Interactions between continental convection and mesoscale circulations across model resolutions

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

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