1. The MJO Cloud Population over the Indian Ocean
H. C. Barnes
R. Houze
S. Brodzik
University of Washington
30th Conference on Hurricanes and Tropical Meteorology
19 April 2012, Ponte Vedra Beach, Florida

2. Objectives
Variability of precipitating clouds in MJO using TRMM Precipitation Radar
Associated humidity, winds, and wind shear

3. Phases of the MJO Phase 1 Phase 2 3 Phase 3 4 Phase 4 5 Phase 5 6
ACTIVE STAGE
Phase 3 4
Phase 4
END OF ACTIVE STAGE 5
Phase 5 6
SUPPRESSED
STAGE
Most widely used, used in my work
Statistical technique called empirical orthogonal function analysis
Take outgoing longwave radiation along with zonal winds at 850 and 200 hPa and develop two new times series called RMM1 and RMM2
Based on relationship can isolate variability associated with MJO and describe its large scale eastward propagation
Subjectively divide into 8 phase and provides a means to reference the location of MJO convection
DJF composite of OLR and 850 wind anomalies
Shading = negative OLR anomalies (clouds)
Hatching = positive OLR anomalies (clear sky)
Wind anomalies significant at 99% level
EOF = empirical orthogonal functions
- remove annual and interannual(between year) mean to better highlight intraseasonal (within season) variability
- Take initially related variables, construct a set of new independent variables that describe the spatial and temporal variability of the orginal variables
Phase 6 7
Phase 7 8
Phase 8
Wheeler and Hendon 2004

4. Tropical Cloud Population
Isolated, Shallow
MESOSCALE CONVECTIVE SYSTEMS (MCSs)
TRMM sensitivity 17 dBz
Means miss none-precipitating and smallest precipitating clouds
Studies have shown that significant sources precipitation captured by TRMM PR
2A23 classification of shallow, isolated radar echoes
storm top << freezing level
Not connected to non-shallow precipitation
Houze et al. 1980

5. TRMM PR Identification of Extreme Precipitating Regions in MCSs
Identify each contiguous 3D echo object seen by TRMM PR
Convective component
Stratiform component
Extreme characteristic
Contiguous 3D volume of convective echo > 30 dBZ
Top height > 8 km
“Deep convective core”
Horizontal area > 800 km2
“Wide convective core”
Contiguous stratiform echo with horizontal area > km2
“Broad stratiform region”
UNIQUE: 3D STORMS
USED PREVIOUSLY FOR INDIAN MONSOON AND SOUTH AMERICAN CONVECTION
Bob Slide
Done previously with indian Monsoon and in South America
Emphasize contiguous 3D echoes
- Not just looking at single pixels in the radar data. Actually analyzing coherent storms
Storms with deep or wide convective cores
Storms containing broad stratiform regions
Not mutuall exclusive
deep and broad or deep and wide in same storm
Analyzing components of a precipitating region
Houze et al, 2007, Romatschke et al. 2010, Rasmussen and Houze 2011

6. Frequency of Isolated, Shallow Radar Echoes Small Variability
GEOGRAPHIC LOCATION %

7. Frequency of Deep Convective Cores Small Variability%

8. Frequency of Broad Stratiform Regions Large Variability With Phase%

9. Summary of TRMM PR Study
SUPPORTS PREVIOUS RESEARCH
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

10. NCEP Reanalysis Study
4x daily data when Wheeler and Hendon amplitude > 1
October – February, 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)

11. 700 hPa Relative Humidity Anomalies Active Stage Moist, Suppressed Stage Dry
DESCRIBE THE PLOT
Shading:
RH anomaly: phase average – total average %

12. 850 hPa Winds Westerly Wind Burst
DESCRIBE THE PLOT
Shading: magnitude of zonal wind
Arrows: wind vectors
ms-1

13. 300 hPa Winds Easterlies Strongest during Phase 3 & 4
COLORBAR CHANGE – ONLY EASTERLIES
ms-1

14. 1000-300 hPa Shear Shear Strongest as MJO exits
DESCRIBE PLOTS!!!!
Shading: magnitude of shear
Vectors: shear vector
Largest areal coverage phase 4
ms-1

15. Conclusions
Broad 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 Humidity
Westerly Wind Burst
Entering
Centered
Exiting
Deep Vertical Wind Shear
Increasing

16. End This research was supported by NSF grant AGS-1059611 and DOE grant DE-SC0001164/er-64752