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

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.