Seasonal Variations in Eastward Propagation Speed of MJO Convection

Friday, 19 December 2014
Tamaki Suematsu and Hiroaki Miura, University of Tokyo, Bunkyo-ku, Japan
Madden-Julian Oscillation (MJO) is a prominent intraseasonal variability in the tropics, which is characterized by eastward moving large-scale convective system along the equator. However their characteristics regard to their propagation paths, duration, and propagation speed varies from event to event. Here, 180 MJO events during 1979-2012 were identified applying Wheeler and Hendon’s (2004) Realtime Multivariative MJO index to 20-120 day Lanczos bandpass filtered NOAA Interpolated Outgoing Longwave Radiation (OLR) data, and NCEP/NCAR Reanalysis1 daily mean horizontal wind data at 850hPa and 200hPa. Location of minimum OLR was tracked daily as MJO convection propagation path, and eastward propagation speed for each event was calculated. Eastward propagation speeds of detected MJOs varied from 2ms^-1 to 10ms^-1, with most events taking propagation speed in the 3ms^-1 to 5ms^-1 range. Further investigation of propagation speed in relation with the MJO event’s occurring latitude and months revealed that propagation speed of MJOs tends to be faster in spring and autumn, and slower in the winter and summer months. This aspect of MJO seasonality was examined in relation with seasonal change in SST distribution by analysis of daily mean NOAA OI SST V2 high resolution dataset. The result suggests that zonal gradient of SST from the equatorial Indian Ocean to equatorial Western Pacific, and equatorial symmetry of SST distribution may have influence on the behavior of MJOs.