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Directional or vector time-dependent observations, such as the flow at a river branch, streamflow, lake flow, ocean currents, or wind data, are commonly observed in the environment. Traditionally, a rose diagram can be used to summarize the possible main orientation using all the data in the time domain. However, it cannot indicate the significant variation in the specific frequency bands that may show dominant periodic fluctuations. Assessment of directional time series often requires the identification of significant components in the specific frequency bands for not only the magnitude but also the orientation. The rotary pattern, main orientation, and magnitude of directional time series in the frequency domain for five sets of seasonal wind velocity observed at the northern, southern, eastern, and western coast of the subtropical island Taiwan and Taiwan Strait have been demonstrated. It shows that the representative pattern is clockwise, counterclockwise, or near rectilinear, and semidiurnal and diurnal components are significant in the frequency domain for most stations. The most important research innovation suggests that the use of rotary spectral analysis in the frequency domain to effectively assess the orientation and magnitude of directional time series, such as hydrological, coastal, or environmental observations, has become feasible. [ABSTRACT FROM AUTHOR]

Summary: It was found that groundwater can be fluctuated by a variety of disturbances. For instance, seismic activity inducing the dilatation of earth can disturb groundwater level fluctuation as observed in groundwater wells. In this research, spectral analysis in the frequency domain was used to quantitatively evaluate coherence between groundwater head fluctuations and the ground motions recorded in Taiwan from a distant earthquake, the 2011 Tohoku earthquake in northern Honshu, Japan with magnitude of 9. The relationship between groundwater fluctuations and the decomposed ground motions of Rayleigh waves are clearly identified. By analyzing autospectral density, cross-spectral density, and resultant coherence for the seismograms and groundwater head, it was found that the Rayleigh waves dominated the groundwater fluctuations at period of about 21–32s for six pair of groundwater and seismograms of broadband distributed around Taiwan; fluctuations of groundwater are highly coherent with the radial and vertical components of ground motions. Our analysis also shows the time from event to station for Rayleigh waves ranged from 780 to 900s approximately. Wave parameter for seismic event to station of groundwater and seismograms were also identified as 3.0–3.5km/s and 64–110km for wave velocity and wave length, respectively. The relationship of groundwater fluctuations and ground motions induced by seismic activity become feasible to assess using spectral analysis. [Copyright &y& Elsevier]

Captured CO2 could be deliberately injected into the ocean at great depth, where most of it would remain isolated from the atmosphere for centuries. CO2 can be transported via pipeline or ship for release in the ocean or on the sea floor. No matter what for medium depth or deep sea, it appears that a potential area exists between 122–122.5°E and 21.8–22.3°N for CO2 sequestration. The east coast of Taiwan can be a candidate for CO2 temporary storage or transmitted plant. To have whole picture of assessment of sea level fluctuation, a completed statistical summary of seasonal sea level at six tidal gauge stations along the east coast of Taiwan is provided herein. Seasonal sea level time series is analyzed using spectral analysis in frequency domain to identify periodic component and phase propagation, especially for the astronomical-driven tidal effects. It identifies that the semi-diurnal and diurnal components in the resultant time series are related to astronomical tides M2, and K1 and O1, respectively. It demonstrates a full analysis of sea level variations, and results can be useful when construction of testing or operating facilities on sea surface becomes desirable in the future. [ABSTRACT FROM AUTHOR]

Summary: It is frequently found that the fluctuations observed in aquifer-well systems demonstrate high coherence to nearby boundary disturbances, or more specific, in response to the vertical motion of seismic Rayleigh waves. This study derives the spectral relationship between groundwater head and vertical displacement disturbed by Rayleigh waves in the time-frequency domain. Essentially, the groundwater storage property, e.g. storage coefficient or specific storage, representing the amount of water released from storage when the head changes from water expansion and aquifer compression occur. They can be determined using the spectral representation of the factors associated to groundwater head and Rayleigh waves. For this study, the Sumatra-Andaman Islands Earthquake with magnitude 9 at UT 2004/12/26 00:58:53.45 is used as the seismic source while a groundwater monitoring well and a seismological station located on the east of Taiwan acted as the receivers. The time series data associated with the observed groundwater head and vertical displacement of Rayleigh waves are used to evaluate spectral response analyzing the autospectral density, cross-spectral density, and coherence between them. The resultant spectral estimates can be used to determine the storage coefficient and specific storage of the case site to be on the order of 10−3 and 10−4 (m−1), respectively. In addition, the matrix bulk modulus also demonstrated a linear trend with porosity by taking the value of standard water modulus. It suggests that the storage of an aquifer can be robustly estimated using spectral representations and responses from head changes in groundwater and vertical displacement of Rayleigh waves. [Copyright &y& Elsevier]