Transcript 060710Boulder_HeatingAndMomentumFeedbacks-NCAR_V10_Houze.ppt

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
Post-GATE view of tropical cloud population
Houze et al. (1980)
Water Budget of a West African Mesoscale Convective System
over ocean (GATE) and land (COPT81)
0
.13R
.37R
1.17R
.41R
GATE
(Gamache & Houze 1983)
COPT81
.16R
(Chong & Hauser 1989)
.29R
.60R
.40R
TRMM precipitation radar rain amount subdivided into
convective and stratiform components
Total rain
Schumacher
and Houze
(2003)
Convective rain
Stratiform rain
Stratiform rain fraction
Heating & Cooling Processes in an MCS
Houze 1982
Assumed heating profiles
Heating Profiles
Height (km)
Stratiform
Convective
Deg K/day
Assumed heating profiles
Net Heating Profiles
70% stratiform
Height (km)
40% stratiform
0% stratiform
Schumacher et al. 2004
Deg K/day
TRMM PR 1998-2000
annual precipitation, 0% stratiform, resting basic state
K/day
250 mb stream function, 400 mb heating
Schumacher et al. 2004
TRMM PR 1998-2000
annual precipitation, 40% stratiform, resting basic state
K/day
250 mb stream function, 400 mb heating
Schumacher et al. 2004
TRMM PR 1998-2000
annual precipitation, 0% stratiform, resting basic state
mb/h
zonal wind and w, 9N-9S
Schumacher et al. 2004
TRMM PR 1998-2000
annual precipitation, 40% stratiform, resting basic state
mb/h
zonal wind and w, 9N-9S
Schumacher et al. 2004
TRMM PR 1998-2000
annual precipitation, observed stratiform, resting basic state
mb/h
zonal wind and w, 9N-9S
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
Circulation associated with idealized MCS
Mid level
inflow
Low level
inflow
Houze 1982
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
Heating & Cooling Processes in an MCS
Houze 1982
Figure CONVSF
Midlevel
Horizontal
inflow
Structure
can
come
of
from any direction
System
Houze
1997a Mesoscale
100 km
Idealized
radar echo pattern
Houze 1997
TOGA COARE
Airborne Doppler Observations of MCSs
25 stratiform region flights
Kingsmill & Houze 1999
TOGA COARE
Airborne Doppler Observations of MCSs
Convective region flights
Stratiform region flights
Kingsmill & Houze 1999
Heating & Cooling Processes in an MCS
Momentum Transport
Buoyancy Produced Pressure Minimum in an MCS
Convective
Region
LeMone 1983
Perturbation pressure field in a simulated MCS
Precip.
Cloud
Yang & Houze 1996
Sizes of MCSs observed in TOGA COARE
“Superclusters”
Chen et al. 1996
TOGA COARE radar data sampling relative to KW wave
strong westerly
westerly
onset
Houze et al. 2000
TOGA COARE
Westerly wind component at 155°E
12-15 Dec 92
21-26 Dec 92
Westerly
jet
Westerly Onset
Strong Westerly
Houze et al. 2000
TOGA COARE radar data sampling relative to KW wave
strong westerly
westerly
onset
Houze et al. 2000
Stratiform region momentum transport in strong westerly region
MCS of 11 February 1993, as seen by ship radar
reflectivity
Stratiform
radar echo
SW
NE
Doppler velocity
Downward
momentum
transport in
stratiform
region
Houze et al. 2000
A
plan view
1000 km
Moncrieff &
Klinker 1997
B
1000 km
cross section
A
B
Stratiform region momentum transport in westerly onset region
MCS of 15 December 1992
As seen by ship radar
Doppler Radial Velocity
0.5 km
Houze et al. 2000
Momentum Transport by Stratiform Region Descent
+ feedback
- feedback
Houze et al. 2000
TOGA COARE: Ship and aircraft radar data relative to Kelvin-Rossby wave
structure
Low-level flow
strong westerly region
westerly
onset region
Houze et al. 2000
Mesoscale model simulation of MCS in westerly onset regime
Perturbation momentum structure
m/s
Mechem et al. 2004
Mesoscale model simulation of MCS in strong westerly regime
Perturbation momentum structure
Mechem et al. 2004
Mechem et al. 2006
Westerly Momentum
Flux Convergence
400 km
x 600 km
Strong
Westerly
Case
+ feedback
200 km
x 300 km
Westerly
Onset
Case
- feedback
Conclusions
• Layer lifting is important in large mesoscale convective
systems, esp. in tropics
• Amount of stratiform precipitation in large MCSs affects largescale 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