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Journal Articles - UP - MSI

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    Effect of the Intensified Sub‐Thermocline Eddy on strengthening the Mindanao undercurrent in 2019
    Azminuddin, Fuad; Lee, Jae Hak; Jeon, Dongchull; Shin, Chang‐Woong; Villanoy, Cesar; Lee, Seok; Min, Hong Sik; Kim, Dong Guk (American Geophysical Union, 2022-02)
    The northward-flowing Mindanao Undercurrent (MUC) was directly measured by acoustic Doppler current profilers from a subsurface mooring at about 8°N, 127°E during 2 years (November 2017–December 2019). Its depth covers a range from 400 m to deeper than 1,000 m with its core appearing at around 900 m. The mean velocity of MUC's core was approximately 5.8 cm s−1 with a maximum speed of about 47.6 cm s−1. The MUC was observed as a quasi-permanent current with strong intraseasonal variability (ISV) with a period of 70–80 days. Further analyses with an eddy-resolving circulation model output suggest that the ISV is closely related to sub-thermocline eddies (SEs). In this study, two types of SEs near the Philippine coast are disclosed: the westward propagating SE (SE-1) and the quasi-stational SE southeast of Mindanao Island (SE-2). The SE-1 has both cyclonic and anticyclonic polarities with the propagation speed of 7–8 cm s−1, while the SE-2 is an anticyclonic eddy that moves erratically within 4–8°N, 127–130°E with the mean translation speed of about 11 cm s−1. Even though the SE-1 plays an important role in modulating the MUC, our results show that the observed strong MUC event (May–July 2019) is evidently induced by the intensified SE-2 that moves northwestward. This study emphasizes that the SE-2 when intensified, receives more energy from the strengthened New Guinea Coastal Undercurrent and loses the energy northward along the Philippine coast by intensifying the MUC.
    This study was part of the project entitled “study on air–sea interaction and process of rapidly intensifying Typhoon in the northwestern Pacific” (PM61670) funded by the Ministry of Oceans and Fisheries, Rep. of Korea. This study was also partly supported by the project entitled “Influences of the Northwest Pacific circulation and climate variability on the Korean water changes and material cycle I—The role of Jeju warm current and its variability” (PEA0011) funded by Korea Institute of Ocean Science and Technology (KIOST). The mooring data used in this study were provided by KIOST and are available from the KIOST live access server (http://las.kiost.ac.kr/data_adcp/). The model data are freely available from Mercator Ocean (https://resources.marine.copernicus.eu/?option=com_csw&view=details&product_id=GLOBAL_ANALYSIS_FORECAST_PHY_001_024).
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    Geomorphological and sedimentological records of recent storms on a volcaniclastic coast in Bicol, Philippines
    Soria, Janneli Lea A.; Switzer, Adam D.; Pile, Jeremy; Siringan, Fernando P.; Brill, Dominik; Daag, Arturo (Elsevier, 2021-08-01)
    Typhoon Durian in November 2006 was most notable for a series of devastating lahars that buried communities at the base of Mayon volcano in Bicol, Philippines. Typhoon Durian delivered extreme rainfall that remobilized volcanic debris that caused more than ~1200 deaths and extensive property damage. Although not as deadly as the lahar, Typhoon Durian also generated a storm surge that caused localized dune breaching on Malinao barrier sand spit in Lagonoy Gulf. In the absence of instrumental data of the storm surge, we used the geomorphical and sedimentary imprints including erosion scarps, washover fans and terraces to infer the inundation heights on the barrier spit. The surface elevations of washover fans, terraces and relic dunes indicate inundation heights above 1.5 m but not exceeding 3 m. Typhoon Durian's overwash deposit is characterized by typical washover fan stratigraphy, and exhibits horizontal to sub-horizontal lamination on the front to mid-fan and foreset stratification near the fan terminus. Subsurface stratigraphy using shore-normal ground penetrating radar (GPR) imaging reveals at least two buried erosional surfaces farther inland from the erosional surface of Typhoon Durian. Similar to Durian, the older erosional surfaces were probably sustained from previous typhoons. We infer that episodic erosional events most likely have repeatedly disrupted the prograding development of the Malinao barrier spit. Typhoon Durian highlights the exposure of volcanic landscapes to multiple hazards from cyclone landfall.
    This work comprises Earth Observatory of Singapore contribution no. 169. This research is supported by the Singapore National Research Foundation fellowship scheme (Grant No: NRF-RF2010-04) and the Singapore Ministry of Education under the Research Centres of Excellence initiative. This paper is a contribution to IGCP Project 639 Sea-Level Changes from Minutes to Millennia. We thank German Gonzaga of the Malinao Local Government Unit who facilitated our access to the study site. We also appreciate Cabria family for being our hospitable host during the series of field campaigns. We thank Mr. Raul Capistrano on behalf of NAMRIA for providing tide gauge data, and the Mines and Geosciences Bureau for granting us permit to transport sediments. We are grateful to Joan Reotita, Ronald Lloren, Yo Muan, Lester Valle, Arlene Tengonciang, Mabelline Cahulogan, Ariel Malonda, Antonio Ceres and Elmer Cas for their generous help in collecting field data.
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    Local tide and geoid corrections significantly improve coastal retracked Jason sea surface heights in the Philippines
    Flores, Paul Caesar; Reyes, Rosalie; Amedo-Repollo, Charina Lyn; Rediang, Abegail; Alfante, Rey Mark; Bauzon, Ma. Divina Angela; Pasaje, Nikki; Bringas, Dennis (Science and Technology Information Institute, 2022-11-08)
    Retracking algorithms increase the accuracy of coastal sea surface height (SSH) measurements. However, it is still important to validate these retracking estimates with tide gauge (SSHtg) observations. We downloaded the freely available Jason altimeter SSH processed using the XTRACK-ALES algorithm, then detided the SSH using different tide models. The first model is the default tidal correction based on Finite Element Solution 2014 (SSHfes), and the second model is the T_Tide harmonic analysis of the nearest tide gauge (SSHaltimeter). SSHfes showed a very poor correlation (< 0.31) and very high root mean square error (RMSE, > 29 cm). In contrast, SSHaltimeter generally showed a very high correlation (> 0.91) and low RMSE (< 17.4 cm). A further quality check based on the average and standard deviation of the difference between the SSH readings (SSHfes – SSHtg and SSHaltimeter – SSHtg) also showed the superior performance of SSHaltimeter,which scored < 9.3 and < 16.5 cm, respectively; compared to SSHfes, which scored < 9.3 cm and > 27 cm for the same parameters. The poor performance from the SSHfes likely comes from the complex bathymetry and coastal geomorphology of the country, which is not accounted for in the FES. The Philippines generally has a narrow shelf, and the FES tide corrections may be related to deep-water tides rather than the shallow-water tides observed from tide gauges. Despite the high correlation and agreement between the SSHaltimeter and SSHtg, the rate of sea level rise from the SSHaltimeter in some sites is more than twice the rate from SSHtg, which indicates the possible influence of the vertical land movement.
    This study was supported by grants to R.B. Reyes by the Department of Science and Technology–Philippine Council for Industry, Energy, and Emerging Technology Research and Development through the Coastal Sea Level Rise Philippines Project. We also thank the anonymous reviewers for their feedback on how to improve the manuscript.
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    Ground deformation analysis caused by post-2013 earthquake in Bohol, Philippines
    Bauzon, Ma. Divina Angela I.; Reyes, Rosalie B.; Blanco, Ariel C.; Siringan, Fernando P. (Springer Science and Business Media LLC, 2022-08-16)
    After the 2013 Mw 7.2 earthquake that occurred in Bohol, the shoreline specifically in Loon and Maribojoc was observed to shift seaward due to ground uplift. This study analyzes the post-earthquake shoreline movement, specifically a 12 km coastal strip in Loon and Maribojoc, and ground deformation of the West Bohol area through Sentinel-1 image processing techniques. From October 2014 to April 2018, the DSAS linear regression shoreline rates were − 4.36 m/yr in Loon and − 1.69 m/yr in Maribojoc, indicative of a landward movement of 91.4% and 88.8% of shoreline transects in Loon and Maribojoc, respectively. PSInSAR revealed varying rates of VLM in the study area from October 2014 to December 2018 such that Loon and Maribojoc exhibit a subsidence rate of − 2 to − 8 mm/yr. The correlation between the shoreline retreat and the land subsidence in the study area is 87%, indicating a possible elastic rebound after the earthquake. The portion of Tagbilaran City on its northern side exhibits land subsidence of − 2 to − 6 mm/yr while its southern side exhibits land uplift of 0–2 mm/yr. The relative sea level fall from TGSL measurements indicates an uplift in the location of the tide gauge in Tagbilaran City.