Coupling Between the Thermosphere and the Stratosphere: the Role of Nitric Oxide

In order to understand the lower ionosphere and its probable control by dynamical processes, the behavior of nitric oxide below 100 km was investigated. A two dimensional model with coupled chemical and dynamical processes was constructed. Calculations based on the model reveal that the chemical conditions at the stratopause are related to the state of the thermosphere. This coupling mechanism can be partly explained by the downward transport of nitric oxide during the winter season, and consequently depends on the dynamical conditions in the mesosphere and in the lower thermosphere (mean circulation and waves). In summer, the photodissociation of nitric oxide plays an important role and the thermospheric NO abundance modulates the radiation field reaching the upper stratosphere. Perturbations in the nitric oxide concentration above the mesopause could therefore have an impact in the vicinity of the stratopause

The potential impact on atmospheric ozone and temperature of increasing trace gas concentrations

The response of the atmosphere to emissions of chlorofluorocarbons (CFCs) and other chlorocarbons, and to increasing concentrations of other radiatively active trace gases such as CO2, CH4, and N2O is calculated by a coupled chemical-radiative transport one-dimensional model. It is shown that significant reductions in the ozone concentration and in the temperature are expected in the upper stratosphere as a result of increasing concentrations of active chlorine produced by photodecomposition of the CFCs. The ozone content is expected to increase in the troposphere, as a consequence of increasing concentrations of methane and nitrogen oxides. Due to enhanced greenhouse effects, the Earth's surface should warm up by several degrees. The amplitude and even the sign of future changes in the ozone column are difficult to predict as they are strongly scenario-dependent. An early detection system to prevent noticeable ozone changes as a result of increasing concentrations of source gases should thus be based on a continuous monitoring of the ozone amount in the upper stratosphere rather than on measurements of the ozone column only. Measurements of NOx, Clx, and HOx are also required for unambiguous trend detection and interpretation

The Invalidity of the Laplace Law for Biological Vessels and of Estimating Elastic Modulus from Total Stress vs. Strain: a New Practical Method

The quantification of the stiffness of tubular biological structures is often obtained, both in vivo and in vitro, as the slope of total transmural hoop stress plotted against hoop strain. Total hoop stress is typically estimated using the "Laplace law." We show that this procedure is fundamentally flawed for two reasons: Firstly, the Laplace law predicts total stress incorrectly for biological vessels. Furthermore, because muscle and other biological tissue are closely volume-preserving, quantifications of elastic modulus require the removal of the contribution to total stress from incompressibility. We show that this hydrostatic contribution to total stress has a strong material-dependent nonlinear response to deformation that is difficult to predict or measure. To address this difficulty, we propose a new practical method to estimate a mechanically viable modulus of elasticity that can be applied both in vivo and in vitro using the same measurements as current methods, with care taken to record the reference state. To be insensitive to incompressibility, our method is based on shear stress rather than hoop stress, and provides a true measure of the elastic response without application of the Laplace law. We demonstrate the accuracy of our method using a mathematical model of tube inflation with multiple constitutive models. We also re-analyze an in vivo study from the gastro-intestinal literature that applied the standard approach and concluded that a drug-induced change in elastic modulus depended on the protocol used to distend the esophageal lumen. Our new method removes this protocol-dependent inconsistency in the previous result.Comment: 34 pages, 13 figure

Comparison between observed and calculated distributions of trace species in the middle atmosphere

The purpose is to identify major discrepancies between empirical models and theoretical models and to stress the need for additional observations in the atmosphere and for further laboratory work, since these differences suggest either problems associated with observation techniques or errors in chemical kinetics data (or the existence of unknown processes which appear to play an important role). The model used for this investigation extends from the earth's surface to the lower thermosphere. It includes the important chemical and photochemical processes related to the oxygen, hydrogen, carbon, nitrogen and chlorine families. The chemical code is coupled with a radiative scheme which provides the heating rate due to absorption of solar radiation by ozone and the cooling rate due to the emission and absorption of terrestrial radiation by CO2, H2O and O3. The vertical transport of the species is expressed by an eddy diffusion parameterization

Local structure of intercomponent energy transfer in homogeneous turbulent shear flow

Intercomponent energy transfer by pressure-strain-rate was investigated for homogeneous turbulent shear flow. The rapid and slow parts of turbulent pressure (decomposed according to the influence of the mean deformation rate) are found to be uncorrelated; this finding provides strong justification for current modeling procedure in which the pressure-strain-rate term is split into the corresponding parts. Issues pertinent to scales involved in the intercomponent energy transfer are addressed in comparison with those for the Reynolds-stress and vorticity fields. A physical picture of the energy transfer process is described from a detailed study of instantaneous events of high transfer regions. It was found that the most significant intercomponent energy transfer events are highly localized in space and are imbedded within a region of concentrated vorticity

Pressure-strain-rate events in homogeneous turbulent shear flow

A detailed study of the intercomponent energy transfer processes by the pressure-strain-rate in homogeneous turbulent shear flow is presented. Probability density functions (pdf's) and contour plots of the rapid and slow pressure-strain-rate show that the energy transfer processes are extremely peaky, with high-magnitude events dominating low-magnitude fluctuations, as reflected by very high flatness factors of the pressure-strain-rate. A concept of the energy transfer class was applied to investigate details of the direction as well as magnitude of the energy transfer processes. In incompressible flow, six disjoint energy transfer classes exist. Examination of contours in instantaneous fields, pdf's and weighted pdf's of the pressure-strain-rate indicates that in the low magnitude regions all six classes play an important role, but in the high magnitude regions four classes of transfer processes, dominate. The contribution to the average slow pressure-strain-rate from the high magnitude fluctuations is only 50 percent or less. The relative significance of high and low magnitude transfer events is discussed

The Importance of fundamental science for society: The success story of Ozone research

The successful story of ozone research from the discovery of this gas in the laboratory in 1839 to the protection of the stratospheric ozone layer by the Montreal Protocol in 1987 highlights the role and importance of fundamental research. None of the scientists who discovered the chemical nature and properties of ozone, and established its presence in the atmosphere, suspected that humans would be able to destroy a protective stratospheric layer that is essential for life on Earth. None of them had anticipated either that the emissions of pollutants associated with industrial activity and road transportation in urban areas would generate summertime ozone smog events with detrimental health effects and premature mortality. Scientific research has provided the knowledge needed to convince governments to take effective legislation to ban the industrial production of stratospheric ozone depleting agents and reduce the emissions of ozone precursors in the troposphere. This perspective paper calls for enhanced support of a strong fundamental research activity that rewards imagination and protects the scientific community from tight administrative and financial constraints. It highlights the need for scientists to keep a free and independent mind that leads to progress and innovation

The response of the middle atmosphere to long-term and short-term solar variability: a two-dimensional model

A two-dimensional chemical-dynamical-radiative model of the middle atmosphere is used to investigate the potential changes of temperature, ozone, and other chemical constituents in response tovariations in the solar ultraviolet flux, associated with the solar rotation (27 days) and the solar cycle (11 years). The model reproduces satisfactorily the response (amplitude and phase) to the 27-day forcing of ozone and temperature in the stratosphere but does not properly explain the ozone and temperature r sponses of opposite sign observed near 70 km altitude. The change in the ozone column abundance associated with the 27-day solar forcing is estimated to be less than 0.5%. Variations in middle and upper atmospheric ozone concentrations and temperatures induced by solar variations on the ll-year time scale are not negligible compared to changes produced as a result of human activities over the same period of time. The calculated change in the ozone column abundance from solar minimum to solar maximum conditions is of the order of 1.1-1.3 % in the tropics and increases with latitude, especially in winter, to reach up to 1.5-1.7 % in the polar regions. There are large unexplained ifferences between the calculated and observed stratospheric responses. For example, in the photochemically controlled region of the upper stratosphere, the model seems to underestimate the ozone response by more than a factor 2. In addition, the negative temperature and ozone responses observed in the lower stratosphere cannot be reproduced by the model. Potential dynamical feedbacks exist, but reliable data sets covering a period longer than one solar cycle have to become available before this problem can adequately be addressed. 1