A numerical simulation of the distribution of water temperature and salinity in the Seto Inland Sea

Constant flows, as well as oscillatory tidal flow, play an important role in the long-term dispersion of water in the Seto Inland Sea. Two kinds of numerical model (1-line and 2-line models) of the Seto Inland Sea have been developed to determine the role of density-induced currents, one type of the constant flow, in water dispersion in the Inland Sea. The seasonal variations of temperature, salinity and density fields are simulated and the density-induced current field is predicted at the same time. It is found that the most appropriate value of the longitudinal eddy diffusion coefficient,K _x, is 5×10⁶–7×10⁶ cm²sec^–1. The value of the overall mean dispersion coefficient is of the order of 10⁷cm²sec^–1 (Hayami and Unoki, 1970). Consequently, it is suggested that 50–70% of the total dispersion in the Seto Inland Sea can be attributed to currents other than density-induced currents,i.e., tidal currents, tide-induced currents and wind-driven currents.In winter, both density and velocity fields, calculated using the 1-line model, satisfy the conditions for the existence of a coastal front in Kii Channel and in the eastern Iyo-nada.     

Environmental factors regulating stream nitrate concentrations at baseflow condition in a large region encompassing a climatic gradient

Though high rates of nitrate (NO₃⁻) leaching from forests are undesirable, the factors significantly regulating stream NO₃⁻ concentration is not clarified yet. In Japan, not only near metropolitan areas but also the Japan Sea-side area with heavy snowfall is well known for receiving more than 10 kg-N ha⁻¹ year⁻¹ of nitrogen (N) deposition. However, NO₃⁻ concentration in stream water is relatively low in the Japan Sea-side area compared with its concentration in other areas. We examined important environmental factors regulating stream NO₃⁻ concentrations at baseflow condition in a large region of Japan, the Kinki region (KIN) including a part of Japan Sea-side (JSK) using Random Forest regression. The amounts of N deposition and precipitation were common regulating factors for stream NO₃⁻ concentration at baseflow condition. Random forest showed the significant correlation between the factors related to ecosystem N retention and stream NO₃⁻ concentration at baseflow condition, and it suggests that large N deposited during the growing season was incorporated into the ecosystem in the entire KIN. Heavy rain and snow flush N and wash out N accumulated in the surface soil, causing small N accumulation in forests. Also, large precipitation dilute NO₃⁻ concentration in baseflows. These things lowered stream NO₃⁻ concentration at baseflow condition. Especially in JSK, most of N deposed with the heavy snow flushed out during the snowmelt period. We provided the first statistical confirmation using Random Forest regression that N accumulation and cycling in forest ecosystems were related to NO₃⁻ leaching from forests into streams.     

Constraining paleo-latitude of a biogeographic boundary in mid-Panthalassa: Fusuline province shift on the Late Guadalupian (Permian) migrating seamount

The Guadalupian paleo-atoll limestone (Iwato Formation) in SW Japan was primarily formed in low-latitude mid-Panthalassa and was later tectonically accreted to South China (Japan) margin during the Jurassic. The present biostratigraphic study clarified that the Iwato Formation consists of 5 biostratigraphical intervals; i.e. four fusuline assemblage zones (Assemblage zones 1 to 4) and a barren interval on the top. Assemblage zones 1 to 4 correspond to the Neoschwagerina craticulifera Zone, N. margaritae Zone, Yabeina globosa Zone, and Lepidolina multiseptata Zone of the conventional Tethyan fusuline stratigraphy, respectively. The present study newly clarified the following significant aspects of paleobiogeography of the Permian fusulines as to the extinction of large-tested taxa in the latest Guadalupian. 1) The long unknown stratigraphic relationship was documented for the first time between the Yabeina-dominant interval and the overlying Lepidolina-dominant one within a single limestone unit. 2) The occurrence of Lepidolina cf. kumaensis Kanmera, the unique last runner of large-tested fusuine, was detected for the first time in mid-oceanic paleo-atoll limestones. 3) With respect to the northbound migration history of the paleo-seamount capped by the Iwato Formation, the development of the two coeval fusuline biogeographic territories in the low-latitude Panthalassa, i.e., the Yabeina territory on the south and the Lepidolina territory on the north, was confirmed. 4) The paleo-latitude of the biogeographic boundary between the Yabeina and Lepidolina territories is constrained around 12° in the southern hemisphere on the basis of the latest geomagnetic data from the same limestone. This new approach utilizing biostratigraphy on ancient migrating seamounts coupled with geomagnetic paleo-latitude data is applicable to other cases in different time-space co-ordinates and of other fossil groups for constraining position of ancient biogeographic boundaries within lost oceanic domains of deep past.     

A method for evaluating the degree of spatial and temporal avoidance in spatial point patterns

Journal of Geographical Systems - This paper develops a new method for evaluating the degree of spatial and temporal avoidance in spatial point patterns. We consider point patterns that change over...     

MJO change with A1B global warming estimated by the 40-km ECHAM5

This study estimates MJO change under the A1B greenhouse gas emission scenario using the ECHAM5 AGCM whose coupled version (ECHAM5/MPI-OM) has simulated best MJO variance among fourteen CGCMs. The model has a horizontal resolution at T319 (about 40 km) and is forced by the monthly evolving SST derived from the ECHAM5/MPI-OM at a lower resolution of T63 (about 200 km). Two runs are carried out covering the last 21 years of the twentieth and twenty-first centuries. The NCEP/NCAR Reanalysis products and observed precipitation are used to validate the simulated MJO during the twentieth century, based on which the twenty-first century MJO change is compared and predicted. The validation indicates that the previously reported MJO variances in the T63 coupled version are reproduced by the 40-km ECHAM5. More aspects of MJO, such as the eastward propagation, structure, and dominant frequency and zonal wavenumber in power spectrum, are simulated reasonably well. The magnitude in power, however, is still low so that the signal is marginally detectable and embedded in the over-reddened background. Under the A1B scenario, the T63 ECHAM5/MPI-OM projected an over 3 K warmer tropical sea surface that forces the 40-km ECHAM to produce wetter tropics. The enhanced precipitation variance shows more spectral enhancement in background than in most wavebands. The zonal winds associated with MJO, however, are strengthened in the lower troposphere but weakened in the upper. On the one hand, the 850-hPa zonal wind has power nearly doubled in 30–60-days bands, demonstrating relatively clearer enhancement than the precipitation in MJO with the warming. A 1-tailed Student’s t test suggests that most of the MJO changes in variance and power spectra are statically significant. Subject to a 20–100-days band-pass filtering of that wind, an EOF analysis indicates that the two leading components in the twentieth-century run have a close structure to but smaller percentage of explained-to-total variance than those in observations; the A1B warming slightly increases the explained percentage and alters the structure. An MJO index formed by the two leading principal components discloses nearly doubling in the number of prominent MJO events with a peak phase occurring in February and March. A composite MJO life cycle of these events favors the frictional moisture convergence mechanism in maintaining the MJO and the nonlinear wind-induced surface heat exchange (WISHE) mechanism also appears in the A1B warming case. On the other hand, the Slingo index based on the 300-hPa zonal wind discloses that the upper-level MJO tends to be suppressed by the A1B warming, although the loose relationship with ENSO remains unchanged. Possible cause for the different change of MJO in the lower and upper troposphere is discussed.     

Spectroscopic properties of Cr-doped and Cr,Li-doped synthetic forsterite crystals

Cr-droped and Cr,Li-doped forsterite crystals were grown and their optical properties were investigated. It was shown that when only Cr is doped, Cr³⁺ is substituted at the site of low crystal field, and the energy level ²E lie above the ⁴T₂ level, while ⁴T₂ is just above ²E when Cr and Li are codoped. The difference was rationalized by a deformation of the Cr substituted site with the introduction of Li.     

Velocity Adjustment and Passive Scalar Diffusion in and Above an Urban Canopy in Response to Various Approach Flows

We used wind-tunnel experiments to investigate velocity-field adjustment and scalar diffusion behaviour in and above urban canopies located downwind of various roughness elements. Staggered arrays of rectangular blocks of various heights H and plan area ratios λ_p were used to model the urban canopies. The velocity field in the roughness sublayer (height \({z \lesssim 2H}\)) reached equilibrium at distances proportional to \({\sqrt{L_{\rm c}H}}\) where L _c is the canopy-drag length scale determined as a function of λ_p and the block side length L. A distance of about \({20\sqrt{L_{\rm c}H}}\) was required for adjustment at z = H/2 (in the canopy), and a distance of about \({10\sqrt{L_{\rm c}H}}\) was required at z = 2H (near the top of the roughness sublayer). Diffusion experiments from a ground emission source revealed that differences in upwind roughness conditions had negligible effects on the plume growth near the source (up to a few multiples of L from the source) if the source was located at a fetch F larger than about \({10\sqrt{L_{\rm c}H}}\) from the upwind edge of the canopy. However, at locations farther downwind (more than several multiples of L from the source), upwind conditions had considerable effects on the plume growth. For a representative urban canopy, it was shown that a much larger fetch than required for velocity-field adjustment in the roughness sublayer was necessary to eliminate the effects of upwind conditions on plume widths at 24L downwind from the source.     

Analysis of the relations among spatial tessellations

A spatial tessellation is a set of regions that are collectively exhaustive and mutually exclusive except for the boundaries. In geographical analysis, it may represent such administrative units as census tracts, postal zones, and electoral or school districts. Spatial tessellations of a certain area are often closely related to each other. Areas of local communities are related to school districts, market areas of retail stores, and administrative units. Postal zones and census tracts are determined by collecting or dividing administrative units. Analysis of such relations among tessellations often reveals their underlying spatial phenomena. To this end, this paper proposes a new exploratory method for analyzing the relations among spatial tessellations. It aims to detect spatial patterns, especially those with a hierarchical structure, and to provide a tessellation classification scheme. Topological relations and similarity measures are introduced to evaluate the relations between tessellation pair. For more tessellations, tree representations are proposed. These not only visualize relations, but also provide a means of classifying tessellations. The method is applied to the analysis of two sets of spatial tessellations: one with five hypothetical tessellations, and another with 34 candidate plans for the new Doshusei administrative system in Japan. The application reveals the properties of the method and quantitative measures used in analysis.     

Accuracy of quantized Voronoi diagrams

Quantization of spatial objects, which usually means vector‐to‐raster conversion in GIS and remote sensing, is a basic operation used for handling spatial data from data creation to visualization. Since quantization is an approximation of spatial objects, it inevitably yields errors in measuring their properties such as area, perimeter, diameter, and so forth. This paper discusses the accuracy of a quantized Voronoi diagram, a spatial tessellation generated from a set of points. A measure is proposed to evaluate the accuracy of the area of Voronoi regions calculated after quantization. In one‐dimensional space the measure is expressed as an explicit function of the expected number of generators in a cell. In two‐dimensional space, on the other hand, the measure is defined by an implicit function, whose approximation is derived in an explicit form. These functions permit us to evaluate the accuracy of quantization in relation to the size of lattice cells and the density of Voronoi generators. This leads to an appropriate choice of a lattice to keep the quality of a quantized Voronoi diagram at a desirable level.     

A numerical investigation of eddy-induced chlorophyll bloom in the southeastern tropical Indian Ocean during Indian Ocean Dipole—2006

An eddy-resolving coupled physical–biological model is used to study the effect of cyclonic eddy in enhancing offshore chlorophyll-a (Chl-a) bloom in the southeastern tropical Indian Ocean during boreal summer–fall 2006. The results demonstrate that the offshore Chl-a blooms are markedly coincident with the high eddy kinetic energy. Moreover, the vertical variations in Chl-a, nitrate, temperature, and mixed-layer depth (MLD) strongly imply that the cyclonic eddies induce surface Chl-a bloom through the injection of nutrient-rich water into the upper layer. Interestingly, we found that the surface bloom only occurs when the deep Chl-a maximum is located within the MLD. On the other hand, the response of subsurface Chl-a to the eddy pumping is remarkable, although it is hardly observable at the surface.