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.     

Structures caused by repeated freezing and thawing in various loamy sediments: A comparison of active,fossil and experimental data

In this paper, the authors present the results of both macroscopic and microscopic investigations on structure development created by repeated ice lensing in various loamy experiments. Experimental data are compared with observations performed on active forms in High Arctic and Alpine Mountain environments. Those observations are also compared with phenomena observed in fossil periglacial formations of Western Europe. Platy and short prismatic structure formation is bonded to the hydraulic and thermal conditions during ice segregation. When a long series of alternating freezing and thawing affects platy structures, the fabric evolves, also being influenced by slope and drainage conditions: cryoturbations, frostcreep, and gelifluction can appear. They are characterized by specific microfabrics which are better developed with an increasing number of cycles: this is clear in experiments where hydraulic and thermal parameters are better controlled. Vesicles are also a prominent characteristic of the surface horizon in experiments and arctic soils. The genesis of vesicles is discussed on the basis of new observations and is related to the mechanical collapse of frost-created aggregates under the mechanical work of soil air escape during soil saturation by water at thaw.     

Flow characteristics above a very low and gently sloping hill

Tower measurements of wind and turbulence in near neutral conditions at the top of a very low and gently sloping hill (height ~ 20 m, with a length scale ~ 1000 m) are analysed in terms of current flow-over-hill theory. Measurements of wind maximum height and the change of the variances of the three wind components from the inner to the outer region are found to be in agreement with predictions from the theory. Spectra of the longitudinal and vertical wind components in the inner region, scaled according to Panofsky et al. (1982), come close to the corresponding Kansas curves in the high frequency range. They have higher energy in the low frequency region, probably a spectral lag effect caused by rougher upwind terrain. In the outer region, the spectra coincide with the corresponding Kansas curves if normalized by their respective variances and plotted against f/f _m.     

On modelling the seasonal thermodynamic cycle of sea ice in studies of climatic change

Recent work in modelling climatic changes due to increased atmospheric CO₂ has shown the maximum change to occur in the polar regions as a result of seasonal reductions in sea ice coverage. Typically, sea ice thermodynamics is modelled in a very simple way, whereby the storage of both sensible and latent heat within the ice is ignored, and the effects of snow cover on conductivity and on surface albedo and of oceanic heat flux on bottom ablation may also be neglected. This paper considers whether omission of these processes is justified within the context of quantitatively determining regional climatic changes. A related question, whether omission of ice dynamics can be justified, is not considered.Relatively complete one-dimensional models of sea-ice thermodynamics have previously been developed and tested for a variety of environmental conditions by Maykut and Untersteiner (1969, 1971) and by Semtner (1976). A simpler model which neglects the storage of sensible and latent heat is described in the Appendix to Semtner (1976). In that model, the errors in annual-mean ice thickness which would arise from neglect of heat storage can be compensated by increases in albedo and in conductivity. Here we examine the seasonal cycle of ice thickness predicted by such a model and find significant errors in phase (one month lead) and in amplitude (50% overestimate). The amplitude errors are enhanced as snowfall and oceanic heat flux diminish (or are neglected). This suggests that substantial errors may occur in climate simulations which use very simple formulations of sea ice thermodynamics, whereby early and excessive melting exaggerates the seasonal disappearance of sea ice.To illustrate the above point, two models are configured to examine the local response of Arctic sea ice to a quadrupling of atmospheric CO₂. The first model neglects a number of physical processes and mimics the behavior of sea ice found in Manabe and Stouffer (1980), both for present and enhanced levels of CO₂. The more complete second model gives a better simulation of Arctic ice for the present level of CO₂ and shows a reduced response to CO₂ quadrupling relative to that in Manabe and Stouffer (1980). In particular, the change in surface temperature is cut by a factor of two. In view of this result, a more complete treatment of sea ice thermodynamics would seem warranted in further studies of climate change. Only a minor computational increase is required.A portion of this study is supported by the U.S. Department of Energy as a part of its Carbon Dioxide Research Program.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

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.     

Effects of deforestation and afforestation on climate

Forests cover 29% of the continents. Their importance for mankind is not only due to wood production but also by their manyfold influences on the biosphere. The properties of forest stands influence climate, water balance, air constituents and the dynamic of atmosphere. The welfare functions of forests can be observed in the global as well as in the local or microscale. Anthropogenic measures, as deforestation and air pollution, endanger the forests and by that one of the main pillars of nature on earth.     

Meeresoptische Messungen während schwerer Stürme auf der Forschungsplattform “Nordsee” vom 14. November bis zum 8. Dezember 1980

Ocean Dynamics - Meeresoptische Messungen auf der Forschungsplattform “Nordsee” haben gezeigt, daß dort während schwerer Stürme, hauptsächlich durch den Einfluß...