A revisit of global wind-sea and swell climate and variability using multiplatform altimeters

Abstract

A well-performed (root mean square error ≈ 0.35 m) look-up table model was established to separate the wind-sea and swell significant wave height (Hs) using 10-m sea surface wind speed (U10) and Hs data from altimeters. Based on this model, global wind-sea and swell climate and variability were investigated using 27-year jointly calibrated altimeter data. The climatology of the swell and wind-sea Hs (HWS and HSW) are in good agreement with those of the total Hs and U10, respectively. This is because of the dominance of swells in the World Ocean with respect to both occurrence frequency and energy proportion and the close coupling between wind and wind-seas. The interannual variability of HWS and HSW are closely related to some climate indices, but the responses of wind-seas and swells are different for the same atmospheric oscillation because of the large propagation distances of swells. For long-term variability, significant positive/negative long-term trends of HWS/HSW were found almost all over the World Ocean. Such opposite trends can be explained by the positive/negative trends of U10/Hs: a shorter fetch or duration of wind leads to a lower Hs, but a higher U10 leads to higher wind-sea probability and energy weight. However, large uncertainty still exists in these trends and further exploration is needed.