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

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

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

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

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 > 50 000 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

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

Frequency of Deep Convective Cores Small Variability %

Frequency of Broad Stratiform Regions Large Variability With Phase %

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

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 Anomalies Active Stage Moist, Suppressed Stage Dry DESCRIBE THE PLOT Shading: RH anomaly: phase average – total average %

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

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

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

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

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