Keywords:ocean mixed layer, Madden Julian Oscillation
The mixed layer variations in the marginal sea off the western coast of Sumatra before and after the passage of the Madden Julian Oscillation (MJO) observed during the R/V Mirai cruises (Pre-YMC [Years of the Maritime Continent]: MR15-04 and YMC: MR17-08) are investigated. During the MR15-04 cruise, the halocline above 20 m depth was very strong before the MJO arrival, and the mixed layer depth (MLD) was very shallow (< 10 m). During the MR15-04 cruise, it was difficult to increase the MLD by the MJO wind bursts because of a very strong surface salinity stratification (> 0.1 psu/m) before the MJO. In contrast, during the MR17-08 cruise, the layer of 20-100 m was relatively mixed well in comparison with that in MR15-04 because of the stronger MJO wind bursts and the MLD was easily fluctuated due to the diurnal cycle of the surface heating. The difference of the MLD variations between MR15-04 and MR17-08 led the difference of the sea surface temperature tendency and could change the air-sea interaction processes under the MJO.