Abstract
Understanding subtidal (a period band of 3–20 days) coastal sea level fluctuations is of increasing importance for the sustainable use of coastal areas under challenging conditions resulting from regional and global sea-level rise. The wind-forced coastal-trapped waves (CTW) theory often accounts for subtidal sea level fluctuations observed off global coasts with a considerable range of propagation speeds. Here, the propagation speeds of subtidal sea level fluctuations observed at seven coastal tide-gauge stations around the Korean Peninsula (KP) from 1997 to 2017 were compared with phase speeds modeled for 10 segments of realistic bottom topography around the KP and four seasons of density stratification using a wind-forced CTW model. Alongshore variations in the modeled phase speed (2.0–10.0 m s–1, increasing with the bottom depth, shelf width, and vertical density difference) were consistent with those of the observed propagation speed (4.7–18.9 m s–1), despite systematic underestimation by 50%, i.e., the mean speed of 6.0 vs. 11.8 m s–1. This underestimation is discussed considering subtidal sea level fluctuations of non-CTW origin that were not incorporated into the CTW model, such as (1) Barometric sea level response to atmospheric pressure disturbances, and (2) Upwelling/downwelling response to local alongshore wind stress. This study suggests that subtidal coastal sea level fluctuates around the KP within and beyond CTW dynamics.
Highlights
Understanding subtidal coastal sea level variability is important for effectively adapting to rising global and regional sea levels (Stammer et al, 2013)
5–7) and lower speed of 8.0 ± 0.5 m s−1 along the west and south coasts (Segs. 8–10). This was similar to the alongshore variations of mode-1 coastaltrapped waves (CTW) (6.8 ± 0.6 m s−1 along the east coast and 4.1 ± 0.4 m s−1 along the west and south coasts), despite systematic underestimation by the CTW model that may be linked to dynamics beyond the wind-forced CTWs
The phase speeds of mode-1 CTWs increased with a deeper water depth, wider shelf width, and larger vertical density difference; these accounted for most alongshore variations in the observed subtidal sea level propagation speeds around the Korean Peninsula (KP) (Figures 12B,C)
Summary
Understanding subtidal (defined as a period from 3 to 20 days) coastal sea level variability is important for effectively adapting to rising global and regional sea levels (Stammer et al, 2013). The subtidal sea level fluctuations in many coastal areas related to stratification and shelf topography have been studied using a classical CTW model; for example, phase speeds ranging from. Despite some previous studies explaining the subtidal coastal sea level fluctuations around the KP based on the classical CTW model under varying conditions of stratification and shelf topography (Lee and Chung, 1982; Lyu et al, 2002; Cho et al, 2014), the reasons for the significant difference between the observed (6.1–15.6 m s−1) and modeled (4.6–10.3 m s−1) propagation speeds are still poorly understood (Cho et al, 2014). Our understanding of subtidal sea level fluctuations around the KP is far from complete; for example, how well the subtidal sea level fluctuations can be explained using the classic CTW and other dynamics beyond CTWs are poorly understood
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