Revised atmospheric excitation function series related to Earth's variable rotation under consideration of surface topography
Revised atmospheric excitation function series related to Earth's variable rotation under consideration of surface topography
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DOI：
10.1029/2005jd006608
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发表时间：
2006-06
影响因子：
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通讯作者：
Yonghong Zhou;D. Salstein;Jingyi Chen
中科院分区：
文献类型：
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作者：
Yonghong Zhou;D. Salstein;Jingyi Chen
[1]大气角动量与地球自转的变化密切相关。本文引入大气激发函数（AEF），即大气有效角动量函数，研究地球自转变化的大气激发。它可以被分成两个部分，即，由于大气相对于地幔的运动而产生的“风”项和由于通过表面压力变化而明显的大气质量分布的变化而产生的“压力”项。利用NCEP/NCAR再分析的6小时风场和气压场，对1948-2004年AEF风场进行再处理。以前的一些计算是近似的，因为风项是从1000 hPa的等压下界积分的。然而，为了考虑表面地形的影响，AEF是通过使用从地球表面到10 hPa（大气模式的最高层）的风而不是从1000 hPa的风进行积分来计算的。对于这两种情况，只有一个很小的差异，相当于0.004毫秒的日长变化，相对于轴向风项存在。然而，相当大的差异，相当于5 <$6毫秒的弧在极移，被发现关于赤道风条款。我们进一步比较了1980-2003年期间的赤道AEF（有和没有地形效应）与极移激发函数（PMEF）。赤道AEF得到一般更接近PMEF，和改善的相干性时，发现它们之间的地形效应。
[1] The atmospheric angular momentum is closely related to variations in the Earth rotation. The atmospheric excitation function (AEF), known also as the atmospheric effective angular momentum function, is introduced in studying the atmospheric excitation of the Earth's variable rotation. It may be separated into two portions, i.e., the “wind” terms due to the atmospheric motion relative to the mantle and the “pressure” terms due to the variations of atmospheric mass distribution evident through surface pressure changes. The AEF wind terms during the period of 1948–2004 are reprocessed from the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP/NCAR) reanalysis 6-hourly wind and pressure fields. Some previous calculations were approximate, in that the wind terms were integrated from an isobaric lower boundary of 1000 hPa. To consider the surface topography effect, however, the AEF is computed by integration using the winds from the Earth's surface to 10 hPa, the top atmospheric model level, instead of from 1000 hPa. For these two cases, only a minor difference, equivalent to ∼0.004 ms in length-of-day variation, exists with respect to the axial wind term. However, considerable differences, equivalent to 5∼6 milliseconds of arc in polar motion, are found regarding equatorial wind terms. We further compare the total equatorial AEF (with and without the topography effect) with the polar motion excitation function (PMEF) during the period of 1980–2003. The equatorial AEF gets generally closer to the PMEF, and improved coherences are found between them when the topography effect is included.