Understanding and reconstructing the coastal sea level variations along the western boundary of the North Pacific

Penghui Li,Fanghua Xu

doi:10.1186/s40562-020-00153-9

Abstract

To better understand the coastal sea level (SL) variations along the western boundary of the North Pacific, we quantitatively estimate the contributions of various forcing to the coastal SL variations on seasonal and longer time scales. Based on a western boundary SL theory and a linear least-squares regression, we obtain a polynomial equation to estimate the coastal SL variations from ocean interior information, atmospheric forcing, as well as local steric effects. The estimated results can explain about 91% (93%) of the SL variations at tide gauges south (north) of the Kuroshio extension jet. It is found that the local thermosteric effect is dominant on seasonal time scales. On interannual time scales, the signals from ocean interior and atmospheric forcing are dominant. For decadal SL trends, the coastal SL rise is mainly resulted from the signals from the open ocean. With the same polynomial equation, the SL variations at 6 new tide gauges were estimated and compared to the nearest satellite measurements. The newly estimated SL is generally in much better agreement with the tide gauge data than the satellite data. It is promising to apply the newly derived polynomial equation to estimate SL variations along the western boundary of the North Pacific where tide gauge data are not available. Particularly, the approach is promising to estimate the future SL change given the required oceanic and atmospheric conditions.

Highlights

The coast of the western boundary of the North Pacific, with a series of islands and large population (Anthoff et al 2006), is under the direct threat of sea level (SL) rise
The estimated SLA0 is in good agreement with Sea level anomalies (SLA) from the tide gauge stations, indicating that the signals from ocean interior are important for the coastal SL change (Fig. 2a)
The magnitude of the coastal-trapped wave term of Eq 1 is always larger than that of the long Rossby wave north of the Kuroshio extension (KE) jet, whereas the situation is mostly reversed south of the KE jet. These results indicate that the long Rossby wave plays an important role on SLA0 south of the KE jet, consistent with the separation of ‘active zone’ and ‘shadow zone’ caused by the jet-trapped Rossby wave (Sasaki et al 2014)

Summary

Introduction

The coast of the western boundary of the North Pacific, with a series of islands and large population (Anthoff et al 2006), is under the direct threat of SL rise. Understanding and reconstructing the coastal SL variations along the western boundary of the North Pacific are greatly desired. Many studies have investigated the dynamical causes of regional SL variability along the western boundary of the North Pacific. The SL variability on short time scales is under the direct influence of tides, local winds and sea level pressure (SLP). Jet-trapped Rossby wave concentrated onto the KE jet could produce higher SL variability south of the KE, because Kelvin and coastal-trapped waves propagate southward along the coast. While north of the KE, the influence of linear long Rossby wave is weak, and results in lower SL variability

Objectives

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Results

Conclusion