16:30 〜 16:45
[ACG33-10] The Physical Process to Cause the Seasonal Change of the Sea Surface Temperature in the Equatorial Atlantic
キーワード：Atlantic Nino、季節サイクル
Atlantic Nino (AN) has a significant seasonal phase lock, which coincides with the seasonal cooling of sea surface temperature (SST) from April to August. This coincidence can be an important key to understanding the onset mechanism of AN. We focused on the mechanism to cause the mean annual cycle of temperature in the equatorial Atlantic region. Most previous studies were done based on the one-dimensional mixed layer heat budget, which may ignore the subsurface processes and the spatial connection. In this research, we adopted the heat budget analysis of the whole equatorial Atlantic region, which expanded zonally and included both the mixed layer and the subsurface layer.
Results show that the rapid decrease of SST in the eastern portion from April is mostly attributed to the vertical diffusion at the bottom of the mixed layer due to the subsurface cooling. This subsurface cooling is caused by the subsurface zonal temperature advection through the eastward equatorial undercurrent. The source of the cold water was found in the South American coastal region, where the equatorward coastal currents contributed to subsurface cooling.
Eventually, the seasonal cycle of SST and its rapid decrease in the eastern Atlantic cannot be explained simply by one-dimensional processes. The seasonal decrease of SST in April could be traced back to the meridional transportation in the western portion, which through an enlarged vertical diffusion in the eastern portion due to the subsurface cooling by the eastward temperature advection. These processes indicate the possible effect of off-equatorial regions in the seasonal cycle. To clarify the physical processes of AN, it is necessary to investigate the interannual variation of both the local and remote processes which contribute to the seasonal cycle of SST.
Results show that the rapid decrease of SST in the eastern portion from April is mostly attributed to the vertical diffusion at the bottom of the mixed layer due to the subsurface cooling. This subsurface cooling is caused by the subsurface zonal temperature advection through the eastward equatorial undercurrent. The source of the cold water was found in the South American coastal region, where the equatorward coastal currents contributed to subsurface cooling.
Eventually, the seasonal cycle of SST and its rapid decrease in the eastern Atlantic cannot be explained simply by one-dimensional processes. The seasonal decrease of SST in April could be traced back to the meridional transportation in the western portion, which through an enlarged vertical diffusion in the eastern portion due to the subsurface cooling by the eastward temperature advection. These processes indicate the possible effect of off-equatorial regions in the seasonal cycle. To clarify the physical processes of AN, it is necessary to investigate the interannual variation of both the local and remote processes which contribute to the seasonal cycle of SST.