Convective Clouds

Lecture Sequence1. Basic convective cloud types

2. Severe convection & mesoscale systems

3. Tropical cloud population

4. Convective feedbacks to large-scales

5. Extreme convection

6. Diurnal variability

7. Clouds in tropical cyclones

The tropical convective cloud population

Lecture, Summer School on Severe and Convective Weather, Nanjing, 11 July 2011

Robert HouzeUniversity of Washington

The tropical convective cloud population

What do we know?

How has technology contributed?

What comes next?

Before Satellites

Small cumulus

Cumulus congestus

Cumulonimbus

Visual Observation

Radiosonde data in the tropics

Riehl & Malkus 1958

“Hot tower hypothesis”“Hot tower hypothesis”

GC

M g

rid

Convective parameterization

Satellite Observations: an “inconvenient truth”

Large cloud shields

Satellite view of the tropical cloud population

•Explained satellite pictures •Retained the hot tower notion •Included smaller clouds

Early 1970’s

Radars: The second “inconvenient

truth”

GATE 1974

197440 ships!

12 aircraft!

197440 ships!

12 aircraft!

4 shipborne scanning digital

C-band radars

4 shipborne scanning digital

C-band radars

More Field Projects to Study Convection

BoB 1979

JASMINE1999

EPIC 2001

TEPPS1997

(Dashed: No sounding network)

Ground, ship, & airborne cm radars

Houze et al. (1980)

Post-GATE view of the tropical cloud population

MESOSCALE CONVECTIVE SYSTEMS (MCSs)

STRATIFORMRAINGCM grid

Hot Tower

Houze 1982

Heating and cooling processes in an MCS

Simplified MCS Heating Profiles

Schumacher et al. 2004

He

igh

t (km

)

Deg K/day

Convective

Stratiform

MCS Net Heating Profiles

He

igh

t (km

)

Deg K/day

0% stratiform

40% stratiform

70% stratiform

Schumacher et al. 2004

Precipitation Radar in Space

The TRMM SatelliteThe TRMM Satellite

Ku-band RadarKu-band Radar

Low altitude, low inclination orbitLow altitude, low inclination orbit

Knowledge of global rainfall before satellites measured rain from space

Knowledge of global rainfall before satellites measured rain from space

Combined satellite rainfall July 2000TRMM plus passive microwave sensors + other

Combined satellite rainfall July 2000TRMM plus passive microwave sensors + other

Rainfall mapping revolutionized!Rainfall mapping revolutionized!

TRMM Satellite InstrumentationTRMM Satellite Instrumentation

Kummerow et al, 1998

λ= 2 cmImportant! PR measures 3D structure of radar echoes

How tropical rain is distributed by cloud size

and type

Schumacher & Houze 2003

2 Years of TRMM PR data

Large CbsMCSs

Smallisolated Cbs

How do the environments of these regimes differ?

SST Climatology (July)TRMM PR Deep Convective

TRMM PR Shallow, Isolated Convective

July SST

Traditional conceptual view of mean meridional distribution of tropical convection

Simpson 1992

Stratocumulus Regime

Trade Wind Regime

Indo/Pacific Warm Pool

“Trimodal” distribution

Johnson et al. 1999

Evidence from TOGA COARE

soundingdata

Cu congestusSmall Cb

“Trimodal distribution”“Trimodal

distribution”

Suggested by

TOGA COARE radiosonde data

Johnson et al. 1999

Cloud Radars

“Trimodal” Distribution

Frequency of

cloud-top heightfrom 9 mm wavelength

vertically pointing radar

XMANUSMANUSMANUSMANUS

Hollars et al. 1999

Cloud Radar in Space

The A-Train Satellites show the complete MCS

Yuan and Houze 2010

MCSs Over the Whole Tropics

Yuan and Houze 2010

(< 12000 km2)

(> 40000 km2)

Morphology of MCS anvils in different parts of the tropics

Data from CloudSat mm-Wavelength Cloud Profiling Radar

Yuan and Houze 2010

Internal structure of MCS anvils shown by CloudSat Cloud Profiling Radar

Yuan, Houze, and Heymsfield 2011

Africa Indian Ocean

convective rain stratiform rain

graupel

snow

Conceptual model of anvil microphysics

Cetrone and Houze 2011

Addu Atoll

Five radars on a tiny island

HUMIDITY

DUAL WAVELENGTHWater vapor

CM-WAVELENGTHPrecipitation

MM-WAVELENGTHNon-precipitating

Cumulus

MM-WAVELENGTHAnvil cloud

POLARIMETRYMicrophysics

DOPPLERAir motions

Radar Supersite ApproachWill document many aspects of the convective population

Summary & Conclusions

Timeline of progress

Pre-satellite eraHot towers

Radars in field projects

MCSs, convective and stratiform precipitation regions

Precipitation radar in space

Global patterns—convective, stratiform, shallow

Cloud radarsGround based—trimodality of the populationSatellite based—global distributions of MCSs, anvils, ...

Dual wavelengthWater vapor

Spectrum of convective cloud types and sizes covers a wide range of types and sizes of convective entities

• Mesoscale systems with stratiform rain• Top-heavy heating profiles• Multimodal size distributions• Shallow isolated cells• Structures of large anvil clouds• Global variability of the population

What we’ve learned

Where we are going

How does convective population project onto larger-scale dynamics?

• Latent heating profiles• Radiative heating profiles in anvils of MCSs • Nonprecipitating convective clouds• Relation between humidity field and cloud

population evolution • Role of clouds in MJO, ENSO, monsoon, & coupled

equatorial waves

End

This research was supported by NASA grants NNX07AD59G, NNX07AQ89G, NNX09AM73G, NNX10AH70G, NNX10AM28G,

NSF grants, ATM-0743180, ATM-0820586, DOE grant DE-SC0001164 / ER-6

Extra Slides

Internal structure of “thick” anvils shown by CloudSat

Yuan, Houze, and Heymsfield 2011

Indian Ocean

Africa

Internal structures of MCS anvils

Cetrone & Houze 2011and also

Yuan et al. 2011-CloudSat

Data from MCSs seen by ARM

W-band radar in Niamey, Niger

Hei

ght

(km

)

Reflectivity (dBZ)

Internal structures of MCS anvils

Cetrone & Houze 2011and also

Yuan et al. 2011-CloudSat

Data from MCSs seen by ARM

W-band radar in Niamey, Niger

Hei

ght

(km

)

Reflectivity (dBZ)