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The Tropical Cloud Population
R. A. Houze
Lecture, Indian Institute of Tropical Meteorology, Pune, 9 August 2010
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Clouds in Low Latitudes
Lecture Sequence1. Basic tropical cloud types
2. Severe convection & mesoscale systems
3. Tropical cloud population
4. Convective feedbacks to large-scales
5. Monsoon convection
6. Diurnal variability
7. Clouds in tropical cyclones
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Before Satellites
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Small cumulus
Cumulus congestus
Cumulonimbus and mesoscale convective systems
Visual Observation
View from an aircraft flying over the South China Sea
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“Hot tower hypothesis”
of
Riehl & Malkus 1958
Radiosonde Data
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Satellite Observations
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Large cloud shields
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Large cloud shields
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Circa 1970
Good:•Explained satellite pictures •Retained the hot tower notion •Included smaller clouds
Satellite view of the tropical cloud population
Not good:•Missing downdraft•No stratiform rain•Unrealistic scale separation
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Radars
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GATE 1974
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GATE SHIP ARRAY
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More Field Projects to Study Convection
BoB 1979
JASMINE1999
EPIC 2001
TEPPS1997
(Dashed: No sounding network)
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Houze et al. (1980)
Post-GATE view of the tropical cloud population
STRATIFORMRAIN
MESOSCALE CONVECTIVE SYSTEMS (MCSs)
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By the early 1980’sIdealized life cycle of tropical MCS
Houze 1982
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Precipitation Radar in Space
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The TRMM SatelliteThe TRMM Satellite
TRMM
Radar
Low altitude, low inclination orbit
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TRMM Satellite InstrumentationTRMM Satellite Instrumentation
Kummerow et al, 1998
λ= 2 cmImportant! PR measures 3D structure of radar echoes
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Knowledge of global rainfall before satellites measured rain from space
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Combined satellite rainfall July 2000TRMM plus passive microwave sensors + other
Knowledge of global rainfall after TRMM & other satellites measured rain from space
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How is tropical rain distributed by cloud size and type?
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Schumacher & Houze 2003
2 Years of TRMM PR data
Large CbsMCSs
Smallisolated Cbs
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How do the environments of these regimes differ?
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Trade Wind Regime
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Stratocumulus Regime
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Trade Wind Regime
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Indo/Pacific Warm Pool
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Traditional conceptual view of mean meridional distribution of tropical convection
Simpson 1992
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“Trimodal” distribution
Johnson et al. 1999
Conceptual
model based on TOGA COARE observations
Cu congestusSmall Cb
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“Trimodal” distribution
Johnson et al. 1999
Evidence from TOGA COARE
soundingdata
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“Trimodal” distribution
Hollars et al. 1999
Evidence
from Manus ARM cloud radar
observations
XMANUSMANUSMANUSMANUS
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Tropical cloud population related to SST
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SST Climatology (July)TRMM PR Deep Convective
TRMM PR Shallow, Isolated Convective
July SST
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Land vs Ocean
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TRMM view of Africa vis a vis the Atlantic
Rain Stratiform Rain Fraction
MCSs with large 85GHz ice scattering
Lightning
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Cloud Radar in Space
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Anvils of Mesoscale Convective Systems (MCSs)
Yuan and Houze 2010
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1 2 3
Three steps of analysis of multi-sensor data
&(GEOPROF-2B)(TB11)
Yuan and Houze 2010
(GEOPROF-2B)(TB11)
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MO
DIS
MO
DIS
CloudSat
Use MODIS and CloudSat to find threshold of thick high cloud
Yuan and Houze 2010
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1-Find“cold centers”2-Use AMSR-E to find rain areas
Use 260 K threshold
Locate 1st closed contour
Use 1 mm/h threshold for rain rate
Yuan and Houze 2010
Associate pixels with nearest cold center
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Define criterion for MCS that is reasonable for all these regions
Yuan and Houze 2010
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TB11 = 220 Area > 2000 km2
account for most of the rainfall
Colors show rain amount
Size of cold cloud top
Tem
pera
ture
def
inin
g co
ld c
ente
r
Yuan and Houze 2010
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“Connected” and “Separated” MCSs
Yuan and Houze 2010
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MCSs Over the Whole Tropics
Yuan and Houze 2010
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MCSs Over the Whole Tropics
Yuan and Houze 2010
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Frequency of MCS anvils over tropics
Yuan and Houze 2010
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Comparison of MCS anvils in different parts of the tropics
CloudSat data
Yuan and Houze 2010
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Milestones in determining the tropical cloud population
Pre-satellite era
Hot towers and smaller clouds
Radars in field projects
MCSs, squall lines, stratiform precipitation
Precipitation radar in space
Patterns of convective, stratiform, shallow isolatedRelation to ocean & land
Cloud radar in space
Global distributions of MCSs & anvils
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Clouds in Low Latitudes
Next
Lecture Sequence1. Basic tropical cloud types
2. Severe convection & mesoscale systems
3. Tropical cloud population
4. Convective feedbacks to large-scales
5. Monsoon convection
6. Diurnal variability
7. Clouds in tropical cyclones
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This research was supported by NASA grants NNX07AD59G, NNX07AQ89G, NNX09AM73G, NNX10AH70G, NNX10AM28G,
NSF grants, ATM-0743180, ATM-0820586, DOE grant DE-SC0001164 / ER-6