1. Mesoscale Convective Systems: Recent Observational and Diagnostic Studies Robert Houze Department of Atmospheric Sciences University of Washington

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. Why do tropical and midlatitude MCSs look different?

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

6. Skamarock et al. 94 Symmetric MCV (Tropics & midlatitudes) No CoriolisCoriolis Asymmetric (Midlatitudes)

7. Parcel vs. layer lifting in an MCS

8. Parcel viewpoint Zipser 1977 Crossover Zone

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

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

11. 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

12. 1000 km Moncrieff & Klinker 1997 plan view cross section AB AB

13. Is rear inflow really from the rear?

14. Diversity of stratiform structure: Parker & Johnson 2000 PATTERNS OF EVOLUTION OF STRATIFORM PRECIPITATION IN MIDLATITUDE SQUALL LINES

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

16. 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

17. 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

18. Factors determining the size of MCS ICAPE, sustainability, diurnal cycle

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

20. Kingsmill & Houze 1999

21. Examples of TOGA COARE MCSs Satellite IR overlaid with A/C radar 100 km

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

23. Statistics for all TOGA COARE satellite/radar comparisons Percent of 24 km square grid covered by A/C radar echo in all the MCS Yuter & Houze 1998

24. Portion of 240 km scale grid covered by convective radar echo Statistics for all TOGA COARE satellite/radar comparisons Yuter & Houze 1998

25. Schumacher & Houze 2003 TRMM Precipitation radar: % of 2.5 deg grid covered by stratiform radar echo Annual Average

26. Factors determining the movement of MCS: Waves in the environment, cold pool dynamics

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

28. 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

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

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

31. JASMINE IR sequence (courtesy P. Zuidema)

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

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

34. JASMINE MCS

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

37. Conclusions Coriolis effect explains why midlatitude MCSs exhibit asymmetry and develop MCVs as they evolve—and why tropical MCSs don’t have asymmetry Parcel lifting gives way to layer lifting in mature MCSs when potentially unstable inflow air becomes moistened—circulations become mesoscale! Midlevel inflow enters stratiform regions from various directions—controlled by environment shear Max size of MCSs related to sustainability of low-level moist inflow—get biggest systems over oceans and with LLJs MCSs motion may be determined by waves propagating through the environment—gravity waves, inertio-gravity waves,…