The MJO Cloud Population over the Indian Ocean

H. C. BarnesR. HouzeS. Brodzik

University of Washington

30th Conference on Hurricanes and Tropical Meteorology

19 April 2012, Ponte Vedra Beach, Florida

Objectives

• Variability of precipitating clouds in MJO using TRMM Precipitation Radar

• Associated humidity, winds, and wind shear

3

4

5

6

7

8

Phase 2

Phase 3

Phase 4

Phase 5

Phase 6

Phase 7

Phase 8

Phases of the MJOACTIVE STAGE

END OF ACTIVE STAGE

SUPPRESSEDSTAGE

Wheeler and Hendon 2004

Phase 1

Houze et al. 1980

MESOSCALE CONVECTIVE SYSTEMS (MCSs)

Tropical Cloud PopulationIsolated, Shallow

2A23 classification of shallow, isolated radar echoes• storm top << freezing level• Not connected to non-shallow precipitation

Identify each contiguous 3D echo objectseen by TRMM PR

Convective component Stratiform component

Extreme characteristicContiguous 3D volume ofconvective echo > 30 dBZ

Top height > 8 km

“Deep convective core” Horizontal area > 800 km2

“Wide convective core”

Extreme characteristicContiguous stratiform echo

with horizontal area > 50 000 km2

“Broad stratiform region”

TRMM PR Identification of Extreme Precipitating Regions in MCSs

Houze et al, 2007, Romatschke et al. 2010, Rasmussen and Houze 2011

Frequency of Isolated, Shallow Radar Echoes Small Variability

%

10N

10S90E60E

EQ

%

Frequency of Deep Convective Cores Small Variability

10N

10S90E60E

EQ

%

Frequency of Broad Stratiform Regions Large Variability With Phase

10N

10S90E60E

EQ

Summary of TRMM PR Study

Isolated, shallow and deep convection is relatively constant

Broad stratiform regions most common during active stage (phase 3) Mapes and Houze 1993, Chen et al. 1996, Yuter and Houze 1998, Morita et al. 2006

NCEP Reanalysis Study• 4x daily data when Wheeler and Hendon

amplitude > 1

• October – February, 1998-2009 Region: 60E – 90E, 10S – 10N

• Composite by phase– Relative humidity anomaly

• Defined relative to the average of all phases

– Wind field– Deep vertical wind shear (1000 – 300 hPa)

700 hPa Relative Humidity AnomaliesActive Stage Moist, Suppressed Stage Dry

%

850 hPa WindsWesterly Wind Burst

ms-1

300 hPa WindsEasterlies Strongest during Phase 3 & 4

ms-1

1000-300 hPa ShearShear Strongest as MJO exits

ms-1

ConclusionsBroad stratiform regions experience the greatest

amount of variability

Active Stage (2 & 3)

End of Active (4)

Suppressed Stage (5 - 7)

Broad Stratiform Frequency Maximum Decreasing Minimum

Mid – Upper Level Relative

HumidityMaximum Decreasing Minimum

Westerly Wind Burst Entering Centered Exiting

Deep Vertical Wind Shear Increasing Maximum Decreasing

EndThis research was supported by NSF grant AGS-1059611 and DOE grant

DE-SC0001164/er-64752