CHARACTERISTICS OF MARINE HEATWAVES IN THE SUBSURFACE LAYER OF SOUTH JAVA SEA YEAR 1993-2019

• Main Author: Afifah Azuga, Nabila
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/71958
• Institution: Institut Teknologi Bandung

Marine heatwaves (MHWs) events can extend up to thousands of kilometers and had been detected in the subsurface layer. There are several metrics that can be use to describe MHWs events in more detail, such as frequency, duration, and cumulative intensity. This study aims to analyze the characteristics of the of MHWs events in the subsurface layer of South Java Sea from 1993-2019. The data used in this study are water temperature at a depth of 0.4 m to 763 m that obtained from the Copernicus Marine Environment Monitoring Service (CMEMS) Ocean Physics Reanalysis with daily temporal resolution and the spatial resolution is 0.083? and ITF (Indonesian Through Flow) transport anomaly data that was digitized from the previous research of Li et al. (2020). This research is located in South Java Sea with geographical coordinate of 5?-14? S and 104?-116? E. Statistical methods were used to calculate the average, trend of MHWs metrics, and descriptive methods were used for the analysis and discussions. This study’s results obtained that the strongest MHWs intensity was found in the thermocline layer (depth 55-186 m). The maximum average value of frequency was found at a depth of 318-763 m in the offshore area that is 2,50 events/year, while the maximum duration and cumulative intensity values were found at a depth of 0,4-109 m in the nearshore area with a value of 32 days /year and 90 ?C/year. The trend of MHWs metrics have increased but the duration tends to have a random pattern, such as at depth of 0,4-186 m the value of tends to increase, meanwhile at depth of 222-763 m the duration tends to have a constant value and did not change throughout the year. The ENSO and IOD phenomena play a substantial role in influencing MHWs. At a depth of 0.4 m it is obtained that the intensity of MHWs events increased during the strongest El Niño decaying period in 1997 and 2015, at a depth of 109-380 m the intensity of MHWs increased during the La Niña period in 1999 and 2011, meanwhile at a depth of 763 m the strengthening of MHWs intensity is not affected by the ENSO factor. In South Java Sea, warm water masses from the ENSO phenomenon were carried out by the ITF transport with different correlations at each depth. At a depth of 0,4 m the correlation between MHWs events and ITF transport was negative (r= -0.64) which means that the intensity of events increase when the direction of ITF transport strengthens to the south. At a depth of 109 m, the correlation value of MHWs events with ITF transport is 0,24 which means that the intensity of events decrease when the direction of ITF transport to the south weakened. Furthermore, at a depth of 763 m the correlation value is -0,14 which means that the intensity of events increase when the direction of the ITF transport strengthens to the south, but the relation between these two variables is very weak and not significant. During the El Niño phase, the percentage of MHWs events at a depth of 0.4 m is 31,73% meanwhile during the La Niña phase the percentage is 26,51%. At a depth of 109 m and 763 m the percentage of MHWs events during the La Niña phase was higher with a value of 30,41% and 29,01% compared to the El Niño phase with a value 28,84% and 28,71%. During the La Niña phase the intensity of MHWs events was greater than the El Niño. In IOD events, the highest percentage of MHWs events was found during the positive IOD phase with a value ranges from 12,05- 16,05%, but the intensity of MHWs events was higher during the negative IOD phase. The intrusion of warmer temperatures from the surface layer into the deeper layers can affect the strengthen of MHWs intensity in the deeper layers, while the phenomenon of lifting the mass water with a cooler temperatures from the deeper layers towards the surface can cause the decreasing of MHWs intensity in the waters.