An anomalous subauroral red arc on 4 August, 1972: comparison of ISIS-2 satellite data with numerical calculations

This study compares the Isis II satellite measurements of the electron density and temperature, the integral airglow intensity and volume emission rate at 630 nm in the SAR arc region, observed at dusk on 4 August, 1972, in the Southern Hemisphere, during the main phase of the geomagnetic storm. The model results were obtained using the time dependent one-dimensional mathematical model of the Earth’s ionosphere and plasmasphere (the IZMIRAN model). The major enhancement to the IZMIRAN model developed in this study to explain the two component 630 nm emission observed is the analytical yield spectrum approach to calculate the fluxes of precipitating electrons and the additional production rates of N⁺₂, O⁺₂, O⁺(⁴S), O⁺(²D), O⁻(²P), and O⁺(²P) ions, and O(¹D) in the SAR arc regions in the Northern and Southern Hemispheres. In order to bring the measured and modelled electron temperatures into agreement, the additional heating electron rate of 1.05 eV cm⁻³ s⁻¹ was added in the energy balance equation of electrons at altitudes above 5000 km during the main phase of the geomagnetic storm. This additional heating electron rate determines the thermally excited 630 nm emission observed. The IZMIRAN model calculates a 630 nm integral intensity above 350 km of 4.1 kR and a total 630 nm integral intensity of 8.1 kR, values which are slightly lower compared to the observed 4.7 kR and 10.6 kR. We conclude that the 630 nm emission observed can be explained considering both the soft energy electron excited component and the thermally excited component. It is found that the inclusion of N₂(v > 0) and O₂(v > 0) in the calculations of the O⁺(⁴S) loss rate improves the agreement between the calculated N_e and the data on 4 August, 1972. The N₂(v > 0) and O₂(v > 0) effects are enough to explain the electron density depression in the SAR arc F-region and above F2 peak altitude. Our calculations show that the increase in the O⁺ + N₂ rate factor due to the vibrationally excited nitrogen produces the 5–19% reductions in the calculated quiet daytime peak density and the 16–24% decrease in NmF2 in the SAR arc region. The increase in the O⁺ + N₂ loss rate due to vibrationally excited O₂ produces the 7–26% decrease in the calculated quiet daytime peak density and the 12–26% decrease in NmF2 in the SAR arc region. We evaluated the role of the electron cooling rates by low-lying electronic excitation of O₂(a¹δ_g) and O₂(b¹σ_g⁺), and rotational excitation of O₂, and found that the effect of these cooling rates on T_e can be considered negligible during the quiet and geomagnetic storm period 3–4 August, 1972. The energy exchange between electron and ion gases, the cooling rate in collisions of O(³P) with thermal electrons with excitation of O(¹D), and the electron cooling rates by vibrational excitation of O₂ and N₂ are the largest cooling rates above 200 km in the SAR arc region on 4 August, 1972. The enhanced IZMIRAN model calculates also number densities of N₂(B³π_g⁺), N₂(C³π_u), and N₂(A³σ_u⁺) at several vibrational levels, O(¹S), and the volume emission rate and integral intensity at 557.7 nm in the region between 120 and 1000 km. We found from the model that the integral integral intensity at 557.7 nm is much less than the integral intensity at 630 nm.     

A distribution law for relative humidity in the upper troposphere and lower stratosphere derived from three years of MOZAIC measurements

Data from three years of MOZAIC measurements made it possible to determine a distribution law for the relative humidity in the upper troposphere and lower stratosphere. Data amounting to 13.5% of the total were obtained in regions with ice supersaturation. Troposphere and stratosphere are distinguished by an ozone concentration of 130 ppbv as threshold. The probability of measuring a certain amount of ice supersaturation in the troposphere decreases exponentially with the degree of ice supersaturation. The probability of measuring a certain relative humidity in the stratosphere (both with respect to water and ice) decreases exponentially with the relative humidity. A stochastic model that naturally leads to the exponential distribution is provided. Mean supersaturation in the troposphere is about 15%, whereas ice nucleation requires 30% supersaturation on the average. This explains the frequency of regions in which aircraft induce persistent contrails but which are otherwise free of clouds. Ice supersaturated regions are 3-4 K colder and contain more than 50% more vapour than other regions in the upper troposphere. The stratospheric air masses sampled are dry, as expected, having mean relative humidity over water of 12% and over ice of 23%, respectively. However, 2% of the stratospheric data indicate ice supersaturation. As the MOZAIC measurements have been obtained on commercial flights mainly between Europe and North America, the data do not provide a complete global picture, but the exponential character of the distribution laws found is probably valid globally. Since water vapour is the most important greenhouse gas and since it might enhance the anthropogenic greenhouse effects via positive feedback mechanisms, it is important to represent its distribution correctly in climate models. The discovery of the distribution law of the relative humidity makes possible simple tests to show whether the hydrological cycle in climate models is represented in an adequate way or not.     

Late spring ultraviolet levels over the United Kingdom and the link to ozone

Erythemally-weighted ultraviolet (UV_ery) levels measured over southern England, during anticyclonic weather between 30 April and 2 May, 1997, were almost 50 higher than normally expected for clear skies and were similar to mid-summer values for the first time since measurements began in 1990. Investigation of this episode suggests that a combination of both meteorological and chemical effects were responsible for generating record low ozone amounts for the time of year. Further, comparisons between the A band ultraviolet (315 to 400 nm wavelength) amounts, and radiative calculations confirm that the high UV_ery was primarily due to the reduction in total ozone. These results are contrasted with a similar period for 1998, in which near climatological ozone amounts were measured. The prospects for enhanced UV_ery levels in future years are briefly reviewed in the light of expected increases in stratospheric halogen levels and greenhouse gases.     

Vertical circulation and thermospheric composition: a modelling study

The coupled thermosphere-ionosphere-plasmasphere model CTIP is used to study the global three-dimensional circulation and its effect on neutral composition in the midlatitude F-layer. At equinox, the vertical air motion is basically up by day, down by night, and the atomic oxygen/molecular nitrogen [O/N₂] concentration ratio is symmetrical about the equator. At solstice there is a summer-to-winter flow of air, with downwelling at subauroral latitudes in winter that produces regions of large [O/N₂] ratio. Because the thermospheric circulation is influenced by the high-latitude energy inputs, which are related to the geometry of the Earth’s magnetic field, the latitude of the downwelling regions varies with longitude. The downwelling regions give rise to large F2-layer electron densities when they are sunlit, but not when they are in darkness, with implications for the distribution of seasonal and semiannual variations of the F2-layer. It is also found that the vertical distributions of O and N₂ may depart appreciably from diffusive equilibrium at heights up to about 160 km, especially in the summer hemisphere where there is strong upwelling.     

A modelling study of aerosol processing by stratocumulus clouds and its impact on general circulation model parameterisations of cloud and aerosol

A model of the aqueous phase processing of an aerosol population undergoing multiple cycling through a stratocumulus (Sc) cloud layer is presented. Results indicate that a significant modification of the aerosol properties is achieved following the first cycle through cloud. In a polluted atmosphere, further modification in subsequent cycles is seen to be hydrogen peroxide limited unless there is a flux of ammonia entering the system through cloud base (CB). The modification of the aerosol population is seen to have little effect on the microphysics (specifically the cloud droplet concentration and effective radius) of the processing cloud. However, it enables processed aerosols to subsequently act as efficient cloud condensation nuclei (CCN) in less vigorous clouds (as a result of reducing the critical supersaturation required to activate them). The effects of variations in the internal mixture of soluble components of aerosols on the microphysics of clouds forming on them are also investigated using the cloud model. A (K2) parameterisation of the effects of variations in internally mixed nitrate loadings on the cloud droplet number concentration is presented. The effects of applying this K2 correction to the droplet number (derived from a parameterisation based on sulphate) for the presence of nitrate in aerosol have been investigated using the HadAM3 version of the Hadley Centre General Circulation Model (GCM). The effect on global annual mean simulations of the indirect forcing and effective radius is small, but more pronounced regionally. Suggestions (based on model results and observations) for parameterising the size distribution and in-cloud growth of aerosols for use in GCMs are presented.     

Modeling the sudden decrease in CH4 growth rate in 1992

A two-dimensional global chemistry model is developed to study the distribution and long-term trends of methane. The model contains 34 species and 104 chemical and photochemical reactions. Using the model, the long-term trends of CH₄, CO and OH in atmosphere are simulated, comparison between the model and observations shows that the simulation is successful. Experiments are done to investigate the causes of dramatic decrease in the growth rate of CH₄ in 1992 such as OH increase due to stratospheric ozone depletion, decrease of temperature in the troposphere due to Mount Pinatubo eruption and descendent of CH₄ sources fluxes. A new explanation is proposed and verified by this model that the decrease of CO emission plays an important role for the abnormal growth rate of CH₄ in 1992. We find that the decreases of CH₄ and CO emissions are the main reasons for the sudden decrease of growth rate of CH₄ in 1992, which account for 73% and 27% respectively.     

应力化学

应力化学是研究应力的性质,作用方式和规模,组合和序列,它们的发生,发展,演化所成生的化学作用和过程,以及物理－化学动态机制。当应力作用于地质体时,接受能量和释放能量的作用方式之一就是应力化学作用,应力化学作用主要受应力性质,应力配置和应力序列的影响,以剪应力化学作用最为重要,应力作用可产生化学作用,改善化学反应所需条件,因而促进和加速了化学作用。     

Speciation and solubility relationships of Al, Cu and Fe in solutions associated with sulfuric acid leached mine waste rock

 Solutions from oxidized waste rock originating from an acid-leached waste dump were studied. The dissolution data suggest that after the majority of the soluble solid phases are removed, remaining solid phases continued to buffer the solutions in the acidic pH range. Incorporating the solution data into MINTEQA2 identified controls on the solubility of Al, Cu and Fe at pH values from about 2.5 to slightly over 5. Sulfate appears to play a significant role in the formation of solubility controlling solid phases for Al and Cu. This is not the case for Fe, and is suggested that Fe and Cu solubility may be controlled by cupric ferrite at low pH values. Received: 5 April 1998 · Accepted: 27 July 1998     

中、新生代吉安盆地沉积环境浅析

运用沉积物物理、化学、生物参数,分析吉安盆地的沉积环境,取得了显著效果,为古沉积环境分析积累了经验,在阐述吉安盆地沉积相,古生物及岩石地球化学的基础上,着重对古气候,古地理进行了探讨。     

大别山同剥露刘家洼杂岩体角闪石、长石的矿物化学

刘家洼岩体是一个碰撞后的侵入杂岩体.它是在大别造山带中生代的高压-超高压变质岩剥露过程中侵位的.本文通过对刘家洼杂岩体角闪石、长石矿物化学的研究,揭示岩体形成时的温度为730～810℃,而结晶压力变化于6.6×108～2.2×108Pa之间,表明在该岩体形成过程中,经历了明显的剥露作用.这些认识对揭示超高压榴辉岩快速折返及剥露过程提供了有意义的信息.