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Mesoscale Convective Systems: Recent Observational and Diagnostic Studies Robert Houze

Mesoscale Convective Systems: Recent Observational and Diagnostic Studies Robert Houze Department of Atmospheric Sciences University of Washington. 10 th Conf. on Mesoscale Meteorology, Portland, OR, June 23-27 2003. DEFINITION Mesoscale Convective System (MCS)

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Mesoscale Convective Systems: Recent Observational and Diagnostic Studies Robert Houze

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  1. Mesoscale Convective Systems: Recent Observational and Diagnostic Studies Robert Houze Department of Atmospheric Sciences University of Washington 10th Conf. on Mesoscale Meteorology, Portland, OR, June 23-27 2003

  2. DEFINITION Mesoscale Convective System (MCS) A cumulonimbus cloud system that produces a contiguousprecipitationarea ~100 km or more in at least one direction

  3. Questions • Why do tropical and midlatitude MCSs look different? • Does layer lifting occur in a mature MCS? • Is rear inflow really from the rear? • What controls the size of MCSs? • What controls the movement of MCSs?

  4. Radarreflectivity Strat. Conv. Houze et al. 1989, 1990 Tropical & midlatitudes “Symmetric” Midlatitudes(later stages) “Asymmetric”

  5. Skamarock et al. 1994 No Coriolis Coriolis Symmetric Asymmetric (Tropics & midlatitudes) (Midlatitudes)

  6. Questions • Why do tropical and midlatitude MCSs look different? • Does layer lifting occur in a mature MCS? • Is rear inflow really from the rear? • What controls the size of MCSs? • What controls the movement of MCSs?

  7. CrossoverZone Parcel viewpointZipser 1977

  8. MAUL Layer viewpoint: Bryan and Fritsch 2000 “Slab” or Layer Overturning

  9. Note! 0.5-4.5 km Layer viewpoint: Kingsmill & Houze 1999 TOGA COARE Airborne Doppler Observations of MCSs Convective region flights

  10. A A B B Moncrieff & Klinker 1997 plan view 1000 km TOGA COARE convection in a GCMwith ~80 kmresolution 1000 km cross section

  11. gravity wave response to heating Pandya & Durran 1996 Mean heatingin convectiveline Horizontalwind

  12. Questions • Why do tropical and midlatitude MCSs look different? • Does layer lifting occur in a mature MCS? • Is rear inflow really from the rear? • What controls the size of MCSs? • What controls the movement of MCSs?

  13. Diversity of stratiform structure: Parker & Johnson 2000 PATTERNS OFEVOLUTION OF STRATIFORM PRECIPITATION IN MIDLATITUDESQUALL LINES

  14. Kingsmill & Houze 1999Documented airflow shown by airborne Doppler inTOGA COARE MCSs Stratiform region flights 0°C

  15. JASMINE: Ship radar, Bay of Bengal, 22 May 1999 Refl. Reflectivity1.5 km level 100 km Horizontal Distance (km) RadialVelocity Radial Velocity3.5 km level 11 Height (km) 0 0 192 11 Height (km) 0 0 192 Horizontal Distance (km) 90 km

  16. JASMINE: Ship radar, Bay of Bengal, 22 May 1999 Refl. Reflectivity1.5 km level 100 km Horizontal Distance (km) RadialVelocity Radial Velocity3.5 km level JASMINE: Ship radar, Bay of Bengal, 22 May 1999 12 Height (km) Reflectivity1.5 km level 0 0 192 100 km Horizontal Distance (km) Horizontal Distance (km) 12 Height (km) Radial Velocity3.5 km level 0 0 192 Horizontal Distance (km) 90 km

  17. Questions • Why do tropical and midlatitude MCSs look different? • Does layer lifting occur in a mature MCS? • Is rear inflow really from the rear? • What controls the size of MCSs? • What controls the movement of MCSs?

  18. “Super Convective Systems”(SCS) Sizes of MCSs observed in TOGA COARE Chen et al. 1996

  19. Yuter & Houze 1998 Percent of 24 km square grid covered by A/C radar echo in all the MCSAll TOGA COARE satellite/radar comparisons Precipitation Convective Stratiform % % %

  20. Yuter & Houze 1998 Percent of 240 km square covered by A/C radar echo in all the MCSAll TOGA COARE satellite/radar comparisons

  21. Hypothesis: The size of the MCS is determined by the environment’s ability to sustain an ensemble of convection over time. Question: What factors control and limit sustainability?

  22. Kingsmill & Houze 1999: TOGA COARE a/c soundings Height (m)

  23. Stratiform Rain Fraction Schumacher & Houze 2003 TRMM Precipitation radar:% of 2.5 deg grid covered by stratiform radar echo Annual Average Inference: Sustainability promoted by moist boundary layer that is not interrupted by the diurnal cycle

  24. Questions • Why do tropical and midlatitude MCSs look different? • Does layer lifting occur in a mature MCS? • Is rear inflow really from the rear? • What controls the size of MCSs? • What controls the movement of MCSs?

  25. Traditional view: Cold pool dynamics Recent studies: Waves in environment

  26. 12 13 14 15 IN TOGA COAREMCSs moved individually with wave much of the time Chen, Houze,& Mapes 1996AnalyzedIR data3°N-10°S208°K threshold A/Cflightson 12-14Dec Time (day) Longitude

  27. NOAA Ship R.H. Brown JASMINE: May 1999 40N equator 60E 100E

  28. Ship track 5 10 15 20 25 30 May 1999 Webster et al. 2002 IR over Bay of Bengal during JASMINE

  29. Mapes et al. (2002) West Coast of South Am. Gravity Wave hypothesis

  30. JASMINEMCS

  31. JASMINEMCS

  32. Conclusions • Coriolis effect explains why midlatitude MCSs exhibit late-stage asymmetry not observed in the tropics. • Layer lifting occurs in mature MCSs, possibly as a gravity wave response to the net heating in the convective region. • Midlevel inflow enters stratiform regions from various directions—controlled by environment wind. • Max size of MCSs related to sustainability of low-level moist inflow—get biggest systems over oceans and with LLJs • Movement of an individual MCS may be in part determined by waves propagating through the environment—gravity waves, inertio-gravity waves,…

  33. Layer viewpoint: Mechem, Houze, & Chen 2002 14 TOGA COARE 23 Dec 92 12 10 150 8 Z (km) 6 100 Y (km) 4 50 2 0 150 200 250 150 200 250 X (km) X (km)

  34. Yuter & Houze 1998 CS map Convective echo % of grid Stratiform echo Satellite IR y (km) % of grid Mean IR temp (K) x (km)

  35. Nakazawa 1988 INTRASEASONALENSEMBLE VARIATION SUB-ENSEMBLE MESOSCALE CONVECTIVE SYSTEM

  36. JASMINE IR sequence (courtesy P. Zuidema)

  37. Serra & Houze 2002TEPPS—East Pacific ITCZ Ship radardata Easterly wave and cold pool propagation hard to distinguish

  38. Carbone et al. 2002 WSR88-Dradar dataover U.S.in time/longitudeformat

  39. 240 km Examplesof TOGACOAREMCSs Satellite IR overlaid with A/C radar

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