Coastal ocean dynamics application radar (CODAR) SeaSonde high-frequency (HF) radars deployed along the coast of Taiwan were used to reveal ocean surface current variations both hourly and through climatological seasons in the Penghu Channel (PHC), southeastern Taiwan Strait (TS), from December 2014 to December 2020. The ocean current in the PHC has a semidiurnal tidal cycle, and the seasonal main flow, wind direction, and wind strength significantly affect the direction and speed of the flow passing through the PHC. The speed of the tidal current in the PHC area can reach more than 1 m/s, and the monthly average flow speed in the PHC is between 0.12 (winter) and 0.24 m/s (summer). Several buoys indicated that the southward flow along the western coast of Taiwan drifted through the PHC in fall and winter. The HF radar observations confirmed the same, implying that this occurred during the strong northeastern monsoon. For a weak northerly wind or even southerly wind, the flow in the PHC can be northward. Different wind directions can affect the speed of the flow passing through the PHC and the branch flow in the northern PHC. The HF radar results are highly consistent with the spatial characteristics of satellite data regarding the sea surface temperature, sea surface salinity, and chlorophyll concentrations; however, there are significant differences from the satellite-derived ocean current.

https://www.mdpi.com/2072-4292/14/8/1816/pdf?version=1649663469

Surface Current Variations and Hydrological Characteristics of the Penghu Channel in the Southeastern Taiwan Strait

Satellite observed new mechanism of Kuroshio intrusion into the northern South China Sea

The Kuroshio Current has its origin in the northwestern Pacific, flowing northward to the east of Taiwan and the northern part of Luzon Island. As the Kuroshio Current flows northward, it quasi-periodically intrudes (hereafter referred to as Kuroshio intrusion (KI)) into the northern South China Sea (SCS) basin through the Luzon Strait. Despite the complex generation mechanisms of KI, the purpose of this study is to improve our understanding of the effects of KI through the Luzon Strait on the regional atmospheric and weather variations. Long-term multiple satellite observations, including absolute dynamic topography, absolute geostrophic currents, sea surface winds by ASCAT, multi-scale ultra-high resolution sea surface temperature (MURSST) level-four analysis, and research-quality three-hourly TRMM multi-satellite precipitation analysis (TMPA), was used to systematically examine the aforementioned scientific problem. Analysis indicates that the KI is interlinked with the consequential anomalous precipitation off southwestern Taiwan. This anomalous precipitation would lead to ~560 million tons of freshwater influx during each KI event. Subsequently, independent moisture budget analysis suggests that moisture, mainly from vertical advection, is the possible source of the precipitation anomaly. Additionally, a bulk formula analysis was applied to understand how KI can trigger the precipitation anomaly through vertical advection of moisture without causing an evident change in the low-level flows. These new research findings might reconcile the divisiveness on why winds are not showing a synchronous response during the KI and consequential anomalous precipitation events.

Impacts of the Kuroshio Intrusion through the Luzon Strait on the Local Precipitation Anomaly

The Kuroshio is the western boundary current of the North Pacific Ocean. Kuroshio intrudes into the north of South China Sea (SCS) through the Luzon Strait. The intruded Kuroshio often forms an anticyclonic current loop north of the Luzon Strait. Previous studies confirmed co-variability of sea surface temperature (SST) influence on the local atmosphere. In this study, by using satellite data and numerical modeling, the impact of Kuroshio intrusion (KI) entering north Luzon Strait on the local atmosphere is investigated. First, satellite data analysis shows that KI causing increased local sea surface temperature and enhanced intensity of wind speed and rainfall off southwestern Taiwan during easterly winds (from November to April). Moreover, based on vertical velocity (w) of atmosphere derived from reanalysis data, the result shows that higher local SST (associated with KI) triggering enhanced wind speed and rainfall by enhancing lower atmosphere vertical motion and thus decreasing vertical wind shear, which leads to intensify of vertical mixing.

Min Chuan Weng

Papers

Impacts of the Kuroshio Intrusion through the Luzon Strait on the Local Precipitation Anomaly

Impacts of the Kuroshio intrusion entering the Luzon Strait on the local atmosphere by satellite observations