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51.
52.
The seasonally varying moisture balance in a montane forest of Southeast Asia is reconstructed for the 20th century from the oxygen isotopic composition (δ18O) of subannual tree cellulose samples of Pinus kesiya growing at 1,500?m elevation on Doi Chiang Dao in northern Thailand. The cellulose δ18O values exhibit a distinctive annual cycle with amplitude of up to 12?‰, which we interpret to represent primarily the seasonal cycle of precipitation δ18O. The annual mean δ18O values correlate significantly with the amount of summer monsoon precipitation, and suggest a temporal weakening relationship between the South Asian monsoon and El Ni?o-Southern Oscillation over the late 20th century. The cellulose δ18O annual maxima values, which reflect the dry season moisture status, have declined progressively over the 20th century by about 3.5?‰. We interpret this to indicate a change in the contribution of the isotopically distinct fog water to the dry season soil moisture in response to rising temperature as well as deforestation. 相似文献
53.
Taku Yoshimura Kenji Morinaga Seiji Oshimo Yoshinobu Konishi Tsuneo Goto 《新西兰海洋与淡水研究杂志》2013,47(2):591-604
The annual distribution and dispersal of early‐stage phyllosoma of the Japanese spiny lobster Panulirus japonicus were examined in the East China Sea and the Sea of Japan off western Japan. Early‐stage larvae were sampled mainly in summer and relatively near the coast off western Kyusyu Island. Few larvae were found in the other three seasons in the East China Sea and the Sea of Japan. This finding suggests that P. japonicus larvae are retained in coastal areas for a few months after hatching until stage V and are transported offshore until autumn, before they grow to stage VI. Examination of archival drifter data off western Kyusyu Island during the spawning season of P. japonicus supported the relatively rapid dispersal of the larvae from the East China Sea near Japan to the Pacific Ocean or the Sea of Japan. Larval transport from the East China Sea to the Pacific Ocean, which is considered to be a main distribution area of middle‐ and late‐stage larvae, would occur in the south at approximately 32–33°N in the East China Sea near western Kyusyu Island. 相似文献
54.
Solar Physics - A new concept concerning sunspot cooling and X-ray bright point heating is presented. Sunspot and X-ray bright point small scale flux ropes detach from global scale solar cycle main... 相似文献
55.
四川黄龙沟景区钙华的起源和形成机理研究 总被引：36，自引：5，他引：36
对四川黄龙沟钙华景区的水化学测试发现，形成黄龙沟钙华的泉水具有很高的Ca^2 和HC03^-离子浓度，相应地，泉水的C02分压显著高于大气和土壤生物成因所能产生的C02分压。结合泉水出露的地质条件和泉口C02气体碳稳定同位素组成(δ^13C＝—6．8‰)的分析，进一步发现，高C02分压与深部成因的C02有关。可见，黄龙沟钙华属于热成因类钙华，而非原来普遍认为的“是气候岩溶作用的产物”。此外，黄龙沟钙华的大量出现与水中方解石的迅速沉积、Ca^2 和HC03^-浓度的大量降低有关。随着地下水自泉口出露，由于水的C02分压远高于大气，水中C02大量释放于大气，结果水的pH值迅速升高，方解石饱和指数由泉口的负值很快转变为高的正值，为方解石的沉积奠定了必要的物理化学基础。放置于水中的大理岩石片观测表明，流速较快的边石坝处的方解石沉积速率是其附近水池内的2—5倍，这清楚地显示了水动力条件对沉积速率的控制。进一步根据DBL理论模型分析发现，水动力条件对方解石沉积速率的控制在于其对固液界面间扩散边界层(DBL)厚度的影响，流速愈快，DBL厚度愈薄。且DBL厚度最终制约着沉积表面的化学组成浓度，即厚度愈小，表面H^ 浓度愈低(或pH愈高)、方解石饱和指数愈高，进而方解石沉积愈快。 相似文献
56.
Beach erosion has advanced in many countries of the world, especially in Japan, because of a decrease in sediment sources from rivers and a lack of longshore sediment transport from the adjacent coasts due to coastal structures. The former cause concerns the reduction of river deltas due to a decrease in sediment input from the river. Two timescales important in beach erosion, a longer timescale which concerns a change in the location of the river mouth, and a shorter one which is due to a decrease in longshore sediment transport, are discussed in the formation and reduction of the delta of the Kurobe River. Based on these timescales, beach erosion control is considered. 相似文献
57.
AbstractFlow regimes play an important role in sustaining biodiversity in river ecosystems. However, the effects of flow regimes on riverine fish have not been clearly described. Therefore, we propose a new methodology to quantitatively link habitat conditions (such as flow indices and physical habitat conditions) to the occurrence probability (OP) of fish species. We developed a basin-scale fish distribution model by integrating the concept of habitat suitability assessment with a distributed hydrological model in order to estimate the OP of fish, with particular attention to flow regime. A generalized linear model was used to evaluate the relationship between the probabilities of fish occurrence and major environmental factors in river sections. A geomorphology-based hydrological model was adopted to simulate river discharge, which was used to calculate 10 flow indices. The occurrence probabilities of 50 fish species in the Sagami River in Japan were modelled. For the prediction accuracy, field survey results that included at least five observations of both the presence and the absence of each species were required to obtain relatively reliable prediction (accuracy > 60%). Using the developed model, important habitat conditions for each species were identified, which showed the importance of low-flow events for more than 10 species, including Hypomesus nipponensis and Rhinogobius fluviatilis. The model also confirmed the positive effects of natural flow and the negative effect of river-crossing structures, such as dams and weirs, on the OP of most species. The suggested approach enables us to evaluate and project the ecological consequences of water resource management policy. The results demonstrate the applicability of the fish distribution model to provide quantitative information on the flow required to maintain fish communities.
Editor Z.W. Kundzewicz; Guest editor M. AcremanCitation Sui, P., Iwasaki, A., Saavedra, V.O.C., and Yoshimura, C., 2013. Modelling basin-scale distribution of fish occurrence probability for assessment of flow and habitat conditions in rivers. Hydrological Sciences Journal, 59 (3–4), 618–628. 相似文献
58.
Winter precipitation isotope slopes of the contiguous USA and their relationship to the Pacific/North American (PNA) pattern 总被引：1，自引：0，他引：1
This study compares the synoptic-dynamic relationship between two phases of the Pacific/North American (PNA) pattern and winter precipitation isotopes at 73 sites across the contiguous USA. We use the spatial pattern of isotope slope—the rate of changes in precipitation isotope ratios with distance—to identify features in the seasonal precipitation isotope fields related to climatic patterns, PNA positive and PNA negative. Our results show relationships between zones of high isotope slopes and the spatial position of the polar jet stream and juxtaposition of air masses associated with the PNA pattern. During a positive PNA winter, zones of high isotope slope in the eastern USA shift southward. This change is coincident with a southward displacement of the polar jet stream in this region, which leads to a greater frequency of polar air masses and 18O-depleted isotope values of precipitation in the region. In the western USA, zones of high slope shift eastward during the positive PNA winter, associated with more frequent penetration of tropical air masses that bring 18O-enriched precipitation to the region. Differences in δ18O/temperature relationships between the PNA-positive and -negative winters and contrasting δ18O/temperature behaviors in the eastern and western USA provide support for the role of variation in moisture source and transport as a control on the isotopic patterns. These findings highlight the importance of synoptic climate driven by PNA pattern in determining the spatial patterns of precipitation isotopes and provide constraints on paleo-water isotope interpretation and modern isotope hydrological processes. 相似文献
59.
M. Ateia J. Ran M. Fujii C. Yoshimura 《International Journal of Environmental Science and Technology》2017,14(4):867-880
The quantity and quality of dissolved organic matters have been widely characterized by fluorescence spectroscopy, yet the relationship between the fluorescence properties of dissolved organic matters and its molecular composition remains poorly described in the literature. Here, we measured the fluorescence excitation–emission matrix of 17 well-characterized humic substance standards to determine a range of fluorescence parameters, including classical fluorescence indices (e.g., fluorescence index, biological index and humification index) and parameters derived from parallel factor analysis (e.g., component contribution). Relationships between humic substance’s fluorescence and compositional parameters were then statistically examined using canonical correspondence and simple correlation analyses. The canonical correspondence analysis generally suggested that most fluorescence parameters determined here are highly associated with the amount of aliphatic and aromatic compounds in humic substances. However, the correlation analysis between single molecular and fluorescence parameters indicated that the fluorescence properties of humic substances including the parallel factor analysis component contribution also significantly correlate well with several aspects of the molecular composition of humic substances, such as elemental composition, carbon species, acidic functional group and iron complexation. Overall, our results suggest that measurement of humic substance’s fluorescence is beneficial in understanding the molecular composition and environmental functions of dissolved organic matters in natural and engineered waters. 相似文献
60.
Hirokazu Yoshimura 《Astronomische Nachrichten》1994,315(3):189-203
In order to explore the mechanism of the solar cycle luminosity change observed by the Active Cavity Radiometer Irradiance Monitor (ACRIM) I experiment on board of the spacecraft Solar Maximum Mission, we examined running mean time profiles of the daily ACRIM data from the declining phase of solar cycle 21 to the rising phase of solar cycle 22. By comparing them with those of the daily sunspot number, integrated surface magnetic field flux, integrated He I 10830 Å line equivalent width data, and two kinds of data sets of the daily integrated Ca II K line index as indices of the surface magnetic activities, we found (i) that the running mean time profiles of the six independent data sets have several peaks and valleys in common in one solar cycle with time intervals on the order of a few hundreds of days, and (ii) that the peaks and valleys of the ACRIM data profiles followed the peaks and valleys of all the other five indices of the surface activities by 40 to 60 days. This time delay phenomenon suggests (i) that the luminosity modulation was not directly caused by dark and bright features of the surface magnetic activities that the other five indices represent, and (ii) that the missing sunspot radiative flux which was blocked by sub-surface magnetic flux tubes of sunspots and sunspot groups should be re-radiated 40 to 60 days after the surface emergence of the magnetic flux tubes. The concept of the time delay resolves the enigma of the missing sunspot radiative flux and the enigma of the ACRIM experiment that the luminosity dropped when a sunspot or a sunspot group appeared on the surface while the yearly mean of the luminosity decreased and increased along with the decrease and increase of the yearly sunspot number of the 11-year solar cycle. A model of the mechanism to understand these phenomena is presented and its application to other stars is suggested. 相似文献