A generalized transformation approach for simulating steady-state variably-saturated subsurface flow

A numerical method is proposed to accurately and efficiently compute a direct steady-state solution of the nonlinear Richards equation. In the proposed method, the Kirchhoff integral transformation and a complementary transformation are applied to the governing equation in order to separate the nonlinear hyperbolic characteristic from the linear parabolic part. The separation allows the transformed governing equation to be applied to partially- to fully-saturated systems with arbitrary constitutive relations between primary (pressure head) and secondary variables (relative permeability). The transformed governing equation is then discretized with control volume finite difference/finite element approximations, followed by inverse transformation. The approach is compared to analytical and other numerical approaches for variably-saturated flow in 1-D and 3-D domains. The results clearly demonstrate that the approach is not only more computationally efficient but also more accurate than traditional numerical solutions. The approach is also applied to an example flow problem involving a regional-scale variably-saturated heterogeneous system, where the vadose zone is up to 1 km thick. The performance, stability, and effectiveness of the transform approach is exemplified for this complex heterogeneous example, which is typical of many problems encountered in the field. It is shown that computational performance can be enhanced by several orders of magnitude with the described integral transformation approach.     

Population Genetic Structure of Rock Bream (<Emphasis Type="Italic">Oplegnathus fasciatus</Emphasis> Temminck &amp; Schlegel, 1884) Revealed by mtDNA COI Sequence in Korea and China

The rock bream, Oplegnathus fasciatus, is a common rocky reef game fish in East Asia and recently has become an aquaculture species. Despite its commercial importance, the population genetic structure of this fish species remains poorly understood. In this study, 163 specimens were collected from 6 localities along the coastal waters of Korea and China and their genetic variation was analyzed with mtDNA COI sequences. A total of 34 polymorphic sites were detected which determined 30 haplotypes. The genetic pattern reveals a low level of nucleotide diversity (0.04 ± 0.003) but a high level of haplotype diversity (0.83 ± 0.02). The 30 haplotypes are divided into two major genealogical clades: one that consists of only Zhoushan (ZS, East China Sea) specific haplotypes from the southern East China Sea and the other that consists of the remaining haplotypes from the northern East China Sea, Yellow Sea, Korea Strait, and East Sea/Sea of Japan. The two clades are separated by approximately 330~435 kyBP. Analyses of AMOVA and F_st show a significant population differentiation between the ZS sample and the other ones, corroborating separation of the two genealogical clades. Larval dispersal and the fresh Yangtze River plume are invoked as the main determining factors for this population genetic structure of O. fasciatus. Neutrality tests and mismatch distribution analyses indicate late Pleistocene population expansion along the coastal waters of Korea and China approximately 133–183 kyBP during which there were periodic cycles of glaciations and deglaciations. Such population information needs to be taken into account when stock enhancement and conservation measures are implemented for this fisheries species.     

Changes in Fish Assemblages after Dike Construction in the Saemangeum Area

In the Saemangeum area, construction of a dike began in 1991 and was completed in 2006; desalination is currently being conducted. In order to investigate     

Benthic habitat quality change as measured by macroinfauna community in a tidal flat on the west coast of Korea

Yellow Sea tidal flats are internationally recognised for their contribution to biological diversity and yet are under enormous pressure from reclamation, pollution and overexploitation. The benthic macroinfauna community is the dominant community on these tidal flats and a reliable indicator of benthic environmental changes. We surveyed the current benthic macroinfauna community of the Ganghwa Southern Tidal Flat, the largest remaining Korean mud flat in the Yellow Sea, in order to examine changes in the environmental situation of this benthic ecosystem. The results show a significant decline in species diversity from the last survey made in 2003, and a shift in species composition with appearances of polychaetes indicative of pollution and physical disturbances and other opportunistic species becoming dominant in both density and biomass. The benthic community shift observed during the two study periods may be associated with increased nutrient pollution as well as increased physical disturbances in this area. However, we recognise the limitations of the data both in frequency and scope but believe the significant changes to the composition of the benthic fauna are sufficient to warrant concern. Observations are required to examine the extent to which these human activities induce benthic community shift in this tidal flat.     

Determining Q of near-surface materials from Rayleigh waves

High-frequency (≥2 Hz) Rayleigh wave phase velocities can be inverted to shear (S)-wave velocities for a layered earth model up to 30 m below the ground surface in many settings. Given S-wave velocity (V_S), compressional (P)-wave velocity (V_P), and Rayleigh wave phase velocities, it is feasible to solve for P-wave quality factor Q_P and S-wave quality factor Q_S in a layered earth model by inverting Rayleigh wave attenuation coefficients. Model results demonstrate the plausibility of inverting Q_S from Rayleigh wave attenuation coefficients. Contributions to the Rayleigh wave attenuation coefficients from Q_P cannot be ignored when Vs/V_P reaches 0.45, which is not uncommon in near-surface settings. It is possible to invert Q_P from Rayleigh wave attenuation coefficients in some geological setting, a concept that differs from the common perception that Rayleigh wave attenuation coefficients are always far less sensitive to Q_P than to Q_S. Sixty-channel surface wave data were acquired in an Arizona desert. For a 10-layer model with a thickness of over 20 m, the data were first inverted to obtain S-wave velocities by the multichannel analysis of surface waves (MASW) method and then quality factors were determined by inverting attenuation coefficients.     

Retracking considerations in spaceborne GNSS-R altimetry

The European Space Agency Passive Reflectometry and Interferometry System In-orbit Demonstrator (IoD) aims to perform mesoscale altimetric observations by measuring the Global Navigation Satellite System (GNSS) opportunity signals reflected over the sea surface. Altimetry based on GNSS reflectometry (GNSS-R) is significantly affected by satellite motion, since it requires relatively long integration times to reduce noise. We present the impact of the satellite motion on the GNSS-R observables and the need to retrack the waveforms. By using a detailed GNSS-R space mission simulator, the change of delay difference between the direct and the reflected signals during the incoherent averaging of the waveform has been investigated. Their effects on the waveform shape and the altimetric performance are presented comparing the aligned and non-aligned waveforms. Results show that the performance of spaceborne GNSS-R altimeter is seriously degraded without a proper alignment of the waveform samples.     

Chromospheric Sunspot Oscillations in Hα and Ca ii 8542 Å

We study chromospheric oscillations including umbral flashes and running penumbral waves in a sunspot of active region NOAA 11242 using scanning spectroscopy in Hα and Ca?ii 8542 Å with the Fast Imaging Solar Spectrograph (FISS) at the 1.6 meter New Solar Telescope at the Big Bear Solar Observatory. A bisector method is applied to spectral observations to construct chromospheric Doppler-velocity maps. Temporal-sequence analysis of these shows enhanced high-frequency oscillations inside the sunspot umbra in both lines. Their peak frequency gradually decreases outward from the umbra. The oscillation power is found to be associated with magnetic-field strength and inclination, with different relationships in different frequency bands.     

Velocities and Temperatures of an Ellerman Bomb and Its Associated Features

We investigated the velocity and temperature characteristics of an Ellerman bomb (EB) and its associated features based on observations made with the Fast Imaging Solar Spectrograph (FISS) and a broadband TiO filter of the 1.6 meter New Solar Telescope at Big Bear Solar Observatory. In the TiO images of the photospheric level, we found a granular cell expanding in two opposite directions near the site of the EB. When one end of this granule reached the EB site, the transverse speed of the tip of the expanding granule rapidly decreased and the EB brightened. The wings of the Hα profile of the EB indicated that the EB was blueshifted up to 7 km?s^?1. About 260 s after the EB brightening, a surge was seen in absorption and varied from a blueshift of 20 km?s^?1 to a redshift of 40 km?s^?1 seen in the Hα and Ca ii 8542 Å lines. From the Doppler absorption width of the two lines determined by applying the cloud model, we estimated the mean temperature of the surge material to be about 29000 K and the mean speed of nonthermal motion to be about 11 km?s^?1. We discuss the physical implications of our results in terms of magnetic reconnection and processes related to it.     

Revisiting Solar and Heliospheric 1.3-Year Signals during 1970 – 2007

We revisit the 1.3-year (yr) signals observed on the Sun, in the interplanetary space, and in the Earth’s magnetosphere to study the coupling among signals from the three regions for about 40 years (1970?–?2007) covering the three solar cycles 21, 22, and 23. For this, we make dynamic spectra of datasets including three different regions. From this, we estimate the peak frequency around 1.3 yr for each region and the corresponding band power. We found that coherent power only appears during 1987?–?1995 and the coherent behavior is found only in the interplanetary space and Earth, not in the Sun. Although the solar surface magnetic field shows significant power around 1.3 yr, their peak frequencies are statistically different from those of the outer regions, which make us dismiss the existence of coherence among the three regions. But it is notable that the peaks in band power corresponding to the 1.3-yr period are clearly simultaneous in the interplanetary space and Earth.     

Non-Gaussian distribution and clustering of hot and cold pixels in the five-year WMAP sky

We present measurements of the clustering of hot and cold patches in the microwave background sky as measured from the Wilkinson Microwave Anisotropy Probe 5-year data. These measurements are compared with theoretical predictions which assume that the cosmological signal obeys Gaussian statistics. We find significant differences from the simplest Gaussian-based prediction. However, the measurements are sensitive to the fact that the noise is spatially inhomogeneous (e.g. because different parts of the sky were observed for different lengths of time). We show how to account for this spatial inhomogeneity when making predictions. Differences from the Gaussian-based expectation remain even after this more careful accounting of the noise. In particular, we note that hot and cold pixels cluster differently within the same temperature thresholds at few-degree scales. While these findings may indicate primordial non-Gaussianity, we discuss other plausible explanations for these discrepancies. In addition, we find some deviations from Gaussianity at sub-degree scales, especially in the W band, whose origin may be associated with extragalactic dust emission.