Warm conveyor belts Heini Wernli – ETH Zurich, Switzerland With contributions from:
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Transcript of Warm conveyor belts Heini Wernli – ETH Zurich, Switzerland With contributions from:
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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
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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
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Airstreams in extratropical cyclones
e.g., Browning 1990
WCB:
Coherent ascent from theboundary layer to the uppertroposphere
Maximum cloud andprecipitation producing airflow
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Wernli and Davies 1997Wernli 1997 (QJ)
950 hPa
320 hPawithin 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
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0.5 pvu
0.5 pvu- PV anomaly
characteristic evolution of potential vorticity (PV) along WCBs:
in low troposphere:increase ~0.5 ~1.5 pvudue to dH/dz > 0
in upper troposphere:decrease ~1.5 ~0.5 pvudue to dH/dz < 0
L
Warm conveyor belts: characteristic PV evolution
1.5 pvu+ PV anomaly
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Warm conveyor belts
Joos and Wernli 2012 (QJ)
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Warm conveyor belts
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Warm conveyor belts
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Warm conveyor belts
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Warm conveyor belts
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Warm conveyor belts
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Warm conveyor beltsImportant cross-isentropic transport of low-PV air
Joos and Wernli 2012 (QJ)
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Case 2: WCB after ET of Hanna
PV on 320 K
Grams et al. 2011 (QJ)
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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
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+6 h +12 h +18 h0 h
WCB small-scale Rossby wave generation
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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)
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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 hPa02 02/00 -13.4 hPa12 07/12 -13.8 hPa12 27/12 -15.6 hPa
2004 12 23/12 +15.7 hPa winter forecasts2005 01 13/12 +20.1 hPa
01 14/00 +17.6 hPa02 08/12 +18.1 hPa02 09/00 +18.2 hPa10 21/12 -14.0 hPa ET of “Wilma”
Interesting: only one similarly “bad” fc in 2006-2010!
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CE forecast busts: example 6
ana +3.5
fc +3.5
ana +5
fc +5
T850 and SLP
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CE forecast busts: example 6
ana +3.5
fc +3.5
ana +5
fc +5
R1T1
T1R1
R1
R1
PV on 320 K
T1
T1
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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
2003 01 26/12 64 3102 02/00 19 512 07/12 164 134
2004 12 23/12 291 1522005 01 13/12 115 2
02 08/12 45 010 21/12 31 14
Forecast busts have too weak WCBs over North Atlantic !
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generation of a positive PV anomaly(downstream trough)
WCB amplified upper-level ridge downstream troughWCB triggers / enhances downstream Rossby wave activity
+
-
-
Hypothesis: errors in WCBs amplify downstream
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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 !!
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WCB climatology
ERAinterim Dataset (T255L60), 1989-2009Forward trajectory calculationTrace 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
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North Atlantic NA
Climatology of WCBs (DJF 1989-2009)
WCB starting points (t=0)
from Erica Madonna
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Climatology of WCBs (DJF 1989-2009)
Time evolution from t = -96 h to +96 h
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Climatology of WCBs (DJF 1989-2009)
Time evolution from t = -96 h to +96 h
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Climatology of WCBs (DJF 1989-2009)
Time evolution from t = -96 h to +96 h
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Climatology of WCBs (DJF 1989-2009)
Time evolution from t = -96 h to +96 h
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Climatology of WCBs (DJF 1989-2009)
Time evolution from t = -96 h to +96 h
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Climatology of WCBs (DJF 1989-2009)
Time evolution from t = -96 h to +96 h
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pre-ascent post-ascentascent
Start at 935 hPa and rise to 310 hPa, non uniform
Pressure evolution along N Atlantic WCBs
from Erica Madonna
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Initial moisture of 9.4 g/kg,final 0.1 g/kg
time [h]
pre-ascent post-ascentascent
Specific humidity evolution along N Atl WCBs
from Erica Madonna
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WCB meeting 2012 – Erica
LWC and IWC evolution along N Atlantic WCBs
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DJF JJA
Climatology of WCB starting regions in North Pacific 2001-2010
Where are evaporative moisture sources of WCBs? do Lagrangain moisture uptake analysis (Sodemann et al. 2008, JGR)along 10-day backward extensions of WCBs
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DJF JJA
Climatology of WCB moisture uptakes
Moisture uptake …… quasi in-situ, purely oceanic, … involves long-range transportno transport from tropics from tropics and land evapotransp. from Stephan Pfahl
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Warm conveyor beltsHydrometeors
Joos and Wernli 2012 (QJ)
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Warm conveyor beltsMicrophysical processes
Joos and Wernli 2012 (QJ)
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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
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Heavy precipitation events & cyclones
HPE: >99 percentile at every grid point (ERAinterim, 1989-2010)
Pfahl and Wernli 2012 (J. Clim., in press)
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Warm conveyor belts & HPE in autumn 2011
from Maxi Böttcher
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Warm conveyor belts & HPE in autumn 2011
from Maxi Böttcher
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Warm conveyor belts & HPE in autumn 2011
from Maxi Böttcher
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Warm conveyor belts & HPE in autumn 2011
from Maxi Böttcher
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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)
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T-NAWDEX: International experiment in 2015?
from Pat Harr
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Thank you for your attention !