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141.
Low-level katabatic wind profiles, which have shapes similar to those of the low-level jet (LLJ) wind profiles, are often observed during strong winds in the summer period at Mizuho Station, which is located at 70°42 S, 44°20 E in East Antarctica. The profiles may be classified according to the height of the maximum wind speed, z m , found below 30 m height. The behavior of z m and of conditions in the layer above z mare explained well by the normalized frequency, f N = Nz/U at 30 m, whose value can be used to predict the existence of a LLJ wind profile. Subsidence and inertial oscillations above z m are related closely to the height and time variations of z m. Thus, not only effects emanating upward from surface but also momentum and heat transported downward from above are significant for the evolution of z m.  相似文献   
142.
The turbulent structure of the planetary boundary layer (PBL) is investigated based on measurements from a 213 m meteorological tower. It is found that the sensible heat flux decreases with height, resulting in a temperature increase during the daytime. On the other hand, the water vapor flux is almost constant with height and the diurnal variation of specific humidity is not so clear. Time variations of sensible heat flux and water vapor flux are closely correlated to the variation of net radiation and some differences are seen in their response times. Transient processes in the mixed layer including those related to the moisture structure are also investigated during periods of development and disappearance of the layer.  相似文献   
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144.
Bulk transfer coefficients were evaluated from eddy correlation flux measurements on a fixed pier during onshore winds. The mean values are C D = 1.69 × 10-3, C H = 2.58 × 10-3 and C E = 1.51 × 10-3. The drag coefficient, C D, gradually increases with wind speed but C H and C E are independent of wind speed. According to theory and empirical formulas based on experimental results over flat grassland, the transfer coefficients should gradually increase with increasing instability. This is confirmed experimentally in the stable region in our case. However, the drag coefficient appears to decrease with increasing instability, which is against the theoretical result. A stability dependence is not clearly observed for C H or C E.  相似文献   
145.
146.
Abstract. The Onsen site is an active submarine hydrothermal system hosted by the Desmos caldera in the Eastern Manus Basin, Papua New Guinea. The hydrothermal fluid is very acidic (pH=1.5) and abundant native sulfur is deposited around the vent. The δ34S values of native sulfur range from -6.5 to -9.3 %o. δ34S values of H2S and SO4 in the hydrothermal fluid are -4.3 to -9.9 %o and +18.6 to +20.0 %o, respectively. These δ34S values are significantly lower than those of the other hydrothermal systems so far reported. These low δ34S values and the acidic nature of the vent fluids suggest that volcanic SO2 gas plays an important role on the sulfur isotope systematic of the Onsen hydrothermal system. Relationship among the δ34S values of S-bearing species can be successively explained by the model based on the disproportionation reaction starting from the volcanic SO2 gas. The predicted δ34S values of SO2 agree with the measured whole rock δ34S values. δD and δ18O values of clay minerals separated from the altered rock samples also suggest the contribution of the magmatic fluid to the hydrothermal system. Present stable isotopic study strongly suggests that the Onsen hydrothermal site in the Desmos caldera is a magmatic submarine hydrothermal system.  相似文献   
147.
Meteorological observation by a helicopter was carried out to investigate the structure of sea breezes over the coastal area of Tosa Bay in Shikoku island, Japan. Several groups of wave trains were found over the sea during a flight made on 25 November 1992. Not only the terrain barrier but the remaining cold air pools formed in valleys hindered further advance of the sea breeze inland, so that the presence of such wave trains may appear to be due to the effect of the secondary flow which supplies moister and cooler air from behind the sea breeze front.  相似文献   
148.
Recent statistical analyses on the isotopic compositions of oceanic, arc, and continental basalts have revealed that the Earth's mantle is broadly divided into eastern and western hemispheres. The present study aimed to characterize the isotopically defined east–west geochemical hemispheres using trace-element concentrations. Basalt data with Rb, Sr, Nd, Sm, Pb, Th, and U in addition to the isotopic ratios 87Sr/86Sr, 143Nd/144Nd, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb were selected mostly from the GEOROC and PetDB databases. A total of 4787 samples were used to investigate the global geochemical variations. The results show that the wide trace-element variations are broadly explained by the melting of melt-metasomatized and fluid-metasomatized mantle sources. The larger amount of the fluid component derived from subducted plates in the eastern hemisphere than that in the western hemisphere is inferred from the basalts. These characteristics support the hypothesis that focused subduction towards the supercontinent created the mantle geochemical hemispheres.  相似文献   
149.
Palau Islands, 7°30′N, are the only emergent feature on the more than 2500‐km‐long Kyushu–Palau Ridge. Small islands are mainly uplifted reef carbonate. Larger islands are volcanic with basalt to dacite and rare boninite. Polymict breccia is abundant: sills, flows, and dykes are common but pillows are rare. Palau Trench samples include all types found on the islands as well as high‐Mg basalt. Volcanism began in the late Eocene and ended by early Miocene. All igneous rocks comprise a low‐K primitive island arc‐tholeiite series. None are mid‐ocean ridge basalts. Rare earth elements and high field‐strength elements indicate a depleted mantle source. Elevated large ion lithophile elements and light rare earth elements indicate influx of ‘dehydration fluid’. Ce/Ce* and Eu/Eu* ratios show no evidence for recycling of arc‐derived clastics. Plate reconstructions and paleomagnetic data suggest that the arc probably formed on the trace of a transform fault that migrated northward and rotated clockwise up to 90°. Episodes of transtension caused upwelling of hot mantle into depleted mantle and sheared altered rocks of the transform. Episodes of transpression may have initiated subduction of old seafloor with a thin cover of pelagic sediments deposited far from terrigenous sediment sources.  相似文献   
150.
人类活动与天山现代冰川退缩   总被引:6,自引:1,他引:5  
在系统分析了中亚天山山两个长期进行物质平衡监测的乌鲁木齐河源1号冰川和图尤克苏冰川的资料,并引用其他研究成果后,发现中亚天山现代冰川1970年-1990年比1930年-1970年明显的退化。近20年多来,中亚天山冰川加速退缩,解体,与被工业排放污染了大气有关。  相似文献   
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