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Mesoscale Convective System Heating and Momentum Feedbacks

Mesoscale Convective System Heating and Momentum Feedbacks. R. Houze. NCAR 10 July 2006. Heating Feedbacks TRMM study Schumacher, Houze, & Kracunas 2004 Momentum Feedbacks TOGA COARE studies Houze, Chen, Kingsmill, Serra &Yuter 2000 Mechem, Chen & Houze 2006. Heating Feedbacks.

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Mesoscale Convective System Heating and Momentum Feedbacks

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  1. Mesoscale Convective System Heating and Momentum Feedbacks R. Houze NCAR 10 July 2006

  2. Heating Feedbacks TRMM study Schumacher, Houze, & Kracunas 2004 Momentum Feedbacks TOGA COARE studies Houze, Chen, Kingsmill, Serra &Yuter 2000 Mechem, Chen & Houze 2006

  3. Heating Feedbacks

  4. Pre-GATE view of tropical cloud population

  5. Post-GATE view of tropical cloud population Houze et al. (1980)

  6. 0 .13R .37R 1.17R .41R COPT81(Chong & Hauser 1989) .16R .29R .60R .40R Water Budget of a West African Mesoscale Convective Systemover ocean (GATE) and land (COPT81) GATE(Gamache & Houze 1983)

  7. TRMM precipitation radar rain amount subdivided intoconvective and stratiform components Total rain Schumacherand Houze (2003) Convective rain Stratiform rain Stratiform rain fraction

  8. Heating & Cooling Processes in an MCS Houze 1982

  9. Assumed heating profiles Heating Profiles Stratiform Height (km) Convective Deg K/day

  10. Assumed heating profiles Net Heating Profiles 70% stratiform 40% stratiform Height (km) 0% stratiform Schumacher et al. 2004 Deg K/day

  11. TRMM PR 1998-2000 annual precipitation, 0%stratiform, resting basic state K/day 250 mb stream function, 400 mb heating Schumacher et al. 2004

  12. TRMM PR 1998-2000 annual precipitation, 40% stratiform, resting basic state K/day 250 mb stream function, 400 mb heating Schumacher et al. 2004

  13. TRMM PR 1998-2000 annual precipitation, 0% stratiform, resting basic state mb/h zonal wind and w, 9N-9S Schumacher et al. 2004

  14. TRMM PR 1998-2000 annual precipitation, 40% stratiform, resting basic state mb/h zonal wind and w, 9N-9S Schumacher et al. 2004

  15. TRMM PR 1998-2000 annual precipitation, observed stratiform, resting basic state mb/h zonal wind and w, 9N-9S Schumacher et al. 2004

  16. Conclusions from the Schumacher et al. TRMM study: • 4-dimensional latent heating derived from TRMM PR produces a reasonable tropical circulation response in a simple climate model—if the stratiform rain fraction is represented accurately • Increasing the stratiform rain fraction moves the circulation centers upward and strengthens the upper-level response • Horizontal variability of the stratiform rain fraction creates more vertical tilt in the wind field

  17. Momentum Feedbacks

  18. Circulation associated with idealized MCS Mid level inflow Low level inflow Houze 1982

  19. Low-level Inflow

  20. Parcel Model of Convection Raymond and others

  21. Layer Model of Convection Moncrieff 92

  22. TOGA COARE Airborne Doppler Observations of MCSs 25 convective region flights Show deep layer of inflow to updrafts Kingsmill & Houze 1999

  23. Mid-level Inflow

  24. Heating & Cooling Processes in an MCS Houze 1982

  25. 100 km Figure CONVSF Horizontal Structure of a Mesoscale System Midlevel inflow can come from any direction Houze 1997 “rear inflow” Idealizedradar echo pattern Houze 1997

  26. TOGA COARE Airborne Doppler Observations of MCSs 25 stratiform region flights Kingsmill & Houze 1999

  27. TOGA COARE Airborne Doppler Observations of MCSs Stratiform region flights Convective region flights Kingsmill & Houze 1999

  28. Heating & Cooling Processes in an MCS

  29. Momentum Transport

  30. Buoyancy Produced Pressure Minimum in an MCS Convective Region LeMone 1983

  31. Precip. Cloud “midlevel inflow” Perturbation pressure field in a simulated MCS Yang & Houze 1996

  32. “Superclusters” Sizes of MCSs observed in TOGA COARE Chen et al. 1996

  33. TOGA COARE radar data sampling relative to KW wave strong westerly westerlyonset Houze et al. 2000

  34. 12-15 Dec 92 21-26 Dec 92 Westerlyjet Westerly Onset Strong Westerly TOGA COAREWesterly wind component at 155°E Houze et al. 2000

  35. TOGA COARE radar data sampling relative to KW wave strong westerly westerlyonset Houze et al. 2000

  36. Stratiform region momentum transport in strong westerly regionMCS of 11 February 1993, as seen by ship radar reflectivity Stratiformradar echo SW NE Doppler velocity Downward momentumtransport in stratiform region “midlevel inflow” Houze et al. 2000

  37. A B plan view Moncrieff &Klinker 1997 1000 km 1000 km cross section B A

  38. Stratiform region momentum transport in westerly onset region MCS of 15 December 1992 As seen by ship radar Doppler Radial Velocity 0.5 km Houze et al. 2000

  39. Momentum Transport by Stratiform Region Descent - feedback + feedback Houze et al. 2000

  40. TOGA COARE: Ship and aircraft radar data relative to Kelvin-Rossby wave structure Low-level flow strong westerly region westerlyonset region Houze et al. 2000

  41. m/s Mesoscale model simulation of MCS in westerly onset regime Perturbation momentum structure Mechem et al. 2004

  42. Mesoscale model simulation of MCS in strong westerly regime Perturbation momentum structure Mechem et al. 2004

  43. Mechem et al. 2006 Westerly MomentumFlux Convergence 400 km x 600 km Strong Westerly Case + feedback 200 km x 300 km Westerly Onset Case - feedback

  44. Conclusions • Layer lifting is important in large mesoscale convective systems, esp. in tropics • Amount of stratiform precipitation in large MCSs affects large-scale circulation by making heating more “top-heavy” • Horizontal variation of stratiform rain fraction affects vertical structure of the the large-scale circulation • Large MCSs produce large momentum transports because of their areal extent • Momentum feedbacks by subsiding midlevel inflows can be either positive or negative

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