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Energetics of lateral eddy diffusion/advection:Part Ⅱ. Numerical diffusion/diffusivity and gravitational potential energy change due to isopycnal diffusion
引用本文:HUANG Rui Xin. Energetics of lateral eddy diffusion/advection:Part Ⅱ. Numerical diffusion/diffusivity and gravitational potential energy change due to isopycnal diffusion[J]. 海洋学报(英文版), 2014, 33(3): 19-39. DOI: 10.1007/s13131-014-0410-0
作者姓名:HUANG Rui Xin
作者单位:Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole 02543-1050, USA
摘    要:Study of oceanic circulation and climate requires models which can simulate tracer eddy diffusion and ad vection accurately. It is shown that the traditional Eulerian coordinates can introduce large artificial hori zontal diffusivity/viscosity due to the incorrect alignment of the axis. Therefore, such models can smear sharp fronts and introduce other numerical artifacts. For simulation with relatively low resolution, large lateral diffusion was explicitly used in models; therefore, such numerical diffusion may not be a problem. However, with the increase of horizontal resolution, the artificial diffusivity/viscosity associated with hori zontal advection in the commonly used Eulerian coordinates may become one of the most challenging ob stacles for modeling the ocean circulation accurately. Isopycnal eddy diffusion (mixing) has been widely used in numerical models. The common wisdom is that mixing along isopycnal is energy free. However, a careful examination reveals that this is not the case. In fact, eddy diffusion can be conceptually separated into two steps: stirring and subscale diffusion. Due to the thermobaric effect, stirring, or exchanging water masses, along isopycnal surface is associated with the change of GPE in the mean state. This is a new type of instability, called the thermobaric instability. In addition, due to cabbeling subscale diffusion of water parcels always leads to the release of GPE. The release of GPE due to isopycnal stirring and subscale diffusion may lead to the thermobaric instability.

关 键 词:涡流扩散  数值扩散  重力势能  对流  能量学  水平分辨率  数字模型  不稳定性
收稿时间:2013-08-30
修稿时间:2013-12-17

Energetics of lateral eddy diffusion/advection: Part II. Numerical diffusion/diffusivity and gravitational potential energy change due to isopycnal diffusion
HUANG Rui Xin. Energetics of lateral eddy diffusion/advection: Part II. Numerical diffusion/diffusivity and gravitational potential energy change due to isopycnal diffusion[J]. Acta Oceanologica Sinica, 2014, 33(3): 19-39. DOI: 10.1007/s13131-014-0410-0
Authors:HUANG Rui Xin
Affiliation:Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole 02543-1050, USA
Abstract:Study of oceanic circulation and climate requires models which can simulate tracer eddy diffusion and advection accurately. It is shown that the traditional Eulerian coordinates can introduce large artificial horizontal diffusivity/viscosity due to the incorrect alignment of the axis. Therefore, such models can smear sharp fronts and introduce other numerical artifacts. For simulation with relatively low resolution, large lateral diffusion was explicitly used in models;therefore, such numerical diffusion may not be a problem. However, with the increase of horizontal resolution, the artificial diffusivity/viscosity associated with horizontal advection in the commonly used Eulerian coordinates may become one of the most challenging obstacles for modeling the ocean circulation accurately. Isopycnal eddy diffusion (mixing) has been widely used in numerical models. The common wisdom is that mixing along isopycnal is energy free. However, a careful examination reveals that this is not the case. In fact, eddy diffusion can be conceptually separated into two steps: stirring and subscale diffusion. Due to the thermobaric effect, stirring, or exchanging water masses, along isopycnal surface is associated with the change of GPE in the mean state. This is a new type of instability, called the thermobaric instability. In addition, due to cabbeling subscale diffusion of water parcels always leads to the release of GPE. The release of GPE due to isopycnal stirring and subscale diffusion may lead to the thermobaric instability.
Keywords:Eulerian coordinates  numerical diffusivity  numerical dissipation  energetics of isopycnal eddy diffusion
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