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