海水中^214Bi水平分布变化的研究

海水中２１４Ｂｉ水平分布变化的研究О．В．Ｇепанец等在解决海水动力学问题时，在很多情况下，同位素参数比标准水文学参数——温度和盐度更具有代表性。放射性“示踪剂”具有一定的半衰期，并载有一些特殊信息：水文物理过程的持续时间和强度。各种物质的迁移速...     

丹麦在地理信息系统方面的经验

现在很多机构组织正在建立信息系统，并且不少系统已经存在。如果建立的是地下信息系统，地理定位将很快得到解决。在丹麦，新生产的地图都要求是数学地图，并且在１９９２－１９９３年以数学地图覆盖全国。此外，许多公用设施注册登记已计算机化。大量的其它信息源，象公用设施网仍需转换。促成这些发展要依靠许多不同的私人组织和政府的组织，本文将论述在激烈的竞争中如何努力协调各项发展工作。由于大例尺与小比例尺存在明显的差     

Terra卫星及其5种新一代遥感探测仪

美国国家航空和航天局(ＮＡＳＡ)地球系统科学委员会(ＥＳＳＣ)在1988年提出了一份研究指导性报告,建议为监测地球变化、测定地球的各种重要信号而建立一项长期战略计划。美国国会迅速作出反应,为此项计划特别拨款74亿美元,到2001年设计并实施该项计划。1991年ＮＡＳＡ出台了与该计划相关的地球观测系统计划(ＥＯＳ),这是一项卫星探测计划,主要是实施对地球变化的监测,而Ｔｅｒｒａ卫星探测计划是此项计划的一个重要组成部分。本文重点介绍该系统中的Ｔｅｒｒａ卫星及其5种先进的遥感探测仪。1　Ｔｅｒｒａ卫星与地球观测系统Ｔｅｒｒａ卫星…     

极地平流层云和臭氧洞

1.引言极地平流层云(PSCs)对南极臭氧洞的形成及北半球臭氧的耗减是至关重要的.首先,极地平流层云通过沉降作用清除平流层中作为云的成分的氮化物.云层内低的氮化物含量,对高水平的活性氯物质的存在是极     

国际气象观测二百周年

国际间进行气象观测合作据认为是从1780年开始的。这一年9月5日,神圣罗马帝国选帝侯(侯爵的一种,有选举帝国皇帝之权)卡尔·西奥多(Karl Theodor)王子指示首相冯维尔格(Von Vieregg),发布了一道关于气象观测规定的通令。通令要求在王     

Simulations of Titan's brightness by a two-dimensional haze model

We have used a 2-D microphysics model to study the effects of atmospheric motions on the albedo of Titan's thick haze layer. We compare our results to the observed variations of Titan's brightness with season and latitude. We use two wind fields; the first is a simple pole-to-pole Hadley cell that reverses twice a year. The second is based on the results of a preliminary Titan GCM. Seasonally varying wind fields, with horizontal velocities of about 1 cm sec-1 at optical depth unity, are capable of producing the observed change in geometric albedo of about 10% over the Titan year. Neither of the two wind fields can adequately reproduce the latitudinal distribution of reflectivity seen by Voyager. At visible wavelengths, where only haze opacity is important, upwelling produces darkening by increasing the particle size at optical depth unity. This is due to the suspension of larger particles as well as the lateral removal of smaller particles from the top of the atmosphere. At UV wavelengths and at 0.89 micrometers the albedo is determined by the competing effects of the gas the haze material. Gas is bright in the UV and dark at 0.89 micrometers. Haze transport at high altitudes controls the UV albedo and transport at low altitude controls the 0.89 micrometers albedo. Comparisons between the hemispheric contrast at UV, visible, and IR wavelengths can be diagnostic of the vertical structure of the wind field on Titan.     

城市化与自然灾害—必须解决的问题

在全球自然灾害现象普遍增多的背景下,城市化区域内自然灾害的数量也在增加。通过分析发现,由于一系列主客观因素,俄岁斯的许多城市遭到自然灾害的严重破坏。本文研究探讨自然风险存在条件下城市建设的发展问题及其解决途径。     

科学和社会的可预测性

任何一种科学的、经济的或社会的理论的有效性和功能都在于它的预测能力,并经得起观测或试验的检验。正是在这个前提下确定了本文的主题。正是科学预测的功能及其成功之所在,当科学家将其注意力转向社会问题和经济问题时,几乎都会遇到挫折并感到失望。任何一个系统的可预测性在很大程度上都取决于该系统的稳定性及其对于随机扰动的敏感性,而且还取决于该系统的基     

A physical model of Titan's aerosols

Microphysical simulations of Titan's stratospheric haze show that aerosol microphysics is linked to organized dynamical processes. The detached haze layer may be a manifestation of 1 cm sec-1 vertical velocities at altitudes above 300 km. The hemispherical asymmetry in the visible albedo may be caused by 0.05 cm sec-1 vertical velocities at altitudes of 150 to 200 km, we predict contrast reversal beyond 0.6 micrometer. Tomasko and Smith's (1982, Icarus 51, 65-95) model, in which a layer of large particles above 220 km altitude is responsible for the high forward scattering observed by Rages and Pollack (1983, Icarus 55, 50-62), is a natural outcome of the detached haze layer being produced by rising motions if aerosol mass production occurs primarily below the detached haze layer. The aerosol's electrical charge is critical for the particle size and optical depth of the haze. The geometric albedo, particularly in the ultraviolet and near infrared, requires that the particle size be near 0.15 micrometer down to altitudes below 100 km, which is consistent with polarization observations (Tomasko and Smith 1982, West and Smith 1991, Icarus 90, 330-333). Above about 400 km and below about 150 km Yung et al.'s (1984, Astrophys. J. Suppl. Ser. 55, 465-506) diffusion coefficients are too small. Dynamical processes control the haze particles below about 150 km. The relatively large eddy diffusion coefficients in the lower stratosphere result in a vertically extensive region with nonuniform mixing ratios of condensable gases, so that most hydrocarbons may condense very near the tropopause rather than tens of kilometers above it. The optical depths of hydrocarbon clouds are probably less than one, requiring that abundant gases such as ethane condense on a subset of the haze particles to create relatively large, rapidly removed particles. The wavelength dependence of the optical radius is calculated for use in analyzing observations of the geometric albedo. The lower atmosphere and surface should be visible outside of regions of methane absorption in the near infrared. Limb scans at 2.0 micrometers wavelength should be possible down to about 75 km altitude.