Scales of Convective Activity in the MJO

Robert A. Houze, Jr.

With contributions from:

S. Powell, M. Zuluaga, H. Barnes, A. Rowe

AGU Annual Meeting, San Francisco, 11 December 2013

The MJO scale

~30-60 days

TOGACOARE

West Pacific 1

2

3

7

8

5

6

4

“ActivePeriod”

~1-3 weeks

Wheeler & Hendon 2004

“ActivePeriod”

~1-3 weeks

IndianOcean

DYNAMO

The convective scales

Examples from DYNAMO

Examples

Broad stratiform

Deep coresShallow isolated

Wide cores

From Powell and Houze 2013

~½-1 h

~5-10 h

TRMM radar shows how the scale of individual convective entities vary with phase of the MJO

Barnes and Houze 2013

Shallow Isolated Echoes

Deep Convective Cores

Broad Stratiform Regions

Wide Convective Cores

Active conditions

Suppressed conditions

Convective Stratiform

Kingsmill and Houze 1999

~50 aircraft surveys in TOGA COARE

x

Kingsmill and Houze 1999

~50 aircraft surveys in TOGA COARE

x

Convective Stratiform

Wide convective elements and broad stratiform regions are like Moncrieff’s mesoscale layer model of deep tropical convection…

Moncrieff 1992

…mesoscale adjustment to shear and thermodynamic stratification

100-200 km

DYNAMO radar data show microphysical stratification ~constant for both convective and stratiform entities

Melting snowGraupel

Dry snow

Small ice

Convective

Stratiform

Convective

Stratiform

Convective

Stratiform

% of observations

October November December

Rowe & Houze 2013

Melting snowGraupel

Dry snow

Small ice

Intermediate scales• Smaller than MJO• Larger than convective entities

S-PolKa Radar Rainfall at Addu Atoll in DYNAMO

Powell and Houze 2013

OLR

Rain seen by the S-PolKa radar in

DYNAMO

Zuluaga and Houze 2013

October Active Period

November Active Period

December Active PeriodOccurred in “episodes”

separated by ~2-7 days

Filter and composite

Zuluaga and Houze 2013

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

Divergence

Variation of the DYNAMO radar echo population relative to a precpitation episode

Zuluaga and Houze 2013

Composite of all 2-day rainfall episodes

The largest scale

Vertical structure of the MJO

Moncrieff 2004

~10,000 km~30-60 days

Vertical structure of the MJO

Moncrieff 2004

~10,000 km~30-60 days

Coupling with the

changeable convective population

Vertical structure of the MJO

Moncrieff 2004

~10,000 km~30-60 days

• Kelvin wave• Rossby wave• 2-7 day waves• Cloud-

humidity feedback

• Mid-latitude interaction

Summary Convection in the MJO has multiple important scales

• Shallow isolated• Deep cores• Wide cores• Broad stratiform rain areas

How does convection accommodate systematically to

• Intermediate scale waves, which account for most of the rainfall

• Larger scale of the MJO itself

EndThis research was supported by

NASA grants NNX10AH70G, NNX13AQ37G and NNX13AG71G NSF grant AGS-1059611

DOE grant DE-SC0008452

Extra Slides

…Barnes talk & upcoming paper

ConvectiveConvective entities

DYNAMO radar data composited relative to the mesoscale airflow

DYNAMO radar data composited relative to the mesoscale airflow

ConvectiveConvective entities0°C

Stratiform entities

…Barnes talk & upcoming paper

Stretched Building Block HypothesisMapes et al. 2006

Large-scale wave structure at the same times

Cloud population at three different times

Vertical structure of the MJO

Moncrieff 2004

~10,000 km

Upper-level eastward propagating Kelvin waves?

…Scott Powell’s poster

u’ at 150 mb

DYNAMO