Environmental Science
M. N. Hidayat; R. Wafdan; M. Ramli; Z. A. Muchlisin; S. Rizal
Abstract
BACKGROUND AND OBJECTIVES: This study aimed to investigate the long-term relationship between chlorophyll-a, sea surface temperature, and sea surface salinity monthly from January 2015 to December 2021. It was carried out in the Northern Bay of Bengal, which experiences extreme monsoons, in the southwest ...
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BACKGROUND AND OBJECTIVES: This study aimed to investigate the long-term relationship between chlorophyll-a, sea surface temperature, and sea surface salinity monthly from January 2015 to December 2021. It was carried out in the Northern Bay of Bengal, which experiences extreme monsoons, in the southwest monsoon and northeast monsoon from June to September and November to February, respectively. Monsoon is the main cause of changes in chlorophyll-a, sea surface temperature and sea surface salinity.METHODS: The seasonal model was used to examine the relationship between these three parameters, which were obtained using the Copernicus Marine Environment Monitoring Service data. The seasonal model was used to observe periodic patterns and predict parameters based on their regularity. Meanwhile, Pearson’s correlation analysis was conducted to determine the relationship between chlorophyll-a, sea surface temperature and sea surface salinity.FINDINGS: This study found that the three parameters, namely chlorophyll-a, sea surface temperature, and sea surface salinity, follow the monsoon pattern, as shown in the seasonal model. The minimum value of chlorophyll-a occurred in February, March and April, while the maximum value of approximately 2 milligram per cubic meter occured at stations 1, 2, 3, 4, 5 and 7, but at 9 and 10, it increased to 12 - 14 mg/m3. This indicates that station positions are very sensitive to changes in chlorohophyll-a values. When the southwest monsoon occurred, it reached the maximum. Furthermore, the minimum sea surface temperature values occurred in January and at almost every station in the year. It was shown to be associated with the northeast monsoon, which causes winter. On the sea surface temperature graph, several peaks were observed in positive local extremes yearly at almost all stations. The maximum sea surface temperature occurred in May, June, and July, according to the shape of the graph, which peaked in the middle of the year. The sea surface salinity graph formed a peak and valley which occurred yearly in May or April, as well as September and October, respectively.CONCLUSION: Chlorophyll-a had 1 trough and 1 peak, with the sea surface temperature graph possessing only 1 peak, while the sea surface salinity graph had 1 peak and 1 trough, respectively. These graph patterns implied that chlorophyll-a first achieved a minimum value before reaching the máximum. The sea surface temperature graph had a maximum value in the middle of the year, while the minimum occurred at the beginning or end. Moreover, the sea surface salinity graph first reached the maximum value and then declined to the minimum. KEYWORDS: Coefficient of correlation; Copernicus Marine Environment Monitoring Service (CMEMS Data); Northern Bay of Bengal; Northeast monsoon; Seasonal model; Southwest monsoon.
Environmental Management
A.V.H. Simanjuntak; U Muksin; A. Arifullah; K. Lythgoe; Y. Asnawi; M. Sinambela; S. Rizal; S. Wei
Abstract
BACKGROUND AND OBJECTIVES: For the first time, an earthquake swarm occurred from April to August 2021 in Lake Toba; Indonesia, the world’s largest caldera lake. Although the earthquakes were located in a volcanic environment, the swarm activities could also be related to tectonic activities on ...
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BACKGROUND AND OBJECTIVES: For the first time, an earthquake swarm occurred from April to August 2021 in Lake Toba; Indonesia, the world’s largest caldera lake. Although the earthquakes were located in a volcanic environment, the swarm activities could also be related to tectonic activities on the Sumatran fault. The swarm activities occurred at shallow depths and may influence the ground surface condition in which soil or rock below the subsurface can amplify the shaking. The research objective was to investigate the characteristics of the earthquake swarm in the Toba Caldera from the spectrum of the earthquake waveforms, site frequency, and horizontal-to-vertical ratio of sites.METHODS: The spectra of very closely located swarm and nonswarm earthquakes were analyzed to investigate the differences between both types of seismic events. The seismic spectral ratio of horizontal-over-vertical components was applied to calculate the spectrum in the active swarm region from all newly installed seismic sensors. The root mean square was applied to average the amplitude of the horizontal components. Then, the values of the horizontal-to-vertical ratios were obtained by comparing the average values of the horizontal and vertical components.FINDING: The microtremor study showed a more complete spectrum waveform from the low-to-high frequency of a non swarm earthquake, while the swarm earthquakes generated high-frequency seismograms. From the combination values of natural site frequencies and the horizontal-to-vertical ratios, the Toba environment can be classified into five clusters: I) Samosir–Hasinggaan, II) Samosir–Parapat, III) Silimapuluh, IV) Balige–Paropo, and V) Panjaitan. Samosir Island located in the middle of the Toba Caldera has the highest frequency and amplification, which are divided into two clusters.CONCLUSION: Cluster I, with high amplification corresponding to the earthquake intensity, was felt by people in northern Samosir. Cluster II is located in the southern part of Samosir Island. Cluster III features moderate values of amplification and seismic vulnerability and therefore needs attention before future infrastructure development. Cluster IV, located in the southern and northern regions with high amplification and vulnerability, is associated with the Quaternary eruption. Cluster V, situated in northeastern Toba, has the lowest amplification and vulnerability compared to other clusters. The microtremor results provide good correlation with the geology in the volcanic environment of the Toba region.
Environmental Engineering
D. Fadhiliani; M. Ikhwan; M. Ramli; S. Rizal; M. Syafwan
Abstract
BACKGROUND AND OBJECTIVES: The hydrodynamic uncertainty of the ocean is the reason for testing marine structures as an initial consideration. This uncertainty has an impact on the natural structure of the topography as well as marine habitats. In the hydrodynamics laboratory, ships and offshore structures ...
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BACKGROUND AND OBJECTIVES: The hydrodynamic uncertainty of the ocean is the reason for testing marine structures as an initial consideration. This uncertainty has an impact on the natural structure of the topography as well as marine habitats. In the hydrodynamics laboratory, ships and offshore structures are tested using mathematical models as input to the wave marker. For large wavenumbers, Benjamin Bona Mahony's equation has a stable direction and position in the wave tank. During their propagation, the generated waves exhibit modulation instability and phase singularity phenomena. These two factors refer to Benjamin Bona Mahony as a promising candidate for generating extreme waves in the laboratory. The aim of this research is to investigate the distribution of energy in each modulation frequency change. The Hamiltonian formula that describes the phenomenon of phase singularity is used to observe energy. This data is critical in determining the parameters used to generate extreme waves.METHODS: The envelope of the Benjamin Bona Mahony wave group can be used to study the Benjamin Bona Mahony wave. The Benjamin Bona Mahony wave group is known to evolve according to the Nonlinear Schrodinger equation. The Hamiltonian governs the dynamics of the phase amplitude and proves the Nonlinear Schrodinger equation's singularity for finite time. The Hamiltonian is derived from the appropriate Lagrangian for Nonlinear Schrodinger and then transformed into the Hamiltonian with the displaced phase-amplitude variable.FINDINGS: Potential energy is related to wave amplitude and kinetic energy is related to wave steepness in the study of surface water waves. When , the maximum wave amplitude and steepness are obtained. When , extreme waves cannot be formed due to steepness. This is due to the possibility of breaking waves into smaller waves on the shore. In terms of position, the energy curve is symmetrical.CONCLUSION: According to Hamiltonian's description of the energy distribution, the smaller the modulation frequency, the greater the potential and kinetic energy involved in wave propagation, and vice versa. While the wave's amplitude and steepness will be greatest for a low modulation frequency, and vice versa. The modulation frequency considered as an extreme wave generator is , because the resulting amplitude is quite high and the energy in the envelope is also quite large.
Environmental Science
M. Ikhwan; R. Wafdan; Y. Haditiar; M. Ramli; Z. A. Muchlisin; S. Rizal
Abstract
BACKGROUND AND OBJECTIVES: El Niño - Southern Oscillation is known to affect the marine and terrestrial environment in Southeast Asia, Australia, northern South America, and southern Africa. There has been much research showing that the effects of El Niño - Southern Oscillation are extensive. ...
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BACKGROUND AND OBJECTIVES: El Niño - Southern Oscillation is known to affect the marine and terrestrial environment in Southeast Asia, Australia, northern South America, and southern Africa. There has been much research showing that the effects of El Niño - Southern Oscillation are extensive. In this study, a simulation of an El Niño event is carried out, which is ideal in the vertical layer of the Pacific Ocean (0-250 meters). The fast Fourier transform is used to process the vertical modeling data so that the results can accurately represent El Niño.METHODS: A non-hydrostatic 3-dimensional numerical model is used in this research. To separate the signal produced and obtain the quantitative difference of each sea layer, the simulation results are analyzed using the fast Fourier transform. Winds blow from the west to the east of the area in perfect El Niño weather, with a reasonably high wind zone near the equator (forming a cosine). Open fields can be found on the north and south sides, while closed fields can be found on the west and east sides. Density is uniform up to a depth of 100 meters, then uniformly increases by 1 kilogram per cubic meter from 100 to 250 meters. FINDINGS: The results of the model simulation show that one month later (on the 37th day), the current from the west has approached the domain's east side, forming a complete coastal Kelvin wave. The shape of coastal Kelvin waves in the eastern area follows a trend that is similar to the OSCAR Sea Surface Velocity plot data obtained from ERDDAP in the Pacific Ocean in October 2015. In this period, the density at a depth of 0-100 meters is the same, while the density at the depth layer underneath is different. CONCLUSION: Strong winds could mix water masses up to a depth of 100 meters, implying that during an ideal El Niño, the stratification of the water column is influenced by strong winds. The eastern domain has the highest sea level amplitude, resulting in perfect mixing up to a depth of 100 m, while wind effect is negligible in the lower layers. The first layer (0-50 m) and the second layer (50-100 m) have the same density and occur along the equator, according to FFT. The density is different and much greater in the third layer (100-150 m).
