Impact of high solar zenith angles on dynamical and chemical processes in a coupled chemistry-climate model

International audienceActinic fluxes at high solar zenith angles (SZAs) are important for atmospheric chemistry, especially under twilight conditions in polar winter and spring. The results of a sensitivity experiment employing the fully coupled 3D chemistry-climate model ECHAM4.L39(DLR)/CHEM have been analysed to quantify the impact of SZAs greater than 87.5° on dynamical and chemical processes in the lower stratosphere, in particular their influence on the ozone layer. Although the actinic fluxes at SZAs larger than 87.5° are small, ozone concentrations are significantly affected because daytime photolytic ozone destruction is switched on earlier, especially the conversion of Cl2 and Cl2O2 into ClO at the end of polar night in the lower stratosphere. Comparing climatological mean ozone column values of a simulation considering SZAs up to 93° with those of the sensitivity run with SZAs confined to 87.5° total ozone is reduced by about 20% in the polar Southern Hemisphere, i.e., the ozone hole is "deeper'' if twilight conditions are considered in the model because there is 2?3 weeks more time for ozone destruction. This causes an additional cooling of the polar lower stratosphere (50 hPa) up to ?4 K with obvious consequences for chemical processes. In the Northern Hemisphere the impact of high SZAs cannot be determined on the basis of climatological mean values due to the pronounced dynamic variability of the stratosphere in winter and spring

The impact of the spacecraft system SÄNGER on the composition of the middle atmosphere

A two-dimensional chemical model and physical considerations are used to estimate the impact of the spacecraft system SÄNGER on stratospheric and mesospheric ozone in relation to other spacecraft and other anthropogenic perturbations. Perturbations of middle atmospheric NOy H2O and H2 concentrations, and their impact on the radiative balance of the atmosphere, including contrail formation, are discussed. It is found, that in case of about 24 launches per year the perturbations due to SÄGER are about negligible on a global scale. However, if a SÄGER version would be used for a hypersonic fleet of commercial aircraft a serious ozone depletion is predicted. © 1992 by Wax Planck Society

Nitrogen compounds and ozone in the stratosphere: comparison of MIPAS satellite data with the Chemistry Climate Model ECHAM5/MESSy1

International audienceThe chemistry climate model ECHAM5/MESSy1 (E5/M1) in a setup extending from the surface to 80 km with a vertical resolution of about 600 m near the tropopause with nudged tropospheric meteorology allows a direct comparison with satellite data of chemical species at the same time and location. Here we present results out of a transient 10 years simulation for the period of the Antarctic vortex split in September 2002, where data of MIPAS on the ENVISAT-satellite are available. For the first time this satellite instrument opens the opportunity, to evaluate all stratospheric nitrogen containing species simultaneously with a good global coverage, including the source gas N2O which allows an estimate for NOx-production in the stratosphere. We show correlations between simulated and observed species in the altitude region between 10 and 50 hpa for different latitude belts, together with the Probability Density Functions (PDFs) of model results and observations. This is supplemented by global charts on pressure levels showing the satellite data and the simulated data sampled at the same time and location. We demonstrate that the model in most cases captures the partitioning in the nitrogen family, the diurnal cycles and the spatial distribution within experimental uncertainty. There appears to be, however, a problem to reproduce the observed nighttime partitioning between N2O5 and NO2 in the middle stratosphere

Nature of the spin dynamics and 1/3 magnetization plateau in azurite

We present a specific heat and inelastic neutron scattering study in magnetic fields up into the 1/3 magnetization plateau phase of the diamond chain compound azurite Cu$_3$(CO$_3$)$_2$(OH)$_2$. We establish that the magnetization plateau is a dimer-monomer state, {\it i.e.}, consisting of a chain of $S = 1/2$ monomers, which are separated by $S = 0$ dimers on the diamond chain backbone. The effective spin couplings $J_{mono}/k_B = 10.1(2)$ K and $J_{dimer}/k_B = 1.8(1)$ K are derived from the monomer and dimer dispersions. They are associated to microscopic couplings $J_1/k_B = 1(2)$ K, $J_2/k_B = 55(5)$ K and a ferromagnetic $J_3/k_B = -20(5)$ K, possibly as result of $d_{z^2}$ orbitals in the Cu-O bonds providing the superexchange pathways.Comment: 5 pages, 4 figure

Effects of Two Energy Scales in Weakly Dimerized Antiferromagnetic Quantum Spin Chains

By means of thermal expansion and specific heat measurements on the high-pressure phase of (VO)$_2$P$_2$O$_7$, the effects of two energy scales of the weakly dimerized antiferromagnetic $S$ = 1/2 Heisenberg chain are explored. The low energy scale, given by the spin gap $\Delta$, is found to manifest itself in a pronounced thermal expansion anomaly. A quantitative analysis, employing T-DMRG calculations, shows that this feature originates from changes in the magnetic entropy with respect to $\Delta$, $\partial S^{m}/ \partial \Delta$. This term, inaccessible by specific heat, is visible only in the weak-dimerization limit where it reflects peculiarities of the excitation spectrum and its sensitivity to variations in $\Delta$.Comment: 4 pages, 4 figures now identical with finally published versio

Magnetoelastic and structural properties of azurite Cu3(CO3)2(OH)2 from neutron scattering and muon spin rotation

Azurite, Cu3(CO3)2(OH)2, has been considered an ideal example of a one-dimensional (1D) diamond chain antiferromagnet. Early studies of this material imply the presence of an ordered antiferromagnetic phase below $T_N \sim 1.9$ K while magnetization measurements have revealed a 1/3 magnetization plateau. Until now, no corroborating neutron scattering results have been published to confirm the ordered magnetic moment structure. We present recent neutron diffraction results which reveal the presence of commensurate magnetic order in azurite which coexists with significant magnetoelastic strain. The latter of these effects may indicate the presence of spin frustration in zero applied magnetic field. Muon spin rotation, $\mu$SR, reveals an onset of short-range order below 3K and confirms long-range order below $T_N$.Comment: 5 pages, 4 figures, PHYSICAL REVIEW B 81, 140406(R) (2010