SAR-imaged spiral eddies in Mutsu Bay and their dynamic and kinematic models

A pattern of slick streaks winding into a spiral, known as a spiral eddy, was identified in 5 images taken by the ERS-1/2 synthetic aperture radar (SAR) in Mutsu Bay (Japan); dynamic and kinematic models of these spiral eddies have been proposed. Common characteristics of the five spiral eddies are: 1) an eddy diameter of about 15 km; 2) their location in the western part of the bay; and 3) their cyclonic direction of rotation. Moreover, the wind conditions over the bay were common: prior to acquiring the images, a strong easterly wind continued blowing for more than one day. The wind field on the bay is known to be orographically steered and has strong windstress vorticity, which generates cyclonic circulation. The diameter and location of the circulation simulated with a numerical ocean model corresponded well to those of the identified spiral eddies. Based on these facts, we propose a dynamic model for the movement of a slick streak, and a kinematic model for the formation of a spiral eddy. We have assumed calm air, a microlayer and seawater with a cyclonic circulation in the dynamic model. The balance of forces is established in the microlayer among the frictional force from the seawater, the frictional force from the calm air, the gravitational force, and the Coriolis force. As a result, the velocity vector of the microlayer deflects slightly towards the center of the cyclonic circulation. We have assumed a point source of the microlayer in the kinematic model. The shapes of a slick streak simulated with the models agree well with the identified patterns in the SAR images.     

Sr2CoO4-δ薄膜中的自旋玻璃态的磁性质研究

用脉冲激光沉积方法(PLD)在铝酸镧衬底上制备了c取向的高氧空位含量的锶钴氧薄膜.X射线衍射分析表明薄膜单一取向且没有明显杂相.原位的高气压反射式高能电子衍射仪(RHEED)监测显示,薄膜为层状生长.通过对薄膜磁化强度随温度、磁场及时间的变化曲线进行测量,发现零场冷曲线上可能存在两个特征温度:T_f和T_a.T_f为对应玻璃态的冻结温度而T_a对应少量的不缺     

Estimation of the <Emphasis Type="Italic">in situ</Emphasis> Ultraviolet-A absorption of seawater by a simple irradiance inversion model

An irradiance inversion model to estimate the in situ absorption coefficient of seawater has been developed for the Ultraviolet-A (UVA) wavelength domain. Input parameters are sun angle and the up-and downward planar irradiances measured for at least two depths. The present method does not require seawater to be sampled, and is a discrete wavelength method which returns the absorption coefficient at a given wavelength from the irradiances measured at that wavelength without assuming a spectral shape of any optical properties a priori. Comparison between the model results and spectrophotometric measurements shows that the model is practically useful when cloud cover in the atmosphere is ≤ 50%. According to the present method, measurements of the irradiances enable simultaneous observation of the in situ underwater UVA radiation level and the absorption capacity of bulk seawater using a radiometer.     

基于内侧缓冲区算法的多边形骨架线提取模型

多边形的骨架线其本质是对多边形的抽象描述,合理的提取多边形的骨架线能够准确描述多边形的形态。给出了内侧缓冲区算法的定义及特性,提出利用内侧缓冲区算法提取多边形骨架线的模型,并给出了提取骨架线的实验。     

Reevaluation of historical ocean heat content variations with time-varying XBT and MBT depth bias corrections

As reported in former studies, temperature observations obtained by expendable bathythermographs (XBTs) and mechanical bathythermographs (MBTs) appear to have positive biases as much as they affect major climate signals. These biases have not been fully taken into account in previous ocean temperature analyses, which have been widely used to detect global warming signals in the oceans. This report proposes a methodology for directly eliminating the biases from the XBT and MBT observations. In the case of XBT observation, assuming that the positive temperature biases mainly originate from greater depths given by conventional XBT fall-rate equations than the truth, a depth bias equation is constructed by fitting depth differences between XBT data and more accurate oceanographic observations to a linear equation of elapsed time. Such depth bias equations are introduced separately for each year and for each probe type. Uncertainty in the gradient of the linear equation is evaluated using a non-parametric test. The typical depth bias is +10 m at 700 m depth on average, which is probably caused by various indeterminable sources of error in the XBT observations as well as a lack of representativeness in the fall-rate equations adopted so far. Depth biases in MBT are fitted to quadratic equations of depth in a similar manner to the XBT method. Correcting the historical XBT and MBT depth biases by these equations allows a historical ocean temperature analysis to be conducted. In comparison with the previous temperature analysis, large differences are found in the present analysis as follows: the duration of large ocean heat content in the 1970s shortens dramatically, and recent ocean cooling becomes insignificant. The result is also in better agreement with tide gauge observations. On leave from the Meteorological Research Institute of the Japan Meteorological Agency.     

Composition of the phytoplankton pigments in the surface waters along a transect from the Northwestern to the southeastern Pacific Ocean

Multidisciplinary oceanic investigation was undertaken in Aug–Sep. 2003 along a transect from Northwestern (Busan, Korea) to Southeastern Pacific (Talcahuano, Chile) to understand the physical, chemical and biological features in the surface water, and to depict their interaction with the atmosphere. Among the twenty parameters measured, we describe the physical, chemical and biological features. Physico-chemical data were analyzed in conjunction with the geographic position and yielded 7 peculiar surface water masses. The first water mass (28.4°N, 130.8°E to 21.5°N, 139.5°E) was warm and low in phosphate and nitrate content, and high in silicate. The concentration of phytoplankton pigment was one of the lowest. The second (20.4°N, 140.7°E to 2.2°S, 162.9°E) was the warmest and the least saline. Nitrate and phosphate concentration were one of the lowest. Chlorophyll a (Chl a) concentration was the lowest among the surface waters. The third (3.4°S, 164.0°E to 14.5°S, 173.3°E) was warm. Nitrate concentration was the lowest. CHL-a, peridinin (Perid), violaxanthin (Viola), zeaxanthin (Zea), chlorophyll-b (Chl b) and β-CAR were abundant. The fourth (18.6°S, 177.5°E to 31.8°S, 123.9°W) was saline and poor in nutrient concentration. The contributions of 19′-butanoyloxyfucoxanthin (But-fuco), 19′-hexanoyloxyfucoxanthin (Hex-fuco), and CHL b to CHL a were non-negligible. The fifth (32.4°S, 122.1°W to 33.8°S, 117.2°W) was relatively cold and well oxygenated. Concentration of Fuco, But-fuco, Hex-fuco and Chl b was high. The sixth (34.2°S, 115.4°W to 37.4°S, 92.1°W) was cold, well oxygenated and enriched with phosphate and nitrate. Concentration of phytoplankton pigment was, however, one of the lowest. The seventh, located off the Chilean coast, from 37.2°S, 87.2°W to 36.1°S, 74.1°W was well oxygenated and highly enriched with nitrate and phosphate. Phytoplankton pigments such as Fuco, Perid, But-fico, and Hex-fuco were rich. The 7 surface water masses are partially attributed to Kuroshio Current, North Equatorial Current and North Equatorial Countercurrent, South Equatorial current, South Pacific Subtropical Gyre, South Pacific Current, Subtropical Front and Chilean coastal water. The differences in physicochemical characteristics and the history of the surface water resulted in difference in quantity and composition of the phytoplankton pigment.     

Long-term bottom water warming in the north Ross Sea

We measured potential temperature, salinity, and dissolved oxygen profiles from the surface to the bottom at two locations in the north Ross Sea (65.2°S, 174.2°E and 67.2°S, 172.7°W) in December 2004. Comparison of our data with previous results from the same region reveals an increase in potential temperature and decreases in salinity and dissolved oxygen concentration in the bottom layer (deeper than 3000 m) over the past four decades. The changes were significantly different from the analytical precisions. Detailed investigation of the temperature, salinity, dissolved oxygen and σ ₃ value distributions and the bottom water flow in the north Ross Sea suggests a long-term change in water mass mixing balance. That is to say, it is speculated that the influence of cool, saline, high-oxygen bottom water (high-salinity Ross Sea Bottom Water) formed in the southwestern Ross Sea has possibly been decreased, while the influences of relatively warmer and fresher bottom water (low-salinity Ross Sea Bottom Water) and the Adélie Land Bottom Water coming from the Australia-Antarctic Basin have increased. The possible impact of global warming on ocean circulation needs much more investigation.     

Bathymetry enhancement by altimetry-derived gravity anomalies in the East Sea (Sea of Japan)

The gravity-geologic method (GGM) was used to enhance the bathymetry of the East Sea (Sea of Japan) with satellite altimetry-derived free-air gravity anomalies and shipborne depth measurements. By comparison with the bathymetry model of Smith and Sandwell’s (SAS) approach (1994), GGM was found to have an advantage with short wavelength (≤12 km) components, while SAS better predicts longer wavelength (≥25 km) components, despite its dependency on density contrast. To mitigate this limitation, a tuning density contrast of 10.25 g/cm³ between seawater and the seafloor was primarily estimated by the downward continuation method and then validated by the check points method with GGM. Similarly, SAS is limited by the “A” value in low-pass part of the Wiener filter, which defines the effective range of the wavelength components on bathymetry. As a final result, we present an enhanced GGM bathymetry model by integrating all available data.     

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.