1. 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

2. DEFINITION Mesoscale Convective System (MCS) A cumulonimbus cloud system that produces a contiguous precipitation area ~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. Houze et al. 1989, 1990 Tropical & midlatitudes “Symmetric” Midlatitudes (later stages) “Asymmetric” Radar reflectivity Conv. Strat.

5. Skamarock et al. 1994 Symmetric (Tropics & midlatitudes) No CoriolisCoriolis Asymmetric (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. Parcel viewpoint Zipser 1977 Crossover Zone

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

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

10. 1000 km Moncrieff & Klinker 1997 plan view cross section AB AB TOGA COARE convection in a GCM with ~80 km resolution

11. Mean heating in convective line Horizontal wind Pandya & Durran 1996 gravity wave response to heating

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 OF EVOLUTION OF STRATIFORM PRECIPITATION IN MIDLATITUDE SQUALL LINES

14. Kingsmill & Houze 1999 Documented airflow shown by airborne Doppler in TOGA COARE MCSs Stratiform region flights 0°C0°C

15. 0 192 Horizontal Distance (km) 11 0 Height (km) 192 11 0 Height (km) 0 90 km Horizontal Distance (km) 100 km Refl. Radial Velocity 3.5 km level JASMINE: Ship radar, Bay of Bengal, 22 May 1999 Radial Velocity Reflectivity 1.5 km level

16. 0 192 Horizontal Distance (km) 12 0 Height (km) 192 Horizontal Distance (km) 12 0 Height (km) 0 Horizontal Distance (km) 100 km Radial Velocity 3.5 km level JASMINE: Ship radar, Bay of Bengal, 22 May 1999 Reflectivity 1.5 km level Horizontal Distance (km) 100 km Refl. Radial Velocity 3.5 km level JASMINE: Ship radar, Bay of Bengal, 22 May 1999 Radial Velocity Reflectivity 1.5 km level 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. Chen et al. 1996 Sizes of MCSs observed in TOGA COARE “Super Convective Systems” (SCS)

19. Yuter & Houze 1998 Percent of 24 km square grid covered by A/C radar echo in all the MCS All TOGA COARE satellite/radar comparisons PrecipitationConvectiveStratiform %%

20. Yuter & Houze 1998 Percent of 240 km square covered by A/C radar echo in all the MCS All 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. 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 Stratiform Rain Fraction

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. Chen, Houze, & Mapes 1996 Analyzed IR data 3°N-10°S 208°K threshold IN TOGA COARE MCSs moved individually with wave much of the time 12 13 15 14 Longitude Time (day) A/C flights on 12-14 Dec

27. equator 40N JASMINE: May 1999 60E100E NOAA Ship R.H. Brown

28. Webster et al. 2002 IR over Bay of Bengal during JASMINE Ship track 51025302015 May 1999

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

30. JASMINE MCS

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,…

34. Layer viewpoint: Mechem, Houze, & Chen 2002 TOGA COARE 23 Dec 92 200 X (km) 150250 200150250 X (km) Z (km) Y (km) 0 2 4 6 8 10 12 14 50 100 150

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

36. Nakazawa 1988 INTRASEASONAL ENSEMBLE VARIATION SUB-ENSEMBLE MESOSCALE CONVECTIVE SYSTEM

37. JASMINE IR sequence (courtesy P. Zuidema)

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

39. Carbone et al. 2002 WSR88-D radar data over U.S. in time/ longitude format

40. Examples of TOGA COARE MCSs Satellite IR overlaid with A/C radar 240 km