Overview of GABLS achievements as relevant for LOCO Bert Holtslag Thanks to Bob Beare, Joan Cuxart,...

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 modelswww.met.wau.nl/gabls.html

http://www.met.wau.nl/gabls.html



Example:Mean model bias for the 2 meter

temperaturein present winter climate (30 years)

Courtesy,Geert Lenderink,

KNMI

Also impact on diurnal cycle

Mean model difference in 2 meter temperature for January 1996 using two different stabilty

functions in ECMWF model (Courtesy A. Beljaars)

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 caseSimple 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

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

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

’Ekman spirals’ (Svensson+Holtslag, 2005)

(u ms-1)

LESOperationalResearch-MesoResearch

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!

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 acceptedfor special issue in Boundary Layer

Meteorology, to appear in 2005/6

Second GABLS model intercomparison

experimentAbout 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

Wind speed


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 SteeneveldExperiences with the (coupled) boundary-layer modelling of the

three day-night period in CASES99

Break

Zbig SorbjanParameterizations of very stable boundary layers, derived from

CASES99

Joan CuxartMesoscale 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 EkSCM experiments at Cabauw

Anne McCabeModeling the stable boundary layer and the role of land surface

heterogeneity

Frank BeyrichSome recent results on land/atmosphere interaction and ABL

structure over the LITFASS area

Fred Bosveld and Peter BaasClassification 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

Fullyturb

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 characteristicsSteeneveld, van de Wiel, Holtslag, 2005 (J.Atmos. Sci, in press)

Int. turb

Fullyturb

Non- turb

Wind and temperature profiles

Overview of GABLS achievements as relevant for LOCO Bert Holtslag Thanks to Bob Beare, Joan Cuxart,...

Documents

Transcript of Overview of GABLS achievements as relevant for LOCO Bert Holtslag Thanks to Bob Beare, Joan Cuxart,...