A new question for the polar motion. What is the origin of phase delay in the gravity response?

为了澄清先前使用超导重力仪数据对极移进行的分析中所示的相位延迟的起源（Sato等人，1997），研究了超导重力仪（SGs）观测到的年重力变化与海面高度（SSH）变化的关系。POCM（并行海洋气候模型，Stammer等人，1996）和TOPEX/POSEIDON（T/P）高度计进行了比较。为了计算由SSH变化引起的重力变化，我们首先利用海表温度（SST）估算了热位阻系数，得到了太平洋和大西洋中部的平均值为0.60E-2 m/degC。利用日本江藏站、澳大利亚堪培拉站和南极昭和站的观测资料，考虑固体潮、海潮、极移和SSH变化四种影响，预测了年重力变化。比较结果表明，预测结果与观测结果吻合较好。因此，它们在每个观测点处的幅度在20%内（即在0.2微间隙内，其中1微Gal=1.E-8 ms-1<-2>）和相位在20度内彼此一致。我们还测试了空间位阻系数的其他值，即0.0E-2 m/degC和1.0xE-2 m/degC，但我们发现，在中纬度地区进行的重力观测的拟合明显更好，在0.60E-2 m/degC。值得注意的是，我们的重力观测指向的空间位阻系数值类似于由SSH和SST数据之间的关系独立确定的值。这些结果表明，重力观测可以用来监测海洋质量的变化。这对于研究地球流体与固体的耦合机制以及地球系统对极移的响应具有重要意义。

In order to clarify the origin of the phase delay shown in the previous analysis for the polar motion using the superconducting gravimeter data (Sato et al., 1997), the annual gravity changes observed Superconducting Gravimeters (SGs) are examined in relation to Sea Surface Height (SSH) variations. Two SSH data sets from the POCM (Parallel Ocean Climate Model, Stammer et al., 1996) and the TOPEX/POSEIDON (T/P) altimeter were compared. In order to compute the gravity changes due to SSH variations, we firstly estimated the thermal steric coefficient using the Sea Surface Temperature (SST), and we obtained a value of 0.60E-2 m/degC averaged over the central parts of the Pacific and Atlantic oceans. The annual gravity change predicted by considering four effects of the solid tide, ocean tide, polar motion and SSH variations with the observations at the three sites (i.e. Esashi in Japan, Canberra in Australia and Syowa Station in Antarctica). The results of the comparison indicate that the predictions well agree with the observations. Thus, they agree each other within 20% in amplitude (i.e. within 0.2 micro Gaps, where 1 micro Gal=1.E-8 ms^<-2>) and 20 deg in phase at each observation site. We have also tested other values of the steric coefficient, i.e. 0.0E-2 m/degC and 1.0xE-2 m/degC, but we find that the fit to gravity observations made at the mid latitudes is clearly better at 0.60E-2 m/degC.It is noted that our gravity observations point to a value of steric coefficient similar to that independently determined from the relationship between the SSH and SST data. The results obtained here may suggest that the gravity observation can be used to monitor the mass changes in the oceans. This is important to study the coupling mechanism between the Earth's fluid parts and solid parts and to investigate the response of the Earth's system to the polar motion.