Simple but realistic cases from Cabauw for GABLS
Simple but realistic cases from Cabauw for GABLS: an Update Towards a new GABLS intercomparison study Fred Bosveld 1 Peter Baas 1 Gert-Jan Steeneveld 2 Sander Tijm 1 Cisco de Bruijn 1 Henk Klein Baltink 1 Sukanta Basu 3 1 : Royal Dutch Meteorological Institute 2 : Wageningen University 3 : Texas Tech University 7 th EMS Annual meeting, October 2007, Spain
GEWEX Atmospheric Boundary Layer Studies • • Improve the understanding and representation of the boundary layer in weather forecast and climate models GABLS 3, using Cabauw data: • – – – GABLS 1 – Academic set-up – LES as reference • • GABLS 2 – Based on (idealized) CASES 99 – Diurnal cycle – Prescribed Ts Focus Comparison with observations Land-atmosphere coupling Low-level jet Morning (and evening) transition SBL benchmark case Lessons from the past – – Careful case selection 3 D runs in advance Atmospheric forcings Stay close to observations GABLS Workshop Stockholm, June 2006 7 th EMS Annual meeting, October 2007, Spain
The Cabauw Site 7 th EMS Annual meeting, October 2007, Spain
The Cabauw Site: some impressions ~ 1500 m ~ 700 m 7 th EMS Annual meeting, October 2007, Spain
Case Selection • 6 -year database (2001 -2006) Criteria – Geostrophic wind : On average between 6 and 8 m/s, at maximum 3 m/s variation – Net radiation < -30 W/m 2 (no clouds) – Relatively constant Ta 200 (to avoid cases with large advection) – No fog formation – Development low-level jet – Availability of data… • 9 Suitable cases remained. Used to identify generic features. Criteria – No frontal passages, change of air mass – No sudden jumps in time series of e. g. dew point – No small scale synoptic features (e. g. sea-breeze) • GABLS 3 case, 1 – 2 July 2006 7 th EMS Annual meeting, October 2007, Spain
Example generic features 7 th EMS Annual meeting, October 2007, Spain
The new GABLS case: synoptic situation 1 – 2 July 2006, 0 UTC 7 th EMS Annual meeting, October 2007, Spain
Observations: LLJ/wind Profiler windspeed 060701 1200 – 060702 1200 1000 8 Height (m) 800 600 10 400 200 012 14 4 12 4 16 8 18 20 22 0 2 4 Time UTC 6 6 8 10 12 7 th EMS Annual meeting, October 2007, Spain
Observations: temperature and turbulence 7 th EMS Annual meeting, October 2007, Spain
Case set-up • Structure 1 D intercomparison Coupling with the surface – 1 st run : each model runs with its own soil-vegetation scheme – 2 nd run : with one simple soil-vegetation module for all models • LES intercomparison (Basu) – Using the simple soil module as lower boundary condition (slab averaged) Next: Boundary / Initial Conditions Initial conditions Lower boundary conditions Atmospheric forcings 7 th EMS Annual meeting, October 2007, Spain
Case set-up – Initialization • Atmosphere – Sounding De Bilt (25 km to NE) from July, 1 st 12: 00 UTC – Piecewise linear approximation – Specific humidity from dew point • Soil – Temperature from local observations 12: 00 UTC 7 th EMS Annual meeting, October 2007, Spain
Case set-up – Atmospheric forcings • Geostrophic forcing • Advection (3 D models) – Temperature – Humidity • Subsidence (3 D models) 7 th EMS Annual meeting, October 2007, Spain
Case set-up – Lower boundary conditions • U Roughness lengths – For GABLS 3 regional z 0 m = 0. 15 m is taken, the local z 0 m = 0. 03 m. – Based on observations, zoh = 0. 0015 m Sensitivity runs are planned for different z 0 h, m values • Soil water / surface conductance z 0 m, local ln(z) • z 0 m, regional z 0 m, local u (z) 7 th EMS Annual meeting, October 2007, Spain
Time schedule • • October 2007 – Preliminary 1 D runs by 3 research groups November 2007 – Definitive case description & release February / March 2008 – Participants hand in results June 2008 – Presentation first results at AMS-BLT in Stockholm • Intercomparison will be coordinated by Cisco de Bruijn (KNMI) • See for more information and the current status: http: //www. knmi. nl/~bosveld/research/gabls/case 2/index. htm 7 th EMS Annual meeting, October 2007, Spain
Estimation of zoh from data Ts from L↑ u*(qs-q 2 m) [Km/s] • Slope: ln(z / z 0 h) / k w’T’ [Km/s] 7 th EMS Annual meeting, October 2007, Spain
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