92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Thursday, 26 January 2012: 2:00 PM
The Convective Cloud Population of the Madden-Julian Oscillation
Room 252/253 (New Orleans Convention Center )
Robert A. Houze Jr., Univ. of Washington, Seattle, WA; and K. L. Rasmussen, S. R. Brodzik, J. Yuan, and H. C. Barnes

A-Train and TRMM satellite data have been analyzed to describe the convective cloud population of the Madden Julian Oscillation (MJO) over the West Pacific and Indian Ocean. We use the TRMM satellite's Precipitation Radar (PR) data to identify isolated shallow convective rain elements, deep convective rain elements, and broad stratiform radar echoes over the West Pacific and Indian Oceans for a multiyear dataset. The PR data are stratified by the eight phases of the MJO, as defined by Wheeler and Hendon (2004). Over the West Pacific, shallow isolated rain elements are always present with little variation from phase to phase. Deeper convective elements show a mild variation in frequency of occurrence with phase. The strongest signal is in the occurrence of broad stratiform rain areas, which are associated with organized mesoscale convective systems and superclusters. They are most frequent in phases 5-7 and nearly absent in phases 2-3. Over the Indian Ocean, shallow isolated convection is again ubiquitous in all phases, the frequency of deep convective elements varies somewhat from phase to phase, and again the largest signal is in the occurrence of broad stratiform radar. The variations in the TRMM PR data with MJO phase are consistent with observations of MCSs with the A-Train satellites. Using the method developed by Yuan and Houze (2010) we identify MCSs objectively with a combination of algorithms applied to the MODIS brightness temperature field and AMSR-E rain data, both from the A-Train's Aqua satellite. Over the West Pacific and Indian Ocean, the occurrence of MCSs is most frequent in the same periods as the maximum frequency of occurrence of broad stratiform regions seen by the TRMM PR. Compared to other locations, the most frequent occurrence of organized deep convective systems (connected/clustering MCSs) have the largest relative variation associated with the MJO over the Indo-Pacific warm pool. This behavior suggests that deep convection not only increases its total frequency of occurrence but also changes its form to become more organized in MJO active phases as it matures and propagates eastward. The increase in MCS activity and broad stratiform regions in the active periods of the MJO corresponds to sharply increased relative humidity in midlevels. The cause and effect relationship between the humidity and the MCSs is, however, not clear. The change in conditions from phases 5-6 to phases 1-2 over the Indian Ocean is the buildup period of the MJO disturbance, which later propagates eastward. Two field campaigns are being carried out to study the initiation of the MJO disturbance: The Dynamics of the MJO experiment (DYNAMO) and the ARM MJO Investigation Experiment (AMIE), in which 2 ships, 2 aircraft, and numerous radars and sounding sites will be deployed. A preliminary report from these field campaigns will be incorporated into this presentation.

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