Jonathan Petters February 20, 2009 Naval Research Lab Marine Meteorology Division

1. Dynamical impacts of surface and atmospheric radiative heating on cloud systems Jonathan Petters February 20, 2009 Naval Research Lab Marine Meteorology Division Howard W. Barker, Eugene E. Clothiaux, Jason N.S. Cole, Jeffrey W. Frame, Jerry Y. Harrington, Paul M. Markowski This work funded by the Department of Energy Atmospheric Radiation Measurement Program (DOE ARM)

2. Atmospheric Solar Radiative Transfer

3. Atmospheric Solar Radiative Transfer -Modeled

4. Each model column is its own plane-parallel atmosphere!

5. Independent Column Approximation (ICA) – leads to radiative heating errors in the atmosphere and surface cloudside heating hotspots

6. Errors in surface heating due to ICA - Cumulonimbus? Markowski et al. (1998) Surface cooling of ~3K observed under anvil shadow

7. Surface solar irradiance – model supercell (ARPS) - ICA - Solar zenith angle of 47° - azimuth just S of W Frame, Petters, Markowski and Harrington (2009)

8. Surface solar irradiance – same supercell – Monte Carlo - Solar zenith angle of 47° - azimuth just S of W Frame, Petters, Markowski and Harrington (2009)

9. How might we rectify these surface heating errors? Tilt model columns (titled ICA -> TICA)

10. Use of TICA lessens error Surfacesolar irradiance ICA – Monte Carlo TICA – Monte Carlo Frame, Petters, Markowski and Harrington (2009)

11. Use of TICA in Supercell – Dynamical impact? For stationary storms and storms moving slowly in the direction of anvil shadow, cooling of surface under anvil shadow can lead to weakening. Frame, PhD Dissertation (2008)

12. Cloud shading in Cb – Dynamical impact? No radiation = no shadow! Little vertical wind shear near surface Frame, PhD Dissertation (2008)

13. Cloud shading in Cb – Dynamical impact? shadow Added vertical wind shear near surface Cooling under anvil -> stabilize surface layer -> less vertical mixing Frame, PhD Dissertation (2008)

14. Anvil With anvil shadowing, rear-flank gust front accelerates, can undercut mesocyclone, leading to weakening of storm Lemon and Doswell (1979)

15. Use of TICA improves atmospheric heating calculations as well cloudside heating Not important here! Where then?

16. Stratocumulus! Radiatively driven Quite homogeneous cloud field Errors due to use of ICA in such a cloud field not likely to be large Photo: Alexei Korolev North of Barrow, AK

17. Inhomogeneous Sc field Errors due to use of ICA in modeling such a cloud field important (?) Photo: Amy M Dobrzyn Bloomsburg, PA

18. What do we know about the impact of solar heating on stratocumulus? Can be thick, overcast, heavy drizzle Can be thin, broken, light drizzle Stabilizes cloud layer with respect to subcloud Examine further with ICA treatment of radiation first!

19. Experimental Platform • Regional Atmospheric Modeling System (RAMS) • Eddy-resolving mode (2-D) • Input sounding – ASTEX (Jiang et al. 2002) • 30 m vertical resolution, 50 m horizontal resolution (64X70X70) • 2 second model and radiative timestep • no surface fluxes Find model Sc cloud fields sensitive to changes in solar heating

20. No Sun Sun at 45° Overhead Sun No drizzle allowed Solar forcing thins model cloud layer significantly CDNC – cloud droplet number concentration

21. No Sun Sun at 45° Overhead Sun Same as above Drizzle allowed Drizzle production lessens as solar forcing increases

22. No Sun Sun at 45° Overhead Sun Same as above High CDNC No drizzle allowed, change CDNC Increased CDNC -> reduced liquid water path when sun is overhead

23. Less heating More heating Difference in integrated radiative heating high CDNC – low CDNC

24. No Sun Sun at 45° Overhead Sun Same as above High CDNC Sensitivity to small changes in solar forcing when sun is overhead – broken Sc commonly observed when sun is overhead too

25. Testing importance of atmospheric radiative heating errors in Sc • Good candidate for study – broken cloud field sensitive to small changes in solar forcing

26. Finding a candidate model Sc field CDNC = 50/cc Overhead Sun Drizzle Calculate radiative fluxes through cloud without ICA offline, note changes in integrated shortwave heating

27. Testing importance of atmospheric radiative heating errors in Sc • Monte Carlo radiative transfer model coupled with RAMS • Accurately represents horizontal transport of radiation through model domain • Simulate broken Sc cloud field • With ICA treatment of radiation • Without ICA treatment of radiation • Observe/analyze dynamical impact (if any)

28. Summary • Modeling of radiative transfer leads to errors in computed radiative heating in numerical atmospheric models • Errors in surface heating can lead to changes in model supercell evolution • Errors in atmospheric heating might impact stratocumulus evolution – analysis continues!

29. Thank You!Questions/Comments?

30. Finding a candidate model Sc field CDNC = 50/cc Sun at 45° Drizzle Calculate radiative fluxes through cloud without ICA offline, note changes in integrated shortwave heating

31. Supercell Schematic and Pic