Modelling the budget of middle atmospheric water vapour isotopes

A one-dimensional chemistry model is applied to study the stable hydrogen (D) and stable oxygen isotope (17O, 18O) composition of water vapour in stratosphere and mesosphere. In the troposphere, this isotope composition is determined by “physical” fractionation effects, that are phase changes (e.g. during cloud formation), diffusion processes (e.g. during evaporation from the ocean), and mixing of air masses. Due to these processes water vapour entering the stratosphere first shows isotope depletions in D/H relative to ocean water, which are 5 times of those in 18O/16O, and secondly is mass-dependently fractionated (MDF), i.e. changes in the isotope ratio 17O/16O are 0.52 times of those of 18O/16O. In contrast, in the stratosphere and mesosphere “chemical” fractionation mechanisms, that are the production of H2O due to the oxidation of methane, re-cycling of H2O via the HOx family, and isotope exchange reactions considerably enhance the isotope ratios in the water vapour imported from the troposphere. The model reasonably predicts overall enhancements of the stable isotope ratios in H2O by up to 25% for D/H, 8.5% for 17O/16O, and 14% for 18O/16O in the mesosphere relative to the tropopause values. The 17O/16O and 18O/16O ratios in H2O are shown to be a measure of the relative fractions of HOx that receive the O atom either from the reservoirs O2 or O3. Throughout the middle atmosphere, MDF O2 is the major donator of oxygen atoms incorporated in OH and HO2 and thus in H2O. In the stratosphere the known mass-independent fractionation (MIF) signal in O3 is in a first step transferred to the NOx family and only in a second step to HOx and H2O. In contrast to CO2, O(1D) only plays a minor role in this MIF transfer. The major uncertainty in our calculation arises from poorly quantified isotope exchange reaction rate coefficients and kinetic isotope fractionation factors

Seasonal and latitudinal variation of atmospheric methane: a ground-based and ship-borne solar IR spectroscopic study

Column-averaged volume mixing ratios of CH4 were retrieved with a precision of better than 0.5% from infrared solar absorption spectra obtained at Ny-Alesund (Spitsbergen, 79 N) between 1997 and 2004 and during two ship cruises (54 N–34 S) on the Atlantic in 2003. The retrieval has been performed in a spectral region available to all operational FTIR (Fourier Transform InfraRed) spectrometers performing solar absorption measurements. The seasonality and the long-term increase of the tropospheric volume-mixing ratio, derived from the infrared measurements agree well with data from surface sampling at this site. The latitudinal variation of shipborne measurements between 54 N and 34 S is in agreement with inverse model simulations which are optimized vs. the global NOAA/ESRL measurements

Entwicklung eines Lagrangeschen Chemiemodells der Stratosphaere Abschlussbericht

Strong ozone losses are observed in the Arctic stratosphere. They can be qualitatively understood in terms of chlorine chemistry. A quantitative understanding is missing however. In the frame of this project, a novel chemical transport model has been developed. It is aimed at a description of the chemistry of the stratosphere together with advection and mixing of air-masses. The model - taking observations into account as well - is used to advance our knowledge of the chemistry and physics of the stratosphere. First calculations for the winter 1996-1997 show strong ozone losses in the polar vortex in denitrified air. The model thus simulates a strong inhomogeneity of the air masses inside the vortex. This was not known previously and can only be simulated with CLaMS owing to the newly developed transport scheme. Future applications of CLaMS regard the ozone loss in mid-latitudes and the coupling of climate issues and ozone loss and thus by implication prognostic questions. (orig.)Starke Ozonverluste in der arktischen Stratosphaere were beobachtet und koennen durch Chlorchemie qualitativ erklaert werden. Ein quantitatives Verstaendnis fehlt jedoch noch. Im Vorhaben wurde eine neuartiges Chemie-Transportmodell entwickelt um die Chemie der Stratosphaere in Zusammenhang mit Advection und Mischung von Luftmassen zu beschreiben. Das Modell wird angewendet um - unter Einbeziehung von Messdaten - Fortschritte im Verstaendnis der stratosphaerischen Chemie und Physik zu erreichen. Erste Rechnungen fuer den Winter 1996-1997 zeigen starke Ozonverluste im Polarwirbel in denitrifizierten Luftmassen. Vom Modell wird daher eine starke Inhomogenitaet der Luftmassen im Wirbel simuliert. Dies war bislang nicht bekannt, laesst sich aber mittels ClaMS aufgrund des neuartigen Transportschemas deutlich nachweisen. Zukuenftige Anwendungen von CLaMS betreffen den Ozonverlust in mittleren Breiten und die Kopplung von Ozonverlust und Klimaentwicklung und somit prognostische Fragen. (orig.)Available from TIB Hannover: F01B511 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

State of the Climate in 2012

International audienceEditors note: For easy download the posted pdf of the State of the Climate for 2012 is a very low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download