Simulation of the deep and intermediate Pacific meridional overturning circulation

Takao Kawasaki, Atmosphere and Ocean Research Institute, the University of Tokyo, Kashiwa, Chiba, Japan, Hiroyasu Hasumi, Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Japan, Yoshimasa Matsumura, The University of Tokyo, Atmosphere and Ocean Research Institute, Kashiwa, Japan, Hiroaki Tatebe, JAMSTEC Japan Agency for Marine-Earth Science and Technology, Research Center for Environmental Modeling and Application, Yokohama, Japan, Yoshiki Komuro, Institute of Arctic Climate and Environment Research, Japan Agency for Marine-Earth Science and Technology, Japan and Shogo Urakawa, Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, Japan
We try to simulate the realistic Pacific meridional overturning circulation (PMOC) by employing the vertical mixing based on a recent observation and geothermal heating by using a global OGCM. The horizontal grid size is 1 degree. The horizontal distributions of local and remote tidal mixing energies are estimated by a tide model. The local mixing energy is enhanced near the bottom and decayed with height. The vertical profile of remote mixing depends on the ocean stratification. The global map of geothermal heating is also applied.

The strength of deep PMOC is significantly increased by using the stratification-dependent remote mixing and geothermal heating. The northward volume transport of deep water originated from the Southern Ocean is slightly smaller than an observational estimate by mooring observation, whereas the isotope ratio of radiocarbon shows the consistency with observation in the deep Pacific Ocean. This discrepancy implies the interannual or decadal variability of northward volume transport in the lower deep Pacific Ocean.

We will obtain (1) the fractions of the deep water returning to the Southern Ocean and inflowing the Indian Oceans and (2) the connection of circulations between the intermediate and deep layers in the North Pacific Ocean by using virtual Eulerian and Lagrangian tracers. Since the intermediate PMOC is influenced by the eddy activity, 1/6 degree OGCM experiment is additionally conducted. We will show these results in our presentation.