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

Mesoscale Convective SystemHeating and Momentum Feedbacks

R. Houze

NCAR 10 July 2006

Heating Feedbacks

TRMM studySchumacher, Houze, & Kracunas 2004

Momentum Feedbacks

TOGA COARE studiesHouze, Chen, Kingsmill, Serra &Yuter 2000Mechem, 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

.16RCOPT81

(Chong & Hauser 1989)

Water Budget of a West African Mesoscale Convective Systemover ocean (GATE) and land (COPT81)

Schumacherand Houze (2003)

TRMM precipitation radar rain amount subdivided intoconvective and stratiform components

Total rain

Convective rain

Stratiform rain

Stratiform rain fraction

Houze 1982

Heating & Cooling Processes in an MCSHeating & Cooling Processes in an MCS

He

igh

t (km

)

Deg K/day

Convective

Stratiform

Assumed heating profilesHeating Profiles

He

igh

t (km

)

Deg K/day

Assumed heating profiles

0% stratiform

40% stratiform

70% stratiform

Net Heating Profiles

Schumacher et al. 2004

TRMM PR 1998-2000annual precipitation, 0% stratiform, resting basic state

250 mb stream function, 400 mb heatingK/day

Schumacher et al. 2004

TRMM PR 1998-2000annual precipitation, 40% stratiform, resting basic state

250 mb stream function, 400 mb heatingK/day

Schumacher et al. 2004

zonal wind and , 9N-9S

TRMM PR 1998-2000annual precipitation, 0% stratiform, resting basic state

mb/h

Schumacher et al. 2004

zonal wind and , 9N-9S

TRMM PR 1998-2000annual precipitation, 40% stratiform, resting basic state

mb/h

Schumacher et al. 2004

zonal wind and , 9N-9S

TRMM PR 1998-2000annual precipitation, observed stratiform, resting basic state

mb/h

Schumacher et al. 2004

Conclusions from the Schumacher et al. Conclusions from the Schumacher et al. TRMM study: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

CirculationCirculation associated with idealized MCS 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 flightsShow deep layer of inflow to updrafts

Kingsmill & Houze 1999

Mid-level Inflow

Houze 1982

Heating & Cooling Processes in an MCSHeating & Cooling Processes in an MCS

Figure CONVSF

Houze 1997

100 km

Houze 1997

“rear inflow”

Idealizedradar echo pattern

Idealizedradar 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 MCSHeating & 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. 1996

Sizes of MCSs observed in TOGA COARE

“Superclusters”

strong westerly westerlyonset

Houze et al. 2000

TOGA COARE radar data sampling relative to KW wave

TOGA COAREWesterly wind component at 155°E

12-15 Dec 92 21-26 Dec 92

Westerly Onset Strong Westerly

Westerlyjet

Houze et al. 2000

strong westerly westerlyonset

Houze et al. 2000

TOGA COARE radar data sampling relative to KW wave

SW NE

Houze et al. 2000

Stratiform region momentum transport in strong westerly region

MCS of 11 February 1993, as seen by ship radar

Stratiformradar echo

Downward momentumtransport in stratiform region

“midlevel inflow”

reflectivity

Doppler velocity

1000 km

1000

kmMoncrieff &

Klinker 1997

plan view

cross section

A B

A B

Stratiform region momentum transport in westerly onset region

MCS of 15 December 1992As seen by ship radar

Doppler Radial Velocity

Houze et al. 2000

0.5 km

Houze et al. 2000

Momentum Transport by Stratiform Region Descent

+ feedback feedback

strong westerly region westerlyonset region

TOGA COARE: Ship and aircraft radar data relative to Kelvin-Rossby wave structure

Houze et al. 2000

Low-level flow

m/s

Mechem et al. 2004

Mesoscale model simulation of MCS in westerly onset regime

Perturbation momentum structure

Mechem et al. 2004

Mesoscale model simulation of MCS in strong westerly regime

Perturbation momentum structure

Mechem et al. 2006

+ feedback

- feedback

Westerly OnsetCase

Strong Westerly

Case

Westerly MomentumFlux 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