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Why are we here, at the UCLA Conf. Center in June 2005?

This conference aims to explore the best ways of representing the physics of the atmospheric Planetary Boundary Layer (PBL) in weather and climate prediction models. We will discuss the challenges of capturing shallow convection, cloud feedbacks on climate sensitivity, PBL parameterization, and the need for an integrated approach. Working groups will focus on boundary layer clouds, PBL-deep convection interaction, PBL-surface interaction, and stable boundary layers.

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Why are we here, at the UCLA Conf. Center in June 2005?

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  1. Why are we here,at the UCLA Conf. Center in June 2005? Simple models (parameterizations)versus a complex nature What is the best way of representing the physics of the atmospheric PBL in weather and climate prediction models?

  2. Shallow convection over land: ARM case 1) Oklahoma ARM site 2) 21 June 1997 3) Several single-column models (SCM) versus LES start-10 am (local time) end - 3 am (next day) 4) Shallow convection develops at around 3 pm (in LES and in reality) Lenderink et al., 2004 No SCM is able to capture the diurnal cycle of convection

  3. GCSS Pacific Crossection Intercomparison: GPCI Mean crossections (JJA98): relative humidity and liquid water GFDL NCAR UKMO g/kg

  4. GPCI: Histograms of total-cloud-cover.vs.latitude (JJA 98) NCAR Number of events (%) MeteoFrance UKMO

  5. Low cloud climate sensitivity Cloud feedbacks on climate sensitivity are a large source of uncertainty in climate change predictions e.g.: GFDL and NCAR have (or used to have) opposite low cloud cover sensitivity to CO2 doubling Courtesy of Chris Bretherton – Climate Process modelling Team (CPT)

  6. General questions in PBL parameterization • How to represent the sub-grid fluxes? • Eddy-diffusivity • Mass-flux • Eddy-diffusivity/mass-flux combination • Higher-order closures • Mixed-layer approaches • How to represent cloud fraction and mean cloud water? • Pdf-based methods • Prognostic cloud fraction • How to represent the interaction with surface boundary? • Ocean – Land – sub-grid orography • How to integrate the equations efficiently? • Non-linear numerical stability • Accuracy and vertical resolution

  7. Current models: do we need an integrated approach? Climate and weather prediction models use modular parameterizations: Radiation Stable PBL • Nature is not modular (underlying physics is the same) • Coupling between modules is often artificial • Need for an integrated/unified approach Turbulence Convective PBL Surface layer Moist convection DYNAMICS Shallow cumulus Clouds/precipitation Deep cumulus Land and Ocean

  8. PBL parameterizations should also take into account: i) Aerosols and chemical constituents Take into account interactive aerosols and chemical components in a natural way (e.g. numerical issues in source/sink terms). ii)Non-linear numerical stability issues System of non-linear advection-reaction-diffusion equations that leads to numerical stability problems. iii)Stochastic physics and model error Fundamental for predictability and data-assimilation aspects (still fairly unexplored). iv)Scale dependent parameterizations Explicit connections to horizontal resolution, leading to a scale-independent model (physics +dynamics).

  9. Working groups Boundary Layer Clouds Bruce A., Chin-Hoh M., Joao T., Adrian L, Martin K., Chris G., Paquita Z., SungSu P., Yunyan W., Margret V. PBL/deep-convection interaction Brian Mapes, Pier S., Chris B., Rich H., Steve K., Gabriel C., Verica S., Pedro S, Steve Klein, Roel N., Vince L. PBL/surface interaction Andy B., Alan B., Chris F., Anton B., Michael E., Ned P., Carol C., James D., Louise N., Jordi V. Stable boundary layers Branko K., Gunilla S., Bert H., Julie L., Thorsten M., Brian Medeiros., Wayne A., Robert B., Bjorn S.

  10. Working group discussions • What has happened during the last ten years? Progress, problems – practical and conceptual (e.g. Stratocumulus, surface, dry convective) • What are the main unsolved issues right now? Are these conceptual problems, technical, social,…? • Are there solutions to these current issues? Or to the older problems? What are these solutions?

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