| Budget Amount *help |
¥2,600,000 (Direct Cost: ¥2,600,000)
Fiscal Year 2000: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1999: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
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.
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