High-frequency ocean radar derived characteristics of sea surface currents in the Ariake Sea,Japan

Composite analysis was conducted using high-frequency radar data obtained during 2006–2015 in order to gain a better understanding of the current field in the Ariake Sea. The seasonally averaged surface current in the Ariake Sea was directed southward in all seasons, except around river mouths during summer. Heavy rainfall enhanced the outflow along the eastern coast of the Shimabara Peninsula from Isahaya Bay to the southern area 2–5 days after heavy rainfall. Spring–neap differences were clearly seen in the southward current along the Shimabara Peninsula. Interannual variation in the M₂ tidal current amplitude was synchronized with the lunar nodal cycle.     

Penetration Depth of Torpedo Anchor in Two-Layered Cohesive Soil Bed by Free Fall

The penetration depth of torpedo anchor in two-layered soil bed was experimentally investigated. A total of 177 experimental data were obtained in laboratory by varying the undrained shear strength of the two-layered soil and the thickness of the top soil layer. The geometric parameters of the anchor and the soil properties (the liquid limit, plastic limit, specific gravity, undrained shear strength, density, and water content) were measured. Based on the energy analysis and present test data, an empirical formula to predict the penetration depth of torpedo anchor in two-layered soil bed was proposed. The proposed formula was extensively validated by laboratory and field data of previous researchers. The results were in good agreement with those obtained for two-layered and single-layered soil bed. Finally, a sensitivity analysis on the parameters in the formula was performed.     

Multi-angle backscatter classification and sub-bottom profiling for improved seafloor characterization

This study applies three classification methods exploiting the angular dependence of acoustic seafloor backscatter along with high resolution sub-bottom profiling for seafloor sediment characterization in the Eckernförde Bay, Baltic Sea Germany. This area is well suited for acoustic backscatter studies due to its shallowness, its smooth bathymetry and the presence of a wide range of sediment types. Backscatter data were acquired using a Seabeam1180 (180 kHz) multibeam echosounder and sub-bottom profiler data were recorded using a SES-2000 parametric sonar transmitting 6 and 12 kHz. The high density of seafloor soundings allowed extracting backscatter layers for five beam angles over a large part of the surveyed area. A Bayesian probability method was employed for sediment classification based on the backscatter variability at a single incidence angle, whereas Maximum Likelihood Classification (MLC) and Principal Components Analysis (PCA) were applied to the multi-angle layers. The Bayesian approach was used for identifying the optimum number of acoustic classes because cluster validation is carried out prior to class assignment and class outputs are ordinal categorical values. The method is based on the principle that backscatter values from a single incidence angle express a normal distribution for a particular sediment type. The resulting Bayesian classes were well correlated to median grain sizes and the percentage of coarse material. The MLC method uses angular response information from five layers of training areas extracted from the Bayesian classification map. The subsequent PCA analysis is based on the transformation of these five layers into two principal components that comprise most of the data variability. These principal components were clustered in five classes after running an external cluster validation test. In general both methods MLC and PCA, separated the various sediment types effectively, showing good agreement (kappa >0.7) with the Bayesian approach which also correlates well with ground truth data (r²?>?0.7). In addition, sub-bottom data were used in conjunction with the Bayesian classification results to characterize acoustic classes with respect to their geological and stratigraphic interpretation. The joined interpretation of seafloor and sub-seafloor data sets proved to be an efficient approach for a better understanding of seafloor backscatter patchiness and to discriminate acoustically similar classes in different geological/bathymetric settings.     

Equatorial Pacific gravity lineaments: interpretations with basement topography along seismic reflection lines

The central equatorial Pacific is interesting for studying clues to upper mantle processes, as the region lacks complicating effects of continental remnants or major volcanic plateaus. In particular, the most recently produced maps of the free-air gravity field from satellite altimetry show in greater detail the previously reported lineaments west of the East Pacific Rise (EPR) that are aligned with plate motion over the mantle and originally suggested to have formed from mantle convection rolls. In contrast, the gravity field 600 km or farther west of the EPR reveals lineaments with varied orientations. Some are also parallel with plate motion over the mantle but others are sub-parallel with fracture zones or have other orientations. This region is covered by pelagic sediments reaching ~?500–600 m thickness so bathymetry is not so useful for seeking evidence for plate deformation across the lineaments. We instead use depth to basement from three seismic reflection cruises. In some segments of these seismic data crossing the lineaments, we find that the co-variation between gravity and basement depth is roughly compatible with typical densities of basement rocks (basalt, gabbro or mantle), as expected for some explanations for the lineaments (e.g., mantle convection rolls, viscous asthenospheric inter-fingering or extensional deformation). However, some other lineaments are associated with major changes in basement depth with only subtle changes in the gravity field, suggesting topography that is locally supported by varied crustal thickness. Overall, the multiple gravity lineament orientations suggest that they have multiple origins. In particular, we propose that a further asthenospheric inter-fingering instability mechanism could occur from pressure variations in the asthenosphere arising from regional topography and such a mechanism may explain some obliquely oriented gravity lineaments that have no other obvious origin.     

Improvements on Fresnel arrays for high contrast imaging

The Fresnel Diffractive Array Imager (FDAI) is based on a new optical concept for space telescopes, developed at Institut de Recherche en Astrophysique et Planétologie (IRAP), Toulouse, France. For the visible and near-infrared it has already proven its performances in resolution and dynamic range. We propose it now for astrophysical applications in the ultraviolet with apertures from 6 to 30 meters, aimed at imaging in UV faint astrophysical sources close to bright ones, as well as other applications requiring high dynamic range. Of course the project needs first a probatory mission at small aperture to validate the concept in space. In collaboration with institutes in Spain and Russia, we will propose to board a small prototype of Fresnel imager on the International Space Station (ISS), with a program combining technical tests and astrophysical targets. The spectral domain should contain the Lyman-α line (λ =?121 nm). As part of its preparation, we improve the Fresnel array design for a better Point Spread Function in UV, presently on a small laboratory prototype working at 260 nm. Moreover, we plan to validate a new optical design and chromatic correction adapted to UV. In this article we present the results of numerical propagations showing the improvement in dynamic range obtained by combining and adapting three methods : central obturation, optimization of the bars mesh holding the Fresnel rings, and orthogonal apodization. We briefly present the proposed astrophysical program of a probatory mission with such UV optics.     

The eccentric case of a fast-rotating,gravity-gradient-perturbed satellite attitude solution

A closed-form first-order perturbation solution for the attitude evolution of a triaxial space object in an elliptical orbit is presented. The solution, derived using the Lie–Deprit method, takes into account gravity-gradient torque and is facilitated by an assumption of fast rotation of the object. The formulation builds on the earlier implementation of Lara and Ferrer, which assumes a circular orbit. The previously presented work—which assumes spin about an object’s axis of maximum inertia—is further extended by the explicit presentation of the transformations required to apply the solution to an object spinning about its axis of minimum inertia. Additionally, several numerical analyses are presented to more completely assess the utility of the solution. These studies (1) validate the elliptical solution, (2) assess the impact of varying the small parameter of the perturbation procedure, (3) analyze the assumption of fast rotation, and (4) apply the solution to the common and important scenario of a tumbling rocket body.     

The Sun–Earth saddle point: characterization and opportunities to test general relativity

The saddle points are locations where the net gravitational accelerations balance. These regions are gathering more attention within the astrophysics community. Regions about the saddle points present clean, close-to-zero background acceleration environments where possible deviations from General Relativity can be tested and quantified. Their location suggests that flying through a saddle point can be accomplished by leveraging highly nonlinear orbits. In this paper, the geometrical and dynamical properties of the Sun–Earth saddle point are characterized. A systematic approach is devised to find ballistic orbits that experience one or multiple passages through this point. A parametric analysis is performed to consider spacecraft initially on \(L_{1,2}\) Lagrange point orbits. Sun–Earth saddle point ballistic fly-through trajectories are evaluated and classified for potential use. Results indicate an abundance of short-duration, regular solutions with a variety of characteristics.     

The Influence of Two Kinds of El Niño Events on the Strong Tropical Cyclone Generation and Strength in the Pacific Ocean

This paper focuses on the effects of two types of El Niño events on tropical cyclone activity. We classified El Niño events from 1961 to 2015 according to their sea surface temperature (SST) anomalies into an eastern type and a central type. Then we selected strong tropical cyclones to statistically analyze the tropical cyclone characteristics during different events and their effects, as well as to study the possible mechanisms related to thermodynamic and dynamic factors. The tropical cyclone generation areas were found to be very similar during the two kinds of events. The average number of tropical cyclone in the eastern event is more than that in central event, and the hurricane in northeastern Pacific (HNP) has more energy than the typhoon in northwestern Pacific (TNP) in all cases. The seasonal distribution of the TNP high-incidence centers during central El Niño events is opposite to that of the HNP. The TNP accumulated cyclone energy (ACE) intensity is similar in the fall and summer, and the HNP ACE intensity in the summer is greater than that in the fall. The SSTs are consistent with the TNP and HNP movement trends. The Walker circulation intensity was strongly affected by the eastern events, but it quickly returned to its normal state, while the intensity was slightly reduced in the central events, and it slowly returned to its normal state. The vertical velocity distributions in the Pacific are different at different stages of both events, and the distributions of vertical velocity anomalies for typhoons and hurricanes are consistent.     

Co-dwelling,Mix-dwelling and Dis-dwelling: The Diversity Among Three Human and Livestock Dwelling Forms in Rural China

Humans and livestock have always dwelling together, especially in rural areas. Based on a multi-method approach of ethnographic fieldwork, grounded theory and one-way multivariate analysis of variance, this paper explores human and livestock dwelling. The findings show that human and livestock dwelling form a special type of human dwelling place, with forms defined as co-, mix- and dis-dwelling. Then, from co-, mix- to dis-dwelling constructed a story line to the evolution of human and livestock dwelling forms, which further explains the entire dwelling situation of humans and livestock, including the dimensions of human dweller, livestock dweller, the rural environment and special events. Among co-, mix- and dis-dwelling significant differences existed between human and livestock individuals, the nature of rural environment, vernacularity and rural tourism development. Between co- and dis-dwelling, significant differences existed in seventeen aspects; between mix- and dis-dwelling, significant differences existed in eleven aspects; meanwhile, no significant differences existed between co- and mix-dwelling. Accordingly, this suggested that human and livestock dwelling forms can be divided into mix- and dis-dwelling. This study on humans and livestock dwelling relationship offer a new perspective on rural and animal geography. This paper is an exploratory foray into rural dwelling geography as part of the Anthrozoology study and broadens the scope of extant scholarship on human dwelling morphology, as well as analyses the spatial relationships between human and livestock dwelling.     

Extreme Flood Events over the Past 300 Years Inferred from Lake Sedimentary Grain Sizes in the Altay Mountains,Northwestern China

Understanding the temporal variations of extreme floods that occur in response to climate change is essential to anticipate the trends in flood magnitude and frequency in the context of global warming. However, long-term records of paleofloods in arid regions are scarce, thus preventing a thorough understanding of such events. In this study, a reconstruction of paleofloods over the past 300 years was conducted through an analysis of grain sizes from the sediments of Kanas Lake in the Altay Mountains of northwestern China. Results showed that grain parameters and frequency distributions can be used to infer possible abrupt environmental events within the lake sedimentary sequence, and two extreme flood events corresponding to ca. 1736–1765 AD and ca. 1890 AD were further identified based on canonical discriminant analysis(CDA) and coarse percentile versus median grain size(C-M) pattern analysis, both of which occurred during warmer and wetter climate conditions by referring to tree-ring records. These two flood events are also evidenced by lake sedimentary records in the Altay and Tianshan mountains. Furthermore, through a comparison with other records, the flood event from ca. 1736–1765 AD in the study region seems to have occurred in both the arid central Asia and the Alps in Europe, and thus may have been associated with changes in the North Atlantic Oscillation(NAO) index.