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

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
WCB:
Coherent ascent from the
boundary layer to the upper
troposphere
Maximum cloud and
precipitation producing airflow
e.g., Browning 1990
Warm conveyor belts: maximum ascending airstream
320 hPa
L
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
950 hPa
colors indicate pressure
Wernli and Davies 1997
Wernli 1997 (QJ)
Warm conveyor belts: characteristic PV evolution
0.5 pvu
- PV anomaly
L
1.5 pvu
+ PV anomaly
0.5 pvu
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
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 belts
Important 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
WCB small-scale Rossby wave generation
0h
+6 h
+12 h
+18 h
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
02
12
12
12
01
01
02
02
10
2004
2005
26/12
02/00
07/12
27/12
23/12
13/12
14/00
08/12
09/00
21/12
-15.9 hPa
-13.4 hPa
-13.8 hPa
-15.6 hPa
+15.7 hPa
+20.1 hPa
+17.6 hPa
+18.1 hPa
+18.2 hPa
-14.0 hPa
winter forecasts
ET of “Wilma”
Interesting: only one similarly “bad” fc in 2006-2010!
CE forecast busts: example 6
ana +3.5
fc +3.5
T850 and SLP
ana +5
fc +5
CE forecast busts: example 6
PV on 320 K
ana +5
ana +3.5
R1
T1
T1
R1
fc +3.5
fc +5
T1
T1
R1
R1
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 “WCBlike ascent” into ridges (criterion  > 15K)
2003
2004
2005
01
02
12
12
01
02
10
26/12
02/00
07/12
23/12
13/12
08/12
21/12
# of “WCB-like” trajectories
ana
fc
64
31
19
5
164
134
291
152
115
2
45
0
31
14
Forecast busts have too weak WCBs over North Atlantic !
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
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), 1989-2009
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
Climatology of WCBs (DJF 1989-2009)
WCB starting points (t=0)
North
Atlantic NA
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
ascent
Pressure evolution along N Atlantic WCBs
post-ascent
Start at 935 hPa and rise to
310 hPa, non uniform
from Erica Madonna
pre-ascent
ascent
Specific humidity evolution along N Atl WCBs
time [h]
post-ascent
Initial moisture of 9.4 g/kg,
final 0.1 g/kg
from Erica Madonna
LWC and IWC evolution along N Atlantic WCBs
WCB meeting 2012
– Erica
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
Climatology of WCB moisture uptakes
DJF
Moisture uptake …
… quasi in-situ, purely oceanic,
no transport from tropics
JJA
… involves long-range transport
from tropics and land evapotransp.
from Stephan Pfahl
Warm conveyor belts
Hydrometeors
Joos and Wernli 2012 (QJ)
Warm conveyor belts
Microphysical 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 !