Overview of GABLS achievements as relevant for LOCO Bert Holtslag Thanks to Bob Beare, Joan Cuxart, Gunilla Svensson and many others… GEWEX Atmospheric Boundary Layer Study: Towards a better representation of the Atmospheric Boundary Layer in Weather and Climate models

Why is the stable boundary layer (SBL) important? Surface temperature forecasting at night Fog forecasting Polar climate Land Climate (night and in winter) Dispersion studies Built up of high CO2 (and other scalar) concentrations at night over land...

Example: Mean model bias for the 2 meter temperature in present winter climate (30 years) Courtesy, Geert Lenderink, KNMI Also impact on diurnal cycle

Stable boundary layer mixing Diffusion coefficients by updated ‘Monin- Obukhov (MO)’ versus alternatives (LTG) FmFm FhFh LTG Revised LTGMO Revised LTG LTG MO MO based on Cabauw data (Beljaars and Holtslag, 1991) LTG ‘s used in ECMWF model (Louis et al; Beljaars et al)

Mean model difference in 2 meter temperature for January 1996 using two different stabilty functions in ECMWF model (Courtesy A. Beljaars)

Sensitivity to SBL parameterization in Hadley Centre Climate Model, over Antarctic Difference between new (2nd order closure ) and current scheme (1st order closure ) for 1.5m Temperature (K), JJA season, 5 year mean (King et al. 2001, QJRMS)

State of the Art for stable boundary layers Large bias and sensitivity to model formulation (at least over Land and Ice!) Operational models typically like enhanced mixing What can we learn from fine-scale modeling (LES)? How do operational models compare?

GABLS first inter comparison case Simple shear driven case (after Kosovic and Curry, 2000) Prescribed surface cooling 0.25 K/h (over ice) for 9 hours to quasi- equilibrium; no surface and radiation scheme Geostrophic wind 8 m/s, latitude 73N

An intercomparison of large-eddy simulations of the stable boundary layer Coordinated by Bob Beare, Malcolm MacVean, Anne McCabe Met Office, UK See: gabls.org for details Domain 400m x 400m x 400m Resolutions: 12.5m, 6.25m, 3.125m, 2m, 1m 10 results sets, 17 investigators Beare et al, 2005 (Accepted for BLM)

Mean potential temperature of LES models after nine hours of cooling Significant spread in results, but convergence at high resolution (Sensitivity to sub-grid model) Beare et al, 2005

Intercomparison of Single-Column Models Coordinated by Joan Cuxart i Rodamilans, Maria Jiménez, Laura Conangla Universitat de les Illes Balears (Mallorca, SP) Results of more than 20 models (Operational and Research): Various SBL parameterizations and resolutions Next slides focus on operational models in comparison with LES Cuxart et al, 2005 (BLM, accepted)

GABLS 1D Intercomparison Resolution (most) operational models is set to 6.25 m! Comparison of Single-Column Models with LES (Cuxart et al, 2005)

Heat Fluxes Momentum Fluxes

Apparent Diffusivities for Momentum and Heat

Steeneveld, Van de Wiel, Holtslag, 2005 (BLM, accepted) Models can represent main LES results after adjusting, e.g. length scale:

’Ekman spirals’ (Svensson+Holtslag, 2005) (u ms -1 ) LES Operational Research- Meso Research 

Boundary-layer height and surface angle LES consistent with Cabauw data!

Why do Operational Models need Enhanced Mixing? To prevent ‘runaway’ surface cooling To have sufficient ‘Ekman pumping’ To compensate for model errors However, Atmospheric Boundary Layer pays the price!

GABLS referenceAlternative with coupling to surface Steeneveld, Van de Wiel, Holtslag, 2005 (BLM, accepted)

Summary First model intercomparison Large variation among 1D models, but all operational models show too strong mixing! Details in Turbulence Schemes do matter! 8 papers are currently accepted for special issue in Boundary Layer Meteorology, to appear in 2005/6

What next in GABLS? Intercomparison for three day and night period in CASES99 (after Steeneveld, Van der Wiel, Holtslag, 2005, JAS in press) Preparation of case by G. Svensson et al for 1D models focussing on PBL (prescribed surface temperature): Case released in May 2005 See

Second GABLS model intercomparison experiment About 20 models by 15 groups Coordinated by Gunilla Svensson Department of meteorology, Stockholm university

Intercomparison of 1D models on basis of CASES99 for a period of 2.5 days (focus on PBL) Prescribed surface temperature Also same initial conditions and forcings for wind and humidity

Potential temperature Preliminary Results +24 h forecasts

Potential temperature Preliminary Results +32 h forecasts

Potential temperature Preliminary Results +36 h forecasts

Potential temperature Preliminary Results +40 h forecasts

Potential temperature Preliminary Results +48 h forecasts

Wind speed Preliminary Results +24 h forecasts

Wind speed Preliminary Results +32 h forecasts

Wind speed Preliminary Results +36 h forecasts

Wind speed Preliminary Results +40 h forecasts

Friction velocity

Sensible heat flux

Boundary-layer height

Further analysis and intercomparison of the 1D models for CASES99 (Diurnal Cycle) Intercomparison of LES and 1D models for specific stable cases Coupling of models to Land Surface What next in GABLS? But HOW and by WHOM?

Theme 1: Stable boundary layers -Experience with coupled land/atmosphere models for stable boundary layers in other regions of the world -Ideas for parameterizations that specifically aim at a proper representation of the land/atmosphere coupling Gert Jan Steeneveld Experiences with the (coupled) boundary-layer modelling of the three day- night period in CASES99 Break Zbig Sorbjan Parameterizations of very stable boundary layers, derived from CASES99 Joan Cuxart Mesoscale simulations of Stable Boundary Layers Bob Beare Large Eddy Simulations of an evening transition

Theme 2: Coupled boundary layer experiments and feedbacks -Observational means for diagnosing land-atmosphere interaction -SCM experiments with cloud and pbl feedbacks for other places in the world -Ideas for parameterizations that specifically aim at a proper representation of the land/atmosphere coupling Michael Ek SCM experiments at Cabauw Anne McCabe Modeling the stable boundary layer and the role of land surface heterogeneity Frank Beyrich Some recent results on land/atmosphere interaction and ABL structure over the LITFASS area Fred Bosveld and Peter Baas Classification of low level jets at Cabauw

Thanks to all the participating scientists within GABLS (about 50) and our colleagues for providing inputs, model runs, advice, et cetera

Int. turb Fully turb Non- turb Example: Results with a 1D high resolution ABL model fully coupled to Land Surface for 3 different nights using dynamic forcings and local surface characteristics Steeneveld, van de Wiel, Holtslag, 2005 (J.Atmos. Sci, in press)

Int. turb Fully turb Non- turb

Int. turb Fully turb Non- turb

Int. turb Fully turb Non- turb

Wind and temperature profiles

LES 1D Striking differences overall Even for this simple case!