Turbulence modelling in the operational circulation model HBM Status and Outlook. Thorger Brüning, Líège Colloquium 2015

Transcription

1 Turbulence modelling in the operational circulation model HBM Status and Outlook Thorger Brüning, Líège Colloquium 2015

2 Contents Why do we need an operational circulation model The circulation model HBM Description of the problem we found Tests with different sets of structure functions Description of the solution Summary Outlook 2

3 Why do we run operational models? BSH provides daily forecasts for a variety of customers and applications Main applications: water level prediction and storm surge warning service drift calculations for oil, other substances & SAR offshore industry & coastal engineering German navy fisheries tourism 3

4 The circulation model HBM History The HIROMB-BOOS-model was born in 2009 within the Project MyOcean as the common model for the Baltic MFC The name HIROMB-BOOS was chosen for political reasons It underlines the origin of the model: The Baltic Sea The physical core based mostly on BSHcmod 4

5 The circulation model HBM Common code development and (operational) usage Today 4 institutes are HBM partners they use HBM operationally and are directly involveld in HBM code development via an subversion- access: Danisch Meteorological Institute Bundesamt für Seeschifffahrt und Hydrographie Marine Systems Institute at Tallinn University of Technology, Finnish Meteorological Institute In addition to that HBM is used by research institutes in Danmark, Germany, Poland, Latvia, Lithiuania and it was also used by INTEL for a benchmark study 5

6 The circulation model HBM Physics 3D baroclinic, prognostic z-co-ordinates / generalised, adaptive vertical co-ordinates (Kleine, 2004) Explicit finite volume advection scheme Thermodynamics and optionally sea ice dynamics (Hibler, 1979) drying and flooding of tidal flats obc (T+S sponge layer) 2-way fully dynamical nesting k-ω turbulence model (Structure functions based on Canuto et al., 2002) 6

7 The Problem BSH-setup storm Xaver u-vel. at 5 th December 2013, 12:00 UTC 7

8 The Problem MyOcean-setup storm and cooling u-vel. at 2 nd December 2013, 00:00 UTC 8

9 The Problem MyOcean-setup storm and cooling 9

10 Tests with different sets of structure functions Canuto et al.,

11 Tests with different sets of structure functions Umlauf/Burchard, 2005; Cheng et al.,

12 Differences Canuto based schemes using double diffusion All schemes in Umlauf/Burchard, 2005 has additional realisability criteria: All used structure functions are 0 (also fullfilled in the Canuto based schemes) To secure sensible velocity variances and to avoid instabilities (in case of more than one numerical solution) a lower bound of (τn)² is given To avoid shear anisotropy an upper bound of (τσ)² is given Because of the double diffusion we decided that we want to use a Canuto based scheme because of the much easier euations we decided to use the one based on Canuto et al.,

13 Adaption of realisability criteria Umlauf and Burchard, (τσ)² K M ((τn)²,(τσ)²) (τσ)² 2. < w, w > 2k gives a lower limit for (τn)² K 3. N (τn)² (τn)² for (τn)² > 0 gives a lower limit 4. G ε = 1 = K N((τN)²,(τΣ)²)) (τn)² gives a lower limit for (τn)² With an additional factor 4 implies 3 and 2, so that only 1 and 4 are imlemented! Adapted functions 1. (τσ)² K M ((τ²rt), (τ²rs),(τσ)²) (τσ)² 2. < w, w > 2k gives an upper limit for τ² in (τ²rt) and (τ²rs) 3. (τ 2 rt) K T τ²rt τ²rt and (τ 2 rs) lower limit for τ²rs > 0 gives a lower limit for K S τ²rs > 0 gives a 4. G ε = 1 = K T((τ²rT), (τ²rs)) (τ²rt) resp. G ε = 1 = K S((τ²rT), (τ²rs)) (τ²rs) gives a lower limit for (τ²rt) and (τ²rs) With an additional factor 4 implies 3, so that only 1,2 and 4 are implemented! 13

14 Adaption of realisability criteria The free convection case 14

15 Results with Canuto et al., 2010 structure functions including additional realisability 15

16 Results with Canuto et al., 2010 structure functions including additional realisability MyOcean Baltic MFC-setup u-vel. at 2 nd December 2013, 00:00 UTC BSH-setup u-vel. at 5 th December 2013, 12:00 UTC 16

17 Positive side effect More technical stability U-velocity profiles without and with realisability using Canuto et al., 2010 structure functions Green with tuning flags, Black without tuning flags 17

18 Summary / Outlook Summary We found instabilities in HBM model during extrem conditions (storms, cooling ) We identified the problem and solved it We got more physical stability Additionally we got more technical stability => more portability and a better reproducibility of results (e.g. if one calculate on different systems) Outlook Combine turbulence model with dynamical vertical co-ordinates Introduce a separate structure function for passive tracers Introduce a local bottom friction factor Introduce the effect of waves into the turbulence model 18

19 Thank you! 19