ANALYSIS OF THE INFLUENCE OF EL NIÑO-SOUTHERN OSCILLATION (ENSO) ON THE CHARACTERISTICS OF TROPICAL CYCLONES IN INDONESIAN WATERS IN 1973-2022

• Main Author: Krisna Yulianti, Kadek
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/84564
• Institution: Institut Teknologi Bandung

Tropical cyclones (TC) are widely known as robust storm systems, and their impact can cause significant damage to the affected and surrounding coastal areas. Moreover, TC can significantly impact society, causing widespread destruction to infrastructure, homes, and livelihoods. Indonesia is prone to TC formation due to its location between oceans, particularly in the western Pacific and the Indian Ocean. Additionally, Indonesia is influenced by the El Niño-Southern Oscillation (ENSO), which can alter atmospheric and ocean parameters, thereby affecting TC behaviour. Based on the TC occurrence and propagation, Indonesia can be grouped into 4 regions. The first region covers Bay of Bengarl, the second area cover Western North Pacific Ocean, the third region is Northeastern Indian Ocean, and the fourth region is Northern Australian Ocean. This study analyses TCs in the waters of Indonesia by using data from the International Best Track Archive for Climate Stewardship (IBTRaCS) for the period 1973-2022 and Kernel Density Estimation (KDE) to identify the number of TC, the intensity, and the shiftness of the the area occurrence during El Niño and La Niña periods when the Indian Ocean Dipole (IOD) is neutral. Over the past 50 years, there have been 2,885 TCs passing through Indonesian waters, with the most active area being in region 2. It has been observed that during El Niño, the number of TCs throughout Indonesia increases, while during La Niña, the number decreases compared to neutral conditions. The study shows significant differences in the total occurrence of TCs during La Niña in regions 2, 3, and 4. In region 2, there is a decrease in TC formation during La Niña due to less supportive environmental parameters such as vertical wind shear (VWS) and vorticity. This results in a 12.5% decrease in the number of TCs per month compared to neutral conditions. Conversely, in regions 3 and 4, the number of TCs per month is higher during La Niña than neutral, increasing by 38.1% and 45.7% respectively. This is attributed to the supportive environmental conditions including sea surface temperature, sea level pressure, humidity, VWS, and vorticity. The study uses iv Accumulated Cyclone Energy (ACE) to represent the duration, intensity, and number of TCs. Monthly ACE also showed significant variations, with a 65.4% increase during La Niña in region 1 and a 12.4% increase during El Niño, and a 35.3% decrease during La Niña in region 2. This finding is attributed to the shorter TC lifetime during La Niña, especially for TCs that emerge east of the Philippines and propagate westward due to less favorable sea surface temperatures in the South China Sea. The spatial distribution of Kernel Density Estimation (KDE) varies with the season, causing more zonal shifts, while ENSO causes more meridional shifts. During La Niña, the density centers in regions 1, 3, and 4 tend to shift further eastward, except for region 2 which shifts westward compared to El Niño. In general, the density centers tend to shift further from neutral during El Niño for regions 1 and 2, while in regions 3 and 4 they shift further during La Niña. The furthest shift, around 632.1 km, occurred in region 4 during La Niña, indicated by the location of TC formation which tends to form in the south of West Nusa Tenggara (NTB) during El Niño, while in the Timor Sea during La Niña. Overall, this study provides insight into TC behavior in Indonesian waters, highlighting the influence of climate phenomena such as ENSO on TC characteristics. These findings can contribute to a better understanding and preparedness for TC events in Indonesian waters.