Wind-Tunnel and Numerical Simulations of the Coastal Thermal Internal Boundary Layer     

Tomohiro Hara  Yuji Ohya  Takanori Uchida  Ryohji Ohba 《Boundary-Layer Meteorology》2009,130(3):365-381

Wind-tunnel experiments in a thermally stratified wind tunnel and direct numerical simulations were performed to simulate the thermal internal boundary layer (TIBL) that developed over a coastal area in a sea-breeze flow. The results of the simulations were analyzed to investigate turbulence structure in the TIBL. To study the effects of the atmospheric stability over the sea on the TIBL, two vertical profiles of temperature were created in the upstream portion of the wind-tunnel experiment and the direct numerical simulation. Turbulence statistics of the TIBL changed significantly according to the temperature profile over the sea, indicating that the stability of the flow over the sea has a significant effect on the structure and turbulence characteristics of the TIBL. Furthermore, the TIBL heights were estimated from the vertical profiles of the local Richardson number. The estimated TIBL heights agreed with those predicted by a pre-existing relation, suggesting that both the wind-tunnel experiment and the direct numerical simulation accurately reproduced the growth of the TIBL.  相似文献   

Recovery of surface albedo and plant cover after wildfire in a Picea mariana forest in interior Alaska   总被引：1，自引：0，他引：1  

Shiro Tsuyuzaki  Keiji Kushida  Yuji Kodama 《Climatic change》2009,93(3-4):517-525

Albedo influences vegetation structure, permafrost thawing, etc., in particular, after wildfires in Picea mariana forests in Alaska, USA, while albedo changes with plant succession. To understand interactions between albedo and ecosystem recovery after wildfire, surface albedo was measured in the spring and summer of 2005 at Poker Flat, interior Alaska, where P. mariana forest was dominant. The ground surface was mostly covered with Sphagnum moss before the 2004 wildfire, and was variously burned by the fire. The measured wavelengths ranged from 0.3 to 3.0 μm. We measured four independent variables, incidence, plant cover on the forest floor, cover of burned ground surface, canopy openness and incidence, to examine the determinants on surface albedo. Multiple regression analysis showed that total plant cover positively and mostly determines albedo, indicating that plant recovery is prerequisite to return high albedo. When the ground surface was damaged by fire, changes in albedo were mostly derived from decrease in reflectance wavelengths between 0.7 and 1.4 μm. The fluctuations of reflectance wavelengths did not differ greatly between damaged-moss and burned surfaces. We must mention the dynamics of Sphagnum to understand various environmental changes including surface albedo.  相似文献   

Nitrogen as the carrier gas for helium emission along an active fault in NW Taiwan     

Wei-Li Hong  Tsanyao Frank Yang  Vivek Walia  Shih-Jung Lin  Ching-Chou Fu  Yue-Gau Chen  Yuji Sano  Cheng-Hong Chen  Kuo-Liang Wen 《Applied Geochemistry》2010

Variations of He gas concentration are widely applied in studies devoted to the location of faults and to monitor seismic activities. Up to now, its migration mechanism in soil is not fully understood. A systematic soil gas survey across an active fault in NW Taiwan provides the opportunity to closely examine the mechanism of He migration in the fault zone. Significant spatial and temporal correlations observed between soil N₂ and He gas support the hypothesis that N₂ is the probable carrier gas for He emission in the studied area. Based on N₂/Ar ratios and N₂ isotopic results, the excess soil N₂ in this study is considered to be largely derived from ancient atmospheric air which was dissolved in groundwater. Furthermore, observations rule out the possibility of CO₂ being the dominant carrier gas for He in the studied area based on the C and He isotopic compositions and the relationship between concentrations of these gases. At least two soil gas sources, A and B, can be identified in the studied area. Source A is an abiogenic gas source characterized by excess N₂ and He, and very low O₂ and CO₂ content. Source B, on the other hand, is a mixture of biogenic gas and atmospheric air. The development of the fault system is an important factor affecting the degree of mixture between sources A and B. Therefore, variations of soil gas composition, in particular those derived from source A, could be a useful proxy for tracing faults in the area.  相似文献   

Atmospheric helium isotope ratio: Possible temporal and spatial variations     

Yuji Sano  Yukiko Furukawa  Naoto Takahata 《Geochimica et cosmochimica acta》2010,74(17):4893-4901

The atmospheric ³He/⁴He ratio has been considered to be constant on a global scale, because the residence time of helium is significantly longer than the mixing time in the atmosphere. However, this ratio may be decreasing with time owing to the anthropogenic release of crustal helium from oil and natural gas wells, although this observation has been disputed. Here, we present the ³He/⁴He ratios of old air trapped in historical slags in Japan and of modern surface air samples collected at various sites around the world, measured with a newly developed analytical system. In air helium extracted from metallurgical slag found at refineries in operation between AD 1603 and 1907 in Japan, we determined a mean ³He/⁴He ratio of (5106 ± 108) × 10^-5 R_HESJ (where R_HESJ is the ³He/⁴He ratio of the Helium Standard of Japan), which is consistent with the previously reported value of (5077 ± 59) × 10^-5 R_HESJ for historical slags in France and United Arab Emirates and about 4% higher than that of average modern air, (4901 ± 4) × 10^-5 R_HESJ. This result implies that the air ³He/⁴He ratio has decreased with time as expected by anthropogenic causes. Our modern surface air samples revealed that the ³He/⁴He ratio increases from north to south at a rate of (0.16 ± 0.08) × 10^-5 R_HESJ/degree of latitude, suggesting that the low ³He/⁴He ratio originates in high-latitude regions of the northern hemisphere, which is consistent with the fact that most fossil fuel is extracted and consumed in the northern hemisphere.  相似文献   

基于克里格回归分析和机器学习算法的日本福岛县土地价格估算与制图的比较分析   总被引：1，自引：0，他引：1  

DERDOURlAhmed  村山佑司 《地理学报(英文版)》2020,30(5):794-822

Finding accurate methods for estimating and mapping land prices at the macro-scale based on publicly accessible and low-cost spatial data is an essential step in producing a meaningful reference for regional planners.This asset would assist them in making economically justified decisions in favor of key investors for development projects and post-disaster recovery efforts.Since 2005,the Ministry of Land,Infrastructure,and Transport of Japan has made land price data open to the public in the form of observations at dispersed locations.Although this data is useful,it does not provide complete information at every site for all market participants.Therefore,estimating and mapping land prices based on sound statistical theories is required.This paper presents a comparative study of spatial prediction of land prices in 2015 in Fukushima prefecture based on geostatistical methods and machine learning algorithms.Land use,elevation,and socioeconomic factors,including population density and distance to railway stations,were used for modeling.Results show the superiority of the random forest algorithm.Overall,land prices are distributed unevenly across the prefecture with the most expensive land located in the western region characterized by flat topography and the availability of well-connected and highly dense economic hotspots.  相似文献   

Helium and carbon isotopes in fluorites: implications for mantle carbon contribution in an ancient subduction zone   总被引：1，自引：0，他引：1  

Junji Yamamoto  Makoto Watanabe  Yoshiyuki Nozaki  Yuji Sano   《Journal of Volcanology and Geothermal Research》2001,107(1-3)

The concentrations of helium and carbon in fluorite associated with Cretaceous to Neogene (90–13 Ma) granitic magmatism in the Japanese arc have been measured. Concentrations of Li, U, Th and Gd were measured to correct for secondary generated ³He. The CO₂/³He of fluorites are almost uniform (1.5×10¹⁰–4×10¹⁰) and in fair agreement with the range of present island arc volcanic gases. The calculated mantle C contribution in the Mesozoic subduction zone appear to have been identical to the present one (7–19%) indicating that the C flux from the mantle in supra-subduction zone environments has remained fairly constant during the past 70 million years.  相似文献   

Secular variations of carbon and helium isotopes at Izu-Oshima Volcano, Japan   总被引：1，自引：0，他引：1  

Yuji Sano  Toshitaka Gamo  Kenji Notsu  Hiroshi Wakita 《Journal of Volcanology and Geothermal Research》1995,64(1-2)

Secular variations in ¹³C/¹²C ratios and chemical compositions of gas samples from October 1986 to July 1992 are reported from a 92–95 °C steam well located about 3 km north of Mt. Mihara, an active volcano on Izu-Oshima Island, Japan. The δ¹³C value steeply increased from −2.97‰ (relative to PDB carbonate) in December 1986 to −1.15‰ in March 1988 and then gradually decreased to −1.75‰ in July 1992. Over the same period, the CO₂ content changed similarly with time, even though the experimental error is relatively large. These variations are consistent with helium isotope changes. Initially rapid and then slow enhancements of ³He/⁴He ratio, δ¹³C value and CO₂ content are invoked by violent eruptions of Izu-Oshima volcano from 15 November to 18 December 1986. After the eruptive activity, depletion of magmatic gas emission and subsequent mixing with crustal fluids in the hydrothermal system may produce the gradual decreases of ³He/⁴He ratio, δ¹³C value and CO₂ content. Taking into account the rates of these decreases, we suggest that helium and carbon isotope ratios will return to the situation of before the magmatic eruption within 15 years.  相似文献   

Helium isotopic ratio in Vulcano island fumaroles: temporal variations in shallow level mixing and deep magmatic supply     

Dario Tedesco  Gerarda Miele  Yuji Sano  Jean Paul Toutain 《Journal of Volcanology and Geothermal Research》1995,64(1-2)

Intensive gas emanations occur throughout the island of Vulcano, Italy. Sharp fluctuations recorded in the crater gas composition suggest the presence of two separate volcanic reservoirs and continuous mixing with another source, “crustal” waters. This mixing differs between the beach and crater fumaroles. Gas samples from three crater fumaroles with temperatures ranging from 200 to 550 ° C were sampled repeatedly over a one year period. During the same interval of time, six samples from submarine and subaerial beach fumaroles and water well gases were also sampled. Gases from one crater fumarole (F5) showed variations of (³He/⁴He)_fumarole to (³He/⁴He)_air between 5 and 6 correlated with variations of several chemical species. High ³He/⁴He ratios for the beach fluids, similar to those of crater fluids, suggest the existence of a unique large magmatic reservoir at depth feeding both the crater and beach intermediate reservoirs. However, temporal changes clearly indicate variable degrees of fluids mixing, and the geographic distribution of the ³He/⁴He ratios as well as the chemical composition of the fluids suggest the existence between the magma reservoir and the surface of two intermediate different reservoirs, independently related to crater and to beach fumaroles.  相似文献   

Space—time correlations between inland earthquakes in central Japan and great offshore earthquakes along the Nankai trough: Implication for destructive earthquake prediction     

Yuji Kanaori  Shin-ichi Kawakami  Kenji Yairi 《Engineering Geology》1993,33(4):289-303

Based on the tectonic framework of central Japan, including the surrounding submarine areas, the space-time relationship between destructive inland earthquakes of magnitudesM 6.4 or greater and great offshore earthquakes along the Nankai trough was examined. From east to west, four tectonic lines are defined as lines linking active faults: the Itoigawa-Shizuoka tectonic line (ISTL), the Tsurugawan-Isewan tectonic line (TITL), the Hanaore-Kongo fault line (HKFL), and the Arima-Takatsuki tectonic line (ATTL). The TITL divides central Japan into the Chubu and Kinki districts, and probably extends southward to the Nankai trough. The Chubu district is subdivided into four blocks by boundary lines linking NW-SE trending active faults having left-lateral strike slip. In the Kinki district, N-S trending, active reverse, steep-dip faults are dominant in the triangular region north of the Median Tectonic line, between the TITL and HKFL, forming a basin-and-range province.

Starting from 1586 A.D., a seismic space-time sequence of high seismic activity in the Chubu district in which earthquake occurrence migrates from the eastern to western tectonic lines of central Japan was identified. The sequence also revealed that inland earthquakes preceded great offshore earthquakes which occurred along the Nankai trough. It was also found that a destructive earthquake tends to occur on the HKFL within 30 years after the occurrence on the TITL, and that the western Nankai trough generated great earthquakes ofM≥7.0 at intervals ranging from 8 to 49 years after the HKFL earthquakes. If the eastern Nankai trough is coupled with the western Nankai trough, a forthcoming greater earthquake measuringM 8.5 may be expected. Since such great earthquakes are always accompanied by large tsunamis, much attention should be focussed on possible tsunami disasters along the Pacific coast of central Japan.

Based on its tectonic structure, a tectonic model of central Japan is proposed. The seismic space-time sequence, which attempts to explain the cause of the sequential earthquake generation, is also discussed.  相似文献   

Terrestrial heat flow around the aseismic front of the Japanese Island Arc     

Yuji Nakamura  Hiroshi Wakita 《Tectonophysics》1982,81(1-2)

Very few data on heat flow are available in the area around the aseismic front of the Japanese Islands. In order to remedy this situation, measurements of the terrestrial heat flow were made at three locations in the eastern part of Fukushima Prefecture, northeastern Honshu, Japan. The observed values of heat flow were 37 mW/m² (0.88 μcal/cm²·s) at Soma, 52 mW/m² (1.25 μcal/cm²·s) at Kashima and 19 mW/m² (0.46 μcal/cm²·s) at Naraha, respectively. These data partially fill the gaps in the terrestrial heat flow data on land in northeastern Honshu, Japan. These values are considerably lower than the average heat flow over the world, but agree well with the previous estimation for the area.  相似文献