Measurements of N2O photolysis coefficients in the stratosphere: Comparison with model calculations

A balloon-borne continuous actinometer has been developed which measures stratospheric N₂O photolysis coefficients, % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOAamaaBa% aaleaacaGGobWaaSbaaWqaaiaaikdaaeqaaSGaci4taiabg2da9iab% gkHiTiGacsgaciGGSbGaaiOBaiaacIcaciGGobWaaSbaaWqaaiaaik% daaeqaaSGaci4taiGacMcacaGGVaGaciizaiaadshaaeqaaaaa!44F2!\[j_{N_2 \operatorname{O} = - \operatorname{d} \ln (\operatorname{N} _2 \operatorname{O} )/\operatorname{d} t} \], with a time resolution of approximately 100 s, and a lower detection limit approaching 10^-10 s^-1. The instrument performed successfully, or was at least partially successful, on five stratospheric balloon flights between October 1982 and September 1986. The experimental profiles are compared with model calculations of % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOAamaaBa% aaleaacaGGobWaaSbaaWqaaiaaikdaaeqaaSGaci4taaqabaaaaa!39A3!\[j_{N_2 \operatorname{O} } \]. The model takes full account of the sphericity of the atmosphere and of the specific flight conditions, but neglects scattering, which should have a negligible effect on % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOAamaaBa% aaleaacaGGobWaaSbaaWqaaiaaikdaaeqaaSGaci4taaqabaaaaa!39A3!\[j_{N_2 \operatorname{O} } \]. The quantitative results, particularly the altitude and solar zenith angle dependences under extreme conditions, support the low absorption cross-sections of oxygen in the Herzberg continuum as recommended by WMO in 1986 and are inconsistent with Ackerman's tabulations of 1971. It is shown that the altitude dependence of Brewer and Wilson's historical irradiance measurements in the stratospheric window region is well reproduced by our model, but should be multiplied by a factor of 1.75.     

Prediction of the abiotic degradability of organic compounds in the troposphere

A statistically relevant correlation between the reaction rate coefficient, k _OH, for the OH radical reaction with 161 organic compounds in the gas phase at 300 K, and the corresponding vertical ionisation energies E _i,v, reveals two classes of compounds: aromatics where –log(k _OH/cm³s^-1)3/2E _i,v(eV)–2 and aliphatics where –log(k _OH/cm³s^-1)4/5E _i,v(eV)+3. The prediction of the rate coefficient, k _OH, for the reaction of OH with organic molecules from the above equations has a probability of about 90%. Assuming a global diurnal mean of the OH radical concentration of 5×10⁵ cm³, the upper limit of the tropospheric half-life of organic compounds and their persistence can be estimated.     

A structural analysis of the Moine Thrust Zone between Loch Eriboll and Foinaven,NW Scotland

The northern part of the Moine Thrust Zone as exposed around the valley of Srath Beag, Sutherland was developed by thrusts propagating in the tectonic transport direction. Deformation on any particular thrust surface evolved from dominantly ductile to dominantly brittle with time.The foreland has been progressively accreted onto the overriding Moine thrust sheet by duplex formation, a process which has continuously folded the roof thrust and the rocks above its hanging-wall. Fold culminations and depression can be related to lateral ramps which may give the rocks above the hanging-wall a complex history of extensional and compressional strains normal to the transport direction.Folds within the thrust zone are laterally independent because they are controlled by short lived variations in deformation style on an evolving thrust footwall topography. Therefore there may be no correlation between structures across or along the thrust zone. This variation limits the construction of balanced cross sections as structure cannot be projected onto particular section lines.     

Kriging of water levels in the Souss aquifer,Morocco

Universal kriging is applied to water table data from the Souss aquifer in central Morocco. The procedure accounts for the spatial variability of the phenomenon to be mapped. With the use of measured elevations of the water table, an experimental variogram is constructed that characterizes the spatial variability of the measured water levels. Spherical and Gaussian variogram models are alternatively used to fit the experimental variogram. The models are used to develop contour maps of water table elevations and corresponding estimation variances. The estimation variances express the reliability of the kriged water table elevation maps. Universal kriging also provides a contour map of the expected elevation of the water table (drift). The differences between the expected and measured water table elevations are called residuals from the drift. Residuals from the drift are compared with residuals obtained by more traditional least-squares analysis.     

Characterization of the Structure of River-Bed Gravels Using Two-Dimensional Fractal Analysis

This paper is concerned with the application of fractal analysis to understand the structure of water-worked gravel-bed river surfaces. High resolution digital elevation models, acquired using digital photogrammetric methods, allowed the application of two-dimensional fractal methods. Previous gravel-bed river studies have been based upon sampled profiles and hence one-dimensional fractal characterisation. After basic testing that bed elevation increments are Gaussian, the paper uses two-dimensional variogram surfaces to derive directionally dependent estimates of fractal dimension. The results identify mixed fractal behavior with two characteristic fractal bands, one associated with the subgrain scale and one associated with the grain scale. The subgrain scale characteristics were isotropic and sensitive to decisions made during the data collection process. Thus, it was difficult to differentiate whether these characteristics were real facets of the surfaces studied. The second band was anisotropic and not sensitive to data collection issues. Fractal dimensions were greater in the downstream direction than in other directions suggesting that the effects of water working are to alter the level of surface organisation, by increasing surface irregularity and hence roughness. This is an important observation as it means that water-worked surfaces may have a distinct anisotropic signal, revealed when using a fractal type analysis.     

Compositional characteristics of olivines from Apollo 12 samples

The olivine phenocrysts of four basalts (12004, 12008, 12009 and 12022) are concentrically zoned and have core compositions about as magnesian as experimentally produced liquidas olivines, features which suggest fractional crystallization and absence of Fe-Mg reequilibration. In the magnesium- and olivine-rich granular basalt 12035, the olivines are either unzoned or are zoned toward adjacent grains and have compositions more iron-rich than either cumulus olivines or liquidus olivines (should the rock represent the composition of a melt), features which suggest extensive Fe-Mg re-equilibration.     

TRIFFID Photometry of Globular Cluster Cores — I. Photometric Techniques and Variable Stars in M15

The Galway/DIAS Image Sharpening Camera, TRIFFID, has been used to make observations in two colours of the centre of the post-core-collapse globular cluster M15. We present here our analysis of the photometry in B over two seasons. We have combined the complementary qualities of the HST 's high astrometric precision and TRIFFID's extended coverage and photometric precision, to perform crowded-field photometry in the innermost region of M15. Our technique virtually eliminates the problem of extreme crowding which has hitherto hampered studies of the variable star populations in globular cluster cores, and thereby provides an extension of the HST 's capability. Candidate variables detected with the HST have been confirmed and monitored over longer periods. We show that most of these are RR Lyrae stars, and that one is a short-period Type II Cepheid (the third to be discovered in M15). Our photometric study also produced evidence of a similar number of new variables. These also appear to be RR Lyrae stars, except for a possible eclipsing system. Further data from an upgraded version of TRIFFID have recently been obtained to help to refine the light curves of all these objects.