近年来大气科学某些进展及其展望

介绍了近几年来大气科学领域内国内外研究的某些最新进展，对目前国际大气科学发展特.点和趋势作了简要回顾，并对今后大气科学研究重点作了讨论。
        

The early history of oxygen and ozone in the atmosphere

There may have been three stages in the growth of oxygen in the terrestrial atmosphere. Prior to the origin of photosynthesis the only source of oxygen was photolysis of water vapor followed by escape of hydrogen to space. The rate of this process was probably less than the rate of release of reduced gases (principally hydrogen) from volcanoes, so the oxygen partial pressure was held to negligibly low values by photochemical reactions with an excess of hydrogen. The photosynthetic source of oxygen was probably in operation as long ago as 3.8 billion years. It released oxygen to the ocean. Presumably most of this oxygen was destroyed in the ocean as long as its rate of supply was less than the rate of supply of readily oxidizable material (principally Fe²⁺) provided by the weathering of rocks. This phase appears to have lasted until about 2 billion years ago, during which period most banded iron formations were deposited. During this period the production of oxygen by algae was limited by competition with photosynthetic bacteria, which preempted the supply of nutrient phosphorus as long as reduced chemicals were available in the environment. Once the photosynthetic oxygen source exceeded the rate of supply of reduced minerals exposed by erosion and weathering, the accumulation of oxygen in the ocean and atmosphere could be controlled only by reaction of oxygen with reduced organic material. This is the stabilization mechanism that operates today. It seems unlikely that oxygen could be consumed at a significant rate by this process until oxygen levels sufficiently high to support respiration had been achieved. I therefore suggest that atmospheric oxygen rose rapidly from essentially zero to approximately its present value (within a factor of 10) when the photosynthetic source of oxygen rose above the weathering source of reduced minerals, probably about 2 billion years ago. The ozone layer and the ultraviolet screen were absent prior to this time and essentially fully developed after this time.Presented at IAGA/IAMAP Symposium on Minor Neutral Constituents in Middle Atmosphere-Chemistry and Transport, Seattle, August, 1977.     

Vertical ozone distribution on a global scale

All available data of the vertical ozone distribution measured with chemical sondes have been assembled and combined with one year's results from the BUV satellite to obtain the best possible information on the vertical ozone distribution averaged over longitude as a function of season (month by month). For the southern hemisphere Umkehr data have been used as a guideline in the necessary smoothing procedure. Especially in the northern hemisphere considerable adaptation to the observed latitudinal mean of the total amount was needed because most sounding stations, are situated in upper air trough positions.The results are presented as vertical distributions, as meridional cross sections of partial pressure and of mixing ratio and as partial pressure isolines as a function of latitude and season at different levels. The interaction between photochemical processes and transport resonsible for the observed distribution is briefly discussed.     

Annual variation of the effects of diffuse radiation on the photodissociation of ozone

Previous work has shown the importance of the diffuse solar field in the photochemistry of atmospheric active species, the solar zenith angle being an effective parameter. In view of the diurnal and seasonal variability of this single quantity, in this paper estimates are presented of the daily-integrated values of the photodissociation coefficient of ozone throughout the year, for a purely molecular atmosphere in the absence of scattering and when the effects of molecular scattering are included, and for an absorbing-scattering turbid atmosphere characterized by two different aerosol loads. Also, different values of the ground albedo have been taken into account.Results are shown for a latitude of 45^oN. The seasonal dependence is strong at altitudes below 20 km and less marked above 20 km. For an albedoA=0.3, the inclusion of molecular scattering increases the daily-integrated photodissociation coefficients approximately by 20% and 40% at 15 km and by 15% and 22% at 30 km, at the winter and summer solstice respectively. The presence of a heavy aerosol load modifies these results by a further factor which is approximately –5% and 10% at 15 km at the winter and summer solstice respectively, and is approximately constant at 8% throughout the year at 30 km.     

Systems modelling of stratospheric ozone transport and photochemistry

A scheme of a system of physical and chemical processes controlling the production, transport and destruction of ozone and its gaseous catalysts, as well as other related gases in the low and high stratosphere is presented. An account is made of temperature variations of the stratospheric layer resulting from changes in ozone content; also included is the effect of temperature variations on photochemical reaction rates and ozone and other gases transport between atmospheric layers. Parameters describing major relations of the system are inferred from the analysis of ozone and trace gas data and from the results of model calculations of interdependence between variations in temperature and ozone content of the layer.An analysis of minor fluctuations of the linearized system shows that photochemical processes are responsible for its aperiodic stability and that gas transport between atmospheric layers destabilizes the system.     

Instantaneous global ozone balance including observed nitrogen dioxide

The catalytic destruction of stratospheric ozone by the oxides of nitrogen is believed to be an important part of the global ozone balance. The lack of sufficient measurements of NO _x concentrations has impeded efforts to quantify this process. Recent measurements of stratospheric nitrogen dioxide from ground-based stations as well as aircraft and balloons have provided a first approximation to a global distribution of NO₂ vertical columns at sunset. These observed vertical columns have been translated into time-dependent vertical NO₂ profiles by means of a one-dimensional atmospheric photochemical model. Using recent observations of air temperature and ozone along with this information, the independent instantaneous (one second) rates of ozone production from oxygen photolysis P(O₃), of ozone destruction from pure oxygen species (Chapman reactions) L(O _x ), and of ozone destruction by nitrogen oxides L(NO _x ) were estimated over the three-dimensional atmosphere. These quantities are displayed as zonal average contour maps, summed over various latitude zones, summed over various altitude bands, and integrated globally between 15 and 45 km. Although the global summation between 15 and 45 km by no means tells the complete story, these numbers are of some interest, and the relative values are: P(O₃), 100; L(O _x ), 15; L(NO _x ), 45±15. It is to be emphasized that this relative NO _x contribution to the integrated ozone balance is not a measure of the sensitivity of ozone to possible perturbations of stratospheric NO _x ; recent model results must be examined for current estimates of this sensitivity.     

A time-splitting pressure-correction projection method for complete two-fluid modeling of a local scour hole

A two-dimensional vertical (2DV), Eulerian two-phase model or complete two-fluid model of the free surface flow was developed to simulate water-sediment flow in a local scour hole. In the model, the complete forms of the vertical, two-dimensional, two-fluid Navier-Stokes equations were discretized using a finite volume scheme. This discretization was done based on a standard staggered grid system using a curvilinear network system in compliance with the bed boundaries and water level. At the beginning of the computational cycle, the equations governing the fluid phase were solved based on the two-step projection method with a pressure-correction technique. In the first step, the intermediate fluid velocities were obtained by solving different phases of the momentum equations of the fluid phase using the time-splitting technique. In the second step, pressure was obtained and fluid velocities were updated. In this step a simple discretization method was applied for decreasing the computational complexity. After obtaining all the fluid phase variables at a new time step, the sediment phase momentum equations were solved using the time-splitting technique and sediment velocities were obtained. Then, at the end of the computational cycle, the sediment phase mass equation was solved and the concentrations of both phases were updated. At last, the capacity of the model for simulating of the longitudinal fluid velocity and sediment concentration in a local scour hole was evaluated. Numerical results were found to be in good agreement with experimental data.     

Mismatch between variations of solar indices, stratospheric ozone and UV-B observed at ground

In solar cycles 22–23, all solar indices showed maxima near 1990 and 2000 and minima in 1996. The maximum to minimum variation was only 1–2% in the UV range 240–350 nm. Dobson ozone intensities did not show any clear relationship with solar cycle and ozone variations were less than 10%. The UV-B (295–325 nm) observed at ground by Brewer spectrophotometers at some locations had variations of 50–100% for 295–300 nm, and 20–50% for 305–325 nm. The maxima were in different years at different locations (even with separations of only 300 km), did not match with the solar cycle, and were far too large to be explained on the basis of ozone changes (1% decrease of ozone is expected to cause 2% increase of UV-B). Thus, if the data are not bad, the UV-B changes do not match with solar activity or ozone changes and must be mostly due to other local effects (clouds, etc.?). When data are averaged over wide geographical regions, UV-B variation ranges are smaller (10–20%, probably because localised, highly varying cloud effects get filtered out), and are roughly as expected from ozone variations.     

射流式液动锤回转冲击孕镶金刚石钻头钻进的实践与分析

金刚石本身力学性质、金刚石钻头结构特点及射流式液动锤冲击力特点决定了射流式液动锤带金刚石钻头进行冲击回转钻进是可行的。经射流式液动锤在科学钻探主孔先导孔中的应用实践，证明了由于液动锤冲击动载作用钻头底唇面与岩面微量问隙有规律地变化，改善钻头金刚石颗粒受力状况、碎岩状态，提高钻头金刚石颗粒切入深度，改善胎体磨损状况、钻头冷却，成倍地提高了榴辉岩、片麻岩等坚硬地层中钻进回次进尺、机械钻速及钻头平均寿命。     

钻孔偏心—套芯法地应力测量中的一个不可忽视的问题

通过有限元法计算，得出偏心钻孔在围压作用下的应力分布，讨论了由于“偏心”导致率定的换算公式失准，表明小孔孔壁应变和位移随“偏心”增大而显改变。利用保角变换以实例对压磁法偏心钻孔的地应力测量数据进行了修正，对比同一钻孔相近深度上基本不偏心的测量结果，表明修正后二着相当吻合。