Abstract

The objective of this paper is to derive representative vertical extreme current profiles for a location offshore Borneo continental shelf using statistical methods. Firstly, 95th percentile was used on one-year through the water column current measurements in 140 m of water to identify extreme current profiles. Principal Component Analysis (PCA) was then applied to the extremes to retain fundamental modes of the current dataset. The statistical approach was followed by K-means clustering analysis to objectively group the extreme current profiles. Lastly, actual weather and sea state conditions are examined to validate and explain each extreme current profile. Extreme currents are typically observed during the Northeast monsoon in South China Sea (boreal winter). From the statistical analysis, there are two prominent ocean current profiles observed at the location, (1) sheared profile with strong surface currents and (2) mid-depth current maxima. Type 1 profile is typically observed during strong winds, which lead to the formation of a wind-driven sheared profile with maxima at the surface. In contrast, Type 2 current profile has relatively weak near sea surface currents, while strong currents are observed at 60-100 m water depth. This profile is accompanied by a formation of mixing layer within a thermocline region and might be associated with the formation of basin-wide Kelvin wave in response to north-easterly monsoon.

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