Seasonal variations of the upper ocean, such as mixed layer depth (MLD) and sea surface temperature (SST), responding to the atmospheric forcing in the North Pacific (10 N-50 N), are investigated by analyzing the Argo and NCEP/NCAR reanalysis 1 data. The OAFlux data are also used for comparison. During the early heating period in the high-latitude ocean north of 30 N, where a seasonal thermocline is formed above the deep mixed layer under strong surface heating, the MLD h is found to be scaled as h (Lλ)1/2, where L is the Monin-Obukhov length scale and λ is the Ekman length scale. On the other hand, in the low-latitude ocean south of 30 N, where the preexisting MLD is shallow and surface heating is weak, h is found to be scaled by λ. It is found that a large amount of heat flux across the MLD occurs, especially in the high-latitude ocean during the late heating period, in which h is small. It suggests the contribution by turbulent mixing across the MLD in addition to radiation penetration, and the eddy diffusivity in the high-latitude ocean is estimated as Kv 10-4-10-3 m2 s-1. The heat budget of the mixed layer reveals that the contribution from the ocean heat transport is much smaller than the surface heat flux in the high-latitude ocean except in the Kuroshio region, but it is sometimes comparable in the low-latitude ocean.
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All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology
- Space and Planetary Science
- Earth and Planetary Sciences (miscellaneous)