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Mesoscale Convective Systems Robert Houze Department of Atmospheric Sciences

Mesoscale Convective Systems Robert Houze Department of Atmospheric Sciences University of Washington. Nebraska. Kansas. Oklahoma. Arkansas. Early View of a Mesoscale Convective System, ca 1974. 100 km. Figure CONVSF. Precipitation in a Mesoscale Convective System. Houze 1997.

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Mesoscale Convective Systems Robert Houze Department of Atmospheric Sciences

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  1. Mesoscale Convective Systems Robert Houze Department of Atmospheric Sciences University of Washington Nebraska Kansas Oklahoma Arkansas

  2. Early View of a Mesoscale Convective System, ca 1974

  3. 100 km Figure CONVSF Precipitation in a Mesoscale Convective System Houze 1997 Houze 1997

  4. Heating & Cooling Processes in an MCS Houze 1982

  5. Idealized Heating Profiles of MCSs Non-dimensional Heating Houze 1982

  6. Circulation Pattern of an MCS, ca 1989 Mesoscale circulation features identified, but suggests air enters updraft from thin surface layer Houze et al. 1989

  7. Layer lifting

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

  9. Bryan and Fritsch 2000Analysis and simulation of midlatitude continental convection “Slab” or Layer Overturning

  10. Height (km) Mechem et al. 2000Simulation of tropical oceanic convection

  11. Pandya & Durran 1996 Mean heating in convective line Horizontal wind

  12. Simulation of an MCS over the tropical ocean, near Kwajalein Courtesy Professor Rob Fovell Gentle, persistent lifting ahead of line Lower troposphere above boundary layer cooler, more moist, and less stable

  13. Discrete Propagation

  14. Loop showing tropical discrete propagation in an MCS over Oklahoma Courtesy Professor Rob Fovell

  15. Loop showing tropical discrete propagation in an MCS over the Bay of Bengal

  16. Midlevel Inflow

  17. Heating & Cooling Processes in an MCS Houze 1982

  18. 100 km Figure CONVSF Midlevel inflow can come from any direction Houze 1997 “rear inflow” Houze 1997

  19. TOGA COARE Airborne Doppler Observations of MCSs 25 Stratiform region flights Kingsmill & Houze 1999

  20. Heating, PV generation, & upscale feedbacks

  21. Sizes of MCSs observed in TOGA COARE Chen et al. 1996

  22. Divergence Profiles of MCSs over West Pacific Courtesy Brian Mapes

  23. PV Generation by an MCS Fritsch et al. 1994(based on Raymond & Jiang 1990)

  24. Vortex Spinup by an MCS Chen & Frank 1993

  25. Development of a Tropical Cyclone from an MCS Bister and Emanuel 1997

  26. Idealized Heating Profiles of MCSs Stratiform region vortex builds down and sfc fluxeswarm low levels Non-dimensional Heating Houze 1982

  27. Thorncroft figures Interaction of MCSs with Synoptic-scale Easterly Wave From AMMA Science Plan Thorncroft et al. 2004

  28. What about momentum feedbacks?

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

  30. “midlevel inflow” Momentum changes produced by different parts of simulated MCS Yang & Houze 1996

  31. Stratiform region momentum transport in TOGA COARE MCS of 11 February 1993 As seen by ship radar reflectivity stratiformecho SW NE Doppler velocity “midlevel inflow” Downward momentumtransport Houze et al. 2000

  32. Stratiform region momentum transport in TOGA COARE MCS of 15 December 1992 As seen by ship radar 0.5 km Houze et al. 2000

  33. 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

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

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

  36. Strong Westerly Case Momentum fluxes and flux convergences for simulated cases + feedback Westerly Onset Case - feedback Mechem et al. 2004

  37. Global satellite observations Global variability of MCS structure

  38. TRMM Precipitation Radar Schumacher & Houze 2003

  39. Large-scale response to precipitation heating Hartmann et al. 1984Schumacher et al. 2004 400 mb heating 200 mb stream function 4 month El Nino season 1998 Most realistic when horizontal distribution of vertical profile of heating is correct

  40. The variation of stratiform and convective structure of MCSs is most pronounced between land & ocean

  41. TRMM view of Africa vis a vis the Atlantic AMMA Science Plan, Thorncroft 2004 Rain Stratiform Rain Fraction MCSs with large 85GHz ice scattering Lightning

  42. India: Another example of continental MCS

  43. Summary • MCSs have rain areas ~hundreds of kilometers in scale

  44. Summary • MCSs have rain areas ~hundreds of kilometers in scale • Stratiform region has cooling at low levels & warming at upper levels

  45. Summary • MCSs have rain areas ~hundreds of kilometers in scale • Stratiform region has cooling at low levels & warming at upper levels • Updrafts are fed by a deep layer, which is a mesoscale response to the net heating profile of the system

  46. Summary • MCSs have rain areas ~hundreds of kilometers in scale • Stratiform region has cooling at low levels & warming at upper levels • Updrafts are fed by a deep layer, which is a mesoscale response to the net heating profile of the system • Discrete propagation (as opposed to lifting over cold pool) is an significant component of the system motion

  47. Summary • MCSs have rain areas ~hundreds of kilometers in scale • Stratiform region has cooling at low levels & warming at upper levels • Updrafts are fed by a deep layer, which is a mesoscale response to the net heating profile of the system • Discrete propagation (as opposed to lifting over cold pool) is an significant component of the system motion • Midlevel inflow direction controlled by large-scale environment relative flow

  48. Summary • MCSs have rain areas ~hundreds of kilometers in scale • Stratiform region has cooling at low levels & warming at upper levels • Updrafts are fed by a deep layer, which is a mesoscale response to the net heating profile of the system • Discrete propagation (as opposed to lifting over cold pool) is an significant component of the system motion • Midlevel inflow direction controlled by large-scale environment relative flow • Positive PV develops in the cloud layer of the stratiform region and can lead to tropical cyclone formation and possibly feedback upscale to synoptic-scale waves

  49. Summary • MCSs have rain areas ~hundreds of kilometers in scale • Stratiform region has cooling at low levels & warming at upper levels • Updrafts are fed by a deep layer, which is a mesoscale response to the net heating profile of the system • Discrete propagation (as opposed to lifting over cold pool) is an significant component of the system motion • Midlevel inflow direction controlled by large-scale environment relative flow • Positive PV develops in the cloud layer of the stratiform region and can lead to tropical cyclone formation and possibly feedback upscale to synoptic-scale waves • Momentum generation in stratiform region can be significant and have either positive or negative upscale feedbacks to large scale flow

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