A laboratory study of directional spectra with maximum likelihood method─I Developing wind wave

INTRODUCTIONDirectionalspectraofwind-generatedwavesareveryimportanttotheresearchrelatedto1.InstituteofPhysicalOceanography,OceanUniversityofQingdao,Qingdao266003,China2.ResearchinstituteforAppliedMechanics,KyUshuUniversity,Kasuga816,Japanwindwaves.Theyfindapplicationinfieldsasdiverseasbasicair-seainteraction,practicalwaveforecasting,satellitesurveillanceandengineeringdesignofmarinestructuresandvehicles.Sincethepioneeringworkofthestereowaveobservationproject(Coteetal.11960),alotofeff…     

Bathymetric influences of the Emperor Seamounts upon the subarctic gyre of the North Pacific: Examining boundary current dynamics along the eastern side of the mountain ridge with an idealized numerical model

The possible influences of the Emperor Seamounts (ESs) upon the subarctic gyre of the North Pacific (NPSAG) were investigated by a series of numerical experiments. In the experiments, a two-layer ocean with a meridional mountain ridge was forced by seasonally varying wind stress. We focused on how the return ratio, the ratio of the boundary transport along the eastern side of the ridge to the interior Sverdrup transport, changes with ridge height, width and density stratification. It was found that the return ratio can be large if the ridge width is greater than the width of the viscous boundary layer. In this case, the bottom pressure torque determines the return ratio; the return ratio is almost proportional to the ridge height when the ridge height is small and some contours of planetary potential vorticity pass over the ridge. However, the return ratio is independent of the ridge height and decreases with the stratification when the ridge height is large and all the contours of planetary potential vorticity are closed. These dependences of the return ratio were understood in terms of barotropic and baroclinic components of the bottom pressure torque. Implications for the bathymetric influences of ESs on the actual NPSAG are also discussed.     

Use of flood chronology for detailed environmental analysis: a case study of Lake Kizaki in the northern Japanese Alps,central Japan

This paper presents a study of the usefulness of flood layers as a time marker in sediments and a report of a case study of Lake Kizaki in central Japan. A flood layer can be identified as a layer having a higher density, coarser grain size, lower TN content, and higher C/N ratio than those of the upper and lower horizons. It can also be characterized by a hyperpycnal sequence composed of a basal coarsening-upward unit and a top fining-upward unit. When flood layers can be correlated with heavy rains in meteorological records, detailed age markers are well established in the sediment. Five flood layers were identified in the surface sediment of Lake Kizaki, and they could be attributed to the historical heavy rainfalls that took place on July 12, 1995; September 28, 1983; August 25, 1974; September 26, 1959; and September 1, 1949 under the constraint of an age model. A precise age model is essential to clarify the environmental changes such as the pollutant history in detail.     

An asteroseismic study of the β Cephei star 12 Lacertae: multisite spectroscopic observations, mode identification and seismic modelling

We present the results of a spectroscopic multisite campaign for the β Cephei star 12 (DD) Lacertae. Our study is based on more than thousand high-resolution high S/N spectra gathered with eight different telescopes in a time span of 11 months. In addition, we make use of numerous archival spectroscopic measurements. We confirm 10 independent frequencies recently discovered from photometry, as well as harmonics and combination frequencies. In particular, the slowly pulsating B-stars (SPB)-like g -mode with frequency 0.3428 d⁻¹ reported before is detected in our spectroscopy. We identify the four main modes as  (ℓ₁, m ₁) = (1, 1), (ℓ₂, m ₂) = (0, 0), (ℓ₃, m ₃) = (1, 0)  and  (ℓ₄, m ₄) = (2, 1)  for   f ₁= 5.178 964 d⁻¹, f ₂= 5.334 224 d⁻¹, f ₃= 5.066 316 d⁻¹  and   f ₄= 5.490 133 d⁻¹  , respectively. Our seismic modelling shows that f ₂ is likely the radial first overtone and that the core overshooting parameter  α_ov  is lower than 0.4 local pressure scale heights.     

MOA-cam3: a wide-field mosaic CCD camera for a gravitational microlensing survey in New Zealand

We have developed a wide-field mosaic CCD camera, MOA-cam3, mounted at the prime focus of the Microlensing Observations in Astrophysics (MOA) 1.8-m telescope. The camera consists of ten E2V CCD4482 chips, each having 2k×4k pixels, and covers a 2.2 deg² field of view with a single exposure. The optical system is well optimized to realize uniform image quality over this wide field. The chips are constantly cooled by a cryocooler at ??80° C, at which temperature dark current noise is negligible for a typical 1–3 min exposure. The CCD output charge is converted to a 16-bit digital signal by the GenIII system (Astronomical Research Cameras Inc.) and readout is within 25 s. Readout noise of 2–3 ADU (rms) is also negligible. We prepared a wide-band red filter for an effective microlensing survey and also Bessell V, I filters for standard astronomical studies. Microlensing studies have entered into a new era, which requires more statistics, and more rapid alerts to catch exotic light curves. Our new system is a powerful tool to realize both these requirements.     

Interannual variability of North Pacific eastern subtropical mode water formation in the 1990s derived from a 4-dimensional variational ocean data assimilation experiment

The interannual variability of eastern subtropical mode water (ESTMW) formation in the North Pacific is examined using a new ocean dataset constructed by a 4-dimensional variational data assimilation experiment covering the decade of the 1990s. The volume of newly formed ESTMW varies due to interannual variability in the following three physical processes taking place in the surface layer: (1) convergence in the transport of surface saline water induced by Ekman flow in the vicinity of the formation region, (2) thermal stratification in the preconditioning phase in association with the insolation anomaly induced largely by low-level cloud coverage, and (3) wintertime surface cooling in the eastern subtropics. We find that, in addition to the surface forcing, the properties of both the ESTMW and the upper mixed-layer water are broadly controlled by the volume of the new ESTMW component, and that the variations in the upper mixed-layer water affect the properties of ESTMW formed in the following winter. Due to the combined effect of these processes, the ESTMW subducts down to subsurface layers with a wide range of σ_θ values lying between 24.8 and 25.4 and with significant interannual variation in water mass formation.     

Occurrence of triterpenyl acetates in soil and their potential as chemotaxonomical markers of Asteraceae

As a part of a wider study aimed at determining new molecular biomarkers in soils and sediments that could be specific for distinct vegetation types with respect to unravelling past changes in land use, we analysed the neutral lipid content of soil developed in the catchment of a small lake in central France. The ketone/acetate lipid fraction of soil under pasture or meadow contained a series of pentacyclic triterpenyl acetates with wide structural diversity, most being reported in soil for the first time. The restricted number of potential plant sources of triterpenyl acetates (some produced by a single species) underlines the potential of triterpenyl acetates as new biomarkers to track past vegetation change in palaeoenvironmental studies, when found in natural archives such as soil, sediments or peat.     

Direct velocity measurements of deep circulation southwest of the Shatsky Rise in the western North Pacific

Direct velocity measurements undertaken using a nine-system mooring array (M1–M9) from 2004 to 2005 and two additional moorings (M7p and M8p) from 2003 to 2004 reveal the spatial and temporal properties of the deep-circulation currents southwest of the Shatsky Rise in the western North Pacific. The western branch of the deep-circulation current flowing northwestward (270–10° T) is detected almost exclusively at M2 (26°15′N), northeast of the Ogasawara Plateau. It has a width less than the 190 km distance between M1 (25°42′N) and M3 (26°48′N). The mean current speed near the bottom at M2 is 3.6±1.3 cm s^?1. The eastern branch of the deep-circulation current is located at the southwestern slope of the Shatsky Rise, flowing northwestward mainly at M8 (30°48′N) on the lower part of the slope of the Shatsky Rise with a mean near-bottom speed of 5.3±1.4 cm s^?1. The eastern branch often expands to M7 (30°19′N) at the foot of the rise with a mean near-bottom speed of 2.8±0.7 cm s^?1 and to M9 (31°13′N) on the middle of the slope of the rise with a speed of 2.5±0.7 cm s^?1 (nearly 4000 m depth); it infrequently expands furthermore to M6 (29°33′N). The width of the eastern branch is 201±70 km on average, exceeding that of the western branch. Temporal variations of the volume transports of the western and eastern branches consist of dominant variations with periods of 3 months and 1 month, varying between almost zero and significant amount; the 3-month-period variations are significantly coherent to each other with a phase lag of about 1 month for the western branch. The almost zero volume transport occurs at intervals of 2–4 months. In the eastern branch, volume transport increases with not only cross-sectional average current velocity but also current width. Because the current meters were too widely spaced to enable accurate estimates of volume transport, mean volume transport is overestimated by a factor of nearly two, yielding values of 4.1±1.2 and 9.8±1.8 Sv (1 Sv=10⁶ m³ s^?1) for the western and eastern branches, respectively. In addition, a northwestward current near the bottom at M4 (27°55′N) shows a marked variation in speed between 0 and 20 cm s^?1 with a period of 45 days. This current may be part of a clockwise eddy around a seamount located immediately east of M4.