Madden-Julian Oscillation and sea level: Local and remote forcing

Abstract

The Madden-Julian Oscillation (MJO) is the dominant mode of atmospheric variability in the tropical atmosphere on intraseasonal time scales (i.e., weeks to seasons). This study examines the connection between the MJO and global sea level measured by altimeters over the last 17 years. We first identify regions exhibiting a significant (both statistical and practical) relationship between sea level and the MJO. The first region consists of the equatorial Pacific and western coastal zones of North and South America. Consistent with previous studies, we identify wind-driven equatorially trapped Kelvin waves that propagate eastward along the equatorial Pacific and then transform into coastal trapped waves that propagate poleward along the western coasts of North and South America. The second region includes the shallow waters of the Gulf of Carpentaria (off Australia's north coast) and the adjacent Arafura and Timor seas. Setup by onshore winds is shown to be the dominant physical process. Finally, the northeastern Indian Ocean is shown to be a complex region involving a combination of equatorially trapped Kelvin waves, coastal trapped waves, and westward-propagating Rossby waves exhibiting characteristics of both local and remote forcing. The implications of the results for deep and coastal ocean forecasting are discussed.