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1.
A summary is presented of the relative importance of the principal aeronomic processes determining the vertical distribution of NO–NO2 in the stratosphere. Formation and destruction of nitric oxide are considered with transport processes for steady-state conditions. Estimates of the vertical distribution of NO
x
are made for extreme conditions of the eddy diffusion coefficient. It is pointed out that NO is determined by the values which are adopted for its photodissociation coefficient which is related to the absorption of solar radiation in the Schumann-Runge bands of molecular oxygen. 相似文献
2.
Diurnal variations in the vertical ozone density distribution have been calculated for the height range 40–150 km by extending our existing computer programs. The steady-state profiles were first calculated for fifteen constituents in the original program and three additional constituents (CH4, CO and CO2); the result was used as the initial condition for the time-dependent solution. The profile of the eddy diffusion coefficient used in this study was determined by comparing the model profile with the observations for CH4, whose density distribution is verysenstive to the eddy diffusion coefficient The effects of hydrogen and nitrogen compounds on the ozone density are discussed somewhat quantitatively; they reduce the ozone density mainly in the mesosphere and stratosphere, respectively. Special attention is given to the large depression of the ozone density at around 70–85 km, which has been obtained in many theoretical models but has neither been explained nor definitely confirmed by observations. Our time-dependent model indicates that the depression develops at night by the effect of hydrogen-oxygen and nitrogen-oxygen reactions and of eddy diffusion transports. The latter effect also produces an increase of the ozone density after midnight at some heights in the depression region. 相似文献
3.
An observation by UHF ST radar of a subsidence pattern on the right side of the exit region of a jet streak is reported. The onset of the subsidence pattern occurred at 23:30 UTC on the 29 November 1991, when a downward motion was initiated above 14 km. The injections of stratospheric air in this region seem to have an intermittent nature; they occur during at least three intervals during the lifetime of the subsidence pattern. Comparison of these results with an ECMWF analysis suggests that it is an unfolding case. However, observation of turbulent intensities w’ greater than 60 cm s−1 at the tropopause level also suggests the existence of a turbulent flux between the stratosphere and the troposphere. From the turbulence characteristics measured by the radar and the potential temperature profile obtained by radiosonde data, the eddy diffusivity at the tropopause level has been calculated. An eddy diffusion coefficient ranging between 5 and 7 m2 s−1 is found. From these values, and with the assumption of a climatological gradient of the volume mixing ratio of ozone in the lower stratosphere, it is possible to deduce a rough estimate of the amount of ozone injected from the stratosphere into the troposphere during this event. A rate of transfer of 1.5×1020 molecules of ozone per day and per square meter is found. 相似文献
4.
The consumption of both methane and carbon monoxide in the lower stratosphere is due predominantly to reaction with OH radicals. The possibility of deriving OH concentration from measurements of the decrease of CH4 and CO mixing ratios above the tropopause is explored. The observations and the basic chemistry are briefly summarized. Simple one-dimensional diffusion models are employed to derive expressions for the decrease of CH4 and CO mixing ratios with altitude above the tropopause, and the influence of important parameters is discussed. Vertical air velocities resulting from large-scale organized mean motion and from synoptic variations are shown to distort the concentration altitude profiles of methane and carbon monoxide, respectively. Suitable averaging of observational data is required to eliminate the effects due to vertical motion. Then a reliable value for the effective OH number density should be obtainable. At present an estimate of 4×106 molecules/cm3 is derived. 相似文献
5.
Darrell F. Strobel 《Pure and Applied Geophysics》1989,130(2-3):533-546
A review of the important constraints on gravity wave induced diffusion of chemical tracers, heat, and momentum is given. Ground-based microwave spectroscopy measurements of H2O and CO and rocket-based mass spectrometer measurements of Ar constrain the eddy diffusion coefficient for constituent transport (K
zz
) to be (1–3)×105 cm2s–1 in the upper mesosphere. Atomic oxygen data also limitsK
zz
to a comparable value at the mesopause. From the energy balance of the upper mesosphere the eddy diffusion coefficient for heat transport (D
H
) is, at most 6×105 cm2s–1 at the mesopause and decreasing substantially with decreasing altitude. The available evidence for mean wind deceleration and the corresponding eddy diffusion coefficient for momentum stresses (D
M
) suggests that it is at least 1×106 cm2s–1, in the upper mesosphere. Consequently the eddy Prandtl number for macroscopic scale lengths is >3. 相似文献
6.
We present the distribution of226Ra in eight vertical profiles from the eastern Pacific. The profiles are located along a meridional trend near 125°W, from 43°S to 29°N. Surface226Ra concentrations are about 7 dpm/100 kg, except for the two stations south of 30°S where the higher values are due to the Antarctic influence. Deep waters show a distinctive south-to-north increase in the226Ra content, from about 26 to 41 dpm/100 kg near the bottom. Unlike in the Atlantic and Antarctic Oceans, the effect of226Ra injection from bottom sediments is clearly discernible in the area. The presence of this primary226Ra can be traced up to at least 1–1.5 km above the ocean floor, making this part of the sea bed among the strongest source regions for the oceanic226Ra. Numerical solutions of a two-dimensional vertical advection-diffusion model applied to the deep (1.2–4 km)226Ra data give the following set of best fits: upwelling velocity(Vz) = 3.5m/yr, vertical eddy diffusivity(Kz) = 0.6cm2/s, horizontal (north-south) eddy diffusivity(Ky) = 1 × 107cm2/s, and water-column regeneration flux of226Ra(J) = 3.3 × 10?5dpmkg?1yr?1 as an upper limit. These parametric values are in general agreement with one-dimensional (vertical) model fits for the Ra-Ba system. However, consideration of226Ra balance leads us to suspect the appropriateness of describing the vertical exchange processes in the eastern Pacific with constantVz and Kz. If future modeling is attempted, it may be preferable to treat the area as a diffusion-dominant mixing regime with depth-dependent diffusivities. 相似文献
7.
At two locations in southern Lake Huron (U.S.A.), twelve 35.5-cm diameter cores of fine-grained sediments were taken for comparison of the vertical distributions of210Pb and falllout137Cs with the distributions of benthic macroinvertebrates, mainly oligochaete worms (Tubificidae) and the amphipod,Pontoporeia affinis. Locations were selected on the basis of210Pb distributions measured a year earlier which indicated contrasting depths of mixing of surface sediments. At one location the activity of210Pb is uniform down to about 6 cm and 95% of total invertebrates occur within this zone; at the other location the zone of constant activity is only 3 cm deep but 90% of the invertebrates occur within it. Comparison of published tubificid defecation rates with sediment accumulation rates based on210Pb shows that oligochaetes alone can account for mixing in one case while the effects of amphipods may be required in the case of shallower mixing. If mixing is represented as a diffusional process, eddy diffusion coefficients are at least 5.8 and 3.3 cm2 yr?1 at respective locations. In comparison with bioturbation, molecular diffusion is of minor importance in the post-depositional mobility of137Cs. The necessity for introducing a diffusion coefficient varying continuously with depth is indicated by characteristics of the distribution of137Cs. Biological reworking of near-surface sediments is an important process affecting radioactivity and chemical profiles in profundal deposits of this and probably other Great Lakes. 相似文献
8.
Jan Lidén 《Aquatic Sciences - Research Across Boundaries》1983,45(2):411-429
The concentrational control of Fe2+ has been studied in the anoxic hypolimnion of an ice-covered lake with special reference to redox equilibria with the suspended phase. The anoxic bottom water formed during ice conditions differed substantially in terms of vertical distributions from that reported from thermally stratified waters. This was particularly evident for the pH and pe gradients. The main process explaining the Fe2+ concentration profile was a diffusional model in which upwards moving Fe2+ met an opposing O2 flux at the redox cline and precipitated as ferric hydroxide. When the anoxic water column is divided into thin stratums an equilibrium reaction between Fe2+ and amorphous FeOOH explained the Fe2+ concentrations in the upper hypolimnion. Increasing supersaturation was observed at greater depths. Similarly equilibration control of the sulfide concentration by Fe2+ could be shown in the lower hypolimnion. Apparent equilibrium constants for FeS and FeOOH have been calculated together with the eddy diffusion coefficient of Fe2+. 相似文献
9.
A new determination of stratospheric methane from 22 km to 35 km altitude with implications on the abundance of this constituent at greater heights is presented. Previous measurements, some of which showed large discrepancies with currently admitted values, have been reinterpreted and brought into agreement. The results are in contradiction according to present theories with thein situ determined CH4 abundances at the upper edge of the stratosphere. Implications on the vertical transport coefficient used in one dimensional models are discussed. 相似文献
10.
利用1992～2005年卤素掩星试验（HALOE）的观测资料分析了中国上空平流层的几种微量气体（NO, NO2, HF, HCl, CH4, H2O 和O3）混合比的垂直分布和变化趋势,以期为研究平流层的辐射和化学过程提供一些有用的数据. 文中除给出我国上空平流层各高度上平均的各种微量气体的含量外,还给出青藏高原上空这些微量气体的含量. 分析结果表明,平流层各种微量气体混合比的垂直分布有其不同的特征,在对流层上层到平流层底部各种微量气体的混合比分布和季节变化与平流层相比有明显的差异;分析结果还表明,这些微量气体的季节变化、准两年周期振荡和长期变化趋势都很明显,并且在平流层的不同高度上它们的变化趋势是不相同的. 在平流层中层,NO, NO2, HCl 和H2O 混合比在1998年以前都是增加而后则是明显下降的,但O3相反,在1998年以前明显减少,1998年后其减少的趋势不明显. 这表明,近年来平流层中层这些微量气体的减少使得它们对臭氧的破坏有所缓解. 但在平流层下层,臭氧的耗损仍然很明显. 相似文献
11.
R. Krishna Rao Vupputuri 《Pure and Applied Geophysics》1978,117(3):448-485
two-dimensional time dependent model of the stratosphere incorporating the major interactions between radiative-photochemical and dynamical processes is described. The main prognostic equations considered are the thermodynamic equation and the general conservation equation for the minor chemical constituents representing the odd oxygen (O
x
=O+('D)+O3), odd hydrogen (HO
x
=HO+HO2), N2O, odd nitrogen (NO
x
=NO+NO2+HNO3), CF2Cl2, CFCl3 and odd chlorine (Cl
x
=Cl+ClO+HCl). The zonal wind and mean meridional circulations are determined diagnostically by the integration of the thermal wind equation and the stream function equation in the meridional plane espectively. The large scale eddy processes are parameterized in terms of zonal mean quantities using the generalized diffusion formulation on a sloping surface. The radiative heating and cooling and the hotochemical sources and sinks are incorporated in a form which allows for the major interactions among the minor trace constituents, temperature and mean circulation.Two integrations consisting of natural stratosphere and a stratosphere contaminated by the chlorofluoromethanes through lower boundary fluxes are carried out for 23 model years by changing the declination of the sun every day and using 6-hour time step. The model simulations of temperature, mean circulation, ozone, HO
x
, N2O and NO
x
in the meridional plane for the normal stratosphere, show satisfactory agreement with the available observations. Based on the results of second integration it is found that the injection of chlorofluoromethanes in the atmosphere at the estimated current production rates can lead to significant changes in the meridional distribution of ozone, temperature and NO
x
in the middle and upper stratosphere. The results also indicate that the percentage total ozone depletion increases from tropics to high latitudes and from summer to winter high latitudes. Also discussed are the results of additional experiments incorporating the reaction of HO2 with NO and the reactions involving ClNO3. 相似文献
12.
Vertical profiles of excess bottom222Rn and potential temperature were measured at 23 stations in the northwestern Pacific Ocean. The Rn profiles were classified into the following three types: quasi-exponential (type E), benthic boundary layer (type B), and horizontally disturbed (type H). The ratio among types E, B and H was approximately 2 : 3 : 1.An apparent vertical eddy diffusivity (K) was calculated by applying a one-dimensional diffusion model to the Rn profiles of types E and B. Type E had K values ranging from 15 to 180 cm2 s?1 (average: 70 cm2 s?1). As to type B, K values for the benthic boundary layer (4.5–260 cm2 s?1, average: 120 cm2 s?1) were always more than an order of magnitude larger than those for the upper layer (0.2–35 cm2 s?1, average: 7 cm2 s?1), indicating more active vertical mixing in the benthic boundary layer than in the upper layer.Rn profiles were measured in regions where the bottom topography is known. It was verified that the occurrence of type H related closely with local bottom topographic features accompanied by lateral transient supply of Rn-rich or Rn-poor water.A couple of Rn profiles at the same location, measured at time intervals of several years, were compared with each other for three locations. The general characteristics of Rn profiles were shown to remain unaltered with time, while the fine structure of Rn profiles may have short-term variations caused by local bottom topography and fluctuations of bottom current as indicated in type H. 相似文献
13.
— Urban terrain poses a challenge for modeling air pollutant diffusion. In tropics, because of the dominant low wind speed environment, the importance of understanding the turbulence diffusion is even more critical, and uncertain. The objective of this study is to estimate the vertical eddy diffusivity of an urban, tropical atmosphere in low–wind speeds. Turbulence measurements at 1 Hz were made at 4-m level over an urban terrain with a roughness length of 0.78 m during winter months. Eddy diffusivity is estimated from spectral quantities of the turbulence data involving turbulent kinetic energy (E) and its dissipation rate (?). The spectral information of the vertical velocity fluctuations is used to estimate the vertical length scale which provides information on the eddy diffusivity. In addition, the product of friction velocity and the vertical length scale has been used to non-dimensionalize the eddy diffusivity, which is shown to increase with increasing instability. Using the eddy diffusivity (K) estimates from the E – ? approach, a relation is suggested for the mixing length based eddy diffusivity models of the form: K = c w .[2.5 ? 0.5(z/L)], where z is the measurement height, L is the Obukhov length, and c w has an average value close to 1 for unstable and near 0.5 for stable conditions for the urban terrains. 相似文献
14.
The results of numerical models or of new observational programs are checked by comparing them with past observations. Also, it is desirable that the eddy diffusion coefficients used in two-dimensional models be derived from the same data set as the circulation statistics which the model outputs are checked against, so that all results refer to the same atmospheric conditions. For the first time, the three components of the eddy diffusion matrix, from 30–60 km, 80°N–10°S are computed, together with the means, variances and covariances of the wind and temperature through the same region using the same data set for 1960–76 and the same handling and analysis methods for all variables. Horizontal diffusivities,K
yy
, are obtained from the variance and integral time scale of the meridional wind speed. The present values are generally smaller than past estimates, presumably because temporal variations longer than a month have been removed in this work. Estimates ofK
yz
are based on the tentative assumption that the diffusivity is proportional to the slope of isentropic surfaces, and estimates ofK
zz
are based on the assumption that small-scale gravity waves are primarily responsible for vertical mixing. 相似文献
15.
《Advances in water resources》2003,26(3):277-294
Two subgrid-scale modeling techniques––Smagorinsky’s postulation for the horizontal eddy viscosity and the Mellor–Yamada level-2 model for the vertical eddy viscosity––are applied as turbulence closure conditions to numerical simulations of resolved-scale baroclinic lake circulations. The use of the total variation diminishing (TVD) technique in the numerical treatment of the advection terms in the governing equations depresses numerical diffusion to an acceptably low level and makes stable numerical performances possible with small eddy viscosities resulting from the turbulence closure parameterizations. The results show that, with regard to the effect of an external wind stress, the vertical turbulent mixing is mainly restricted to the topmost epilimnion with the order of magnitude for the vertical eddy viscosity of 10−3 m2 s−1, whilst the horizontal turbulent mixing may reach a somewhat deeper zone with an order of magnitude for the horizontal eddy viscosity of 0.1–1 m2 s−1. Their spatial and temporal variations and influences on numerical results are significant. A comparison with prescribed constant eddy viscosities clearly shows the importance of subgrid-scale closures on resolved-scale flows in the lake circulation simulation. A predetermination of the eddy viscosities is inappropriate and should be abandoned. Their values must be determined by suitable subgrid-scale closure techniques. 相似文献
16.
The role of water depth and bottom boundary layer turbulence upon lee-wave generation in sill regions is examined. Their effect
upon vertical mixing is also considered. Calculations are performed using a non-hydrostatic model in cross-section form with
a specified tidal forcing. Initial calculations in deeper water and a sill height such that the sill top is well removed from
the surrounding bed region showed that downstream lee-wave generation and associated mixing increased as bottom friction coefficient
k increased. This was associated with an increase in current shear across the sill. However, for a given k, increasing vertical eddy viscosity A
v reduced vertical shear in the across sill velocity, leading to a reduction in lee-wave amplitude and associated mixing. Subsequent
calculations using shallower water showed that for a given k and A
v, lee-wave generation was reduced due to the shallower water depth and changes in the bottom boundary layer. However, in this
case (unlike in the deepwater case), there is an appreciable bottom current. This gives rise to bottom mixing which in shallow
water extends to mid-depth and enhances the mid-water mixing that is found on the lee side of the sill. Final calculations
with deeper water but small sill height showed that lee waves could propagate over the sill, thereby reducing their contribution
to mixing. In this case, bottom mixing was the major source of mixing which was mainly confined to the near bed region, with
little mid-water mixing. 相似文献
17.
本文根据气体分子运动论导出了垂直动力传输函数,此函数可以代替Nicolet和Mangc的混合比,较好地描述高层大气中从完全混合状态向扩散分离状态的过渡过程。分析了高层大气中湍流运动的观测结果,给出了湍流系数随高度分布的几个模式,利用这些模式计算了惰性气体氩、氦与氮的数密度比的高度剖面,并与箭载质谱仪探空资料作了比较。根据光化-动力传输理论,计算了上中层及低热层大气主要化学成份的高度分布。结果表明:垂直动力传输明显地影响着大气成份的分布。文中还指出,氧分子的光离解系数与其数密度的高度剖面耦合在一起,因而应当由上向下数值求解有源有汇的连续方程组,这样可避免由于光离解系数的假设所造成的误差。 相似文献
18.
The absolute integral intensity of the IR components of the continuum emission is calculated from the laboratory velocities of photochemical reactions between NO and nonexcited and excited O3 molecules. The vertical intensity distribution of the continuous radiation spectrum of the upper atmosphere (continuum) in the IR area spans a range of heights of the middle atmosphere from 10 to 15 km. A comparison of the calculated values of the continuum intensity with the results of its spectrophotometric surface measurements in the near-IR spectrum allowed refinement of the coefficient of velocity of the NO-ozone reaction responsible for origination of the continuum emission in the IR spectrum range. 相似文献
19.
Available data on halogenated molecules in the stratosphere will be reviewed. Presently vertical profiles of CFCl3 and CF2Cl2 in the stratosphere exist to 50 km altitude. Only measurements in the lower stratosphere are reported for the other major halocarbons, CCl4 and CH3Cl. Profiles of the product species ClO, Cl, HCl, and HF exist to about 35 km.Comparison with theoretical profiles from 1-D models shows generally good agreement except for ClO where the earliest measured concentrations exceed the calculated ones considerably. 相似文献
20.
A. Aitsam H.P. Hansen J. Elken M. Kahru J. Laanemets M. Pajuste J. Pavelson L. Talpsepp 《Continental Shelf Research》1984,3(3):291-310
An area of 25 × 30 nmi with a subarea of 20 × 20 nmi in the Baltic Sea Gotland Basin was surveyed for about one month by vertical CTD and fluorometric chlorophyll a casts, and by towed profiles with a chemical profiler (nutrients, CTD, O2, pH) and an undulating CTD. Autonomous current meter data were available for the same period.Five CTD surveys with a 5-mile spacing showed the existence of synoptic eddies and several other perturbations. A first mode eddy (with all the isopycnals lifted within the halocline) had reduced salinities in the upper layer and chlorophyll concentrations were reduced by 2 to 3-fold. A second mode eddy (with the isopycnals lifted in the top of the halocline and lowered in the bottom layers) with a diameter of 20 km was under prolonged observation. Anticyclonic currents at 96-m depth were up to 25 cm s?1. Along the section across the eddy at 80-m depth, the mean nitrate concentration dropped from about 7 to 8 to 5 μmol dm?3 while other chemical parameters lacked intense variations. An increased activity of the intrusive fine-structure was detected in the eddy center. The Baltic eddies are essentially non-linear, and transport water in their ‘nuclei’. An internal front, separating waters with different T,S composition, was discovered in the upper layers.The observations are discussed with respect to discovering long-term trends while monitoring the Baltic environment. 相似文献