[A-CG33] Multi-scale ocean-atmosphere interaction in the tropics

[ACG33-04] Australian monsoon modulates the eastward propagation, amplitude and teleconnection of the MJO

*Shion Sekizawa^1,2, Hisashi Nakamura², Yu Kosaka² (1.Meteorological Research Institute, Japan Meteorological Agency, 2.Research Center for Advanced Science and Technology, University of Tokyo)

The Madden-Julian Oscillation (MJO) is often modulated by low-frequency variability in its background. This study demonstrates that the interannual variability of the Australian summer monsoon (AUSM) is one such low-frequency variability that modulates the MJO. The amplitude of the MJO is significantly enhanced (suppressed) in weak (strong) AUSM years, and the eastward propagation from the Maritime Continent into the western Pacific tends to be distinct (ambiguous). Possible mechanisms of the AUSM-MJO relationship are examined through a moist static energy budget analysis. In weak (strong) AUSM years, drier (wetter) air over the Australian continent enhances (weakens) the horizontal moisture gradient over the ocean to its northeast. When the anomalous convective activity associated with the MJO reaches northern Australia, the strong (weak) background moisture gradient leads to stronger (weaker) moisture advection over the western Pacific and promotes (inhibits) the eastward propagation. The more persistent propagation of the MJO in weak AUSM years than in strong AUSM years results in the stronger MJO amplitude. The MJO modulation in response to the seasonal AUSM strength also affects subseasonal variability of early spring temperature and precipitation in the Northern Hemisphere extratropics, including East Asia and North America.