外核液态铁粘滞度的分子动力学研究

MOLECULAR DYNAMICS STUDY OF BULK AND SHEAR VISCOSITY OF LIQUID IRON IN THE EARTH'S OUTER CORE:A CRITICAL REVIEW

地球外核液态铁的不断流动造成了地球磁场 ,决定这一流动的基本性质之一是剪切粘滞度。研究外核液态铁的剪切粘滞度对认识地球磁场的运转机制具有非常重要的意义。地震波和大地测量研究表明地球内部除了剪切衰减外 ,还具有体积衰减。研究外核液态铁的体粘滞度对认识地球内部非弹性性质具有重要意义。由于外核所处的温度和压力状态 ,目前还无法从实验的角度对外核的粘滞度进行测量 ,因此必须采用实际观测和理论模拟计算相结合的方法。在考察了地球外核的主要成分和所处的温压状态后 ,简要介绍了研究外核的一种有效的理论方法———分子动力学。在此基础上 ,重点评述了国际上对外核液态铁剪切粘滞度和体粘滞度的研究现状。在剪切粘滞度方面 ,理论计算值位于实际地球观测值区间的下限。在体粘滞度方面 ,理论计算与实际地球观测之间均存在巨大的差别。这一巨大差异的解决将加深人们对地球内部非弹性性质的认识。

It's a consensus that the flow of liquid iron in the outer core generates the Earth's magnetic field.One of the key factors that control the flow is shear viscosity.Consequently,knowledge on the shear viscosity of liquid iron will help us to understand the working mechanism of the the Earth's magnetic field.Seismic and geodetic studies show that there can be not only shear dissipation,but also bulk dissipation in the interior of the Earth.Understanding of the outer core's bulk viscosity will help us to infer the anelastic properties of the inner Earth.Due to the very high temperature and pressure involving in the outer core,it's still impossible to obtain its viscosity experimentally.For that purpose,observations and theoretical calculation must be combined.After a brief examination of the composition,temperature and pressure state of the outer core,this article presents one of the efficient theoretical method—the molecular dynamics for study of the outer core.Then it critically reviews research on shear and bulk viscosity of the outer core in the world.On the part of shear viscosity,theoretical calculations agree with the lower bound of observations.On the contrary,a large discrepancy in bulk viscosity exists.Resolving the problem of discrepancy will certainly give us a better understanding of anelastic properties of the interior of the Earth.