Fundamental framework and experiments of the third generation of IAP / LASG world ocean general circulation model |
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| Authors: | Xiangze Jin Xuehong Zhang Tianjun Zhou |
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| Institution: | (1) State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics, Chinese Academy of Sciences, 100080 Beijing;(2) Department of Geophysics, Peking University, 100871 Beijing |
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| Abstract: | A new generation of the IAP / LASG world ocean general circulation model is designed and presented based on the previous 20-layer
model, with enhanced spatial resolutions and improved parameterizations. The model uses a triangular-truncated spectral horizontal
grid system with its zonal wave number of 63 (T63) to match its atmospheric counterpart of a T63 spectral atmosphere general
circulation model in a planned coupled ocean-atmosphere system. There are 30 layers in vertical direction, of which 20 layers
are located above 1000 m for better depicting the permanent thermocline. As previous ocean models developed in IAP / LASG,
a free surface (rather than “rigid-lid” approximation) is included in this model. Compared with the 20-layer model, some more
detailed physical parameterizations are considered, including the along / cross isopycnal mixing scheme adapted from the Gent-MacWilliams
scheme.
The model is spun up from a motionless state. Initial conditions for temperature and salinity are taken from the three-dimensional
distributions of Levitus’ annual mean observation. A preliminary analysis of the first 1000-year integration of a control
experiment shows some encouraging improvements compared with the twenty-layer model, particularly in the simulations of permanent
thermocline, thermohaline circulation, meridional heat transport, etc. resulted mainly from using the isopycnal mixing scheme.
However, the use of isopycnal mixing scheme does not significantly improve the simulated equatorial thermocline. A series
of numerical experiments show that the most important contribution to the improvement of equatorial thermocline and the associated
equatorial under current comes from reducing horizontal viscosity in the equatorial regions. It is found that reducing the
horizontal viscosity in the equatorial Atlantic Ocean may slightly weaken the overturning rate of North Atlantic Deep Water. |
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| Keywords: | Ocean general circulation model Thermocline Isopycnal mixing |
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