1. Interactions between continental convection and mesoscale circulations across model resolutions
Cathy Hohenegger 1,2
Linda Schlemmer 1,2
Bjorn Stevens 1
Levi Silvers 1
1Max Planck Institute for meteorology, Hamburg, Germany
2Hans-Ertel-Centre for Weather Research, MPI, Hamburg, Germany

3. Mesoscale circulations influence convective precipitation
Lynn et al. 1997
2D model
512 x 20 km
Δx = 500 m
Cloud microphysics
Radiation
Land surface scheme

4. How well represented in NWP systems?
Cloud-resolving
(Δx = 4 km)
Parameterized convection
(Δx = 12 km)
See also CASCADE work, e.g. Marsham et al. 2013
Taylor et al. 2013

5. This talk
Idealized case of convection interacting with a thermally induced mesoscale circulation
How does convection interact across model resolutions?
LES resolution Δx=400 m fully explicit convection
Cloud-resolving Δx=2.2 km partly explicit convection
Coarse resolution Δx=11 km parameterized convection
What are the main mechanisms/factors controlling the interactions across resolutions?

6. Outline Case and model set-up Interactions in a control case
Sensitivity to change in circulation characteristics
Conclusions

7. Case and model set-up Doubly periodic domain 820 x 410 km2
Half ocean - half land
Surface fluxes over ocean/land constant
Initial sounding from observations over North Sea coast during summer

8. Case and model set-up Large-eddy Cloud-resolving Parameterized Model
UCLA-LES
COSMO Δx
0.4 km
2.2 km
11 km
Convection
Explicit
Partly explicit
Tiedtke (1989)
Microphysics
2 moment
1 moment
Turbulence
Smagorinsky
3D TKE

9. Overview LES

10. Precipitation characteristics
PR 11 km
CR 2.2 km
LES 0.4 km

11. Clouds and circulation
LES 0.4 km
CR 2.2 km
PR 11. km
Height (km)

12. Circulation characteristics
PR 11 km
CR 2.2 km
LES 0.4 km

13. Circulation characteristics
PR 11 km
CR 2.2 km
LES 0.4 km

14. Reasons for different circulation characteristics?
PR 11 km
CR 2.2 km
LES 0.4 km
PR 11 km
CR 2.2 km
LES 0.4 km

15. Reasons for different circulation characteristics?
PR 11 km
CR 2.2 km
LES 0.4 km

16. Reasons for different circulation characteristics?

17. Intermediate summary
Typical differences in the representation of convection across scales reflect themselves in the representation of the interaction between convection and a thermally induced mesoscale circulation
How does the coupled system respond to changes in external parameters across resolution?
Three main parameters:
Sensible heat flux
Latent heat flux
Land size

18. Response in the LES simulation
Increase land SH -> Faster propagation -> Rain unchanged

19. Response in the LES simulation
Increase land SH -> Faster propagation -> Rain unchanged Decrease land -> Prop. Unchanged -> More rain

20. Response in the LES simulation
Increase land SH -> Faster propagation -> Rain unchanged Decrease land -> Prop. Unchanged -> More rain Increase land LH -> Faster propagation -> More rain

21. Response as function of model resolution

22. Response as function of model resolution

23. What happens with CR?
CR 2.2 km
LES 0.4 km

24. What happens with CR?

25. How robust are the results?

26. Conclusions
Interactions between convection and thermally induced circulation across resolutions
Typical differences in the representation of convection across scales reflect themselves in the representation of the interactions between convection and mesoscale circulation
Systematic differences in the response of the coupled system to changes in external parameters