Mesoscale Convective Systems Recent Observational and Diagnostic Studies

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

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

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?

Why do tropical and midlatitude MCSs look different?

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

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

Parcel vs. layer lifting in an MCS

Parcel viewpoint Zipser 1977 Crossover Zone

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

Layer viewpoint: Kingsmill & Houze 1999 TOGA COARE Airborne Doppler Observations of MCSs Convective region flights Note! 0. 5 -4. 5 km

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

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

Is rear inflow really from the rear?

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

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

JASMINE: Ship radar, Bay of Bengal, 22 May 1999 11 Height (km) Refl. 0 0 11 Horizontal Distance (km) 192 Reflectivity 1. 5 km level 100 km Height (km) Radial Velocity 0 0 Horizontal Distance (km) 192 Radial Velocity 3. 5 km level 90 km

JASMINE: Ship radar, Bay of Bengal, 22 May 1999 12 Height (km) Refl. 0 0 12 Horizontal Distance (km) 192 Reflectivity 1. 5 km level 100 km Height (km) Radial Velocity 0 0 Horizontal Distance (km) 192 Radial Velocity 3. 5 km level 90 km

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

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

Kingsmill & Houze 1999

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

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

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

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

Schumacher & Houze 2003 TRMM Precipitation radar: % of 2. 5 deg grid covered by stratiform radar echo Annual Average

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

Nakazawa 1988 INTRASEASONAL ENSEMBLE VARIATION SUB-ENSEMBLE MESOSCALE CONVECTIVE SYSTEM

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

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

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

JASMINE IR sequence (courtesy P. Zuidema)

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

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

JASMINE MCS

JASMINE MCS

Carbone et al. 2002 WSR 88 -D radar data over U. S. in time/ longitude format

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, …