Analyses of Sea Surface Height, Bottom Pressure and Acoustic Travel Time in the Japan/East Sea; Doctoral thesis

摘要

The observed water motions in the Japan/East Sea (JES) and the associated sea surface height and bottom pressure fields are heavily influenced by the semi-enclosed nature and the specific configuration of this marginal sea. As part of the United States Office of Naval Research JES program, a two- dimensional array of pressure-gauge-equipped inverted echo sounders (PIESs) was deployed in the southwestern JES for two years, from June 1999 to July 2001. The PIESs recorded hourly vertical acoustic travel time and pressure, which are respectively good proxies of baroclinic and barotropic sea level variability. Three topics are investigated based on the PIESs data sets: (1) implications of the in-situ measurements for improving interpretation of satellite altimetric data in the JES; (2) basin-mode oscillations in the JES; (3) vertical coupling between upper circulation and abyssal eddy fields in the JES. All the pressure records exhibit a strong remarkably similar signal (common mode). The common mode is driven by sea level changes outside the JES, atmospheric pressure, and along-strait wind stress in the straits connecting the JES to the outside ocean. The common mode has a barotropic wavelength much larger than the size of the JES, so it is in phase throughout the basin. The rms of the common mode is about 5 cm, and is energetic at time scales of 2-70 days, which are shorter than the ERS-2 satellite altimetry Nyquist period of 70 days. Our results show the common mode produces a substantial alias when sampled by satellite altimeter; furthermore, the combined aliasing effects on multi-tracks can mimic mesoscale eddies and may qualitatively alter the synoptic mapping. The alias can be suppressed by removing the common mode from satellite SSH. For time periods other than 1999-2001, 78% of the common mode variance can still be removed in the Japan/East sea by using coastal tide gauge data to infer the common mode.