Doppler Patterns Outline Doppler Basics Doppler Signatures Basic
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. 1
Doppler Patterns Analysis and Diagnosis for All Seasons The Doppler Mantra ‘Look for Something “Odd”’ “Look UP ” 2
What You Know from Part 1 of the Radar Course • • • The Doppler Effect and Shift Doppler Weather Radar Velocity Determination – – • PPI Displays of Raw Doppler Data of Radial Wind – • Signal Processing Limitations More on Velocity Aliasing Solving the Doppler Dilemma Determining Wind Direction Wind Profiles – – – Vertical Profiles Broadscale Flows Mesoscale Flows 3
Doppler Radar Quantities – The Data • Backscattered power (R) Mean Radial V – 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) Spectral Width R= Integral of S(v) over V 4
Spectral Width and “Doppler Display Texture” Rain Doppler Texture Snow Doppler Texture 5
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 Outbound Maximum Inbound Maximum Outbound No Radial 6 Maximum Inbound
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? 7
Doppler Wind Shifts – Viewing Angles B A The angle of viewing is very important and determines what one sees! 8
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… 9
Horizontal Wind Determination Max/Min Method Comes in … Goes out Caution: • Not all flows are uniform • Important flows not uniform 10
Horizontal Wind Determination Co m es i n … Go es ou t Zero Isodop Method Caution: • Think the pattern through • Deduces important nonuniform flows The Purple Vectors Have ZERO radial Component – Not measured. 11
Doppler Wind Signatures Constant Direction and Speed Comes in … Goes out Constant Direction But Speed Increases With Height (Range) 12
Doppler Wind Signatures Constant Direction But Speed Maximum Horizontal Flow Comes in … Goes out Comes in …Goes out Constant Direction But Ascending Speed Maximum 13
Doppler Wind Signatures Divergence Continuity requires ascent from below Convergence Continuity requires descent to below 14
Doppler Wind Signatures Backing With Height Counter-clockwise Isodop Cold Advection Veering With Height Clockwise Isodop Warm Advection 15
Doppler Wind Signatures - Doppler Vortex ‘Look for Something “Odd”’ d a ro le a c ow l F S B 16
Doppler Wind Signatures - Doppler Downburst ‘Look for Something “Odd”’ Doppler Radial Divergence Doppler Radial Convergence… 17
Doppler Wind Shear Back Winds Back with height = VWS = Cold advection Zero Isodop Method Isodop Arc backs or is counterclockwise with height/range Cold VWS Cold Advection 18
Doppler Wind Shear • “look for something odd” Veer Winds Veer with height = VWS = Warm advection Think in 3 -D Isodop Arc veers or is clockwise with height/range Warm VWS Warm Advection 19
Vertical Discontinuities SE SW -L ev el “look for something odd” follow a range ring for vertical discontinuities SW -L ev el el ev -L 20
Horizontal Discontinuities “look for something odd” follow a radial looking for discontinuities that do NOT follow along a range ring… N Le ve ev el l? -L – SW W ? 21
Doppler Practice Warming Cooling “look for something odd” Black range ring separates Veering Isodop from Backing Isodop Low Level Veering Under High Level Backing What are the implications for vertical stability? 22
Doppler Practice ‘Look for Something “Odd”’ Vertical SWLY NNELY LLJ QS Horizontal LLJ Winds Backing with Height - Cold Air Advection Cold Conveyor Belt ahead of a synoptic system… Horizontal or Vertical Discontinuity? Cold front with surface discontinuity to the southeast. 23 March 93 – the storm of the century! Snow!
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 24
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 radar Analyze areas of nonuniform flow • curvature from direction • confluence from speed At 5. 3 km … Anticyclonic Ridge with mass convergence Subsidence below. Nil pcpn above. What’s your short range forecast? 25
Doppler Wind Analysis – Even More Practice Range Ring Discontinuity - Difference in the Vertical Below Discontinuity • NLY winds veering 30 o with height • Warm advection • Max wind rising a lot • ACYC curvature • No sig convergence …. 23 kts in 23 kts out…. Isodop Discontinuity • Veers clockwise • Warm front Above Discontinuity • SLY winds nil directional shear • Nil thermal advections • ACYC curvature • Mass convergence … 60 kts in only 45 kts out. . Discontinuity Slope • 2. 4 km SE rising to 2. 8 km NW • 2. 7 km S steady to 2. 7 N 23 23 Synoptic Situation … Zonal frontal zone with stable waves Warm front slanted toward the NNW. Subsidence below. but strong Cold Conveyor Belt – nil motion 26
Diagnosis of VWS – Isodop Method • 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. C = VWS Inflection A Summary B D Thermal Advection Intensity • The larger the angle subtended by the arc, the larger the wind shift and stronger 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. 27
Thermal Advections and VWS D 1. • 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): C A B C D 2. A B C Radial D 3. Isodop A Range Ring VWS = B WS Depth = • Strongest for 1 ~1/Small Area • Moderate for 2 ~1/Medium Area • Weakest for 3. ~1/Large Area • 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 Isodop Angle Radial Height Change ~ 1 Isodop Area (BCD) 29
Doppler Isodops for Increasing Stability ? D Weaker cold advection CD Stronger cold advection BC C 1. Level D Level C Backing Wind Turning Along the Radial A Stabilization Level B B C B 2. A Stronger warm advection CD A B Level C Weaker warm advection BC DVeering Wind Turning Along the Rings (Strong) Warm advection CD C 3. Level D (Weak) Cold advection BC D Stabilization Level B Level D Level C Stabilization Level B Note: Angles kept constant. Changing the Thermal Advection Intensity by changing the depth of the directional wind shear. 32
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, C A B • Warm advection increasing with height: – Angle of veering Doppler isodop veers to become more aligned along the range rings, C B A D • Cold advection under warm advection: – Doppler isodop backing counterclockwise with height (range) under Doppler isodop veering A clockwise with height (range). C B D • Following the Isodop – for Stabilization Remember: Veering with Height = Cold Advection - Backing Veers Warming with Height = Warm Advection - Veering Veers Stabilization (Red = Stop) Important Generalization: For Stabilization Isodop veers with height/range 33
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 D C A B • 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 B C D A D B C A the Isodop – for Destabilization Remember: Backing with Height = Cold Advection - Backing backs Cooling with Height = Warm Advection - Veering backs Destabilization (Green = GO) Important Generalization: For Destabilization Isodop backs with height/range 35
Doppler Example Isodops for Increasing Instability – Differential Warm Advection in the Vertical Stronger Destabilization • Southeast of the radar isodop CD subtends a veering, clockwise angle with range/height. This is warm advection. • 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. A • Smaller angle • Along range ring The Virga Hole Ba c ks Weaker Destabilization op • The air mass is strongly destabilizing southeast of the radar. Isodop backs with height/range. F C Is od • Warm advection CE is stronger than that for ED. • Larger angle • Along range ring B Isodop Backs with height (relative to the D range rings) Destabilization E 39
Doppler Analysis & Diagnosis Strategies 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 Advections Angle subtended by Isodop veers for Warm Advection Angle subtended by Isodop backs for Cold Advection • Decreasing Increasing Determine Trends in the VWS - Angle between the Isodop and Range Rings If angle (area) increases (in time) then vertical wind shear/thermal advection is decreasing If angle (area) decreases (in time) then vertical wind shear/thermal advection is increasing • • Determining Stability Trends -Isodop backing & veering with height relative to range rings For Stabilization Isodop veers with height/range For Destabilization Isodop backs with height/range Stronger Destabilization Stabilization/Destabilization rate stronger for longer legs… Stronger Destabilization Diagnosing Vertical versus Spatial wind discrepancies Along a Range Ring versus along Radial in thenew to you … Discontinuities in the … some. Discontinuities of this is probably I made it up : >) Vertical Horizontal Follow the range rings Tend to be lines 40
The Doppler Twist Signature - Example • 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. The Virga Hole • Length of the vectors indicate the relative magnitude of thermal advection. • An example of the Virga Hole Signature 41
The Doppler Twist Signature - Example • White vectors match the colours from one level to a higher level – difficult to do. 21 0 o The Virga Hole ga o 260 Vir ga • Length of the vectors indicate the relative magnitude of thermal advection. Lower Vir • Direction of rotation indicates the type of thermal advection associated with the Doppler Twist. Higher • An example of the Virga Hole Signature 42
The Doppler Twist Signature - Example • The obvious white line separates different wind regimes in the vertical. The white line is the warm front. The layer immediately below is where the snow is melting into rain. See the Doppler Texture… • 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 Is the dashed line a better analysis for the ground. warm front! Were we analyzing the melting • Consider the dashed line. layer before … Typically cold air gets deeper & warm front gets higher to the north. Keep an open mind & get all the data you can! 43
12 Z March 10, 2009 Virga R-R Winds veer from SE at the surface to SSW in 2. 6 km Any chance of ZR-? Nil chance of ZRdue veering, warm advection under the warm front – no below freezing layer at ground. NO ZR- Doppler adds a lot of information to the surface map… 44
L C R Doppler and the Conveyor Belt Conceptual Model North of the Surface Warm Front Conceptual Models R = Right of the Col C = Centered on the Col L = Left of the Col 46 End
Risin g s Flow ly ical rop Think in 3 -D SLY ent g Is kin Sin Isent ws Flo ropic NLY ally The Conveyor Belt Conceptual Model 47 End
B Veering C Nil C B C DC DC B C WCB kin c a B WCB overrides the warm front CCB undercuts the warm front CCB wind shear variable Frontal surface overlies mixing layer C g Vertical Deformation Zone Distribution & CBM Simplified Summary 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 48 End
CCB Doppler Diagnosis – Conceptual Models B The CCB Conceptual Model is independent of that in the WCB. Like Mr. Potato Head, B one can mix and match conceptual models in the distinctly different conveyor belts. C A A 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 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 49 End
WCB to the Right of the Col 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. C Mixing layer Warm frontal surface Warm CB g in W Cold CB Le ft Within the WCB: • East of radar veering, warm advection • West of radar nil VWS o Right Wing Within the CCB: • Probable Ekman spiral nearest surface • Probable cold advection above Ekman spiral Signature of Warm Frontal surface Warm advection 50 End
B Warm Frontal Cross-section along Leading Branch of the Warm Conveyor Belt (WCB) Common location for virga WCB Surface Warm Front for d t nte rie tal lif o B on WC ss fr e le on Z ing Mix A r ted fo t n e i r o if WCB m frontal l u maxim n itatio p i c e a Pr Virg Increasing CCB r Lowe eor Moistening omet Hydr sity Den CCB A B 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 WCB typically veers with height (it is after all, a warm 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 51 End
Inactive or Katabatic Warm Front Descent into DIV Winds in warm air Above front slower Than front Winds veer with height above the warm front to the right of the COL Veering winds mean stable Knot active Red for “Stop”End
WCB Approaching the Col The Warm Screaming Eagle CM Both wings are fully extended to catch the lift of the WCB. This is a divergent signature. C Warm CB Warm frontal surface Signature of Warm Frontal surface discontinuity Mixing layer Cold CB Within the WCB: • East of radar veering, warm advection – katabatic warm front. • West of radar backing, cold advection – anabatic warm front. Le ft W in g o Right Wing Within the CCB: • Probable Ekman spiral nearest surface • Probable cold advection above Ekman spiral 53 End
B Warm Frontal Cross-section along Central Branch of the Warm Conveyor Belt (WCB) A Common location for both precipitation and virga WCB Surface Warm Front Precipitation At Surface r d fo ift e t n rie al l B o front n C W mum itatio p i c i e a Pr max Virg Increasing CCB e wer r Moistening n o o L Z eo ing omet r x i d y H M ity Dens CCB A B 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 WCB shows little directional shift with height. A greater WCB depth is frontal perpendicular Frontal slope is near the typical 1: 200 Precipitation extends further into the moistened, modified CCB. Horizontal rain area begins to expand as CCB moistens. 54 End
D A C B G E F Need to emphasize The PPI nature of the Doppler scan - The cone H The Warm Screaming Eagle Conceptual Model 55 End
WCB to the Left of the Col 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. C Within the WCB: • West of radar backing, cold advection • East of radar nil VWS Cold CB Mixing layer Warm frontal surface Warm CB Left Wing Within the CCB: • Probable Ekman spiral nearest surface • Probable cold advection above Ekman spiral Signature of Warm Frontal surface … odd? Signature of Warm Frontal surface Warm advection o Right Win g 56 End
B Warm Frontal Cross-section along Trailing Branch of the Warm Conveyor Belt (WCB) A Common location for precipitation to ground! WCB Surface Warm Front Precipitation At Surface r d fo ift e t n rie al l B o front n C W mum itatio p i c i e a Pr max Virg Increasing CCB e wer r Moistening n o o L Z eo ing omet r x i d y H M ity Dens CCB A B 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 backs slightly with height in spite of the warm air advection. A greater WCB depth is frontal perpendicular Frontal slope likely steeper than the typical 1: 200 Precipitation extends further into the moistened, modified CCB. Horizontal rain area expands rapidly as CCB moistened. 57 End
B A G D C A B F 58 End
Convergence UP Active or Anabatic Warm Front Winds in warm air Above front faster Than front Winds back with height above the warm front to the left of the COL Backing winds mean unstable Active Green for “Go” 59 End
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! Thank you for your attention! Remote sensing is your Friend! Take Home Message (THM): 60 Doppler Radar is useful to A&D winds, VWS, Stability & Stability Trends!
And Now You Know What This Means… The Headless Screaming Eagle Conceptual Model These patterns happen every day – somewhere… 61
- Slides: 53