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991.
Emissions of N2O, CH4, and CO2 from soils at two sites in the tropical savanna of central Venezuela were determined during the dry season in February 1987. Measured arithmetic mean fluxes of N2O, CH4, and CO2 from undisturbed soil plots to the atmosphere were 2.5×109, 4.3×1010, and 3.0×1013 molecules cm-2 s-1, respectively. These fluxes were not significantly affected by burning the grass layer. Emissions of N2O increased fourfold after simulated rainfall, suggesting that production of N2O in savanna soils during the rainy season may be an important source for atmospheric N2O. The CH4 flux measurements indicate that these savanna soils were not a sink, but a small source, for atmospheric methane. Fluxes of CO2 from savanna soils increased ninefold two hours after simulated rainfall, and remained three times higher than normal after 16 hours. More research is needed to clarify the significance of savannas in the global cycles of N2O, CH4, CO2, and other trace gases, especially during the rainy season. 相似文献
992.
993.
A. V. Pavlov 《Pure and Applied Geophysics》1988,127(2-3):529-544
Theoretical and experimental aspects of the production, transformation, diffusion and loss of N2 in the upper atmosphere are considered. The N2-CO2 near-resonant system in theD andE regions is taken into account. We describe our understanding of the methods necessary to find the vibrational populations of N2 and CO2 (asymmetric mode of CO2). The calculations of the vibrational temperatures in theD, E, andF regions for the mid-latitude ionosphere and an aurora are presented. The connection between the excited species and the 4.26-m radiation intensities is considered. The models for the rate coefficient of the reaction of O+ with N2 and the electron density decrease resulting from N2 in the F region are discussed. 相似文献
994.
995.
Attenuation of compressional waves in peridotite measured as a function of temperature at 200 MPa 总被引:3,自引:0,他引:3
Hiroki Sato I. Selwyn Sacks Tsutomu Murase Gregory Muncill Hiroyuki Fukuyama 《Pure and Applied Geophysics》1988,128(1-2):433-447
A technique has been developed to determine attenuation in rocks at high temperature using a gas-media, high-pressure apparatus. A pulse transmission technique and a spectral ratio method are used to study compressional seismic properties of rocks. Seismic waves are transmitted to and from the sample through buffer rods of mullite. The effect of seismic wave reflections within the sample assembly are cancelled out by taking ratios of the spectra measured at different temperatures. In order to obtain good signal-to-noise ratio for resolving the attenuation at high pressure and temperature, special care is taken in the sample assembly and the ultrasonic coupling between the sample, buffer rods and transducers. A very tight connection of the sample-buffer rod-transducer is essential for obtaining high frequency signals (>300 kHz) at high temperature. A small mass is attached to each outside end of the transducer to drive low frequency signals (<250 kHz) into the sample. Before attenuation measurements, the sample and the buffer rods are tightly compacted in a platinum tube at high pressure and room temperature to ensure pressure seal of the sample assembly. The frequency range of measurement covers 50 to 450 kHz for the sample. Attenuation is very small in the buffer rod compared to the sample for the entire temperature range of the study. Because of the small attenuation, a wide frequency band of 50 kHz to 3.2 MHz can be covered for investigating the attenuation in the buffer rod. The technique has been used to measure attenuation at high confining pressure, and temperatures including sub- and hyper-solidus of upper mantle rocks. Therefore, effects of partial melting on attenuation can be studied.The method is applied to the attenuation measurement in a peridotite as a function of temperature to 1225°C at 200 MPa confining pressure. At high temperature, signal amplitude decays more rapidly at high frequency than at low frequency, from which attenuation (andQ) can be determined using a spectral ratio method. No frequency dependence ofQ is resolved for both the sample and the buffer rod over the entire temperature and frequency ranges of the measurement. The results show thatQ decreases rapidly with increasing temperature even in the temperature range below the solidus of peridotites. Such temperature sensitivity ofQ is probably more useful to probe thermal structure in the upper mantle than that of conductivity at temperatures below the solidus. The results in this study are compared with available seismic velocity, electrical conductivity and solidus data for peridotites, suggesting that there is no discontinuous change in both mechanical and electrical properties of peridotites at the solidus temperature. Even at hypersolidus temperatures, it appears that velocity drops and conductivity increases continuously (not abruptly) with increasing melt fraction. This implies that mechanical and electrical properties of the upper mantle will gradually change at the boundary where the geotherm crosses the solidus. 相似文献
996.
997.
998.
Two microwave radiative transfer models of precipitating cloud are used to simulate the microwave upwelling radiances emerging from precipitating clouds. Comparison of the simulation results shows that significant difference of microwave upwelling radiances exists between these two radiative transfer models. Analysis of these differences in different cloud and precipitation conditions shows that it is complicated but has certain trend for different microwave frequencies. The results may be useful to quantitative rainfall rate retrieval of real precipitating clouds. 相似文献
999.
深源地震机理的新认识──反向裂隙断层作用 总被引:1,自引:0,他引:1
高温高压实验究表明,地幔矿物相交与深源地震有着密切的关系。在具有放热效应的橄榄石一尖晶石相变过程中形成的反向裂隙(anticrach)是诱发深源地震的主要原因;而发生在下地幔的相变作用(例如钛铁矿-钙钛矿相变)因其具有吸热效应的特征,不形成反向裂隙,从而导致深源地震终止于下地幔顶界。 相似文献
1000.
具有重要岩石学和构造学意义的科马提岩,最吸引人同时又最令人困惑的特征之一是它的鬣刺结构和分层构造。本文从喷出地表的岩桨冷凝时温度分布、熔体性质与结晶作用的密切联系,把科马提岩浆喷发形成的岩流作为一个冷凝整体。通过与金属铸锭浇注成形和矿石冶炼生产的比较,发现它们在冷凝固结过程中温度场特征、熔体的性质、结晶能力和结晶方式都有十分相似的特点,并以此为出发点详细解析了科马提岩的鬣刺结构和岩石分层构造的形成 相似文献