Relation between length‐of‐day variation and angular momentum of geophysical fluids
Relation between length‐of‐day variation and angular momentum of geophysical fluids
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DOI：
10.1029/2009jb007024
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发表时间：
2010-10
影响因子：
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通讯作者：
B. Chao;Haoming Yan
中科院分区：
文献类型：
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作者：
B. Chao;Haoming Yan
[1]日长变化（ΔLOD）和大气轴向角动量变化（ΔAAM）之间的显著关系（加上海洋对应物，在较小程度上）是地球角动量守恒的结果。我们在本研究中所寻求的ΔLOD-ΔAAM关系的精确量化，在很大程度上取决于地核在轴向ΔAAM从地幔到地核的传递中参与的程度，或者与地幔的动力耦合程度。如果在转换为假设核幔解耦的等效ΔLOD后（如当前标准实践），计算的轴向ΔAAM（根据大气环流模型[GCM]）系统地大于观测的ΔLOD，那么我们可以得出结论，并进一步估计所述动态核幔耦合的强度。然而，在这项研究中，我们发现相反，计算的ΔAAM（加上小海洋对应物）在季节内和季节时间尺度上始终比观测的ΔLOD小10%-20%。我们的主要逻辑结论是，大气GCM总体上低估了ΔAAM，在上述时间尺度上至少低估了10%-20%，这对于GCM的评估来说是一个重要的事实。因此，在Δ AAM预测和观测到的ΔLOD之间发现的系统性差异掩盖了我们所寻求的核幔耦合的相关信息。
[1] The remarkable relation well observed between variation in the length of day (ΔLOD) and variation in 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 planet Earth. Quantification of the exact ΔLOD-ΔAAM relation, which we seek in the present study, depends significantly on the extent to which the core participates, or is dynamically coupled with the mantle, in transmission of the axial ΔAAM from the mantle to the core. If, after conversion to the equivalent ΔLOD assuming core-mantle decoupling (as in 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 intraseasonal and seasonal time scales. Our main logical conclusion is that the atmospheric GCMs in general underpredict the ΔAAM, by at least 10%–20% at the mentioned time scales, a fact of importance with respect to the assessment of GCMs. Therefore, the systematic discrepancy found between the ΔAAM-predicted and the observed ΔLOD masks the relevant information on core-mantle coupling that we seek.