Stratospheric processes: Observations and interpretation

Explaining the observed ozone trends discussed in an earlier update and predicting future trends requires an understanding of the stratospheric processes that affect ozone. Stratospheric processes occur on both large and small spatial scales and over both long and short periods of time. Because these diverse processes interact with each other, only in rare cases can individual processes be studied by direct observation. Generally the cause and effect relationships for ozone changes were established by comparisons between observations and model simulations. Increasingly, these comparisons rely on the developing, observed relationships among trace gases and dynamical quantities to initialize and constrain the simulations. The goal of this discussion of stratospheric processes is to describe the causes for the observed ozone trends as they are currently understood. At present, we understand with considerable confidence the stratospheric processes responsible for the Antarctic ozone hole but are only beginning to understand the causes of the ozone trends at middle latitudes. Even though the causes of the ozone trends at middle latitudes were not clearly determined, it is likely that they, just as those over Antarctica, involved chlorine and bromine chemistry that was enhanced by heterogeneous processes. This discussion generally presents only an update of the observations that have occurred for stratospheric processes since the last assessment (World Meteorological Organization (WMO), 1990), and is not a complete review of all the new information about stratospheric processes. It begins with an update of the previous assessment of polar stratospheres (WMO, 1990), followed by a discussion on the possible causes for the ozone trends at middle latitudes and on the effects of bromine and of volcanoes

Structure cristalline du bromhydrate de pipéridine

A crystallographic study of HBr piperidine, C₅H₁₁N • HBr was made by X-ray diffraction and optical transform methods. A comparison is made with the HCl piperidine structure. The refinement has been conducted by least squares applied to 214 reflections measured from precession photographs obtained with MoKα radiation. The cell constants are : a = 9.98 ± 0.03 Å b = 9.97 ± 0.01 Å c = 7.69 ± 0.02 Å with space group Pcmb.On a fait l'étude cristallographique du bromhydrate de pipéridine C₅H₁₁N • HBr au moyen de la diffraction de rayons X et des méthodes de la transformée optique. La structure est comparée à celle du chlorhydrate de pipéridine. L'affinement a été fait par la méthode des moindres carrés sur 214 taches de diffraction mesurées sur les clichés obtenus sur une chambre de précession avec la radiation MoKα. Les paramètres de la maille élémentaire sont : a = 9,98 ± 0,03 Å b = 9,97 ± 0,01 Å c = 7,69 ± 0,02 Å avec le groupe spatial Pcmb.Escobar Carmen, Cid Hilda, Boys Daphné, Prendez Margarita. Structure cristalline du bromhydrate de pipéridine. In: Bulletin de la Société française de Minéralogie et de Cristallographie, volume 96, 3, 1973. pp. 215-217