The composite Lagrangian cases: LES intercomparison
description
Transcript of The composite Lagrangian cases: LES intercomparison
The composite Lagrangian cases:LES intercomparison
Irina Sandu,
Andy Ackerman, Peter Blossey, Chris Bretherton, Johan van der Dussen, Adrian Lock, Stephan de Roode, Bjorn Stevens
Lagrangian analysis of the air mass flow
MODIS (Terra, Aqua)AMSR-E
ERA-INTERIMHYSPLIT(ERA-INTERIM)
Trajectories + Re-analysis + Satellite data
2002-2007 (May to October in NE, July to December SE)Starting time: 11 LT, Duration: 6 days, Height: 200m
How?
When?
Where? Klein&Hartmann (1993) zones : NE/SE Atlantic, NE/SE Pacific
NEA
SEA
NEP
SEP
Sandu, Stevens and Pincus, ACP, 2010
An ensemble of composite cases: slow, intermediate and fast transitions
CF MODIS
SST LTS D
3 days
refslowfast
Composites NEP JJA 2006-2007
Our questions
Are the LES able to reproduce:
the observed changes in cloudiness induced by changes in the SST/LTS?
the transition’s pace and its dependence on the inversion strength?
Do they agree in term of :
The decrease in cloud albedo and cloud cover during the 3 days
The time evolution of the cloud fraction
The growth rate of the boundary layer
Outline
Simulations : initial conditions, requirements, models
First results for the reference case
The fast/slow cases
Conclusions & Next steps
Composite REF case : NEP - JJA 2006-2007Initial profiles (10 LT) Forcing
Calipso
Time (days)
l (K) qt (g/kg)
u (m/s) v (m/s)
Time (days)
D (x106 s-1)
SST (K)
Initial conditions l
ql
SST
refslowfast
Cts divergence (the same)No advective tendency
Simulations
initial time : 10 LT, duration: 72 hours
initial date: 15 July (but 15 June for UCLA )
diurnal cycle of solar radiative forcing taken into account
cloud droplet number concentration: 100 cm-3
resolution : x = 35m, z = 5m (at cloud top)
domain size : 4.48 X 4.48 X 3.2 km (128 x 128 X 428 points)
Models & participants
UCLA-LES (Irina Sandu)
DALES (Johan van der Dussen, Stephan de Roode)
UKMO (Adrian Lock)
SAM (Peter Blossey, Chris Bretherton)
DHARMA (Andy Ackerman)
REF FAST SLOW
Outline
Simulations : initial conditions, requirements, models
First results for the reference case
The fast/slow cases
Conclusions & Next steps
Difficult to compare to the observed cloud cover
( ! Qualitative comparison only)
UCLA
The simulated SCT (UCLA – big domain)
Albedo decreases by 41 %
The simulations capture the major observed features of the SCT, and corroborate the conceptual model proposed by Bretherton (1992) to explain it
CF
w’v’
UCLA
Do the models agree? (I –time series)
Do the models agree? (I – time series)
Hopefully, it does not matter a lot…
Do the models agree ? (II – decoupling)
UCLA SAM DALES DHARMA
w’v’ (10-4 m2/s3)
Do the models agree ? (III – cloud fraction)
Cloud fraction
UCLA SAM DALES DHARMA
Do the models agree ? (IV – entrainment rate)
Do the models agree ? (V – FT state)
l qt ql
CFqr w’’v
w’2
SW
LW
Do the models agree ? (V – FT state)
l qt ql
CFqr w’’v
w’2
SW
LW
Do the models agree ? (V – FT state)
l qt ql
CFqr w’’v
w’2
SW
LW
Is there a drift in time ? (UCLA)
1h12h24h36h48h60h68h
Is there a drift in time ? (SAM)
1h12h24h36h48h60h68h
Is there a drift in time ? (DALES)
1h12h24h36h48h60h68h
Is there a drift in time ? (DHARMA)
1h12h24h36h48h60h68h
Outline
Simulations : initial conditions, requirements, models
First results for the reference case
The fast/slow cases
Conclusions & Next steps
Slow against fast SCT (UCLA – big domain)
Slow against fast SCT
Role of the inversion strength
Role of the inversion strength
Boundary layer growth rate during the first 24 hours
Conclusions
LES reproduce well not only the main features of the SCT, but also subtle details like differences between slow and fast transitions (UCLA)
The SCT timescale is mostly related to the strength of the temperature inversion capping the Sc topped boundary layer (UCLA)
striking resemblance of the 4 simulations of the reference case (differences well rather understood)
Next steps
fix l,qt at 3km
check why LWD is different in DHARMA (fix LWD)
correct surface fluxes in UCLA-LES
re-run the 3 cases (same domain) - perhaps just the reference case in the beginning