Warm conveyor belts Heini Wernli – ETH Zurich, Switzerland With contributions from: Maxi...
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Transcript of Warm conveyor belts Heini Wernli – ETH Zurich, Switzerland With contributions from: Maxi...
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
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
Airstreams in extratropical cyclones
e.g., Browning 1990
WCB:
Coherent ascent from theboundary layer to the uppertroposphere
Maximum cloud andprecipitation producing airflow
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
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
Warm conveyor belts
Joos and Wernli 2012 (QJ)
Warm conveyor belts
Warm conveyor belts
Warm conveyor belts
Warm conveyor belts
Warm conveyor belts
Warm conveyor beltsImportant cross-isentropic transport of low-PV air
Joos and Wernli 2012 (QJ)
Case 2: WCB after ET of Hanna
PV on 320 K
Grams et al. 2011 (QJ)
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
+6 h +12 h +18 h0 h
WCB small-scale Rossby wave generation
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)
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!
CE forecast busts: example 6
ana +3.5
fc +3.5
ana +5
fc +5
T850 and SLP
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
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 !
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
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 !!
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
North Atlantic NA
Climatology of WCBs (DJF 1989-2009)
WCB starting points (t=0)
from Erica Madonna
Climatology of WCBs (DJF 1989-2009)
Time evolution from t = -96 h to +96 h
Climatology of WCBs (DJF 1989-2009)
Time evolution from t = -96 h to +96 h
Climatology of WCBs (DJF 1989-2009)
Time evolution from t = -96 h to +96 h
Climatology of WCBs (DJF 1989-2009)
Time evolution from t = -96 h to +96 h
Climatology of WCBs (DJF 1989-2009)
Time evolution from t = -96 h to +96 h
Climatology of WCBs (DJF 1989-2009)
Time evolution from t = -96 h to +96 h
pre-ascent post-ascentascent
Start at 935 hPa and rise to 310 hPa, non uniform
Pressure evolution along N Atlantic WCBs
from Erica Madonna
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
WCB meeting 2012 – Erica
LWC and IWC evolution along N Atlantic WCBs
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
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
Warm conveyor beltsHydrometeors
Joos and Wernli 2012 (QJ)
Warm conveyor beltsMicrophysical processes
Joos and Wernli 2012 (QJ)
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
Heavy precipitation events & cyclones
HPE: >99 percentile at every grid point (ERAinterim, 1989-2010)
Pfahl and Wernli 2012 (J. Clim., in press)
Warm conveyor belts & HPE in autumn 2011
from Maxi Böttcher
Warm conveyor belts & HPE in autumn 2011
from Maxi Böttcher
Warm conveyor belts & HPE in autumn 2011
from Maxi Böttcher
Warm conveyor belts & HPE in autumn 2011
from Maxi Böttcher
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)
T-NAWDEX: International experiment in 2015?
from Pat Harr
Thank you for your attention !