VARIABILITY AND CHARACTERISTICS OF EDDIES IN SULAWESI SEA OVER 30 YEARS (1993 – 2022)

• Main Author: Apdillah Akbar, M.
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/84083
• Institution: Institut Teknologi Bandung

The Sulawesi Sea serves as the gateway for the Indonesian Throughflow (ITF), known as the western route. Most of the ITF entering the Sulawesi Sea flows into the Makassar Strait, while the rest returns as the North Equatorial Counter Current (NECC). The ITF, carrying water masses, induces variability in oceanographic parameters in the Sulawesi Sea. The Sulawesi Sea is geographically bordered by Sulawesi Island on the south side, Mindanao Island and the Sulu Sea on the north side, Kalimantan Island on the west side, and the Sangihe Islands on the east side. The interaction of the currents and the topography of the Sulawesi Sea, which is bounded by numerous islands, can lead to the formation of circular currents known as eddies. Eddies are one of the natural phenomena that significantly impact water dynamics. Eddies are circular currents that detach from the main current, the mesoscale eddies having spatial scales of tens to hundreds of kilometers and temporal scales from weeks to months. In terms of their rotation, eddies are divided into two types: cyclonic eddies (CE) in the Northern Hemisphere rotate counterclockwise, while anticyclonic eddies (AE) rotate clockwise. The rotation of CE and AE can cause divergence and convergence in the ocean. Eddy variability is influenced by several key factors, including current interactions, seasonal changes, and global climate phenomena interactions such as the El Niño Southern Oscillation (ENSO). Many previous studies have examined the presence of eddies in Indonesia; however, there has not been a comprehensive analysis of the variability and characteristics of iv eddies in the Sulawesi Sea over the past 30 years. Therefore, this study aims to present an analysis of the variability and characteristics of eddies over 30 years using daily satellite altimetry data from 1993 to 2022. The method used is a hybrid approach combining the Okubo-Weiss method and closed SLA contours. Eddies in this method are defined as coherent regions detected within closed SLA contours, and negative value of Okubo-Weiss parameters. The Okubo-Weiss parameter is used to assess vorticity and strain within eddies, while closed SLA contours help define the spatial extent of the eddies. The characteristics examined include the number, radius, lifespan, and amplitude of eddies over 30 years. Eddies in the Sulawesi Sea are predominantly characterized by a radius of 80-90 km, a lifespan of approximately 1-2 weeks, and an amplitude of 2-3 cm, were more CE was observed than AE, 455 CE and 365 AE in total. Over the 30 year, the average radius for CE (AE) is 87.2 km (82.8 km), the lifespan for CE (AE) is 18.5 days (16.5 days), and the amplitude for CE (AE) is 3.11 cm (2.74 cm). Eddies in the Sulawesi Sea are most frequently found in the areas of 1200 - 1240 E and 20 - 40 N. Large CE (>100 km), with long lifespans (>21 days) and high amplitudes (>4 cm), occur most frequently in the second transitional season, while AE are most frequently in the western season. The presence of CE in the Sulawesi Sea was associated with sea level rise, decreased sea surface temperature, and increased chlorophyll-a concentration, while the opposite occurs for AE. This study also examines the impact of La Niña and El Niño phenomena on eddy characteristics. Although La Niña and El Niño did not influence the number of formed eddies, they did affect other eddy characteristics such as radius, lifespan, and amplitude. During La Niña events, affected parameters tended to increase, whereas they decreased during El Niño.