The Tropical Cloud Population

R. A. Houze

Lecture, Indian Institute of Tropical Meteorology, Pune, 9 August 2010

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

Before Satellites

Small cumulus

Cumulus congestus

Cumulonimbus and mesoscale convective systems

Visual Observation

View from an aircraft flying over the South China Sea

“Hot tower hypothesis”

of

Riehl & Malkus 1958

Radiosonde Data

Satellite Observations

Large cloud shields

Large cloud shields

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

Radars

GATE 1974

GATE SHIP ARRAY

More Field Projects to Study Convection

BoB 1979

JASMINE1999

EPIC 2001

TEPPS1997

(Dashed: No sounding network)

Houze et al. (1980)

Post-GATE view of the tropical cloud population

STRATIFORMRAIN

MESOSCALE CONVECTIVE SYSTEMS (MCSs)

By the early 1980’sIdealized life cycle of tropical MCS

Houze 1982

Precipitation Radar in Space

The TRMM SatelliteThe TRMM Satellite

TRMM

Radar

Low altitude, low inclination orbit

TRMM Satellite InstrumentationTRMM Satellite Instrumentation

Kummerow et al, 1998

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

Knowledge of global rainfall before satellites measured rain from space

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

Knowledge of global rainfall after TRMM & other satellites measured rain from space

How is tropical rain 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?

Trade Wind Regime

Stratocumulus Regime

Trade Wind Regime

Indo/Pacific Warm Pool

Traditional conceptual view of mean meridional distribution of tropical convection

Simpson 1992

“Trimodal” distribution

Johnson et al. 1999

Conceptual

model based on TOGA COARE observations

Cu congestusSmall Cb

“Trimodal” distribution

Johnson et al. 1999

Evidence from TOGA COARE

soundingdata

“Trimodal” distribution

Hollars et al. 1999

Evidence

from Manus ARM cloud radar

observations

XMANUSMANUSMANUSMANUS

Tropical cloud population related to SST

SST Climatology (July)TRMM PR Deep Convective

TRMM PR Shallow, Isolated Convective

July SST

Land vs Ocean

TRMM view of Africa vis a vis the Atlantic

Rain Stratiform Rain Fraction

MCSs with large 85GHz ice scattering

Lightning

Cloud Radar in Space

Anvils of Mesoscale Convective Systems (MCSs)

Yuan and Houze 2010

1 2 3

Three steps of analysis of multi-sensor data

&(GEOPROF-2B)(TB11)

Yuan and Houze 2010

(GEOPROF-2B)(TB11)

MO

DIS

MO

DIS

CloudSat

Use MODIS and CloudSat to find threshold of thick high cloud

Yuan and Houze 2010

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

Define criterion for MCS that is reasonable for all these regions

Yuan and Houze 2010

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

“Connected” and “Separated” MCSs

Yuan and Houze 2010

MCSs Over the Whole Tropics

Yuan and Houze 2010

MCSs Over the Whole Tropics

Yuan and Houze 2010

Frequency of MCS anvils over tropics

Yuan and Houze 2010

Comparison of MCS anvils in different parts of the tropics

CloudSat data

Yuan and Houze 2010

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

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

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

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