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Radar Palette Home Click Doppler Pre-warm Frontal 1 Ahead of WCB Classic area for virga Probability of virga increases with strength and dryness of the.

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Presentation on theme: "Radar Palette Home Click Doppler Pre-warm Frontal 1 Ahead of WCB Classic area for virga Probability of virga increases with strength and dryness of the."— Presentation transcript:

1 Radar Palette Home Click Doppler Pre-warm Frontal 1 Ahead of WCB Classic area for virga Probability of virga increases with strength and dryness of the CCB and the strength and moisture of leading branch of the WCB Katabatic portion of warm front – winds veer above the warm frontal mixing zone Lack of precipitation in this area may limit Doppler interpretation Click for the Conceptual Model and Explanation

2 Radar Palette Home Click Doppler Pre-warm Frontal 2 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 backed 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) Link to Classic Example

3 Radar Palette Home Click Doppler Pre-warm Frontal 3 Vertical Deformation Zone Distribution and the CBM Simplified Summary C C WCB DCB CCB DCB C The WCB overrides the warm front The CCB undercuts the warm front The frontal surface overlies the mixing layer Wind shear in the CCB is variable Looking along the 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

4 Radar Palette Home Click Doppler Pre-warm Frontal 4 Vertical Deformation Zone Distribution and the CBM Simplified Flows in the Vertical C C WCB DCB CCB DCB C Xr Xc Xl Warm Sector: Winds veer with Height and distance from Xr Above frontal surface: Winds veer with Height and distance from Xr Below frontal surface: Winds could veer or back Warm Sector: Winds back with Height and distance from Xl Above frontal surface: Winds back with Height and distance from Xl Below frontal surface: Winds could veer or back but likely veer No VWS

5 Radar Palette Home Click Doppler Pre-warm Frontal 5 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

6 Radar Palette Home Click Doppler Inactive or Katabatic Warm Front

7 Radar Palette Home Click Doppler Pre-warm Frontal 7 WCB Approaching the Col 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

8 Radar Palette Home Click Doppler Pre-warm Frontal 8 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

9 Radar Palette Home Click Doppler Inactive or Katabatic Warm Front Active or Anabatic Warm Front Approaching 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

10 Radar Palette Home Click Doppler Pre-warm Frontal 10 The PPI Virga Hole Signature – Typical in this Region of the CBCM The difference between PPI and CAPPI displays can be used to advantage. Each display must be consulted in an analysis of the atmosphere. This is most often seen in Doppler Radar which is typically a PPI display. A B The Virga Hole signature is only revealed in the PPI radar display. The CAPPI cannot reveal the true extent of the precipitation if the precipitation lies above the CAPPI level. A cross-section can reveal the vertical distribution of the precipitation. The lowest level CAPPI display can be misleading as at longer ranges, the true level of the radar rises to follow the lowest PPI scan of the radar. This is depicted in this 1.5km CAPPI example. Click. 1.5km CAPPI Cross-section from A (left) to B (right) 3.5 PPIVirga Hole

11 Radar Palette Home Click Doppler Pre-warm Frontal 11 Under WCB Virga only likely on the leading edge of the WCB The CCB is becoming increasingly moist Frontal overrunning and isentropic lift is increasing thus increasing the intensity of the precipitation process. Warm front becoming more likely Anabatic Click for the Conceptual Model and Explanation

12 Radar Palette Home Click Doppler Pre-warm Frontal 12 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. Horizontal rain area begins to expand as CCB moistens. Increasing CCB Moistening WCB oriented for maximum frontal lift Virga Precipitation Lower Hydrometeor Density Common location for virga A B A B WCB shows little directional shift with height. A greater WCB depth is frontal perpendicular Precipitation At Surface

13 Radar Palette Home Click Doppler Pre-warm Frontal 13 Vertical Deformation Zone Distribution and the CBM Simplified Summary C C WCB DCB CCB DCB C The WCB overrides the warm front The CCB undercuts the warm front The frontal surface overlies the mixing layer Wind shear in the CCB is variable Looking along the flow: In WCB to the right of the Col expect veering winds with height – Katabatic warm front In WCB approach to the right of 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

14 Radar Palette Home Click Doppler Pre-warm Frontal 14 WCB Approaching the Col 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

15 Radar Palette Home Click Doppler Pre-warm Frontal 15 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

16 Radar Palette Home Click Doppler Inactive or Katabatic Warm Front Active or Anabatic Warm Front Approaching 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

17 Radar Palette Home Click Doppler Pre-warm Frontal 17 CCB Doppler Diagnosis 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 with 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

18 Radar Palette Home Click Doppler Pre-warm Frontal 18 B C A D E F G H WCB Doppler Diagnosis

19 Radar Palette Home Click Doppler Pre-warm Frontal 19

20 Radar Palette Home Click Doppler Pre-warm Frontal 20

21 Radar Palette Home Click Doppler Pre-warm Frontal 21 Behind WCB Virga much less likely The CCB has become moist Frontal overrunning and isentropic lift is maximized thus maximizing the intensity of the precipitation process. Warm front is likely Anabatic Click for the Conceptual Model and Explanation

22 Radar Palette Home Click Doppler Pre-warm Frontal 22 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 Warm Conveyor Belt (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. Horizontal rain area expands rapidly as CCB moistened. Increasing CCB Moistening WCB oriented for maximum frontal lift Virga Precipitation Lower Hydrometeor Density Common location for virga A B A B WCB probably backs slightly with height in spite of the warm air advection. A greater WCB depth is frontal perpendicular Precipitation At Surface

23 Radar Palette Home Click Doppler Pre-warm Frontal 23 Vertical Deformation Zone Distribution and the CBM Summary C C C C C WCB DCB CCB DCB C

24 Radar Palette Home Click Doppler Pre-warm Frontal 24 WCB to the Left of the Col 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?

25 Radar Palette Home Click Doppler Pre-warm Frontal 25 A B C D F G

26 Radar Palette Home Click Doppler Pre-warm Frontal 26 Active or Anabatic Warm Front

27 Radar Palette Home Click Doppler Pre-warm Frontal 27 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

28 Radar Palette Home Click Doppler Pre-warm Frontal 28 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 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 narrow wing in the gull is associated with weak advections The Gull Conceptual Model - weaker thermal advections

29 Radar Palette Home Click Doppler Pre-warm Frontal 29

30 Radar Palette Home Click Doppler Pre-warm Frontal 30

31 Radar Palette Home Click Doppler Pre-warm Frontal 31 Doppler Oriented Reference Conceptual Models

32 Radar Palette Home Click Doppler Pre-warm Frontal 32 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 Gull Patterns

33 Radar Palette Home Click Doppler Pre-warm Frontal 33 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.

34 Radar Palette Home Click Doppler Pre-warm Frontal 34 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) ABC 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

35 Radar Palette Home Click Doppler Pre-warm Frontal 35 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.

36 Radar Palette Home Click Doppler Pre-warm Frontal 36 Diagnosis of Vertical Windshear – Using the Zero line A B 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 radar Thermal 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.

37 Radar Palette Home Click Doppler Pre-warm Frontal 37 Diagnosis of Vertical Windshear – Using the Zero line A B 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. A B 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.

38 Radar Palette Home Click Doppler Pre-warm Frontal 38 Thermal Advections and Vertical Wind Shear A B C A B C A B 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 D D D

39 Radar Palette Home Click Doppler Pre-warm Frontal 39 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. A B C 1. D A B C 2. D A B 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

40 Radar Palette Home Click Doppler Pre-warm Frontal 40 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).

41 Radar Palette Home Click Doppler Pre-warm Frontal 41 Doppler Examples for Increasing Stability 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.

42 Radar Palette Home Click Doppler Pre-warm Frontal 42 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:

43 Radar Palette Home Click Doppler Pre-warm Frontal 43 Doppler Examples for Increasing Instability A B C 2. D Stronger warm advection BC Level C Weaker warm advection BC 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. 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

44 Radar Palette Home Click Doppler Pre-warm Frontal 44 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.

45 Radar Palette Home Click Doppler Pre-warm Frontal 45 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. 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 The 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.

46 Radar Palette Home Click Doppler Pre-warm Frontal 46 Doppler Examples for Increasing Instability 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 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 The 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.

47 Radar Palette Home Click Doppler Pre-warm Frontal 47 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

48 Radar Palette Home Click Doppler Pre-warm Frontal 48 Doppler Rate of Thermal Advections with Height 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)

49 Radar Palette Home Click Doppler Pre-warm Frontal 49 Doppler Rate of Thermal Advections 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)

50 Radar Palette Home Click Doppler Pre-warm Frontal 50 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

51 Radar Palette Home Click Doppler Pre-warm Frontal 51 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 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 narrow wing in the gull is associated with weak advections The Gull Conceptual Model - weaker thermal advections


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