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Warm conveyor belts Heini Wernli – ETH Zurich, Switzerland With contributions from: Maxi Böttcher, Christian Grams, Hanna Joos, Erica Madonna, Stephan.

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Presentation on theme: "Warm conveyor belts Heini Wernli – ETH Zurich, Switzerland With contributions from: Maxi Böttcher, Christian Grams, Hanna Joos, Erica Madonna, Stephan."— Presentation transcript:

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

4 Wernli and Davies 1997 Wernli 1997 (QJ) 950 hPa 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 Warm conveyor belts: maximum ascending airstream colors indicate pressure

5 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 Warm conveyor belts: characteristic PV evolution 1.5 pvu + PV anomaly

6 Warm conveyor belts Joos and Wernli 2012 (QJ)

7 Warm conveyor belts

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12 Important cross-isentropic transport of low-PV air Joos and Wernli 2012 (QJ)

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

14 Case 3: WCBs and Xynthia 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 +6 h +12 h +18 h 0 h WCB small-scale Rossby wave generation

16 Identification of top-10 Central European forecast busts in ECMWF 5-day forecasts during 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 select forecasts with 5 largest positive and 5 largest negative SLP errors over Central Europe YEARMONTHDAY/HH / hPa 0202/ hPa 1207/ hPa 1227/ hPa / hPawinter forecasts / hPa 0114/ hPa 0208/ hPa 0209/ hPa 1021/ hPaET of Wilma Interesting: only one similarly bad fc in !

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

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

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 anafc / / / / / / / Forecast busts have too weak WCBs over North Atlantic !

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

22 Forecast busts: how well represented by EPS? Look at bust no.1: _ daysSLP average over C. Europe analysis1003 hPa deterministic fc1024 hPa EPS1012 – 1037 hPa !!

23 WCB climatology ERAinterim Dataset (T255L60), 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 North Atlantic NA Climatology of WCBs (DJF ) WCB starting points (t=0) from Erica Madonna

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

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

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

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

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

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

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

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

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

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

36 Warm conveyor belts Hydrometeors Joos and Wernli 2012 (QJ)

37 Warm conveyor belts Microphysical processes 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, ) 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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