Department of Earth Science Education, Seoul National University, Seoul, 08826, Republic of Korea.
Center for Educational Research, Seoul National University, Seoul, 08826, Republic of Korea.
Sci Rep. 2022 Apr 22;12(1):6617. doi: 10.1038/s41598-022-10628-8.
Global mean sea level has increased about 3 mm/yr over several decades due to increases in ocean mass and changes in sea water density. Ocean mass, accounting for about two-thirds of the increase, can be directly measured by the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GFO) satellites. An independent measure is obtained by combining satellite altimetry (measuring total sea level change) and Argo float data (measuring steric changes associated with sea water density). Many previous studies have reported that the two estimates of global mean ocean mass (GMOM) change are in good agreement within stated confidence intervals. Recently, particularly since 2016, estimates by the two methods have diverged. A partial explanation appears to be a spurious variation in steric sea level data. An additional contributor may be deficiencies in Glacial Isostatic Adjustment (GIA) corrections and degree-1 spherical harmonic (SH) coefficients. We found that erroneous corrections for GIA contaminate GRACE/GFO estimates as time goes forward. Errors in GIA corrections affect degree-1 SH coefficients, and degree-1 errors may also be associated with ocean dynamics. Poor estimates of degree-1 SH coefficients are likely an important source of discrepancies in the two methods of estimating GMOM change.
由于海洋质量的增加和海水密度的变化，过去几十年中全球平均海平面每年上升约 3 毫米。海洋质量约占海平面上升的三分之二，可以通过重力恢复和气候实验（GRACE）和 GRACE 后续任务（GFO）卫星直接测量。另一种独立的测量方法是结合卫星测高（测量总海平面变化）和 Argo 浮标数据（测量与海水密度相关的位变）。许多以前的研究报告称，全球平均海洋质量（GMOM）变化的两种估计值在规定的置信区间内非常吻合。最近，特别是自 2016 年以来，两种方法的估计值已经出现分歧。部分原因似乎是位变海平面数据的虚假变化。另一个因素可能是冰川均衡调整（GIA）校正和 1 阶球谐系数的不足。我们发现，随着时间的推移，GIA 校正中的错误会污染 GRACE/GFO 估计值。GIA 校正中的误差会影响 1 阶 SH 系数，而 1 阶误差也可能与海洋动力有关。1 阶 SH 系数估计不佳可能是两种方法估计 GMOM 变化差异的重要原因。
