Study On Global Wind-sea And Swell Climate And Variability Based On Altimeter Wind Speed And Wave Height Simultaneous Observations

Ocean waves are very important for many aspects of human life,such as navigation,coastal engineering,port operation and geophysical processes.In recent years,many progresses have been made in the research on the climatic characteristics of ocean waves.However,because of the different causes and characteristics of wind-seas and swells,as well as their impacts,people have gradually realized the importance of studying the global wind-sea and swell climate and variability separately.This paper summarized the progress in the separation of wind-sea and swell,and in global wave climate.Based on previous studies,using the wind speed(U₁₀)and wave spectrum data from buoys,a look-up table model was established to separate the wind-sea and swell significant wave height（SWH）based on wind speed and wave height simultaneous observations.With a large number of test data,it is proved that the model can be directly applied to altimeter data.Based on this model,global wind-sea and swell climate and variability were investigated using 28-year jointly calibrated altimeter data.The paper then studied the global distributions of wind-sea and swell SWH in different seasons first.The results showed that the seasonal distributions of wind-sea SWH and wind speed are similar,which is caused by the strong coupling between wind and the wind-seas.In contrast,the distribution of the swell SWH is similar to the overall SWH.We calculated the swell probability and swell energy weight,and found that swells dominate the global ocean waves with respect to both frequency and energy proportion.In addition,according to the global swell probability and energy weight obtained by this method,the phenomenon of"eastward intensification"and the seasonal shifting of"swell pools"identified by previous studies can also be obviously observed in this study.However,the"seasonal swell pools"is not observed.Further studies show that the interannual variability of wind-sea and swell SWHs are closely correlated 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,a significant positive trend of wind-sea SWH was found in the Southern Ocean and the North Atlantic,which is about 0.5-1 cm/yr.However,the swell SWH shows a significant negative trend almost all over the World Ocean.Such opposite trends can be explained by the positive/negative trends of U₁₀/SWH:a shorter fetch or duration of wind leads to a lower SWH,but a higher U₁₀leads to higher wind-sea probability and energy weight.However,large uncertainty and some differences with previous studies still exist in these trends and further exploration is needed.