Relation Between Length-of-Day Variation and Angular Momentum of Geophysical Fluids

由于受到地球物理过程激发，地球自转速率会随着时间有明显的变化。在考虑角动量守恒的情况下，地球表面流体（大气、海洋等）在轴向角动量的变化会引起地球自转速率产生一个反向的变化。随着近年来气象数据的不断丰富和各种模式数据的不断进步，我们已能比较好的解释地球自转速率的变化。现在，需要更加关注另一个问题，即地球动力学参数的确定。我们现在拥有了地球这个系统的输入（大气、海洋等角动量变化），也更好的量测到了这个系统的输出（地球自转速率的变化）。从地球这个系统的输入和输出，我们想看到地球动力学参数的确定是否准确，这是地球系统的一个性质。但我们很难深入到地球内部去了解地球的结构和性质，只能通过对地球这个系统的输入和输出来反演地球的一些性质。我们在这里，通过研究地球自转速率的变化，来反演地球的转动惯量，从而了解核幔耦合情况。

Abstract. The remarkable relation well observed between the variations in the length of day (ΔLOD) and the axial atmospheric angular momentum (ΔAAM) (plus the oceanic counterpart to a much lesser extent) is a consequence of the conservation of angular momentum on the planet Earth. The quantification of the exact ΔLOD-ΔAAM relation, which we aim to seek in the present study, depends significantly on the extent to which the core participates, or is dynamically coupled with the mantle in the transmission of the axial ΔAAM from the mantle to the core. If, after converted into the equivalent ΔLOD assuming core-mantle de-coupling (as in the current standard practice), the calculated axial ΔAAM (according to atmospheric general circulation models GCMs) is systematically greater than the observed ΔLOD, then we can conclude the presence, and furthermore estimate the strength, of the said dynamic core-mantle coupling. However, in this study we find the opposite instead, that the calculated ΔAAM (plus the small oceanic counterpart) is smaller than the observed ΔLOD by 10-20% consistently across the intra-seasonal and seasonal timescales. Our main logical conclusion is that the atmospheric GCMs in general underpredict the ΔAAM, by at least 10-20% in the said timescales, a fact of importance w.r.t. assessing the GCMs. Therefore, the systematic discrepancy found between the ΔAAM-predicted and the observed ΔLOD masks out the relevant information towards the core-mantle coupling that we set out to seek.

Paper Link： http://www.agu.org/pubs/crossref/2010/2009JB007024.shtml