Conveyor Belt (WCB) is high and veered from frontal perpendicular – katabatic tendency

Dry lower levels of WCB originate from ahead of the system and veered from frontal perpendicular

Mixing Zone

SurfaceWarm Front

Frontal slope is more shallow than the typical 1:200

Precipitation extends equidistant into the unmodified CCB

Precipitation extends further into the moistened, modified CCB

Increasing CCB Moistening

WCB oriented for

maximum frontal lift

WCB oriented for

less frontal lift

Virga Precipitation

Lower

Hydrometeor

Density

Common location for virga A

B

A B

WCB typically veers with height (it is after all, a warm front)

End

Inactive or Katabatic Warm Front

Winds veer with height above the warm front to the right of the COL

Winds in warm airAbove front

slower Than front

Descen

t into

DIV

EndVeering winds mean stable Knot active Red for “Stop”

Doppler 53

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

End

WCB Approaching the Col

Doppler 54

WCB

CCB

Warm Frontal Cross-section along Central Branch of the Warm Conveyor

Belt (WCB)

Cold air in Cold Conveyor Belt (CCB) more shallow and moist

Moist portion of Warm Conveyor Belt (WCB) is thicker, higher and perpendicular to front

Lower levels of WCB have the same origin as the upper level of the WCB - frontal perpendicular

Mixing Zone

SurfaceWarm Front

Frontal slope is near the typical 1:200Precipitation extends further into the moistened, modified CCB.


WCB oriented for


Virga Precipitation

Lower

Hydrometeor

Density

Common location for both precipitation and virga A

B

A B

WCB shows little directional shift with height. A greater WCB depth is frontal perpendicular

PrecipitationAt Surface

End

Horizontal rain area begins to expand as CCB moistens.

Doppler 55

BCAD

E

F

G

H

Need to emphasizeThe PPI nature of theDoppler scan- The cone

The Warm Screaming Eagle Conceptual Model End

Doppler 56

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?

End

WCB to the Left of the Col

Doppler 57

WCB

CCB

Warm Frontal Cross-section along Trailing Branch of the Warm Conveyor

Belt (WCB)

Cold air in Cold Conveyor Belt (CCB) even more shallow and more moist

Moist portion of WCB is thicker, higher and backed from frontal perpendicular – anabatic tendency

Lower levels of WCB have the same origin as the upper level of the WCB

Mixing Zone

SurfaceWarm Front

Frontal slope likely steeper than the typical 1:200

Precipitation extends further into the moistened, modified CCB.


WCB oriented for


Virga Precipitation

Lower

Hydrometeor

Density

Common location for precipitation to ground! A

B

A B

WCB backs slightly with height in spite of the warm air advection. A greater WCB depth is frontal perpendicular

PrecipitationAt Surface

End

Horizontal rain area expands rapidly as CCB moistened.

Doppler 58

ABC

D

F

G

End

A

B

Doppler 59

Active or Anabatic Warm Front

Winds back with height above the warm front to the left of the COL

Winds in warm airAbove front

faster Than front

Co

nve

rge

nce

UP

EndBacking winds mean unstable Active Green for “Go”

Doppler 60

Doppler Patterns - Outline• Doppler Basics• Doppler Signatures

– Basic Signatures• Wind Analysis (Convection,

Synoptic Flows)

– Advanced Signatures• Atmospheric Diagnosis

(VWS, Stability)

• Conveyor Belt Conceptual Model (CBCM)

• Summary

Keep Looking UP!

Take Home Message (THM):Doppler Radar is useful to A&D winds, VWS, Stability & Stability Trends!

Thank you for your attention!Remote sensing is your Friend!

Doppler 61

And Now You Know What This Means…

These patterns happen every day – somewhere…

The Headless Screaming Eagle Conceptual Model

doppler 1 doppler patterns - outline doppler basics doppler signatures –basic signatures wind...

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