Multi‑time scale variability of surface currents in the Sunda Strait observed by high‑frequency radar

An in-depth analysis of the variability of surface currents in the Sunda Strait has been undertaken using high-frequency (HF) radar currents. The novelty of this study lies in the use of HF radial data, which enriched the investigation with more extended coverage, spatial monthly mean currents, seasonal variation of the velocity along and across the strait, wind, tides gauge, sea level anomalies (SLA), the intraseasonal variation from HF velocity along the strait, and tidal harmonic analysis on a daily scale. On a shorter scale, HF currents and FES2014 demonstrate some similarities, namely primarily diurnal tidal currents, with a dominant constituent of K1 in the northern part of the Sunda Strait. A counterclockwise tidal current dominated the strait except for the narrowest area. Monthly mean currents show that the circulation is mainly directed from the Java Sea toward the Indian Ocean throughout the year. Seasonally, currents in the Sunda Strait are driven by winds with 0.73 and 0.74 absolute complex correlations and angle rotation 52.41o and 84.16o of HF counterclockwise to the wind. Additional variability, such as intraseasonal, is detected by HF velocity along the strait, tides observation, and SLA due to the effect of the propagation of Kelvin waves. The fastest phase speed is 4 m/s within 16 days of duration. Significant events occurred in May 2020 and June 2021. The flow of surface currents is reversed northward following the arrival of the Kelvin wave approaching south Java and modulated velocity in the period of the northwest monsoon.