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 Seasons The 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 Doppler Texture Snow Doppler Texture

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 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 what one 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 Vectors Have ZERO radial Component – Not measured. Comes in … Goes out

Doppler 12 Doppler Wind Signatures Constant Direction and Speed Constant Direction But Speed Increases With Height (Range) Comes in … Goes out

Doppler 13 Doppler Wind Signatures Constant Direction But Speed Maximum Horizontal Flow Constant Direction But Ascending Speed Maximum Comes in … Goes out

Doppler 14 Doppler Wind Signatures Divergence Convergence Continuity requires ascent from below Continuity requires descent to below

Doppler 15 Doppler Wind Signatures Backing Counter-clockwise Isodop Veering Clockwise Isodop Cold Advection Warm Advection With Height

Doppler 16 Doppler Wind Signatures - Doppler Vortex ‘Look for Something “Odd”’ Broad Scale Flow

Doppler 17 ‘Look for Something “Odd”’ Doppler Radial Divergence Doppler Radial Convergence… Doppler Wind Signatures - Doppler Downburst

Doppler 18 Doppler Wind Shear Zero Isodop Method Back Winds Back with height = VWS = Cold advection Isodop Arc backs or is counter- clockwise with height/range Cold VWS Cold Advection

Doppler 19 Doppler Wind Shear “look for something odd” Winds Veer with height = VWS = Warm advection Veer Isodop Arc veers or is clockwise with height/range Warm VWS Warm Advection Think in 3-D

Doppler 20 Vertical Discontinuities “look for something odd” SW - Level SE - Level SW - Level 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 - Level ? NW – Level ?

Doppler 22 Doppler Practice Low Level Veering What are the implications for vertical stability? “look for something odd” Warming Cooling 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 Advection Cold Conveyor Belt ahead of a synoptic system… Horizontal or Vertical Discontinuity? Cold front with surface discontinuity to the southeast. ‘Look for Something “Odd”’ Vertical 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 radar Analyze areas of non- uniform 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?

Doppler 26 Doppler Wind Analysis – Even More Practice Below Discontinuity NLY winds veering 30 o 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 waves Warm 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 Range Ring Discontinuity- Difference in the Vertical Isodop Discontinuity Veers clockwise Warm front

Doppler 27 A B 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 28 Diagnosis of VWS – Using the Isodop A B C D The angle subtended by the counter-clockwise isodop BC would be the same regardless of the exact location of C anywhere along the radial AC from the Doppler radar. The amount of wind shear (cold) is dependent only on the subtended angle and not the orientation of the arc. A B C D The amount of wind shear (warm) is dependent only on the subtended angle and not the orientation of the arc. The thermal VWS is thus the angle subtended by the isodop divided by the elevation change that this thermal advection occurred over. The following slide illustrates these concepts.

Doppler 29 Thermal Advections and VWS A B C A B C A B 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 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 30 Thermal Advections and VWS Given these isodops, which has the strongest Thermal VWS? A B C 1. D A B C 2. D A B C 3. D For a given isodop subtended angle, the smaller the area CBD, the smaller the height interval, the more intense the thermal advections. the strongest Thermal VWS occurs with a isodop closely following the range rings the weakest Thermal VWS occurs with a isodop closely following the radar radial lines

Doppler 31 Thermal Advections and VWS Given these isodops, which has the strongest Thermal VWS? A B C For a given isodop height interval radial: the strongest Thermal VWS occurs with the largest subtended angle the weakest Thermal VWS occurs with the smallest subtended angle A B C A B C

Doppler 32 Doppler Isodops for Increasing ? A B C 1. D Stronger cold advection BC Level C Weaker cold advection CD Stabilization Level D Level B A B C 2. D Weaker warm advection BC Level C Stronger warm advection CD Stabilization Level D Level B A B C 3. D (Weak) Cold advection BC Level C (Strong) Warm advection CD Stabilization 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 A B C A B C D A B 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 34 Doppler Isodops for Increasing ? 2. A B C D Stronger warm advection BC Level C Weaker warm advection CD Destabilization Level D Level B A B C 3. D (Strong) Warm advection BC Level C (Weak) Cold advection CD Destabilization Level D Level B Note: Angles kept constant for simplicity. Changing the Thermal Advection Intensity by changing the depth of the directional wind shear. A B C 1. D Weaker cold advection BC Level C Stronger cold advection CD Destabilization Level D Level B Backing Wind Turning Along the Rings Veering Wind Turning Along the Radial Instability

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 B C D A B C D A B 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 36 Changing Stability by Changing the Angle of the VWS As the angle subtended by the isodop 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 isodop relative to the range rings is an essential technique in an operational setting.

Doppler 37 Doppler Isodops for Increasing ? 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. A B C 1. D Stronger cold advection BC Level C Weaker cold advection CD Stabilization Level D Level B A B C 2. D Weaker warm advection BC Level C Stronger warm advection CD Stabilization Level D Level B oo Cold Advection Decreasing with Height Stabilization Warm Advection Increasing with Height Stabilization CAA angle increasing with range/height. WAA angle decreasing with range/height. Stability Once again … for Stabilization Isodop veers with height/range

Doppler 38 Doppler Isodops for Increasing ? A B 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 wind shear and the enclosed area. Weaker cold advection BC Level C Stronger cold advection CD Destabilization Level D Level B A B C 2. D Stronger warm advection BC Level C Weaker warm advection CD Destabilization Level D Level B oo Cold Advection Increasing with Height Destabilization Warm Advection Decreasing with Height Destabilization CAA angle decreasing with range/height. WAA angle increasing with range/height. Instability Once again … f or Destabilization Isodop backs with height/range

Doppler 39 Doppler Example Isodops for Increasing Instability – Differential Warm Advection in the Vertical A B The Virga Hole 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 Isodop Backs

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 Advections Angle subtended by Isodop veers for Warm Advection Angle subtended by Isodop backs for Cold Advection 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 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 :>) Stronger Destabilization Doppler Analysis & Diagnosis Strategies Increasing Decreasing Stronger Destabilization Discontinuities in the Vertical Follow the range rings Discontinuities in the Horizontal Tend to be lines

Doppler 41 The Doppler Twist Signature - Example The Virga Hole 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 Doppler Twist Signature - Example The Virga Hole 260 o 210 o 260 o Higher Lower 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 Doppler Twist Signature - Example 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 surface to SSW in 2.6 km Any chance of ZR-? Nil chance of ZR- due veering, warm advection under the warm front – no below freezing layer at ground. NO ZR-

Doppler 45 12Z March 10, 2009

Doppler 46 Doppler and the Conveyor Belt Conceptual Model North of the Surface Warm Front Conceptual Models R C L R = Right of the Col C = Centered on the Col L = Left of the Col End

Doppler 47 The Conveyor Belt Conceptual Model End SLY Flows Rising Isentro pically NLY Flows Sinking Isentropically Think in 3-D

Doppler 48 Vertical Deformation Zone Distribution & CBM Simplified Summary C C WCB DCB CCB DCB C WCB overrides the warm front CCB 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 Veering Nil Backing CCB 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 Wing Left Wing Signature of Warm Frontal surface Warm 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 Surface 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 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 air Above front slower Than front Descent into DIV End Veering winds mean stable Knot active Red for “Stop”

Doppler 53 o C Warm frontal surface 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. Within the CCB: Probable Ekman spiral nearest surface Probable cold advection above Ekman spiral The Warm Screaming Eagle CM Both wings are fully extended to catch the lift of the WCB. This is a divergent signature. Right Wing Left Wing Signature of Warm 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 Surface Warm Front Frontal slope is near the typical 1:200 Precipitation extends further into the moistened, modified CCB. Increasing CCB Moistening WCB oriented for maximum frontal lift 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 Precipitation At Surface End Horizontal rain area begins to expand as CCB moistens.

Doppler 55 B C A D E F G H Need to emphasize The PPI nature of the Doppler scan - The cone The Warm Screaming Eagle Conceptual Model End

Doppler 56 C Warm frontal surface Mixing layer Cold CB Warm CB Within the WCB: West of radar backing, cold advection East of radar nil VWS Within the CCB: Probable Ekman spiral nearest surface Probable cold advection above Ekman spiral 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 Left Wing Signature of Warm Frontal surface Warm advection Signature of Warm 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 Surface Warm Front Frontal slope likely steeper than the typical 1:200 Precipitation extends further into the moistened, modified CCB. Increasing CCB Moistening WCB oriented for maximum frontal lift 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 Precipitation At Surface End Horizontal rain area expands rapidly as CCB moistened.

Doppler 58 A B C 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 air Above front faster Than front Convergence UP End Backing 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