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Warm conveyor belts Heini Wernli – ETH Zurich, Switzerland With contributions from:

Warm conveyor belts Heini Wernli – ETH Zurich, Switzerland With contributions from: Maxi Böttcher, Christian Grams, Hanna Joos, Erica Madonna, Stephan Pfahl, Nicolas Piaget PDP WG meeting, Reading, 19 June 2012. Outline of the talk The concept of WCBs

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Warm conveyor belts Heini Wernli – ETH Zurich, Switzerland With contributions from:

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  1. Warm conveyor belts Heini Wernli – ETH Zurich, Switzerland With contributions from: Maxi Böttcher, Christian Grams, Hanna Joos, Erica Madonna, Stephan Pfahl, Nicolas Piaget PDP WG meeting, Reading, 19 June 2012

  2. Outline of the talk The concept of WCBs WCBs and amplification of upper-level ridges WCBs and forecast busts Climatology of WCBs Moisture sources of WCBs Microphysical processes in WCBs WCBs and HPEs

  3. Airstreams in extratropical cyclones WCB: Coherent ascent from the boundary layer to the upper troposphere Maximum cloud and precipitation producing airflow e.g., Browning 1990

  4. Warm conveyor belts: maximum ascending airstream 320 hPa • within 2 days: • ascent > 600 hPa • polew. transport > 3500 km • latent heating > 20 K • flow structure in extratropical cyclones with strongest latent heat release & precipitation L 950 hPa colors indicate pressure Wernli and Davies 1997 Wernli 1997 (QJ)

  5. Warm conveyor belts: characteristic PV evolution 0.5 pvu - PV anomaly characteristic evolution of potential vorticity (PV) along WCBs: in low troposphere: increase ~0.5  ~1.5 pvu due to dH/dz > 0 in upper troposphere: decrease ~1.5  ~0.5 pvu due to dH/dz < 0 L 1.5 pvu + PV anomaly 0.5 pvu

  6. Warm conveyorbelts Joos and Wernli 2012 (QJ)

  7. Warm conveyorbelts

  8. Warm conveyorbelts

  9. Warm conveyorbelts

  10. Warm conveyorbelts

  11. Warm conveyorbelts

  12. Warm conveyorbelts Importantcross-isentropictransport of low-PVair Joos and Wernli 2012 (QJ)

  13. Case 2: WCB after ET of Hanna PV on 320 K Grams et al. 2011 (QJ)

  14. Case 3: WCBs and Xynthia PV@320K and SLP at 00 UTC 26 Feb with WCB intersection points Intense WCBs associated with US snowstorm and early phase of Xynthia from Nicolas Piaget

  15. WCB small-scale Rossby wave generation +18 h +12 h +6 h 0 h

  16. Identification of top-10 Central European forecast busts in ECMWF 5-day forecasts during 2003-2005 based upon simple error measure: SLP-error = difference in domain-averaged SLP (fc - ana) domain: Central Europe (0-30E, 45-60N)

  17. Identification of top-10 Central European forecast busts in ECMWF 5-day forecasts during 2003-2005 select forecasts with 5 largest positive and 5 largest negative SLP errors over Central Europe YEAR MONTH DAY/HH 2003 01 26/12 -15.9 hPa 02 02/00 -13.4 hPa 12 07/12 -13.8 hPa 12 27/12 -15.6 hPa 2004 12 23/12 +15.7 hPa winter forecasts 2005 01 13/12 +20.1 hPa 01 14/00 +17.6 hPa 02 08/12 +18.1 hPa 02 09/00 +18.2 hPa 10 21/12 -14.0 hPa ET of “Wilma” Interesting: only one similarly “bad” fc in 2006-2010!

  18. CE forecast busts: example 6 T850 and SLP ana +5 ana +3.5 fc +3.5 fc +5

  19. CE forecast busts: example 6 PV on 320 K ana +5 ana +3.5 T1 R1 T1 R1 fc +3.5 fc +5 T1 T1 R1 R1

  20. Forecast busts: common dynamical pattern? In all cases: forecasts have too weak UT ridges (not broad enough, PV values not low enough) Backward trajectory analysis of these UT ridges, look for “WCB-like ascent” into ridges (criterion  > 15K) # of “WCB-like” trajectories ana fc 2003 01 26/12 64 31 02 02/00 19 5 12 07/12 164 134 2004 12 23/12 291 152 2005 01 13/12 115 2 02 08/12 45 0 10 21/12 31 14 Forecast busts have too weak WCBs over North Atlantic !

  21. Hypothesis: errors in WCBs amplify downstream - - + generation of a positive PV anomaly (downstream trough) WCB  amplified upper-level ridge  downstream trough WCB triggers / enhances downstream Rossby wave activity

  22. Forecast busts: how well represented by EPS? Look at bust no.1: 20050113_12 + 5 days SLP average over C. Europe analysis 1003 hPa deterministic fc 1024 hPa EPS 1012 – 1037 hPa !!

  23. WCB climatology ERAinterim Dataset (T255L60), 1989-2009 Forward trajectory calculation Trace TH, THE, Q, LWC, IWC, PV WCBs selection criteria 1) start in the atmospheric boundary layer ( p > 790 hPa) and ascent larger than 600 hPa within 2 days (48 hrs) 2) ascent in the vicinity of extratropical cyclones

  24. Climatology of WCBs (DJF 1989-2009) WCB starting points (t=0) North Atlantic NA from Erica Madonna

  25. Climatology of WCBs (DJF 1989-2009) Time evolution from t = -96 h to +96 h

  26. Climatology of WCBs (DJF 1989-2009) Time evolution from t = -96 h to +96 h

  27. Climatology of WCBs (DJF 1989-2009) Time evolution from t = -96 h to +96 h

  28. Climatology of WCBs (DJF 1989-2009) Time evolution from t = -96 h to +96 h

  29. Climatology of WCBs (DJF 1989-2009) Time evolution from t = -96 h to +96 h

  30. Climatology of WCBs (DJF 1989-2009) Time evolution from t = -96 h to +96 h

  31. Pressure evolution along N Atlantic WCBs ascent pre-ascent post-ascent Start at 935 hPa and rise to 310 hPa, non uniform from Erica Madonna

  32. time [h] Initial moisture of 9.4 g/kg, final 0.1 g/kg Specific humidity evolution along N Atl WCBs ascent pre-ascent post-ascent from Erica Madonna

  33. WCB meeting 2012 – Erica LWC and IWC evolution along N Atlantic WCBs

  34. Climatology of WCB starting regions in North Pacific 2001-2010 DJF JJA Where are evaporative moisture sources of WCBs?  do Lagrangain moisture uptake analysis (Sodemann et al. 2008, JGR) along 10-day backward extensions of WCBs

  35. Climatology of WCB moisture uptakes DJF JJA Moisture uptake … … quasi in-situ, purely oceanic, … involves long-range transport no transport from tropics from tropics and land evapotransp. from Stephan Pfahl

  36. Warm conveyorbelts Hydrometeors Joos and Wernli 2012 (QJ)

  37. Warm conveyorbelts Microphysicalprocesses Joos and Wernli 2012 (QJ)

  38. Warm conveyor belts & HPE Climatology: what percentage of HPE occurs simultaneously with the presence of a cyclone? HPE and WCBs in pre-HYMEX autumn 2011

  39. Heavy precipitation events & cyclones HPE: >99 percentile at every grid point (ERAinterim, 1989-2010) Pfahl and Wernli 2012 (J. Clim., in press)

  40. Warm conveyor belts & HPE in autumn 2011 from Maxi Böttcher

  41. Warm conveyor belts & HPE in autumn 2011 from Maxi Böttcher

  42. Warm conveyor belts & HPE in autumn 2011 from Maxi Böttcher

  43. Warm conveyor belts & HPE in autumn 2011 from Maxi Böttcher

  44. Summary • WCBs are key airflows in extratropical cyclones • strong ascent and cross-isentropic transport • preferred regions of occurrence • some WCBs associated with HPE • characteristic PV evolution • impact on downstream flow evolution • critical process for medium-range forecasting • associated with different microphysical processes •  Several aspects that could be investigated within aircraft field experiments (DIAMET, T-NAWDEX-Falcon)

  45. T-NAWDEX: International experiment in 2015? from Pat Harr

  46. Thank you for your attention !

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