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Radar signatures in complex terrain during the passage of mid-latitude cyclones

Radar signatures in complex terrain during the passage of mid-latitude cyclones. Socorro Medina Department of Atmospheric Sciences University of Washington. MSC/COMET Mountain Weather Course, Boulder CO , 7 December 2007. Observational Perspective Field Experiments.

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Radar signatures in complex terrain during the passage of mid-latitude cyclones

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  1. Radar signatures in complex terrain during the passage of mid-latitude cyclones Socorro Medina Department of Atmospheric Sciences University of Washington MSC/COMET Mountain Weather Course, Boulder CO , 7 December 2007

  2. Observational Perspective Field Experiments • “MAP” – Mesoscale Alpine Programe • “IMPROVE-2” – Second phase of the Improvement of Microphysical PaRameterization through Observation Verification Experiment

  3. MAPEuropean AlpsSeptember-November 1999 500-mb geopotential height (black lines) and temperature (shaded) Orography

  4. IMPROVE-2Oregon Cascade MountainsNovember-December 2001 500-mb geopotential height (black lines) and temperature (shaded) Orography

  5. Synoptic conditions of MAP and IMPROVE-2 storms:◘ Baroclinic system approaching orographic barrier ◘ Flow far upstream nearly perpendicular to terrain

  6. NOAA WP-3D MAP and IMPROVE-2 radar observations Mean crest = 2 km MSL Mean crest = 3 km MSL S-Pol = NCAR S-band polarimetric radar

  7. Range-Height Indicator (RHI) Fix the azimuth and scan in elevation Radar scanning modes range Horizontal distance Vertical distance range Azimuth (fixed) Elevation (scan) Horizontal distance Horizontal distance RADAR RADAR

  8. Range-Height Indicator (RHI) Fix the azimuth and scan in elevation Radar scanning modes range Horizontal distance Vertical distance Azimuth (fixed) Horizontal distance Horizontal distance RADAR RADAR

  9. Plan Position Indicator (PPI): Fix the elevation angle and scan in azimuth Radar scanning modes range Horizontal distance Vertical distance range Azimuth (scan) (Elevation fixed) Horizontal distance Horizontal distance RADAR RADAR

  10. Plan Position Indicator (PPI): Fix the elevation angle and scan in azimuth Radar scanning modes Horizontal distance Vertical distance range (Elevation fixed) Horizontal distance Horizontal distance RADAR RADAR

  11. Radar measurements • Reflectivity factor (often called reflectivity): Quantity proportional to the sixth-power of the diameters of all the raindrops in a unit volume • Radial velocity: The flow component in the direction of the radar beam

  12. Methodology: Time-averaged vertical cross-sections (from RHI data) MAP IMPROVE-2

  13. Mean Radial velocity (m s-1; from RHIs) Type A  low-level flow rises over terrain MAP Case (IOP2b, 3-hour mean) IMPROVE-2 Case (IOP6, 2-hour mean) NNW E S-POL S-POL

  14. Mean Radial velocity (m s-1; from RHIs) Type B  low-level flow doesn’t rise over terrain ; shear layer MAP (IOP8, 3-hour S-Pol mean) IMPROVE-2 (IOP1, 3-hour mean) E S-POL NNW S-POL

  15. IOP8 (Type B) Airborne radar-derived low-level winds Bousquet and Smull (2006)

  16. IOP8 (Type B) Airborne radar-derived down valley flow Bousquet and Smull (2003)

  17. Summary of terrain-modified airflow in MAP and IMPROVE-2 storms:◘ Type A: Low-level jet rises over the first peaks of the terrain◘ Type B: Shear layer rises over terrain

  18. Measure of stability in moist flow moist Brunt-Vaisala frequency to include latent heating effects (Durran and Klemp, 1982)

  19. Type A cases stability profiles STABLE UNSTABLE

  20. Type B cases stability profiles STABLE UNSTABLE

  21. Summary of static stability in MAP and IMPROVE-2 storms: ◘ Type A: Potential instability ◘ Type B: Statically stable

  22. Mean Reflectivity (dBZ) Type A  Maximum over first major peak MAP Case (IOP2b, 3-hour mean) IMPROVE-2 Case (IOP6, 2-hour mean) NNW E S-POL S-POL

  23. Mean Reflectivity (dBZ) Type B  Bright band MAP Case (IOP8, 3-hour mean) IMPROVE-2 Case (IOP1, 3-hour mean) NW E S-POL S-POL

  24. Summary of reflectivity patterns in MAP and IMPROVE-2 storms:◘ Type A: Localized maximum on terrain peak ◘ Type B: Bright band

  25. cloud droplets graupel growing by riming rain growing by coalescence snow rain Slightly unstable air TYPE A conceptual model of precipitation enhancement for flow rising over terrain 0ºC Low static stability TERRAIN Medina and Houze (2003) Medina and Houze (2003)

  26. Small-scale cells in Type B (Case 01) Vertically pointing radar

  27. Kevin-Helmholtz billows in Type B (Case 1)

  28. Region of enhanced growth by riming and aggregation Region of enhanced growth by coalescence TYPE B conceptual Model of precipitation enhancement for cases with statically stable and retarded low-level flow Shear layer and overturning cells 0°C SNOW RAIN OVERTURNING CELLS Houze and Medina (2005)

  29. Results shown so far from RHI scans, but RHIs are not available in operational scanning - What do Type A and B flow structures look like in PPIs?

  30. Range Z1 < Z2 PPI range as a proxy of height

  31. Orography (km) 4.0 Ticino 3.5 Toce 3.0 2.5 S-Pol 2.0 32 Sounding 24 1.5 16 1.0 Po Basin 8 0.5 0 0.0 -8 -16 -24 -32 Radial velocity (m s-1); PPI = 3.8° Type A case MAP IOP2b 10 UTC 20 Sep (b)

  32. Orography (km) 4.0 Ticino 3.5 Toce 3.0 2.5 S-Pol 2.0 32 Sounding 24 1.5 16 1.0 Po Basin 8 0.5 0 0.0 -8 -16 -24 -32 Radial velocity (m s-1); PPI = 3.8° Type A case MAP IOP2b 10 UTC 20 Sep (b)

  33. MAP Case (IOP2b, 3-hour mean) 32 24 NNW S-POL 16 8 0 -8 -16 -24 -32 Radial velocity (m s-1); PPI = 3.8° Type A case MAP IOP2b 10 UTC 20 Sep Range < 20 km  Height < 1.5 km MSL

  34. Orography (km) 4.0 Ticino 3.5 Toce 3.0 2.5 S-Pol 2.0 32 Sounding 24 1.5 16 1.0 Po Basin 8 0.5 0 0.0 -8 -16 -24 -32 Radial velocity (m s-1); PPI = 3.8° Type A case MAP IOP2b 10 UTC 20 Sep (b)

  35. 500-mb geopotential height (black lines) and temperature12 UTC 20 Sep 32 24 16 8 0 -8 -16 -24 -32 Radial velocity (m s-1); PPI = 3.8° Type A case MAP IOP2b 10 UTC 20 Sep 30 km < Range < 70 km  2 km < Height < 5 km MSL (b)

  36. 4.0 Ticino 3.5 Toce 3.0 2.5 S-Pol 2.0 32 Sounding 24 1.5 16 1.0 Po Basin 8 0.5 0 0.0 -8 -16 -24 -32 Orography (km) Radial velocity (m s-1); PPI = 3.8° Type B case MAP IOP8 06 UTC 21 Oct

  37. 4.0 Ticino 3.5 Toce 3.0 2.5 S-Pol 2.0 32 Sounding 24 1.5 16 1.0 Po Basin 8 0.5 0 0.0 -8 -16 -24 -32 Orography (km) Radial velocity (m s-1); PPI = 3.8° Type B case MAP IOP8 06 UTC 21 Oct (b)

  38. MAP (IOP8, 3-hour S-Pol mean) 32 24 16 8 NNW S-POL 0 -8 -16 -24 -32 Radial velocity (m s-1); PPI = 3.8° Type B case MAP IOP8 06 UTC 21 Oct (b) Range < 10 km  Height < 1 km MSL

  39. MAP (IOP8, 3-hour S-Pol mean) 32 24 16 8 NNW S-POL 0 -8 -16 -24 -32 Radial velocity (m s-1); PPI = 3.8° Type B case MAP IOP8 06 UTC 21 Oct 20 km < Range < 30 km  1.5 km < Height < 2 km MSL Mid-level flow

  40. 32 24 16 8 0 -8 -16 -24 -32 Orography (km) Radial velocity (m s-1); PPI = 3.8° Type B case MAP IOP8 06 UTC 21 Oct 20 km < Range < 30 km  1.5 km < Height < 2 km MSL (b) Mid-level flow

  41. 32 24 16 8 0 -8 -16 -24 -32 500-mb geopotential height (black lines) and temperature06 UTC 21 Oct Radial velocity (m s-1); PPI = 3.8° Type B case MAP IOP8 06 UTC 21 Oct 30 km < Range < 70 km  2 km < Height < 5 km MSL

  42. 4.0 Ticino 3.5 Toce 3.0 2.5 S-Pol 2.0 32 Sounding 24 1.5 16 1.0 Po Basin 8 0.5 0 0.0 -8 -16 -24 -32 Orography (km) Radial velocity (m s-1); PPI = 3.8° Type B case MAP IOP8 06 UTC 21 Oct

  43. u p p e r – l e v e l f l o w cross-barrier flow low-level flow Using flows below 5 km (from PPI scans) for nowcasting of precipitation Low-Level Flow : 1.5 - 2 km height over the closest plane Cross-Barrier Flow: 2.5 - 3.5 km height just South of the Alpine crest Upper-Level Flow: 4 - 5 km height in a circle Work by Panziera and Germann 2007 (MeteoSwiss)

  44. Using flows below 5 km (from PPI scans) for nowcasting of precipitation A decrease of the three flows intensities seems to anticipate the end of the heavy rain. Magnitude (m/s) Rain (averaged over several basins) Panziera and Germann (2007)

  45. Conclusions • -Two predominant terrain-modified flow patterns during orographic enhancement of precipitation have been identified (Types A and B) • -Both patterns produce strong updrafts (>2m/s) • -During Type A cases static instability is responsible for the updraft generation versus turbulent instability in Type B • -During both Types the enhancement of precipitation is produced by the accretion processes (coalescence, aggregation and riming) • -The flows at low-levels have some potential for nowcasting precipitation

  46. Whistler topography

  47. 16 March 2007 Whistler case TYPE B case (MAP IOP8)

  48. 16 March 2006 Whistler case

  49. 16 March 2006 Whistler case

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