Recent weakening in MJO-related convective activity over the equatorial Indian Ocean and Maritime Continent

Abstract

We document the observed changes in the intraseasonal variability of precipitation and outgoing longwave radiation (OLR) associated with the Madden-Julian Oscillation (MJO) from 1998 to 2015 when reliable and simultaneous satellite-derived daily precipitation and OLR are available. Tropical Rainfall Measuring Mission (TRMM) observations show a statistically significant weakening trend in variance of convective activity associated with the MJO across the equatorial Indian Ocean (EQIO) and Maritime Continent (MC) in boreal summer and winter seasons. During northern summer, the MJO variability in the POST period (2007–2015) displays a remarkable reduction in convection at all wavenumbers compared with that in the PRE period (1998–2006). During northern winter, along with a reduction in variance, the MJO-related activity is shifted from lower to higher wavenumbers by breaking down the associated convection into smaller scales. EQIO and MC experience a shift from a higher probability of stronger events to weaker events during both seasons in the multivariate Wheeler-Hendon Index. Moreover, there is a southward shift in the location of maximum variance, increasing (reducing) meridional symmetry in MJO variance during boreal summer (winter). This is manifested by a significant increase in boreal winter MJO variance over northern Australia. We also observed that over western EQIO, OLR anomalies associated with dry (wet) phase of MJO are higher (lower) in POST as compared with the PRE period indicating warmer surface temperatures and taller clouds during dry and wet phases of MJO respectively, which is consistent with observation. The exact opposite behavior is seen over the MC and Western Pacific Oceans. These variations in MJO can have important implications for the local and remote climate systems across the globe.