Presentation on theme: "Warm conveyor belts Heini Wernli – ETH Zurich, Switzerland"— 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 PiagetPDP WG meeting, Reading, 19 June 2012
2 Outline of the talk The concept of WCBs WCBs and amplification of upper-level ridgesWCBs and forecast bustsClimatology of WCBsMoisture sources of WCBsMicrophysical processes in WCBsWCBs and HPEs
3 Airstreams in extratropical cyclones WCB:Coherent ascent from theboundary layer to the uppertroposphereMaximum cloud andprecipitation producing airflowe.g., Browning 1990
4 Warm conveyor belts: maximum ascending airstream 320 hPawithin 2 days:ascent > 600 hPapolew. transport > 3500 kmlatent heating > 20 Kflow structure in extratropical cyclones with strongest latent heat release & precipitationL950 hPacolors indicate pressureWernli and Davies 1997Wernli 1997 (QJ)
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 EuropeYEAR MONTH DAY/HH/ hPa02 02/ hPa12 07/ hPa12 27/ hPa/ hPa winter forecasts/ hPa01 14/ hPa02 08/ hPa02 09/ hPa10 21/ hPa ET of “Wilma”Interesting: only one similarly “bad” fc in !
18 CE forecast busts: example 6 T850 and SLPana +3.5ana +5fc +3.5fc +5
19 CE forecast busts: example 6 PV on 320 Kana +3.5ana +5T1R1T1R1fc +3.5fc +5T1T1R1R1
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” trajectoriesana fc/02 02/12 07///02 08/10 21/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 troughWCB triggers / enhances downstream Rossby wave activity
22 Forecast busts: how well represented by EPS? Look at bust no.1:_ days SLP average over C. Europeanalysis hPadeterministic fc hPaEPS – 1037 hPa !!
23 WCB climatology ERAinterim Dataset (T255L60), 1989-2009 Forward trajectory calculationTrace TH, THE, Q, LWC, IWC, PVWCBs selection criteria1) 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 cyclonesTo identify WCBs we start forward trajectories calculation in the ABL (p>790) and we select those trajectories that ascend more than 600hPa within 48 hours. Afterward we consider the physical relationship between WCBs and extratropical cyclone to filter out trajectories related to tropical convection.
24 Climatology of WCBs (DJF 1989-2009) WCB starting points (t=0)North Atlantic NAThe situation for DJF is displayed here. In North Hemisphe we observe more maxima than for JJA, a shifting of the maximum from chine over the North Pacific and a strong intensification of the maximum over the North Atlantic.In the Southern hemisphere there is less variability than in the northen and we obsere still a peak in the lee of the Andes.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 Start at 935 hPa and rise to 310 hPa, non uniform Pressure evolution along N Atlantic WCBsascentpre-ascentpost-ascentStart at 935 hPa and rise to 310 hPa, non uniformfrom Erica Madonna
32 Initial moisture of 9.4 g/kg, Specific humidity evolution along N Atl WCBsInitial moisture of 9.4 g/kg,final 0.1 g/kgtime [h]For the next we focus on the North Atlantic region in the wintertime. We look at all the trajectories that starts in this regions and performed a statistic of the temporal evolution of the pressure and specific humidity and like before 0 refer to the moment where the ascent begin. In the representation is to see the mean and the median (black and red) and the 50 and 90 percentile as green areas.In Winter WCBs start above 935 hPa and rise up to 310 hPa in two day but not linearly. In average the WCBs contain around 10 g of water vapor pro Kg air and they lose almost all the vapor in the first 36 hours, first trough condensation and deposition. Then most of the water will leave the air parcel and reach the ground in form of precipiation.ascentpre-ascentpost-ascentfrom Erica Madonna
33 LWC and IWC evolution along N Atlantic WCBs This graphics represent all the WCBs that start in the NA during Decemer, Januaray and February in the last 21 year. In the representation I plot tge mean and the median (black and red) and the 50 and 90 percentile as green areas. Display is the temporal evolution (like before 0 refer to the moment where the ascent begin) of the pressure, specific humidity, lWC, IWC.In Winter WCBs start above 900 hPa and rise up to 300 hPa in two day but not linearly. In average the WCBs contain around 10 g of water vapor pro Kg air and they lose almost all the vapor in the first 36 hours. As the air parcel rise vapor condense and as we can see from the following pictures, we observe first an increase in the LWC and then, as the parcel reach higher altitude, an increase in LWC.Most of the water will leave the air parcel and reach the ground in form of precipiation as it can be seen in the amount of water after 48h: the parcels contain almost no water.However we still have some ice, which indicate the capacity of WCBs to form cirrus clouds.WCB meeting – Erica
34 Climatology of WCB starting regions in North Pacific 2001-2010 DJFJJAWhere 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 DJFJJAMoisture uptake …… quasi in-situ, purely oceanic, … involves long-range transportno transport from tropics from tropics and land evapotransp.from Stephan Pfahl
36 Warm conveyor beltsHydrometeorsJoos and Wernli 2012 (QJ)
37 Warm conveyor beltsMicrophysical processesJoos 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 Pfahl and Wernli 2012 (J. Clim., in press) Heavy precipitation events & cyclonesHPE: >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 transportpreferred regions of occurrencesome WCBs associated with HPEcharacteristic PV evolutionimpact on downstream flow evolutioncritical process for medium-range forecastingassociated 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
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