Some thermal consequences of a gravitationally powered dynamo
Some thermal consequences of a gravitationally powered dynamo
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DOI：
10.1029/jb083ib12p05961
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发表时间：
1978-12
影响因子：
--
通讯作者：
D. Loper
中科院分区：
文献类型：
--
作者：
D. Loper
有人认为，地球发电机的最合理的电源是由固体内核的增长释放的引力能，这种机制的基本特征进行了概述。研究了发电机由重力驱动时外核可能出现的热状态，发现了一些有趣的可能性：首先，如果液相线梯度TL′小于导热梯度TC′，则外核底部的流体中必然会出现浆状物;第二，它表明，成分驱动的对流可以发生，即使实际的温度梯度T′是小于在TA′的温度梯度。这允许热量可以通过运动径向向内传递的可能性。因此，在地核向外传导热量的速率和向地幔传递热量的速率之间没有直接的关系。第三，它被发现，希金斯和肯尼迪的假设并不排除对流翻转驱动的成分浮力提供的外核的热导率是足够大的。第四，外核中的浆液是稳定的，并且与任何类型的对流驱动发电机不相容。有人认为，只有当核心的成分比共晶更金属化时，引力发电机才是可能的。考虑了地球的热演化过程，发现当TA′ < TC′时，地核和地幔的热传递问题与地核的条件解耦，导致地幔底部有一个预定的温度，地幔底部的热通量则由地核决定。结果表明，如果T′ = TL′，大的热通量可能从核心流出，而温度几乎没有变化。
It is argued that the most plausible source of power for the geodynamo is gravitational energy released by the growth of the solid inner core, and the essential features of this mechanism are outlined. The thermal regimes of the outer core which are possible if the dynamo is gravitationally powered are studied, and a number of interesting possibilities are found. First, if the liquidus gradient TL′ is less than the conduction gradient TC′, a slurry must occur in the fluid at the bottom of the outer core. Second, it is shown that compositionally driven convection can occur even if the actual temperature gradient T′ is less than the adiabat TA′. This allows the possibility that heat may be transferred radially inward by the motions. Hence there is no direct relation between the rate that heat is conducted outward in the core and the rate of heat transfer to the mantle. Third, it is found that Higgins and Kennedy's hypothesis does not preclude convective overturning driven by compositional buoyancy provided the thermal conductivity of the outer core is sufficiently large. Fourth, a slurry in the bulk of the outer core is stabilizing and incompatible with a convectively driven dynamo of any kind. It is argued that the gravitationally powered dynamo is possible only if the composition of the core is more metallic than the eutectic. The thermal evolution of the earth is considered, and it is found that if TA′ < TC′, the heat transfer problems for the core and mantle decouple with conditions in the core leading to a prescribed temperature at the base of the mantle and the mantle then prescribing the heat flux which must emanate from the core. It is shown that if T′ = TL′, a large flux of heat may flow from the core with virtually no change in temperature.