Papers in Meteorology and Geophysics

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The invasion of anthropogenic carbon dioxide (CO₂) in the ocean is simulated with an ocean biogeochemical circulation model. The model includes an isopycnal diffusion scheme for realistic tracer distributions in the ocean interior. Anthropogenic CO₂ is added to a one-box atmosphere in the course of a simulated time integration from the preindustrial state to the present day. The atmospheric CO₂ concentration in the model increases and reaches 354 μatm in 1990. The ocean uptake of anthropogenic CO₂ is 2.1 GtC year^-1 of the anthropogenic CO₂ emission of 6 GtC year^-1. The subpolar and polar regions in the basins, the equatorial Pacific and the Southern Ocean are strong sinks. In these regions deep waters, which are not equilibrated with atmospheric CO₂, are supplied to the surface primarily by wind-driven upwelling. Much anthropogenic CO₂ is accumulated in the subtropical gyres by Ekman convergence of surface waters and is transported to the depths in the North Atlantic through the deep western boundary current, respectively. These results are consistent with previous observational and model studies. The isopycnal diffusion in the model plays an important role in the uptake of anthropogenic CO₂ at subpolar and polar latitudes and in its transport to the depths. The time integration into the future indicates that advection by the North Atlantic Deep Water is most effective in the century-scale transport of anthropogenic CO₂ into the ocean interior. Central regions of subtropical gyres become filled with anthropogenic CO₂ and are less effective for the uptake of anthropogenic CO₂.

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   In this paper, we studied the equatorial monsoon systems and its association with the dipole mode in the Indian Ocean using NCEP/NCAR reanalysis data, outgoing long-wave radiation (OLR) and sea-surface temperature (SST) data.
   The western Indian Ocean is characterized by a prominent semi-annual cycle, in contrast, the eastern Indian Ocean is dominated by an annual cycle. Because of the above phase difference in the tropical Indian Ocean between its western and eastern regions, the east-west (colder-warmer) SST contrast is usually enhanced in autumn. The inter-annual dipole mode, usually seen in autumn, can be understood as a result of the enforced climatological SST contrast. The termination of the dipole mode is closely connected with the appearance of the climatological suppressed convection during February-March over the entire tropical Indian Ocean.
   The influence of the reversed Walker Circulation on the Indian Ocean, in response to the ENSO event, exhibits a distinct seasonal difference. If a divergent wind appears in summer over the Indian Ocean, the resultant SST becomes warmer (colder) in the western (eastern) Indian Ocean through air-sea interaction.
   Thus, the seasonal differences of the coupling process between the monsoon and the ENSO may be a significant factor for understanding the phase-locking feature of the dipole mode.

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