Onset of convection in the icy Galilean satellites: Influence of rheology
Onset of convection in the icy Galilean satellites: Influence of rheology
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DOI：
10.1029/2004je002371
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发表时间：
2005-12-07
影响因子：
4.8
通讯作者：
Pappalardo, RT
中科院分区：
文献类型：
--
作者：
Barr, AC;Pappalardo, RT
[1]冰I在温度和压力条件下表现出复杂的流变学，适合于木卫二，木卫三和木卫四的冰I壳的内部。我们使用数值方法和临界瑞利数的现有参数来确定在具有Goldsby和Kohlstedt（2001）在实验室实验中测量的应力、温度和粒度依赖的流变学的冰I壳中触发对流所需的条件。临界瑞利数取决于冰颗粒的大小和温度扰动的幅度和波长发出一个最初的导电冰I壳。如果壳体具有小于0.4 mm的假定均匀晶粒尺寸，则初始羽流生长期间的变形由牛顿体积扩散调节。如果冰颗粒的尺寸是在0.4毫米和3厘米之间，在羽流生长过程中的变形是由弱非牛顿晶界滑动，对流的临界冰壳厚度取决于温度扰动的幅度为-0.5功率容纳。当冰粒径超过2cm时，无论温度扰动的幅度或波长如何，伽利略卫星冰壳内都不可能发生对流。如果对流冰I壳中的颗粒尺寸发展到大于2厘米的有效值，对流将停止。如果冰壳的颗粒尺寸大到足以通过位错蠕变进行流动，那么冰就太硬而不能进行对流，即使在尽可能厚的冰壳中也是如此。考虑到复杂的冰流变学意味着，在判断其冰I壳的对流不稳定性时，需要估计的粒度在卫星和知识的初始热状态。
[1] Ice I exhibits a complex rheology at temperature and pressure conditions appropriate for the interiors of the ice I shells of Europa, Ganymede, and Callisto. We use numerical methods and existing parameterizations of the critical Rayleigh number to determine the conditions required to trigger convection in an ice I shell with each of the stress-, temperature- and grain size - dependent rheologies measured in laboratory experiments by Goldsby and Kohlstedt ( 2001). The critical Rayleigh number depends on the ice grain size and the amplitude and wavelength of temperature perturbation issued to an initially conductive ice I shell. If the shells have an assumed uniform grain size < 0.4 mm, deformation during initial plume growth is accommodated by Newtonian volume diffusion. If the ice grain size is between 0.4 mm and 3 cm, deformation during plume growth is accommodated by weakly non-Newtonian grain boundary sliding, where the critical ice shell thickness for convection depends on the amplitude of temperature perturbation to the - 0.5 power. If the ice grain size exceeds 2 cm, convection can not occur in the ice I shells of the Galilean satellites regardless of the amplitude or wavelength of temperature perturbation. If the grain size in a convecting ice I shell evolves to effective values greater than 2 cm, convection will cease. If the ice shell has a grain size large enough to permit flow by dislocation creep, the ice is too stiff to permit convection, even in the thickest possible ice I shell. Consideration of the complex ice rheology implies that estimates of the grain size in the satellites and knowledge of their initial thermal states are required when judging the convective instability of their ice I shells.