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COSMO General Meeting, WG3, Krakow, 2008 - 1 - Revised parameter settings in the COSMO-DE boundary layer (TKE) scheme Axel Seifert Deutscher Wetterdienst,

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Präsentation zum Thema: "COSMO General Meeting, WG3, Krakow, 2008 - 1 - Revised parameter settings in the COSMO-DE boundary layer (TKE) scheme Axel Seifert Deutscher Wetterdienst,"—  Präsentation transkript:

1 COSMO General Meeting, WG3, Krakow, Revised parameter settings in the COSMO-DE boundary layer (TKE) scheme Axel Seifert Deutscher Wetterdienst, Germany Deutscher Wetterdienst GB Forschung und Entwicklung

2 COSMO General Meeting, WG3, Krakow, Modifications of PBL scheme Blackadars parameterization of the turbulent length scale: ECMWF/IFS: l turlen = 375 m COSMO model: l turlen = 500 m New COSMO-DE:l turlen = 150 m In the olde COSMO-DE setup sub-grid cloudiness started early, compared to the original Sommeria and Deardorff (1977) scheme. The revised settings use the linearization as originally suggested by SD77

3 COSMO General Meeting, WG3, Krakow, Fraction Skill Score A scale dependent precipitation skill score for convective-scale NWP models Δ = 1: 0 vs 1 bad forecast on 1Δ-scale Δ = 3: 4/9 vs 3/9 OK forecast on 3Δ-scale Δ = 5: 6/25 vs 6/25 perfect forecast on 5Δ-scale Roberts and Lean (2005)

4 COSMO General Meeting, WG3, Krakow, Fraction Skill Score Roberts and Lean (2005) In the following we chose 21x21 grid points, i.e., 60x60 km 2.

5 COSMO General Meeting, WG3, Krakow, Precip and QPF-Scores 01. Juni UTC Weak large-scale forcing by quasi-stationary occlusion zone

6 COSMO General Meeting, WG3, Krakow, Precip and QPF-Scores 15. Mai UTC Slowly moving warm front over Rheinland-Pfalz/Hessen/Sachsen

7 COSMO General Meeting, WG3, Krakow, Precip and QPF-Scores 03. Juni UTC Occlusion zone in the Elbe region with several convergence lines

8 COSMO General Meeting, WG3, Krakow, Precip and QPF-Scores 07. Juni UTC Weak slowly moving cold front (?)

9 COSMO General Meeting, WG3, Krakow, Total scores from 1 May to 9 June 2008 Significantly more strong (convective) precipitation events. Slight improvement of ETS for thresholds larger than 5 mm / 12 h Much better FSS especially for high thresholds UTC

10 COSMO General Meeting, WG3, Krakow, Total scores from 1 May to 9 June 2008 Including day and night in the statistics gives a less clear signal! UTC und UTC!

11 COSMO General Meeting, WG3, Krakow, Hovmöller diagramms or precipiation rate 1 May to 9 June 2008 In the operational COSMO-DE almost no diurnal cycle, the afternoon maximum is very weak. Clear improvement in the model behavior using the modified PBL parameters. Reduced nocturnal drizzle, better afternoon maximum

12 COSMO General Meeting, WG3, Krakow, Monthly precipitation accumulations form May 2008 The total accumulated precipitation is robust. Both variants of COSMO- DE give a good monthly budget.

13 COSMO General Meeting, WG3, Krakow, Conclusions Changing the PBL parameters (turlen, SGS cloud) has a strong effect on the initiation of convection and the diurnal cycle of precipiation during summer. For COSMO-DE this resolves the notorious problem of the underestimation of convective activity. Therefore the modification was made operational at DWD on 10 Sep The modifications have also a strong effect on the temperature profile and 2m-temperature. Both increase, making the profile more unstable. This might introduce a positive bias in the temperature forecasts. More research on improved PBL schemes is necessary (UTCS). The work presented here shows that the mixing length, and the moist turbulence assumption are important and need special attention. Deutscher Wetterdienst GB Forschung und Entwicklung

14 COSMO General Meeting, WG3, Krakow,

15 COSMO General Meeting, WG3, Krakow, Was bewirkt das physikalisch? Beide Änderungen bewirken generell einen reduzierten vertikalen Austausch in der Grenzschicht: Die Längenskala geht insbesondere in die Dissipationsrate ein: Kleinere Längenskala mehr Dissipation weniger TKE weniger Austausch Die Änderungen in der Feuchtturbulenz reduzieren die subskaligen Wolken: Weniger Wolken reduzierte TKE-Produktion weniger TKE weniger Austausch Weniger vertikale Durchmischung führt dann zu größerer vertikalen Gradienten, d.h. erhöhter lokaler Instabilität, was dann die skalige Konvektionsauslösung erleichtert oder ermöglicht. Insbesondere in der Nacht kann eine zu starke Durchmischung zu skaligen Grenzschichtwolken führen, die sogar Niederschlag produzieren, und dann am Vormittag die Ausbildung eine konvektiven Grenzschicht verhindern oder verlangsamen.

16 COSMO General Meeting, WG3, Krakow, Precip and QPF-Scores 14. Mai UTC

17 COSMO General Meeting, WG3, Krakow, Precip and QPF-Scores 18. Mai UTC

18 COSMO General Meeting, WG3, Krakow, Precip and QPF-Scores 02. Juni UTC Wetterlage: Okkulsionszone im Bereich Elbe, Konvergenzlinie in Bereich Rheinland- Pfalz/Baden-Württemberg

19 COSMO General Meeting, WG3, Krakow, Precip and QPF-Scores 31. Mai UTC

20 COSMO General Meeting, WG3, Krakow, Precip and QPF-Scores 29. Mai UTC

21 COSMO General Meeting, WG3, Krakow, Zeitpunkt der max. Niederschlagsrate 03. Juni UTC

22 COSMO General Meeting, WG3, Krakow, Precip and QPF-Scores 03. Juni UTC

23 COSMO General Meeting, WG3, Krakow, Case study 9 June 2007: Prä-frontale Konvergenzline führt zu starker Konvektion: Radar turlen=500m, clc=0.75 turlen=250m, clc=0.50 turlen=150m, clc=0.50turlen=150m, clc=0.25turlen=150m, SD77

24 COSMO General Meeting, WG3, Krakow, Radar turlen=500m, clc=0.75 turlen=250m, clc=0.50 turlen=150m, clc=0.50turlen=150m, clc=0.25turlen=150m, SD77 Hovmöller diagrams of precipitation rate from 1 June to 21 June 2007

25 COSMO General Meeting, WG3, Krakow, Hovmöller diagramms of precipitation frequency 1 May to 9 June 2008 Confirms the findings seen in the precip rate diagramms.

26 COSMO General Meeting, WG3, Krakow, Radar turlen=500m, clc=0.75 turlen=250m, clc=0.50 turlen=150m, clc=0.50turlen=150m, clc=0.25turlen=150m, SD77 Hovmöller diagrams of precipitation frequency from 1 June to 21 June 2007

27 COSMO General Meeting, WG3, Krakow, Standard SYNOP-Verifikation: 00 UTC Lauf (Achtung: Hier Experiment für Juni 2007) 2m-Temperatur und -Feuchte zeigen ein deutliche Änderung.

28 COSMO General Meeting, WG3, Krakow, Akkumulierter Niederschlag und QPF-Scores 13. Mai UTC


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