Mesoscale Convective System Heating and Momentum Feedbacks R. Houze NCAR 10 July 2006

Heating Feedbacks TRMM study Schumacher, Houze, & Kracunas 2004 Momentum Feedbacks TOGA COARE studies Houze, Chen, Kingsmill, Serra &Yuter 2000 Mechem, Chen & Houze 2006

Heating Feedbacks

Pre-GATE view of tropical cloud population

Houze et al. (1980) Post-GATE view of tropical cloud population

GATE (Gamache & Houze 1983).60R.40R 1.17R.41R.29R.37R 0.13R.16R COPT81 (Chong & Hauser 1989) Water Budget of a West African Mesoscale Convective System over ocean (GATE) and land (COPT81)

Schumacher and Houze (2003) TRMM precipitation radar rain amount subdivided into convective and stratiform components Total rain Convective rain Stratiform rain Stratiform rain fraction

Houze 1982 Heating & Cooling Processes in an MCS

Height (km) Deg K/day Convective Stratiform Assumed heating profiles Heating Profiles

Height (km) Deg K/day Assumed heating profiles 0% stratiform 40% stratiform 70% stratiform Net Heating Profiles Schumacher et al. 2004

TRMM PR annual precipitation, 0% stratiform, resting basic state 250 mb stream function, 400 mb heating K/day Schumacher et al. 2004

TRMM PR annual precipitation, 40% stratiform, resting basic state 250 mb stream function, 400 mb heating K/day Schumacher et al. 2004

zonal wind and , 9N-9S TRMM PR annual precipitation, 0% stratiform, resting basic state mb/h Schumacher et al. 2004

zonal wind and , 9N-9S TRMM PR annual precipitation, 40% stratiform, resting basic state mb/h Schumacher et al. 2004

zonal wind and , 9N-9S TRMM PR annual precipitation, observed stratiform, resting basic state mb/h Schumacher et al. 2004

Conclusions from the Schumacher et al. TRMM study:  4-dimensional latent heating derived from TRMM PR produces a reasonable tropical circulation response in a simple climate model—if the stratiform rain fraction is represented accurately  Increasing the stratiform rain fraction moves the circulation centers upward and strengthens the upper-level response  Horizontal variability of the stratiform rain fraction creates more vertical tilt in the wind field

Momentum Feedbacks

Houze 1982 Low level inflow Mid level inflow Circulation associated with idealized MCS

Low-level Inflow

Parcel Model of Convection Raymond and others

Layer Model of Convection Moncrieff 92

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

Mid-level Inflow

Houze 1982 Heating & Cooling Processes in an MCS

Figure CONVSF Houze km Houze 1997 “rear inflow” Idealized radar echo pattern Horizontal Structure of a Mesoscale SystemMidlevel inflow can come from any direction

Kingsmill & Houze 1999 TOGA COARE Airborne Doppler Observations of MCSs 25 stratiform region flights

Kingsmill & Houze 1999 Convective region flights Stratiform region flights TOGA COARE Airborne Doppler Observations of MCSs

Heating & Cooling Processes in an MCS

Momentum Transport

LeMone 1983 Buoyancy Produced Pressure Minimum in an MCS Convective Region

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

Chen et al Sizes of MCSs observed in TOGA COARE “Superclusters”

strong westerlywesterly onset Houze et al TOGA COARE radar data sampling relative to KW wave

TOGA COARE Westerly wind component at 155°E Dec Dec 92 Westerly OnsetStrong Westerly Westerly jet Houze et al. 2000

strong westerlywesterly onset Houze et al TOGA COARE radar data sampling relative to KW wave

SWNE Houze et al Stratiform region momentum transport in strong westerly region MCS of 11 February 1993, as seen by ship radar Stratiform radar echo Downward momentum transport in stratiform region “midlevel inflow” reflectivity Doppler velocity

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

Stratiform region momentum transport in westerly onset region MCS of 15 December 1992 As seen by ship radar Doppler Radial Velocity Houze et al km

Houze et al Momentum Transport by Stratiform Region Descent + feedback  feedback

strong westerly regionwesterly onset region TOGA COARE: Ship and aircraft radar data relative to Kelvin-Rossby wave structure Houze et al Low-level flow

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

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

Mechem et al feedback - feedback Westerly Onset Case Strong Westerly Case Westerly Momentum Flux Convergence 400 km x 600 km 200 km x 300 km

Conclusions Layer lifting is important in large mesoscale convective systems, esp. in tropics Amount of stratiform precipitation in large MCSs affects large- scale circulation by making heating more “top-heavy” Horizontal variation of stratiform rain fraction affects vertical structure of the the large-scale circulation Large MCSs produce large momentum transports because of their areal extent Momentum feedbacks by subsiding midlevel inflows can be either positive or negative