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1.
Concentrations of the halocrbons CCl(3)F (F-11), CCl(2)F(2) (F-12), CCl(4), and CH(3)CCl(3), methane (CH(4)), and nitrous oxide (N(2)O) over the decade between 1975 and 1985 are reported, based on measurements taken every January at the South Pole and in the Pacific Northwest. The concentrations of F-11, F-12, and CH(3)CCl(3) in both hemispheres are now more than twice their concentrations 10 years ago. However, the annual rates of increase of F-11, F-12, and CH(3)CC1(3) are now considerably slower than earlier in the decade, reflecting in part the effects of a ban on their nonessential uses. Continued increases in these trace gas concentrations may warm the earth and deplete the stratospheric ozone layer, which may cause widespread climatic changes and affect global habitability.  相似文献   

2.
Halogens influence the oxidizing capacity of Earth's troposphere, and iodine oxides form ultrafine aerosols, which may have an impact on climate. We report year-round measurements of boundary layer iodine oxide and bromine oxide at the near-coastal site of Halley Station, Antarctica. Surprisingly, both species are present throughout the sunlit period and exhibit similar seasonal cycles and concentrations. The springtime peak of iodine oxide (20 parts per trillion) is the highest concentration recorded anywhere in the atmosphere. These levels of halogens cause substantial ozone depletion, as well as the rapid oxidation of dimethyl sulfide and mercury in the Antarctic boundary layer.  相似文献   

3.
Determination of the atmospheric concentrations and lifetime of trichloroethane (CH(3)CCI(3)) is very important in the context of global change. This halocarbon is involved in depletion of ozone, and the hydroxyl radical (OH) concentrations determined from its lifetime provide estimates of the lifetimes of most other hydrogen-containing gases involved in the ozone layer and climate. Global measurements of trichloroethane indicate rising concentrations before and declining concentrations after late 1991. The lifetime of CH(3)CCI(3) in the total atmosphere is 4.8 +/- 0.3 years, which is substantially lower than previously estimated. The deduced hydroxyl radical concentration, which measures the atmosphere's oxidizing capability, shows little change from 1978 to 1994.  相似文献   

4.
Additional plasma measurements in the vicinity of Venus are presented which show that (i) there are three distinct plasma electron populations-solar wind electrons, ionosheath electrons, and nightside ionosphere electrons; (ii) the plasma ion flow pattern in the ionosheath is consistent with deflected flow around a blunt obstacle; (iii) the plasma ion flow velocities near the downstream wake may, at times, be consistent with the deflection of plasma into the tail, closing the solar wind cavity downstream from Venus at a relatively close distance (within 5 Venus radii) to the planet; (iv) there is a separation between the inner boundary of the downstream ionosheath and the upper boundary of the nightside ionosphere; and (v) during the first 4.5 months in orbit the measured solar wind plasma speed continued to vary, showing a number of high-speed, but generally nonrecurrent, streams.  相似文献   

5.
基于三维数值模式ECOM,建立了长江口以及近岸海域的水动力耦合盐度数值模式。该模式考虑了移动潮滩边界和深水航道等地形特点。计算结果与实测值比较符合良好,较好地放映了长江口区域盐度场的时空分布特点。模式模拟长江口盐水入侵的三维特征,表层盐度较低而底层盐度较高。利用此模式计算了2003年2月枯季大、小潮时期,在长江口代表性的断面处2个连续潮周期内的盐通量情况。2月1-2日大潮期间北支SEC01、SEC02断面分别为3333600t、957600t,崇头SEC03、SEC04断面分别为-270000t、-71640t,南支SEC05、SEC06断面分别为1364400t、1512000t;2月7-8日小潮期间北支SEC01、SEC02断面分别为205200t、82800t,崇头SEC03、SEC04断面分别为-36360t、-12960t,南支SEC05、SEC06断面分别为309600t、28800t。计算结果显示长江口枯季大、小潮期间盐量变化明显,枯季大潮时期外海向长江口区域输送了巨量的盐分,盐水直接入侵十分明显。此计算结果可为以后在长江口建立相应的挡咸蓄淡工程方案提供重要的科学依据。  相似文献   

6.
Plasma observations at Jupiter show that the outer regions of the Jovian magnetosphere are remarkably similar to those of Earth. Bow-shock precursor electrons and ions were detected in the upstream solar wind, as at Earth. Plasma changes across the bow shock and properties of the magnetosheath electrons were much like those at Earth, indicating that similar processes are operating. A boundary layer populated by a varying mixture of solar wind and magnetospheric plasmas was found inside the magnetopause, again as at Earth. In the middle magnetosphere, large electron density excursions were detected with a 10-hour periodicity as planetary rotation carried the tilted plasma sheet past Ulysses. Deep in the magnetosphere, Ulysses crossed a region, tentatively described as magnetically connected to the Jovian polar cap on one end and to the interplanetary magnetic field on the other. In the inner magnetosphere and lo torus, where corotation plays a dominant role, measurements could not be made because of extreme background rates from penetrating radiation belt particles.  相似文献   

7.
A combination of experimental, molecular dynamics, and kinetics modeling studies is applied to a system of concentrated aqueous sodium chloride particles suspended in air at room temperature with ozone, irradiated at 254 nanometers to generate hydroxyl radicals. Measurements of the observed gaseous molecular chlorine product are explainable only if reactions at the air-water interface are dominant. Molecular dynamics simulations show the availability of substantial amounts of chloride ions for reaction at the interface, and quantum chemical calculations predict that in the gas phase chloride ions will strongly attract hydroxl radicals. Model extrapolation to the marine boundary layer yields daytime chlorine atom concentrations that are in good agreement with estimates based on field measurements of the decay of selected organics over the Southern Ocean and the North Atlantic. Thus, ion-enhanced interactions with gases at aqueous interfaces may play a more generalized and important role in the chemistry of concentrated inorganic salt solutions than was previously recognized.  相似文献   

8.
The oxidizing capacity of the global atmosphere is largely determined by hydroxyl (OH) radicals and is diagnosed by analyzing methyl chloroform (CH(3)CCl(3)) measurements. Previously, large year-to-year changes in global mean OH concentrations have been inferred from such measurements, suggesting that the atmospheric oxidizing capacity is sensitive to perturbations by widespread air pollution and natural influences. We show how the interannual variability in OH has been more precisely estimated from CH(3)CCl(3) measurements since 1998, when atmospheric gradients of CH(3)CCl(3) had diminished as a result of the Montreal Protocol. We infer a small interannual OH variability as a result, indicating that global OH is generally well buffered against perturbations. This small variability is consistent with measurements of methane and other trace gases oxidized primarily by OH, as well as global photochemical model calculations.  相似文献   

9.
By providing cold, dense water that sinks and mixes to fill the abyssal world ocean, high-latitude air-sea-ice interaction is the main conduit through which the deep ocean communicates with the rest of the climate system. A key element in modeling and predicting oceanic impact on climate is understanding the processes that control the near surface exchange of heat, salt, and momentum. In 1992, the United States-Russian Ice Station Weddell-1 traversed the western Weddell Sea during the onset of winter, providing a platform for direct measurement of turbulent heat flux and Reynolds stress in the upper ocean. Data from a storm early in the drift indicated (i) well-formed Ekman spirals (in both velocity and turbulent stress); (ii) high correlation between mixed layer heat flux and temperature gradients; (iii) that eddy viscosity and eddy thermal diffusivity were similar, about 0.02 square meters per second; and (iv) that the significant turbulent length scale (2 to 3 meters through most of the boundary layer) was proportional to the wavelength at the peak in the weighted vertical velocity spectrum. The measurements were consistent with a simple model in which the bulk eddy viscosity in the neutrally buoyant mixed layer is proportional to kinematic boundary stress divided by the Coriolis parameter.  相似文献   

10.
不同灌木覆盖状态下防风机理研究   总被引：2，自引：0，他引：2  
.通过野外观测,定量研究毛乌素沙地西南缘不同灌木覆盖状态下的防风机理。以沙蒿灌木林地和沙柳灌木 林地为研究对象,裸沙地作为对照,用多剖面自计式遥测风速仪连续观测、记录距离地面0.1、0.5、1.0、2.0、3.0、 4.0、5.0 和6.0 m 8 个不同垂直高度位置的风速变化。通过对风速测定结果的统计分析,绘制3 种状态下的风速廓 线图,并计算风速廓线方程、边界层位移厚度、边界层动量损失厚度和空气动力学粗糙度。结果表明:沙蒿灌木林 和沙柳灌木林在近地层较裸露沙地有明显的降低风速作用,随着风速增大这种作用逐渐减弱。不同地表覆盖的空 气动力学粗糙度随着风速的增大而呈对数减小。当风速较大时,边界层位移厚度比空气动力学粗糙度能更实际地 反映整体观测高度范围内风速降低的状况。从空气动量的角度分析,有植被覆盖的地表空气动量损失比较稳定, 裸沙地的空气动量损失则随风速增大而减小。   相似文献   

11.
提出了一种检测斜拉索PE保护层表面伤痕算法的设计。首先,在图像的预处理阶段,对原始图像进行灰度化和滤波处理;其次,运用边缘检测、边界跟踪及Hough变换获得了拉索轮廓的连续边界;然后,利用原始的灰度图像和基于拉索轮廓的掩模板,获得了无背景的拉索表面图像;最后,通过基于图像间空间差分的伤痕检测算法,获得斜拉桥拉索表面伤痕的图像,结果表明该算法能有效地从爬升机器人采集的图像中提取出斜拉索PE保护层表面伤痕的图像。  相似文献   

12.
[目的]分析不同边界层参数化方案对此次暴雨过程中物理量场的影响。[方法]利用WRF模式3.4版本,选取不同边界层参数化方案对"7.18"山东暴雨过程进行敏感性试验,分析不同边界层参数化方案对此次暴雨过程中垂直速度场、水汽通量散度场、相对湿度、对流有效位能和边界层高度等物理量场的影响。[结果]不同的边界层参数化方案对于暴雨过程中垂直速度场的空间分布及其中心强度具有显著的影响,从而使得降水中心的分布和强度发生变化。尽管不同边界层参数化方案模拟得到的水汽通量散度在水平分布与实际结果具有较好的一致性,但其在垂直分布、中心位置及其强度上存在明显的差异。不同边界层参数化方案引起的边界层高度和对流有效位能的差异与其引起的降水分布差异直接相关。[结论]WRF模式中不同边界层参数化方案对暴雨过程中不同物理量场模拟效果的影响较大,选择合适的边界层参数化方案能显著提高对物理量场的模拟效果。  相似文献   

13.
The phase boundary between spinel (gamma phase) and MgSiO3 perovskite + MgO periclase in Mg2SiO4 was determined by in situ x-ray measurements by a combination of the synchrotron radiation source (SPring-8) and a large multianvil high-pressure apparatus. The boundary was determined at temperatures between 1400 degrees to 1800 degreesC, demonstrating that the postspinel phase boundary has a negative Clapeyron slope as estimated by quench experiments and thermodynamic analyses. The boundary was located at 21.1 (+/-0.2) gigapascals, at 1600 degreesC, which is approximately 2 gigapascals lower than earlier estimates based on other high-pressure studies.  相似文献   

14.
The objective of this study was to investigate the effect of different geometric sizes of wind tunnels on aerial boundary layers above the emission surface and therefore their effect on ammonia emission using CFD tool. Five wind tunnels of different sizes were used for the CFD simulation. Detail experimental measurements on air velocity and concentration profiles above the emission surface were realised using average inlet velocities of 0.1, 0.2, 0.3, and 0.4 m s−1 in two wind tunnels under isothermal condition. The TAN (Total Ammoniacal Nitrogen) and pH of ammonia aqueous solution were kept constant during the experiments. The boundary conditions necessary for the CFD study were obtained from the measured experimental data. The CFD model used for simulations was first validated using the data from the two wind tunnel experiments. For assessing the effects of wind tunnel size, the air velocity range of 0.1-0.6 m s−1 was used in CFD investigations. It was found that the velocity and concentration boundary layer thickness decreased with the increase of inlet air velocity where the concentration boundary was thinner than the corresponding velocity boundary layer. Wind tunnel sizes affected both velocity and concentration boundary layer thicknesses (P < 0.001). The velocity and concentration boundary layer was thicker in a wind tunnel with larger heights than in small height. The over estimation of ammonia emission of smaller wind tunnels were observed comparing to the largest wind tunnel or open field situation (P < 0.001). Non-linear regression equations were developed using four wind tunnels data for velocity boundary layer thickness (δu), concentration boundary layer thickness (δc), and ammonia mass transfer coefficient (kG) as a function of wind tunnel height (H) and average inlet velocity (um), which given clear quantitative indication of effects of H, and um on δu, δc, and kG, respectively.  相似文献   

15.
New particle formation in a tropical marine boundary layer setting was characterized during NASA's Pacific Exploratory Mission-Tropics A program. It represents the clearest demonstration to date of aerosol nucleation and growth being linked to the natural marine sulfur cycle. This conclusion was based on real-time observations of dimethylsulfide, sulfur dioxide, sulfuric acid (gas), hydroxide, ozone, temperature, relative humidity, aerosol size and number distribution, and total aerosol surface area. Classic binary nucleation theory predicts no nucleation under the observed marine boundary layer conditions.  相似文献   

16.
Extensive measurements of low-energy positive ions and electrons in the vicinity of Uranus have revealed a fully developed magnetosphere. The magnetospheric plasma has a warm component with a temperature of 4 to 50 electron volts and a peak density of roughly 2 protons per cubic centimeter, and a hot component, with a temperature of a few kiloelectron volts and a peak density of roughly 0.1 proton per cubic centimeter. The warm component is observed both inside and outside of L = 5, whereas the hot component is excluded from the region inside of that L shell. Possible sources of the plasma in the magnetosphere are the extended hydrogen corona, the solar wind, and the ionosphere. The Uranian moons do not appear to be a significant plasma source. The boundary of the hot plasma component at L = 5 may be associated either with Miranda or with the inner limit of a deeply penetrating, solar wind-driven magnetospheric convection system. The Voyager 2 spacecraft repeatedly encountered the plasma sheet in the magnetotail at locations that are consistent with a geometric model for the plasma sheet similar to that at Earth.  相似文献   

17.
【目的】定量分析干旱区农田撂荒前后土壤甲烷(CH4)排放通量的日变化,着重探讨影响土壤CH4排放的环境因子,为解释人类活动对该地区农田生态系统的土壤CH4排放的影响提供数据支持。【方法】用静态箱法结合Li-7700快速CH4分析仪(Li-7700,Li-cor Inc,USA)对艾比湖地区农田生态系统中棉田及撂荒地生长季(2010年8月)的土壤CH4排放浓度和密度进行实时测定,并分析水热因子对土壤CH4排放的影响。【结果】棉田、撂荒地CH4排放具有较明显的昼夜变化,棉田呈双峰曲线,撂荒地呈单峰或双峰曲线。在观测时间内,10 a棉田的平均通量为2.23 mg/(m2.h),最大值为61.01 mg/(m2.h),最小值为-41.05 mg/(m2.h);10 a撂荒地的平均通量为-3.90 mg/(m2.h),最大值为50.25 mg/(m2.h),最小值为-87.39mg/(m2.h)。棉田、撂荒地土壤CH4排放与土壤含水量、空气相对湿度相关不显著;所有样地CH4排放量与15、20 cm的土壤温度相关性最高(相关系数:棉田为-0.70,-0.71;撂荒地为-0.52,-0.52,P<0.01);综合考虑水分、温度因素可以解释土壤CH4排放变化的70.60%～85.61%,这比单独考虑水分或温度对土壤CH4排放变化的解释度都高。【结论】棉田是土壤CH4微弱的源,撂荒地是土壤CH4微弱的汇,水分、温度是影响生长季棉田和撂荒地土壤CH4排放变化最主要的环境因子。  相似文献   

18.
CH4是引起全球变暖的温室气体之一,土壤是CH4的重要排放源和汇,土壤CH4的研究对控制CH4排放、延缓气候变暖具有重要意义。在介绍土壤CH4产生与排放机理的基础上,概述了土壤理化特性、土地利用方式、农业管理措施等对土壤CH4排放的影响,并在此基础上对土壤CH4及其他温室气体的研究进行了展望。  相似文献   

19.
中国稻田甲烷排放及其影响因素的统计分析   总被引：13，自引：3，他引：10  
魏海苹  孙文娟  黄耀 《中国农业科学》2012,45(17):3531-3540
【目的】阐明中国不同稻作类型CH4排放的区域特征以及稻田CH4排放与环境因子和水肥管理的定量关系。【方法】通过文献调研,获得1987-2011年中国稻田CH4排放观测的有效文献111篇,含生长季CH4排放总量或平均排放通量的有效观测数据495组,涵盖67个观测点。采用方差分析、相关分析和逐步回归方法对上述观测数据进行分析。【结果】中国单季稻、双季早稻和晚稻田的CH4季节排放总量（均值±标准误差）分别为（383.5±31.1）、（234.3±16.8）和（361.8±25.0）kg•hm-2。西南单季稻区CH4排放分别是华北、华中和东北单季稻区的2.3、2.2和4.3倍;华中早、晚稻区的CH4排放分别是两广早、晚稻区的2.6和1.9倍。稻田CH4排放与有机肥施用量呈正相关,与化肥氮施用量及土壤pH呈负相关;单季稻区CH4排放随纬度升高和经度增加而降低,双季稻区CH4排放则随纬度升高而增加;单季稻区CH4排放随土壤全氮含量的增加而降低,但晚稻区则反之。综合影响中国单季稻田CH4排放的因子为纬度、土壤C/N比、砂粒含量、水分管理方式、有机肥和化肥氮施用量,这6个因子的变化可解释CH4排放空间变异的72%;早稻田CH4排放空间变异的35%可由土壤C/N比、砂粒含量、移栽-抽穗期平均温度、水分管理和有机肥施用量等5个因子的变化得以解释;纬度、土壤C/N比、黏粒含量、pH值、全生育期平均温度和有机肥施用量等6个因子可解释中国晚稻田CH4排放空间变异的47%。【结论】中国稻田单位面积CH4排放量总体为单季稻＞晚稻＞早稻,但单季稻与晚稻田的CH4排放无显著差异。西南单季稻区的CH4排放显著高于其它单季稻区,华中双季稻区的CH4排放显著高于两广稻区。由环境和水肥管理因子决定的多元统计模型能较好地解释中国稻田CH4排放的空间变异,单季稻CH4排放模型的可解释性优于双季稻。  相似文献   

20.
Bennett radio-frequency ion mass spectrometers have returned the first in situ measurements of the Venus dayside ion composition, including evidence of pronounced structural variability resulting from a dynamic interaction with the solar wind. The ionospheric envelope, dominated above 200 kilometers by O(+), responds dramatically to variations in the solar wind pressure, Which is observed to compress the thermal ion distributions from heights as great as 1800 kilometers inward to 280 kilometers. At the thermal ion boundary, or ionopause, the ambient ions are swept away by the solar wind, such that a zone of accelerated suprathermnal plasma is encountered. At higher altitudes, extending outward on some orbits for thousands of kilometers to the bows shock, energetic ion currents are detected, apparently originating from the shocked solar wind plasma. Within the ionosphere, observations of pass-to-pass differences in the ion scale heights are indicative of the effects of ion convection stimlulated by the solar wind interaction.  相似文献   

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