The motion of a 9.1 m yacht hull buoy moored in open sea

A 9.1 m yacht hull was instrumented to measure its three-dimensional motion when moored in the open sea. The hull was deployed on three occasions for a total period of about 2 months and encountered a wide range of wind-wave conditions including a strong gale. The data have been analysed to give the response for each component of motion in terms of amplitude and relative phases. The hull motion is compared spectrally to the waves observed by a nearby Waverider. The hull was found to behave as a surface-keyed buoy, with a well defined response for a wide range of conditions. The presence of a resonance in pitch and roll is evident in the data with typical rms values being 5° and 10°, respectively, for significant wave height of 5 m. From data on the mooring dynamics it is concluded that the peaks observed in the tension are a result of the viscous drag opposing the change in the catenary of the mooring and the slow drift oscillations of the buoy. This type of hull is a versatile and economical candidate as a platform for meteorological and oceanographic instrumentation.     

Heterogeneity influences on stream water–groundwater interactions in a gravel-dominated floodplain

ABSTRACT

Floodplains are composed of complex depositional patterns of ancient and recent stream sediments, and research is needed to address the manner in which coarse floodplain materials affect stream–groundwater exchange patterns. Efforts to understand the heterogeneity of aquifers have utilized numerous techniques typically focused on point-scale measurements; however, in highly heterogeneous settings, the ability to model heterogeneity is dependent on the data density and spatial distribution. The objective of this research was to investigate the correlation between broad-scale methodologies for detecting heterogeneity and the observed spatial variability in stream/groundwater interactions of gravel-dominated alluvial floodplains. More specifically, this study examined the correlation between electrical resistivity (ER) and alluvial groundwater patterns during a flood event at a site on Barren Fork Creek, in the Ozark ecoregion of Oklahoma, USA, where chert gravels were common both as streambed and as floodplain material. Water table elevations from groundwater monitoring wells for a flood event on 1–5 May 2009 were compared to ER maps at various elevations. Areas with high ER matched areas with lower water table slope at the same elevation. This research demonstrated that ER approaches were capable of indicating heterogeneity in surface water–groundwater interactions, and that these heterogeneities were present even in an aquifer matrix characterized as highly conductive. Portions of gravel-dominated floodplain vadose zones characterized by high hydraulic conductivity features can result in heterogeneous flow patterns when the vadose zone of alluvial floodplains activates during storm events.

EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR X. Chen     

Studying local sources in the radio range based on the partial solar eclipse of January 4, 2011, at the Mountain Astronomical Station, Central Astronomical Observatory, Russian Academy of Sciences

Data are presented on a partial solar eclipse, which occurred on January 4, 2011, and was observed with RT-3 (?? = 4.9 cm) and RT-2 (?? = 3.2 cm) radio telescopes at the Mountain Astronomical Station, Central Astronomical Observatory, Russian Academy of Sciences (MAS CAO RAS). The radioemission flux in two channels was registered using digital methods with a time resolution of 0.5 s. Comparisons were performed with observations in the optical, UV, and X-ray ranges. The following local sources of increased radioemission on the solar disk have been identified: sunspot groups 1 (NOAA 1142) and 126 (NOAA 1141), unipolar sunspot 127 (NOAA 1140), facula areas, and polar and midlatitude coronal holes. It has been indicated that the brightness of a unipolar sunspot (for ?? = 4.9 cm, I _rel = 29.5; for ?? = 3.2 cm, I _rel = 10.1) and two sunspot groups (for ?? = 4.9 cm, I _rel = 10.1 and 14.2; for ?? = 3.2 cm, I _rel = 5.1 and 6.2) is maximal. The radioemission flux of all found coronal holes is decreased, and the decrease is more contrasting in the 4.9-cm range as compared to such a decrease in the 3.2-cm range. Radio maps of the Sun and changes in the radioemission flux of undisturbed solar regions from the center to the limb for ?? = 4.9 and 3.2 cm have been constructed based on the eclipse data.     

Fast and direct nonparametric procedures in the L-moment homogeneity test

Regional frequency analysis is an important tool to properly estimate hydrological characteristics at ungauged or partially gauged sites in order to prevent hydrological disasters. The delineation of homogeneous groups of sites is an important first step in order to transfer information and obtain accurate quantile estimates at the target site. The Hosking–Wallis homogeneity test is usually used to test the homogeneity of the selected sites. Despite its usefulness and good power, it presents some drawbacks including the subjective choice of a parametric distribution for the data and a poorly justified rejection threshold. The present paper addresses these drawbacks by integrating nonparametric procedures in the L-moment homogeneity test. To assess the rejection threshold, three resampling methods (permutation, bootstrap and Pólya resampling) are considered. Results indicate that permutation and bootstrap methods perform better than the parametric Hosking–Wallis test in terms of power as well as in time and procedure simplicity. A real-world case study shows that the nonparametric tests agree with the HW test concerning the homogeneity of the volume and the bivariate case while they disagree for the peak case, but that the assumptions of the HW test are not well respected.     

Probabilistic Assessment of Tsunami Recurrence in the Indian Ocean

The Indian Ocean is one of the most tsunamigenic regions of the world and recently experienced a mega-tsunami in the Sumatra region on 26 December 2004 (M _W 9.2 earthquake) with tsunami intensity I (Soloviev-Imamura intensity scale) equal to 4.5, causing heavy destruction of lives and property in the Indian Ocean rim countries. In this study, probabilities of occurrences of large tsunamis with tsunami intensities I ≥ 2.0 and I ≥ 3.0 (average wave heights H ≥ 2.83 m and H ≥ 5.66 m, respectively) during a specified time interval were calculated using three stochastic models, namely, Weibull, gamma and lognormal. Tsunami recurrence was calculated for the whole Indian Ocean and the special case of the Andaman-Sumatra-Java (ASJ) region, excluding the 1945 Makran event from the main data set. For this purpose, a reliable, homogeneous and complete tsunami catalogue with I ≥ 2.0 during the period 1797–2006 was used. The tsunami hazard parameters were estimated using the method of maximum likelihood. The logarithm of likelihood function (ln L) was estimated and used to test the suitability of models in the examined region. The Weibull model was observed to be the most suitable model to estimate tsunami recurrence in the region. The sample mean intervals of occurrences of tsunamis with intensity I ≥ 2.0 and I ≥ 3.0 were calculated for the observed data as well as for the Weibull, gamma and lognormal models. The estimated cumulative and conditional probabilities in the whole Indian Ocean region show recurrence periods of about 27–30 years (2033–2036) and 35–36 years (2039–2040) for tsunami intensities I ≥ 2.0 and I ≥ 3.0, respectively, while it is about 31–35 years (2037–2041) and 41–42 years (2045–2046) for a tsunami of intensity I ≥ 2.0 and I ≥ 3.0, respectively, in the ASJ region. A high probability (>0.9) of occurrence of large tsunamis with I ≥ 2.0 in the next 30–40 years in the Indian Ocean region was revealed.     

影响b值计算误差的Monte Carlo实验研究

本文假设地震的发生与时间的关系遵循稳态泊松模型,假设地震震级M服从参数为1/β的指数分布,其中β=b/loge,在此基础上生成地震目录.用最小二乘法估算b值,分别从样本数量、震级间隔、震级误差三方面分析b值误差的大小.统计分析结果表明,b值的标准偏差随着样本数量的增多而减小;随着震级间隔的增大而减小;震级误差使b值的标准误差变大.本文可以为利用真实地震目录求b值时选择适当的方法提供参考.