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The world's first Global Positioning System Radio Occultation (GPS-RO) constellation, the joint Taiwan-U.S. Formosa Satellite No. 3 - Constellation Observing System for Meteorology, Ionosphere & Climate (FORMOSAT-3/COSMIC) has demonstrated the value of GPS-RO data in terrestrial weather, space weather, and climate study. The RO measurement technique was dubbed as "the most accurate and stable thermometer in space" because of its high accuracy, high vertical resolution, and high stability, which does not require calibration. Since its launch in 2006, FORMOSAT-3/COSMIC has accumulated over 6.9 million atmospheric and 4.6 million ionospheric RO sounding profiles. Encouraged by the success of FORMOSAT-3/COSMIC, Taiwan's National Space Organization (NSPO, https://www.nspo.narl.org.tw/index.php?ln=en) and the U.S. National Oceanic and Atmospheric Administration (NOAA) started the planning for the FORMOSAT-7/COSMIC-2 mission in 2008 as a follow-on program to FORMOSAT-3/COSMIC. The FORMOSAT-7/COSMIC-2 satellite constellation, consisting of six small satellites, was successfully launched in June 2019 as the world's first operational RO satellite constellation focusing over the tropics. After fourteen years in service, providing valuable data to operational and research communities, FORMOSAT-3/COSMIC was officially decommissioned ten months after FORMOSAT-7/COSMIC-2 has been sent to space, and replaced by the FORMOSAT-7/COSMIC-2. As expected, the first results from FORMOSAT-7/COSMIC-2 showed positive impact on operational weather prediction and has observed interesting phenomenon in the ionosphere. In this paper, we will summarize the progress from FORMOSAT-7/COSMIC-2 up to date. [ABSTRACT FROM AUTHOR]

The Taiwan-Philippine VOTE (Volcano, Ocean, Typhoon, and Earthquake)- Meteorology project, funded jointly by DOST (Department of Science and Technology) of the Philippines and MOST (Ministry of Science and Technology) of Taiwan, is primarily focused on improving the forecast capability of typhoons in different time scales. It is a bilateral collaboration between Taiwan and the Philippines governments. Data from satellites, coastal weather radars, and numerical forecasting models such as Weather Research and Forecasting Model (WRF) and the Cloud-Resolving Storm Simulator (CReSS) are used to study the typhoon track and intensity and the associated precipitation over Taiwan and the Philippine areas. On the other hand, long-term behavior of typhoons, e.g., the seasonal and intra-seasonal variability of typhoons in the region near Taiwan and the Philippines is also studied. The papers collected in this special issue are mostly based on the research work during this VOTE-Meteorology project, and their major results are summarized in this introduction. [ABSTRACT FROM AUTHOR]

Taiwan and Philippine (TWPH) (117°E-129°E, 5°N-26°N) is a region with most frequent and intense tropical cyclone (TC) influence in the world. This paper documents the climatology and variability of TWPH TC activity with specific attention to the difference in the TCs formed over the western North Pacific (WNP) and over the South China Sea (SCS). The spatial characteristics of TWPH TCs are analyzed based on the accumulated cyclone kinetic energy (ACE) in four sub-areas where distinctly different TC seasonality and variability is found. Different from over the broad Northwest Pacific Basin (0°-60°N, 100°E-180°) where the WNP-born TC frequency dropped sharply in late-1990s and the SCS-born TC frequency slightly increased in mid-1990s, over TWPH three distinct epochs are identified. A weakvariability epoch occurred during 1979-1996, a persistent low-ACE epoch during 1997-2002, and a more variable epoch during 2003-2018. The second epoch is most noteworthy. The unusually weak TC activity during this period in particular over the Philippines was associated with anomalously strong anticyclone over the SCS and the Philippine Sea during the East Asian summer monsoon season. The strong anticyclonic circulation appeared as a descending leg of the enhanced East Asian summer monsoon during summer (July-September). During autumn and early winter (September-December) the Philippine Sea anticyclone was interpreted as the descending Rossby wave response to the suppressed convection over tropical western Pacific. The anomalous anticyclone strengthened the low-level confluent flow and convection over the SCS. The findings are useful to real-time TWPH TC activity monitoring and analysis. [ABSTRACT FROM AUTHOR]

Near-fault ground motion is a key to understanding the seismic hazard along a fault and is challenged by the ground motion prediction equation approach. This paper presents a developed stochastic-slip-scaling source model, a spatial stochastic model with slipped area scaling toward the ground motion simulation. We considered the near-fault ground motion of the 1999 Chi-Chi earthquake in Taiwan, the most massive near-fault disastrous earthquake, proposed by Ma et al. (2001) as a reference for validation. Three scenario source models including the developed stochastic-slip-scaling source model, meanslip model and characteristic-asperity model were used for the near-fault ground motion examination. We simulated synthetic ground motion through 3D waveforms and validated these simulations using observed data and the ground-motion prediction equation (GMPE) for Taiwan earthquakes. The mean slip and characteristic asperity scenario source models over-predicted the near-fault ground motion. The stochastic-slip-scaling model proposed in this paper is more accurately approximated to the near-fault motion compared with the GMPE and observations. This is the first study to incorporate slipped-area scaling in a stochastic slip model. The proposed model can generate scenario earthquakes for predicting ground motion. [ABSTRACT FROM AUTHOR]

The Yuli Belt exposed in the retro-wedge of the eastern part of the Taiwan orogen hosts slivers of a heterogeneous unit of blueschist-facies rocks. However, the question pertaining to its palaeogeographic provenance is still debated despite new geochronological data. This is largely because the structural geometries and kinematics of the Yuli Belt's tectonic contacts with its adjacent units are improperly understood. This paper presents new structural data from field work along several river transects in the Yuli Belt, which we combine with published data into a new tectonic model. Fieldwork and microstructural analyses indicate three deformation phases in the Yuli Belt. Based on cross sections and a review of available P-T-t data, we suspect that blueschist-facies units could have been emplaced on top of greenschist- facies metasedimentary units along a thrust during a first deformation phase D1. This assembly was later thrust over the Eurasian-derived Tailuko Belt along the Shoufeng Fault during D2, as suggested by W-plunging stretching lineations on fault-parallel foliation planes. D3 produced E-vergent folds with W- to NW-dipping axial planes, refolding earlier foliations as well as the D1 nappe contact. We suspect that this E-vergent folding could be related to top-E backthrusting observed along the Shoufeng Fault, involving its reorientation from an initially E-dipping to a presently W-dipping contact. The blueschist-facies metamorphic unit of the Yuli Belt likely represents a mid-Miocene fragment of oceanic crust and mantle issued in the South China Sea. It could hence be considered as part of the suture between the Eurasian and the Philippine Sea plates. [ABSTRACT FROM AUTHOR]

This paper presents the seafloor survey results obtained in 2016 and 2017 using four deep-towed vehicles, developed by the Institute of Undersea Technology at National Sun Yat-sen University, for investigating mineral resource potential offshore northeastern Taiwan. The deep-towed vehicles include the Abyss Twist-pair Imaging System (ATIS), the Video-guided Multi-corer (V-Corer), the TV-guided Grabber (TVG), and the Fiber-optical Instrumentation Towed System (FITS). The seafloor video surveys and sampling were conducted at five survey sites in the southern Okinawa Trough through five survey cruises. A total of 82.69 km of seafloor survey tracks were accomplished and plenty of seafloor characteristics and ecological phenomena were observed through the four deep-towed vehicles. The seafloor survey results, including the video data and the samples of animals, sediments, and mounds, have been provided to different scientific teams for conducting research on marine geophysics, marine geology, marine geochemistry, and marine ecology. The video data can be cross-checked and used as the supporting evidence for the analysis results from the scientific researchers. [ABSTRACT FROM AUTHOR]

The complete volcanic sequences restored in the Coastal Range of Taiwan are key archives for better understanding the magmatic and tectonic evolution of the Northern Luzon Arc. This paper reports (1) new zircon U-Pb ages and Hf isotopic data of fourteen volcanic samples from different sequences of four major volcanoes in the Coastal Range, (2) Hf isotopic data of dated magmatic and detrital zircons from two offshore volcanic islands, Lutao and Lanyu. These data indicate that the arc magmatism in the Coastal Range started at ~15 Ma, most active at ~9 Ma, and ceased at ~4.2 Ma. Magmatic zircons from the arc rocks show a significant variation in Hf isotopic composition, with eHf(T) values varying from +24.9 to +4.8. As pointed out by our previous studies, old continental zircons that show Cathaysian-type ages and Hf isotope features are common in samples from the Yuemei, Chimei, and Lanyu volcanoes, supporting the notion for the influence of the existence of an accreted micro-continent or continental fragment plays a role in the petrogenesis. Such inherited zircons are not observed in the Chengkuang'ao and Tuluanshan volcanoes and uncommon in Lutao, implying the discontinuity or a limited extent of the accreted continental fragment. The eHf(T) values are high and positive from ~15 - 8 Ma (+25 to +15; ±5e-unit variation), and became lower from ~6 to 4.2 Ma (+20 to +8; ±6e units) and the lowest from ~1.3 Ma (+19 to +5; ±7e units). Such a temporal variation in zircon Hf isotopic ratios can be also identified in whole-rock Hf and Nd isotopic compositions, which decrease from ~6 Ma when the Northern Luzon Arc may have started colliding with the Eurasian continental margin. [ABSTRACT FROM AUTHOR]

This paper utilizes 10 stations of co-located seismometer, QuakeFinder/infrasound to observe co-seismic signatures triggered by the 6 February 2016 M 6.6 Meinong Earthquake. Each QuakeFinder system consists of a 3-axes induction magnetometer, an air conductivity sensor, a geophone, and temperature/relative humidity sensors. There are no obvious charges in the positive/negative ions, the temperature, and the humidity, while the magnetometer, the geophone, and infrasound data detect clear co-seismic signatures, similar to seismic waves recorded by seismometers. The magnetometers register high-frequency pulsations, like seismic waves, and superimpose with low-frequency variations, which could be caused by the magnetometer shaking/tilting and/or the underground water level change, respectively, upon the arrival of seismic waves. The spectrum centering around 2.0 Hz of the co-seismic geophone fluctuations is similar to that of the seismic waves. However, the energy of co-seismic geophone fluctuations (also magnetometer pulsations) yields an exponential decay to the distance of a station to the epicenter, while the energy of the seismic waves is inversely proportional to the square of the distance. This suggests that the mechanisms for detecting seismic waves of the QuakeFinder system and seismometers are different. In general, the geophone and magnetometer/infrasound system are useful to record high- and low-frequency seismic waves, respectively. [ABSTRACT FROM AUTHOR]

This paper reports on the recent developments in spectroimagers for sprite campaigns in Taiwan. We first introduce two types of spectroimagers, the slit and slitless types, and discuss their advantages and shortcomings. Next we explore the instrument development and procedures undertaken for this study. In 2006, a slit spectroimager was installed for a sprite campaign and on 15 August of that year, two sprite spectra were recorded using the slit spectroimager along with seven sprites, one halo, one ELVES emission and two jets. By the end of 2015, a slitless spectroimager had been successfully constructed and was ready to conduct additional investigations. On 7 May 2016, a sprite spectrum was recorded using the slitless spectroimager. Following an examination of the calibrations (comprising detection region field of view, wavelength calibration, and response curve), data analysis, and additional calibrations (comprising elevation and azimuthal angles, atmospheric transmittance, and theoretical wavelength calculations) performed in this study, we present the results from our observed sprite spectra using the slit and slitless spectroimagers. [ABSTRACT FROM AUTHOR]

The Imager of Sprites and Upper Atmospheric Lightning (ISUAL), on board the FORMOSAT-2 satellite launched in 2004, is the first instrument primarily dedicated to transient luminous event (TLE) surveys from space. The ISUAL TLE geolocation accuracy and detection efficiency are validated in this paper through two coordinated observation events using ISUAL and the Taiwan TLE ground campaign, the first coordinated space and ground observations. Due to the long distances between TLEs and the observation stations, triangulation required taking the Earth's curvature into account using spherical trigonometry. After a series of systematic triangulation procedures, the results indicate that the coordinated ISUAL and ground station geolation accuracy is less than 7 km. Moreover, three columniform sprites were recorded at multiple sites during the ground campaign. The triangulation of individual elements shows that the map projection of columniform sprites is nearly circular, parallel and fan shaped. The aforementioned events demonstrate that the columniform sprite distribution patterns are diverse. The average base altitude of the columns is 72.4 ± 2.4 km, and the average terminal altitude is 82.3 ± 1.8 km. The sprite column width is estimated to be < 0.5 km. [ABSTRACT FROM AUTHOR]

The Taiwan Earthquake Model (TEM) was established to assess the seismic hazard and risk for Taiwan by considering the social and economic impacts of various components from geology, seismology, and engineering. This paper gives the first version of TEM probabilistic seismic hazard analysis for Taiwan in these aspects. We named it TEM PSHA2015. The model adopts the source parameters of 38 seismogenic structures identified by TEM geologists. In addition to specific fault source-based categorization, seismic activities are categorized as shallow, subduction intraplate, and subduction interplate events. To evaluate the potential ground-shaking resulting from each seismic source, the corresponding ground-motion prediction equations for crustal and subduction earthquakes are adopted. The highest hazard probability is evaluated to be in Southwestern Taiwan and the Longitudinal Valley of Eastern Taiwan. Among the special municipalities in the highly populated Western Taiwan region, Taichung, Tainan, and New Taipei City are evaluated to have the highest hazard. Tainan has the highest seismic hazard for peak ground acceleration in the model based on TEM fault parameters. In terms of pseudo-spectral acceleration, Tainan has higher hazard over short spectral periods, whereas Taichung has higher hazard over long spectral periods. The analysis indicates the importance of earthquake-resistant designs for low-rise buildings in Tainan and high-rise buildings in Taichung. [ABSTRACT FROM AUTHOR]

A dense seismic network can increase Earthquake Early Warning (EEW) system capability to estimate earthquake information with higher accuracy. It is also critical for generating fast, robust earthquake alarms before strong-ground shaking hits the target area. However, building a dense seismic network via traditional seismometers is too expensive and may not be practical. Using low-cost Micro-Electro Mechanical System (MEMS) accelerometers is a potential solution to quickly deploy a large number of sensors around the monitored region. An EEW system constructed using a dense seismic network with 543 MEMS sensors in Taiwan is presented. The system also incorporates the official seismic network of Taiwan's Central Weather Bureau (CWB). The real-time data streams generated by the two networks are integrated using the Earthworm software. This paper illustrates the methods used by the integrated system for estimating earthquake information and evaluates the system performance. We applied the Earthworm picker for the seismograms recorded by the MEMS sensors (Chen et al. 2015) following new picking constraints to accurately detect P-wave arrivals and use a new regression equation for estimating earthquake magnitudes. An off-line test was implemented using 46 earthquakes with magnitudes ranging from ML 4.5 - 6.5 to calibrate the system. The experimental results show that the integrated system has stable source parameter results and issues alarms much faster than the current system run by the CWB seismic network (CWBSN). [ABSTRACT FROM AUTHOR]

This paper presents a numerical study of a heavy rain event that occurred in southern Taiwan in June 2005. From 11 - 13 June 2005, a weak Mei-yu front moved southeastward from China to Taiwan, while mesoscale convective systems (MCSs) were developing and moving northward over the northern South China Sea (SCS). During the first day of the event the southwesterly flow intensified when a ridge associated with the Pacific high extended northwestward from the Philippines to the southern Taiwan Strait (TS). This pressure pattern produced a large northwestward pressure gradient force that created a southeasterly wind speed increase followed by intensification of the southwesterly flow through Coriolis acceleration. An low-level jet (LLJ) formed consequently and transported moisture and unstable air toward the southwestern coast of Taiwan. MCSs were triggered in the southwesterly flow because the potentially unstable air was lifted in a low-level convergence and shearing vorticity environment. They intensified, became organized, and moved northeastward overland, resulting in heavy rainfall in southern Taiwan. On the second day, low pressure formed near the southern TS because of the combined effect of a travelling short-wave trough and a pressure reduction resulting from the latent heat release by the evolving MCSs. This pressure change produced down-gradient acceleration in the northeastward direction, resulting in southwesterly flow strengthening. The local wind acceleration was smaller than that of the first day because the dominant pressure system was local scale, while that of the first day was synoptic scale. [ABSTRACT FROM AUTHOR]