Low clouds in the atmosphere never a dull moment
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Low clouds in the atmosphere: Never a dull moment. stratocumulus. cumulus. Stephan de Roode (GRS). 1100 km. 1100 km. Stratocumulus off the coast of California. Low clouds above the North Sea (and a part of the coast). Outstanding questions 1. Stratocumulus and climate change.

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Low clouds in the atmosphere: Never a dull moment

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Low clouds in the atmosphere never a dull moment

Low clouds in the atmosphere:Never a dull moment

stratocumulus

cumulus

Stephan de Roode (GRS)


Stratocumulus off the coast of california

1100 km

1100 km

Stratocumulusoff the coast of California


Low clouds above the north sea and a part of the coast

Low cloudsabove the NorthSea (and a part of the coast)


Outstanding questions 1 stratocumulus and climate change

Outstandingquestions1. Stratocumulus and climatechange

Randall et al. 1984:

"A 4% increase in globalstratocumulusextendwould offset 2-3K global warming from CO2 doubling"

cloud layer geometric thickness [m]


Outstanding questions problems 2 poor representation of stratocumulus in weather forecast models

Outstandingquestions/problems2. Poorrepresentation of stratocumulus in weatherforecast models

Stevens et al. 2007:

"ECMWF products are more deficient in theirrepresentation of the stratocumulustoppedboundarylayeritself...... cloudliquid water pathsstilltend to be a factor of 2–4 lessthanobserved, and boundarylayertemperatures are found to correlatepoorlywith the observations."

* Can we improve the predictionwith a high-resolution model?


Contents

Contents

* Stratocumulusformation

* Stratocumulusclimate feedback

* High-resolutionmodeling of stratocumulus


Global stratocumulus amount

Global stratocumulusamount


Necessary ingredients for stratocumulus formation

Necessaryingredientsforstratocumulusformation

high pressurearea &

coldsurface water


Stratocumulus frequently present in the subsiding branch of hadley circulation

Stratocumulusfrequently present in the subsidingbranch of Hadleycirculation

warm and dry

cold and moist

deep convection

shallow cumulus

stratocumulus


Stratocumulus frequently present in the arctic area but we can hardly observe them from satellite

Stratocumulusfrequently present in the Arcticarea(but we canhardlyobservethemfromsatellite)

Infrared: very low thermal contrast betweenicesurface and low clouds

Shortwave: albedoice and cloudsimilar (and long dark winters)


Stratocumulus clouds 31 january 2011 radiosonde observations for de bilt

Stratocumulus clouds, 31 January 2011Radiosonde observations for De Bilt

00 UTC

12 UTC

31 January 2011

Sharp inversionlayerstructurecannotbecapturedbyweatherforecast models


Longwave radiative cooling at the cloud top

Longwaveradiativecooling at the cloud top

Duynkerke et al. (1995)

radiativecoolingtendency at cloud top ~ -8 K/hr


Turbulence causes entrainment of warm and dry inversion air into the cloud layer

Turbulencecausesentrainment of warm and dry inversion air into the cloudlayer


Low clouds in the atmosphere never a dull moment

AtmosphericModels

Cloud dynamics

mm

10 m

100 m

1 km

10 km

100 km

1000 km

10000 km

Cloud microphysics

turbulence

Cumulus

clouds

Cumulonimbus

clouds

Mesoscale

Convective systems

Extratropical

Cyclones

Planetary

waves

DNS

Subgrid

Large Eddy Simulation (LES) Model

LimitedAreaWeather Model (LAM)

Numerical Weather Prediction (NWP) Model

Global Climate Model

Engineering

Fundamental

Slidecourtesy Harm Jonker and Pier Siebesma


Low clouds in the atmosphere never a dull moment

Currentdevelopments

Cloud dynamics

mm

10 m

100 m

1 km

10 km

100 km

1000 km

10000 km

Cloud microphysics

turbulence

Cumulus

clouds

Cumulonimbus

clouds

Mesoscale

Convective systems

Extratropical

Cyclones

Planetary

waves

DNS

Subgrid

Large Eddy Simulation (LES) Model

LimitedAreaWeather Model (LAM)

NumericalWeatherPrediction (NWP) Model

Global Climate Model

Engineering

Fundamental


Low clouds in the atmosphere never a dull moment

Feedback effects in a changing climate

Cloud feedback

Surface albedo feedback

Water vapor feedback

Radiative effects only

Dufresne & Bony, Journal of Climate 2008


Low clouds in the atmosphere never a dull moment

Perturbed Future

Present

Neg. Feedback

Pos. Feedback

Strong Pos. Feedback

slide Pier Siebesma


Low clouds in the atmosphere never a dull moment

Can models faithfullyrepresent low clouds?Simulations of the ASTEX Lagrangianstratocumulus experiment


Modeling results for astex case

Modelingresultsfor ASTEX case

  • Case set-up basedon De Roode and Duynkerke (1997)

  • 20 international institutionsparticipate in this model intercomparison case

Van der Dussen et al. (2012)


Results of single column model versions of climate models cloud fraction

Results of single-column model versions of climate models: cloudfraction

Plot by Roel Neggers (KNMI)


What did we learn from the lagrangian transition

Whatdid we learnfrom the Lagrangiantransition?

Movieby Johan van der Dussen


Low clouds in the atmosphere never a dull moment

The CGILS project (Zhang et al.2013)

Equilibrium states are computed for three selected columns in the Hadley circulation

* Single-column model (SCM) versions of climate models

* Large-eddy simulation (LES) models

S6

cumulus

S11 cumulus under stratocumulus

S12

stratocumulus

  • Run to steady state with diurnally-averaged insolation

  • Vertical profiles of temperature, humidity and ozone above the LES domain are used for radiative transfer


Low clouds in the atmosphere never a dull moment

CloudRadiative Feedback (CRF) if the large-scaleforcing is perturbed (higherseasurfacetemperature)

S12

stratocumulus

red =

positive feedback

blue=

negative feedback

S11 cumulus under stratocumulus


Low clouds in the atmosphere never a dull moment

"phasespace” experimentswith a conceptual model:how do inversionjumpscontrolequilibriumsolutions?

0=surface flux+entrainment flux -source


Liquid water path lwp response to a perturbation in the sea surface temperature q 0

Liquid water path (LWP) response to a perturbation in the seasurfacetemperatureq0

more humidinversionlayer

warmer inversionlayer

De Roode et al. (2013)


Low clouds in the atmosphere never a dull moment

Cloud regimes: Resultsfromtwo different transport schemesused in weather and climate models ("dualM" and "TKE")

liquid water path LWP

cloud cover CC

Dal Gesso et al. (2013)


Cloud response to warming of atmosphere

Cloud response to warming of atmosphere

cloud cover (CC)liquid water path (LWP)

more humidinversionlayer

warmer inversionlayer

Dal Gesso et al. (manuscript in preparation)


Cold air outbreak

Cold air outbreak

mean wind

Satellite


Cold air outbreak case simulated with the les model

Cold air outbreak case simulatedwith the LES model

simulatedcloudliquid water path (kg/m2)

Thomas Frederikse (MSc student)

MSc thesis defense: Tuesday 2 April, 15.00 pm


Low clouds in the atmosphere never a dull moment

Summary

  • Physics of stratocumulus

  • Smallscaleprocesses (longwaveradiation, entrainmentacrossthininversionlayer)

  • Weatherforecast models

  • Have a coarseverticalresolutioncausingdifficulties to capturesmall-scaleprocesses

  • High-resolutionlarge-eddysimulation models

  • Invaluabletoolforstudyingdynamics of stratocumulus

  • Ambition: Detailedweatherpredictionfor wind and solarenergy

  • Current model intercomparisonprojects

  • Phasespaceexperiments, cold air outbreak


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