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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). 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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  1. Low clouds in the atmosphere:Never a dull moment stratocumulus cumulus Stephan de Roode (GRS)

  2. 1100 km 1100 km Stratocumulusoff the coast of California

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

  4. 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]

  5. 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?

  6. Contents * Stratocumulusformation * Stratocumulusclimate feedback * High-resolutionmodeling of stratocumulus

  7. Global stratocumulusamount

  8. Necessaryingredientsforstratocumulusformation high pressurearea & coldsurface water

  9. Stratocumulusfrequently present in the subsidingbranch of Hadleycirculation warm and dry cold and moist deep convection shallow cumulus stratocumulus

  10. 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)

  11. Stratocumulus clouds, 31 January 2011Radiosonde observations for De Bilt 00 UTC 12 UTC 31 January 2011 Sharp inversionlayerstructurecannotbecapturedbyweatherforecast models

  12. Longwaveradiativecooling at the cloud top Duynkerke et al. (1995) radiativecoolingtendency at cloud top ~ -8 K/hr

  13. Turbulencecausesentrainment of warm and dry inversion air into the cloudlayer

  14. 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

  15. 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

  16. Feedback effects in a changing climate Cloud feedback Surface albedo feedback Water vapor feedback Radiative effects only Dufresne & Bony, Journal of Climate 2008

  17. Perturbed Future Present Neg. Feedback Pos. Feedback Strong Pos. Feedback slide Pier Siebesma

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

  19. 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)

  20. Results of single-column model versions of climate models: cloudfraction Plot by Roel Neggers (KNMI)

  21. Whatdid we learnfrom the Lagrangiantransition? Movieby Johan van der Dussen

  22. 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

  23. CloudRadiative Feedback (CRF) if the large-scaleforcing is perturbed (higherseasurfacetemperature) S12 stratocumulus red = positive feedback blue= negative feedback S11 cumulus under stratocumulus

  24. "phasespace” experimentswith a conceptual model:how do inversionjumpscontrolequilibriumsolutions? 0 = surface flux + entrainment flux - source

  25. Liquid water path (LWP) response to a perturbation in the seasurfacetemperatureq0 more humidinversionlayer warmer inversionlayer De Roode et al. (2013)

  26. 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)

  27. Cloud response to warming of atmosphere cloud cover (CC) liquid water path (LWP) more humidinversionlayer warmer inversionlayer Dal Gesso et al. (manuscript in preparation)

  28. Cold air outbreak mean wind Satellite

  29. 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

  30. 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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