Simulation of Stratospheric Water Vapor Trends: Impact on Stratospheric Ozone Chemistry

A transient model simulation of the 40-year time period 1960 to 1999 with the coupled climate-chemistry model (CCM) ECHAM4.L39(DLR)/CHEM shows a stratospheric water vapor increase over the last two decades of 0.7 ppmv and, additionally, a short-term increase after major volcanic eruptions. Furthermore, a long-term decrease in global total ozone as well as a short-term ozone decline in the tropics after volcanic eruptions are modeled. In order to understand the resulting effects of the water vapor changes on lower stratospheric ozone chemistry, different perturbation simulations were performed with the CCM ECHAM4.L39- (DLR)/CHEM feeding the water vapor perturbations only to the chemistry part. Two different long-term perturbations of lower stratospheric water vapor, +1 ppmv and +5 ppmv, and a short-term perturbation of +2 ppmv with an e-folding time of two months were applied. An additional stratospheric water vapor amount of 1 ppmv results in a 5–10% OH increase in the tropical lower stratosphere between 100 and 30 hPa. As a direct consequence of the OH increase the ozone destruction by the HOx cycle becomes 6.4% more effective. Coupling processes between the HOx-family and the NOx/ClOxfamily also affect the ozone destruction by other catalytic reaction cycles. The NOx cycle becomes 1.6% less effective, whereas the effectiveness of the ClOx cycle is again slightly enhanced. A long-term water vapor increase does not only affect gas-phase chemistry, but also heterogeneous ozone chemistry in polar regions. The model results indicate an enhanced heterogeneous ozone depletion during antarctic spring due to a longer PSC existence period. In contrast, PSC formation in the northern hemisphere polar vortex and therefore heterogeneous ozone depletion during arctic spring are not affected by the water vapor increase, because of the less PSC activity. Finally, this study shows that 10% of the global total ozone decline in the transient model run can be explained by the modeled water vapor increase, but the simulated tropical ozone decrease after volcanic eruptions is caused dynamically rather than chemically

A strategy for climate evaluation of aircraft technology: an efficient climate impact assessment tool ? AirClim

International audienceClimate change is a challenge to society and to cope with requires assessment tools which are suitable to evaluate new technology options with respect to their impact on climate. Here we present AirClim, a model which comprises a linearisation of the processes occurring from the emission to an estimate in near surface temperature change, which is presumed to be a reasonable indicator for climate change. The model is designed to be applicable to aircraft technology, i.e.~the climate agents CO2, H2O, CH4 and O3 (latter two resulting from NOx-emissions) and contrails are taken into account. It employs a number of precalculated atmospheric data and combines them with aircraft emission data to obtain the temporal evolution of atmospheric concentration changes, radiative forcing and temperature changes. The linearisation is based on precalculated data derived from 25 steady-state simulations of the state-of-the-art climate-chemistry model E39/C, which include sustained normalised emissions at various atmospheric regions. The results show that strongest climate impacts from ozone changes occur for emissions in the tropical upper troposphere (60 mW/m²; 80 mK for 1 TgN emitted), whereas from methane in the middle tropical troposphere (?2.7% change in methane lifetime; ?30 mK per TgN). The estimate of the temperature changes caused by the individual climate agents takes into account a perturbation lifetime, related to the region of emission. A comparison of this approach with results from the TRADEOFF and SCENIC projects shows reasonable agreement with respect to concentration changes, radiative forcing, and temperature changes. The total impact of a supersonic fleet on radiative forcing (mainly water vapour) is reproduced within 5%. For subsonic air traffic (sustained emissions after 2050) results show that although ozone-radiative forcing is much less important than that from CO2 for the year 2100. However the impact on temperature is of comparable size even when taking into account temperature decreases from CH4. That implies that all future measures for climate stabilisation should concentrate on both CO2 and NOx emissions. A direct comparison of super- with subsonic aircraft (250 passengers, 5400 nm) reveals a 5 times higher climate impact of supersonics

Climatologies of streamer events derived from a transport model and a coupled chemistry-climate model

International audienceStreamers, i.e. finger-like structures, reach from lower into extra-tropical latitudes. They can be detected in N2O or O3 distributions on single lower stratospheric layers in mid-latitudes since they are characterised by high N2O or low O3 values compared to undisturbed mid-latitude values. If irreversible mixing occurs, streamer events significantly contribute to the transfer of tropical air masses to mid-latitudes which is also an exchange of upper tropospheric and stratospheric air. A climatology of streamer events has been established, employing the chemical-transport model KASIMA, which is driven by ECMWF re-analyses (ERA) and operational analyses. For the first time, the seasonal and the geographical distribution of streamer frequencies has been determined on the basis of 9 years of observations. For the current investigation, a meridional gradient criterion has been newly formulated and applied to the N2O distributions calculated with KASIMA. The climatology has been derived by counting all streamer events between 21 and 25 km for the years 1990 to 1998. It has been further used for the validation of a streamer climatology which has been established in the same way employing data of a multi-year simulation with the coupled chemistry-climate model ECHAM4.L39(DLR)/CHEM (E39/C). It turned out that both climatologies are qualitatively in fair agreement, in particular in the northern hemisphere, where much higher streamer frequencies are found in winter than in summer. In the southern hemisphere, KASIMA analyses indicate strongest streamer activity in September. E39/C streamer frequencies clearly offers an offset from June to October, pointing to model deficiencies with respect to tropospheric dynamics. KASIMA and E39/C results fairly agree from November to May. Some of the findings give strong indications that the streamer events found in the altitude region between 21 and 25 km are mainly forced from the troposphere and are not directly related to the dynamics of the stratosphere, in particular not to the dynamics of the polar vortex. Sensitivity simulations with E39/C, which represent recent and possible future atmospheric conditions, have been employed to answer the question how climate change would alter streamer frequencies. It is shown that the seasonal cycle does not change but that significant changes occur in months of minimum and maximum streamer frequencies. This could have an impact on mid-latitude distribution of chemical tracers and compounds. The influence of streamers on the mid-latitude ozone budget has been assessed by applying a special E39/C model configuration. The streamer transport of low ozone is simply inhibited by filling up its ozone content according to the surrounding air masses. It shows that the importance of streamers for the ozone budget strongly decreases with altitude. At 15 km streamers lead to a decrease of ozone by 80%, whereas around 25 km it is only 1 to 5% and at mid-latitude tropopause, ozone decreases by 30% (summer) to 50% (winter)

The Hubbard Model at Infinite Dimensions: Thermodynamic and Transport Properties

We present results on thermodynamic quantities, resistivity and optical conductivity for the Hubbard model on a simple hypercubic lattice in infinite dimensions. Our results for the paramagnetic phase display the features expected from an intuitive analysis of the one-particle spectra and substantiate the similarity of the physics of the Hubbard model to those of heavy fermion systems. The calculations were performed using an approximate solution to the single-impurity Anderson model, which is the key quantity entering the solution of the Hubbard model in this limit. To establish the quality of this approximation we compare its results, together with those obtained from two other widely used methods, to essentially exact quantum Monte Carlo results.Comment: 29 pages, 16 figure

Attribution of ozone changes to dynamical and chemical processes in CCMs and CTMs

Chemistry-climate models (CCMs) are commonly used to simulate the past and future development of Earth's ozone layer. The fully coupled chemistry schemes calculate the chemical production and destruction of ozone interactively and ozone is transported by the simulated atmospheric flow. Due to the complexity of the processes acting on ozone it is not straightforward to disentangle the influence of individual processes on the temporal development of ozone concentrations. A method is introduced here that quantifies the influence of chemistry and transport on ozone concentration changes and that is easily implemented in CCMs and chemistry-transport models (CTMs). In this method, ozone tendencies (i.e. the time rate of change of ozone) are partitioned into a contribution from ozone production and destruction (chemistry) and a contribution from transport of ozone (dynamics). The influence of transport on ozone in a specific region is further divided into export of ozone out of that region and import of ozone from elsewhere into that region. For this purpose, a diagnostic is used that disaggregates the ozone mixing ratio field into 9 separate fields according to in which of 9 predefined regions of the atmosphere the ozone originated. With this diagnostic the ozone mass fluxes between these regions are obtained. Furthermore, this method is used here to attribute long-term changes in ozone to chemistry and transport. The relative change in ozone from one period to another that is due to changes in production or destruction rates, or due to changes in import or export of ozone, are quantified. As such, the diagnostics introduced here can be used to attribute changes in ozone on monthly, interannual and long-term time-scales to the responsible mechanisms. Results from a CCM simulation are shown here as examples, with the main focus of the paper being on introducing the method

Anomalous Normal-State Properties of High-Tc_c Superconductors -- Intrinsic Properties of Strongly Correlated Electron Systems?

A systematic study of optical and transport properties of the Hubbard model, based on Metzner and Vollhardt's dynamical mean-field approximation, is reviewed. This model shows interesting anomalous properties that are, in our opinion, ubiquitous to single-band strongly correlated systems (for all spatial dimensions greater than one), and also compare qualitatively with many anomalous transport features of the high-T$_c$ cuprates. This anomalous behavior of the normal-state properties is traced to a ``collective single-band Kondo effect,'' in which a quasiparticle resonance forms at the Fermi level as the temperature is lowered, ultimately yielding a strongly renormalized Fermi liquid at zero temperature.Comment: 27 pages, latex, 13 figures, Invited for publication in Advances in Physic

Staggered Pairing Phenomenology for UPd_2Al_3 and UNi_2Al_3

We apply the staggered-pairing Ginzburg-Landau phenomenology to describe superconductivity in UPd_2Al_3 and UNi_2Al_3. The phenomenology was applied successfully to UPt_3 so it explains why these materials have qualitatively different superconducting phase diagrams although they have the same point-group symmetry. UPd_2Al_3 and UNi_2Al_3 have a two-component superconducting order parameter transforming as an H-point irreducible representation of the space group. Staggered superconductivity can induce charge-density waves characterized by new Bragg peaks suggesting experimental tests of the phenomenology.Comment: 4 pages, REVTeX, 2 Postscript figure

Phase Diagram of the Two-Channel Kondo Lattice

The phase diagram of the two-channel Kondo lattice model is examined with a Quantum Monte Carlo simulation in the limit of infinite dimensions. Commensurate (and incommensurate) antiferromagnetic and superconducting states are found. The antiferromagnetic transition is very weak and continuous; whereas the superconducting transition is discontinuous to an odd-frequency channel-singlet and spin-singlet pairing state.Comment: 5 pages, LaTeX and 4 PS figures (see also cond-mat/9609146 and cond-mat/9605109

Climate sensitivity of radiative impacts from transport systems

Comparing individual components of a total climate impact is traditionally done in terms of radiative forcing. However, the climate impact of transport systems includes contributions that are likely to imply climate sensitivity parameters distinctly different from the “reference value” for a homogeneous CO2 perturbation. We propose to introduce efficacy factors for each component into the assessment. The way of proceeding is illustrated using aviation as an example, and prospects for evaluating the other transport system in the EU project QUANTIFY are given

"Exhaustion" Physics in the Periodic Anderson Model using Iterated Perturbation Theory

We discuss the "exhaustion" problem in the context of the Periodic Anderson Model using Iterated Perturbation Theory(IPT) within the Dynamical Mean Field Theory. We find that, despite its limitations, IPT captures the exhaustion physics, which manifests itself as a dramatic, strongly energy dependent suppression of the effective Anderson impurity problem. As a consequence, low energy scales in the lattice case are strongly suppressed compared to the "Kondo scale" in the single-impurity picture. The IPT results are in qualitative agreement with recent Quantum Monte Carlo results for the same problem.Comment: 13 preprint pages including 1 table and 4 eps figures, replaced by revised version, accepted for publication in Europhysics Letters, added references and conten