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41.
Late Holocene record of environmental changes,cyclones and tsunamis in a coastal lake,Mangaia, Cook Islands 下载免费PDF全文
A 4.3 m‐long peat sequence from the shore of Lake Tiriara, Mangaia, Cook Islands, was analyzed using an ITRAX core scanner equipped with a magnetic susceptibility meter. Variations in the elemental profiles, providing insights into long‐ and short‐term environmental changes over the last 3500 years, are supported by grain size data and diatom assemblages. The scattering ratio (Mo Inc/Mo Coh) was evaluated and found to represent a good proxy for organic matter in peat. X‐Ray Fluorescence (XRF) data were processed by principal component analysis that confirmed the distinction of biogenic and detrital phases, organic matter and elements of marine origin. The record preserved in the peat sequence includes a peatland infilling stage followed by alternating drier and wetter periods. A notable steady increase in clay associated with high counts of detrital elements from 2000–1700 cal yr BP is attributed to increased erosion, which is most probably linked with human colonization and/or more intense chemical weathering linked with a wetter climate. Freshwater gastropods (Melanoides sp.), which were possibly introduced by humans, or are native, occupied the wetland during a period of lower water level about 1000–1100 cal yr BP. Short‐term changes in the elemental profiles are often linked with slight coarsening of the inorganic fraction that is, however, only revealed after grain size analysis. Peaks in marine indicators (Br, Cl, S, and/or Ca) associated with marine‐dominated diatom assemblages most probably represent marine incursions through the underground tunnel in the makatea, a fossilized, uplifted coral limestone rim. While none of the marine event units present characteristics typical of cyclone or tsunami deposits, the concurrent or absent peak of detrital elements (Fe, Si, Rb, Ti, K) attributed to increased erosion of the volcanic cone associated with a cyclone is used to distinguish both types of events, as also suggested by principal component analysis. 相似文献
42.
Tsunami deposit associated with the 2011 Tohoku‐oki tsunami in the Hasunuma site of the Kujukuri coastal plain,Japan 下载免费PDF全文
Dan Matsumoto Yuki Sawai Koichiro Tanigawa Osamu Fujiwara Yuichi Namegaya Masanobu Shishikura Kyoko Kagohara Haruo Kimura 《Island Arc》2016,25(5):369-385
We describe the detailed sedimentary characteristics of a tsunami deposit associated with the 2011 Tohoku‐oki tsunami in Hasunuma, a site on the Kujukuri coastal plain, Japan. The thick tsunami deposit was limited to within 350 m from the coastline whereas the inundation area extended about 1 km from the coastline. The tsunami deposit was sampled by excavation at 29 locations along three transects and studied using peels, soft‐X imaging and grain‐size analysis. The deposit covers the pre‐existing soil and reached a maximum measured thickness of 35 cm. It consists mainly of well‐sorted medium to fine sand. On the basis of sedimentary structures and changes in grain size, we divided the tsunami deposit into several sedimentary units, which may correspond to multiple inundation flows. The numbers of units and their sedimentary features vary among the three transects, despite the similar topography. This variation implies a considerable influence of local effects such as elevation, vegetation, microtopography, and distance from footpaths, on the tsunami‐related sedimentation. 相似文献
43.
本文对6年春运期江苏附近几个经圈和纬圈850hPa温度格点序列, 分别计算15-25天带通滤波。结果表明110°E和35°N剖面的低频波与江苏连阴 雨(雪)天气过程有较好的对应关系。 相似文献
44.
The extratropical transitions(ETs)of tropical cyclones(TCs)over China and the ocean east to 150°E are investigated by the use of best-track data and JRA-25 reanalysis spanning 1979-2008.The ET events occurring north of 25°N and in the warm season(from May to October)are extracted from the reanalysis to emphasize the interaction between TC and midlatitude circulation.Statistical analysis shows that 18.5%of the warm-season TCs go through land ETs north of 25°N in the western North Pacific.And 20.5%of the ET events occur over the ocean east of 150°E.Most(62.2%)ET TCs over China gradually die out after ET,but more(70.7%)ocean ET cases have post-ET reintensification.The evolutions in cyclone phase space and the composite fields for land and ocean ETs,as well as the ET cases with and without post-ET reintensification,are further analyzed.It is found that most TCs with ET over China and those without post-ET reintensification evolve along the typical ET phase path as follows:emergence of thermal asymmetry→losing upper-level warm core→losing lower-level cold core→evolving as extratropical cyclone.The TCs undergoing ETs over ocean and those with post-ET reintensification form a high-level cold core before the ET onset.The TCs with land ET have long distance between the landing TC and a high-level trough.That makes the TC maintain more tropical features and isolates the TC flow from the upstream and downstream jets of the midlatitude trough.The structure of circulation leads to weak development of baroclinicity in land ET.On the contrary,shorter distance between ocean TC and high-level trough makes the high-level trough absorb the TC absolutely.Under that baroclinicity-favorable environment,strong cold advection makes the TC lose its high-level warm core before ET onset.The composite fields confirm that the TC with ocean ET has stronger baroclinic features.Generally,the TC at land ET onset is located to the south of the ridge of the subtropical high,which tends to prevent the TCs from interacting with midlatitude circulation.But for the ocean ET,the situation is just the opposite.Similar analyses are also carried out for the TCs with and without post-ET reintensification over both land and ocean east of 150°E.The results further prove that the TC with stronger baroclinic characteristics,especially in the circumstance favorable to its interaction with high-level midlatitude systems,has more opportunity to reintensify as an extratropical cyclone after ET. 相似文献
45.
A numerical model for the computation of the wind field,air temperature and humidity in the atmospheric boundary layer (ABL) including the urbancanopy was developed for urban climate simulation. The governing equations of the modelare derived by applying ensemble and spatial averages to the Navier–Stokes equation, continuityequation and equations for heat and water vapour transfer in the air. With the spatial averagingprocedure, effects of buildings and other urban structures in the urban canopy can be accounted for byintroducing an effective volume function, defined as the ratio between the volume of air in acomputational mesh over the total volume of the mesh. The improved k - model accounts for the anisotropyof the turbulence field under density stratification. In the improved k - model, the transportof momentum and heat in the vertical direction under density stratification is evaluated based onthe assumption of a near-equilibrium shear flow where transport effects on the stresses andheat fluxes are negligible. The heating processes at surfaces of buildings and ground are alsomodelled. The comparison of the computational results obtained with the present modeland existing observational data and numerical models shows that the present model is capableof predicting the structure of turbulence in the urban canopy layer under density stratification.Numerical experiments with the new model show that the flow behaviour of the air in the urbancanopy layer is strongly affected by the existence of buildings and density stratification. 相似文献
46.
We present photometric observations of Centaur (60558) 2000 EC98 and trans-neptunian object (55637) 2002 UX25 at different phase angles and with different filters (mainly R but also V and B for some data). Results for 2000 EC98 are: (i) a rotation period of 26.802±0.042 h if a double-peaked lightcurve is assumed, (ii) a lightcurve amplitude of 0.24±0.06 for the R band, (iii) a phase curve with H=9.03±0.01 and G=−0.39±0.08 (R filter) and H=9.55±0.04 and G=−0.50±0.35 (V filter) or a slope of (R filter) and 0.22±0.06 (V filter), (iv) the color indices B-V=0.76±0.15 and V-R=0.51±0.09 (for α=0.1-0.5°) and 0.55±0.08 (for α=1.4-1.5°). The rotation period is amongst the longest ever measured for Centaurs and TNOs. We also show that our photometry was not contaminated by any cometary activity down to magnitude ?27/arcsec2. For 2002 UX25 the results are: (i) a rotation period of 14.382±0.001 h or 16.782±0.003 h (if a double-peaked lightcurve is assumed) (ii) a lightcurve amplitude of 0.21±0.06 for the R band (and the 16.782 h period), (iii) a phase curve with H=3.32±0.01 and G=+0.16±0.18 or a slope of (R filter), (iv) the color indices B-V=1.12±0.26 and V-R=0.61±0.12. The phase curve reveals also a possible very narrow and bright opposition surge. Because such a narrow surge appears only for one point it needs to be confirmed. 相似文献
47.
Thomas R. Gregory Christopher W. Smart Malcolm B. Hart Guillaume Massé Lindsay L. Vare Simon T. Belt 《第四纪科学杂志》2010,25(6):903-910
Holocene changes in the benthic and planktic foraminiferal fauna (>63 µm) from a marine sediment core (ARC‐3 Canadian Arctic Archipelago, 74° 16.050′ N, 91° 06.380′ W, water depth 347 m) show that significant environmental and palaeoceanographic variations occurred during the last 10 ka. Foraminiferal assemblages are restricted to the ca. 4.5–10 ka interval as younger samples are mostly barren of foraminifera due to intense carbonate dissolution after ca. 4.5 ka. Foraminiferal assemblages in the ca. 4.5–10 ka interval are dominated by the benthic species Islandiella helenae and Cassidulina reniforme (57% of total), with Elphidium clavatum, Cibicides lobatulus and Buccella frigida also being common in this interval. The dominance of these species indicates a seasonal sea ice regime which is consistent with the occurrence of the sea ice diatom‐derived organic geochemical biomarker IP25 throughout the core. The abundances of C. reniforme and E. clavatum decline upcore; consistent with more frequent mixing of the Barrow Strait water column during the early Holocene. It is likely that the influence of CO2‐rich Arctic surface water masses have caused an increase in bottom water corrosivity after ca. 8.5 ka, and dissolution has been further enhanced by sea ice‐related processes after ca. 6 ka, concomitant with increased IP25 fluxes. Dissolution is strongest when IP25 fluxes are highest, suggesting a link between the sea ice and benthic systems. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
48.
尝试地运用1/2.5万不规则网土壤地球化学测量方法,对吉林省珲春市小西南岔金铜矿外围某勘查区的1/20万区域化探直接进行了查证,圈出两处地球化学综合异常,异常主成矿元素Au、Cu异常连续,浓集中心突出,浓度分带清晰,与伴生的As、Bi、Pb、Ag、Zn等元素异常套合较好,具有指导找矿作用。 相似文献
49.
50.
Ayesha Begum Jayaram N. Chengalur 《Monthly notices of the Royal Astronomical Society》2005,362(2):609-611
We present a deep Giant Metrewave Radio Telescope (GMRT) search for H i 21-cm emission from three dwarf galaxies, viz. POX 186, SC 24 and KKR 25. Based, in part, on previous single-dish H i observations, these galaxies have been classified as a blue compact dwarf (BCD), a dwarf irregular and a transition galaxy, respectively. However, in conflict with previous single-dish detections, we do not detect H i in SC 24 or KKR 25. We suggest that the previous single-dish measurements were probably confused with the local Galactic emission. In the case of POX 186, we confirm the previous non-detection of H i but with substantially improved limits on its H i mass. Our derived upper limits on the H i mass of SC 24 and KKR 25 are similar to the typical H i mass limit for dwarf spheroidal (dSph) galaxies, whereas in the case of POX 186, we find that its gas content is somewhat smaller than is typical of BCD galaxies. 相似文献