Mechanisms controlling mixed-layer temperature variability in the eastern tropical Pacific on the intraseasonal timescale

The Madden Julian Oscillation (MJO) is a prominent mode of intraseasonal (~35-95 day) variability in the tropical Indian and western Pacific Oceans. Its impacts on ocean mixed-layer temperatures (MLT) in the eastern tropical Pacific Ocean (ETPO) are not well-understood. A previous study of mooring data at (110°W, EQ) implies vertical advection forced by MJO-generated Kelvin waves is important to ETPO intraseasonal MLT; another, based on model output over (120-100°W, 3°S-3°N), indicates meridional advection dominates. We analyze an ocean state estimate at (110°W, EQ) and find combined subsurface processes, including a notable vertical advection component like that expected from MJO-forced Kelvin waves, dominate. However, when averaged over (120-100°W, 3°S-3°N), subsurface processes and horizontal advection are both important, and effects of thermocline forcing (e.g., Kelvin waves) are small compared to those by local wind driven mixing and horizontal advection. The results highlight the importance of understanding regional physics on different spatial scales.