Tropical Convection: A Half Century Quest for Understanding

Bjerknes Memorial Lecture, AGU, San Francisco, 4 December 2012

Robert HouzeUniversity of Washington

UW Atmospheric Sciences Colloquium, Seattle, 18 January 2013

A personal story of three great field campaigns and the evolution of

meteorological satellites

Tropical Convection: A Half Century Quest for Understanding

Before Satellites

Small cumulus

Cumulus congestus

Cumulonimbus

Visual Observation

Radiosonde data in the tropics

Riehl & Malkus 1958

“Hot tower hypothesis”

TIROS I1960

…the atmospheric sciences require worldwide observations and, hence, international cooperation…

John F. Kennedy, New York, 1961

“If we are genuinely interested in forecasting a few weeks in advance, we should give serious consideration to enlarging our network of observing stations, particularly over the oceans.”

Edward Lorenz, NYAS, 1963

Detente

The promise of global prediction

Satellites

Global Atmospheric Research Program

“ GATE ”

The era of field campaigns

GATE 1974

Convective parameterization

Glo

bal m

odel

grid

Problem: How to deal with tropical convection in a global model

Small area assumption

Satellite Observations produced an

“inconvenient truth”

Convective cloudsare actually large

…“mesoscale”

“No particular significance is attached to the interaction between the [mesoscale]

and the other scales.”

…NAS Plan for U.S. Participation in GATE

Satellite view of the tropical cloud population

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

Prevailing view of tropical convection in the early 1970’s

The grandest field campaign:GATE 1974

197440 ships!

12 aircraft!

4 shipborne scanning digital

C-band radars

16 sounding sites

The GATE radarsled to a

second “inconvenient truth”

Houze et al. (1980)

Post-GATE view of the tropical cloud population

Global model grid

Hot Tower

Houze 1982

Heating and cooling processes in a mesoscale system

Simplified Mesoscale System Heating Profiles

Schumacher et al. 2004

Hei

ght (

km)

Deg K/day

Convective

Stratiform

Mesoscale System Heating Profiles

Hei

ght (

km)

Deg K/day

0% stratiform

40% stratiform

70% stratiform

Schumacher et al. 2004

Does this matter?

0% stratiform

250 mb stream function, 400 mb heatingK/day

Schumacher et al. 2004

250 mb stream function, 400 mb heatingK/day

Schumacher et al. 2004

40% stratiform

More Field Projects

BoB 1979

JASMINE1999

EPIC 2001TEPPS

1997

(Dashed: No sounding network)

Soundings and radars on aircraft, ships, and islands

AtlanticGATE1974

W. PacificTOGA COARE

1992-3Indian Ocean

DYNAMO2011-12

The West Pacific, 1992-93TOGA COARE Array

Shipborne and airborne Doppler radars

+ Rawinsondes

Cu congestusSmall Cb

“Trimodal distribution”

Richard Johnson’s

analysis of the TOGA COARE

rawinsonde data

Johnson et al. 1999

TOGA

COARE

ARM’s Manus Island cloud

radar confirmed the “trimodal distribution”

Hollars, Fu, Comstock, & Ackerman 1999

XMANUS

Madden and Julian 1971, 1972

The “MJO”

TOGA COARE

West Pacific 1

2

3

7

8

5

6

4

“Active Phase” ~1-2 weeks

Wheeler & Hendon 2004

Doppler radar sampling relative to the MJO in TOGA COARE

RossbyGyres

Kelvin WaveConvergence

Moncrieff’s Mesoscale Layer Model of Tropical Convection

Moncrieff 92

Synthesis of TOGA COARE Doppler radar observationsconfirms Moncrieff’s model

TOGA COARE Airborne Doppler Observations of MCSs

25 convective region flightsShow deep layer of inflow to updrafts

Kingsmill & Houze 1999

<

Kingsmill & Houze 1999

TOGA COARE Airborne Doppler Observations of MCSs

25 stratiform region flights

Houze 1982

Empirical Model of an MCS

Layer inflow

Midlevel

inflow

BoB 1979

JASMINE1999

EPIC 2001TEPPS

1997

(Dashed: No sounding network)

AtlanticGATE1974

W. PacificTOGA COARE

1992-3Indian Ocean

DYNAMO2011-12

DYNAMO: The third of the 3 great field campaigns

DYNAMO-AMIE-CINDY

Two radarsRawinsondeOceanography

Two radarsRawinsondeOceanography

Four radarsRawinsonde Falcon aircraft

Rawinsonde P3 aircraft

IndianOcean

Focus of DYNAMO/AMIE:

Convective cloudpopulation

Multi-radar ApproachTo document more aspects of the convective population

HUMIDITY

DYNAMO/AMIE:DUAL WAVELENGTH

Water vapor

GATE:CM-WAVELENGTH

Precipitation

DYNAMO/AMIE:MM-WAVELENGTHNon-precipitating

Cumulus

CUMULUS

DYNAMO/AMIE:MM-WAVELENGTH

Anvil cloud

ANVIL

TOGA COARE: DOPPLER

Air motions

DYNAMO/AMIE:POLARIMETRYMicrophysics

Stretched Building Block HypothesisMapes et al. 2006

Large-scale wave structure at the same times

Cloud population at three different times

“We speculate that there is a natural selection in the atmosphere for wave packets whose phase structure produces a local, Eulerian sequence of cloud zone-supporting anomalies that aligns with the convective cloud system life cycle.”

Mapes et al. 2006

Indian Ocean

1

2

3

4

5

6

7

8

The MJOover the Indian Ocean

4

5

6

“Active Phase” ~1-2 weeks

DYNAMO Wheeler & Hendon 2004

October Active Period

November Active Period

December Active Period

Rain seen by the S-PolKa radar

Zuluaga and Houze 2013

Zuluaga and Houze 2013

Composite large-scale divergence and vertical motion during 2-day rainfall episodes

Variation of the DYNAMO radar echo population

Composite of all 2-day rainfall episodes

Vertical structure of the MJO

Moncrieff 2004

TRMM Radar Observations of the MJO over the Indian Ocean

Phase 7

Active Phase Suppressed Phase

Deep Convective

Cores

Broad Stratiform

Rain Areas

Summary & ConclusionsThe three great oceanic field campaigns

• GATE 1974 • Mesoscale systems• Heating profiles

• TOGA COARE 1992-3 • Trimodality• Mesoscale circulations

• DYNAMO/AMIE 2011-2• Convective population• Relation to large-scale waves

Summary & ConclusionsSatellites (& reanalysis)

• TIROS 1960• Global awareness

• TRMM 1997 • Precipitation radar in space

• A-Train 2000’s• Cloud radar and lidar in space

• Next generation & beyond• GPM, Earth Care, MeghaTropique, …

End

This research was supported by NASA grants NNX10AH70G, NNX10AM28G,

NSF grants, AGS-1059611DOE grant DE-SC0008452