A sensitivity analysis study for RADM2 mechanism using automatic differentiation

International audienceA sensitivity analysis of an atmospheric multiphase mechanism is performed using an automatic differentiation tool. The sensitivity of some key concentrations is computed with respect to some input parameters (kinetic rates, microphysical parameters). The package odyssee is used in order to obtain the so-called linear tangent model giving the derivatives of outputs with respect to inputs. The direct model takes into account gas-phase reactions, aqueous-phase reactions and interfacial mass transfer and is based on the radm2 mechanism. Local sensitivity coefficients are computed for two different scenarii, rural and sub-urban. We focus in this study on the sensitivity of the gas-phase O3–NOx–HOx system with respect to some aqueous phase reactions and we investigate the influence of the reduction in the photolysis rates in the area below the cloud region. This preliminary work illustrates how powerful automatic differentiation tools may be for the study of large chemical mechanisms. We show for instance that the oxidation of trace metals (FeII, FeIII, Cu+ and Cu2+) in the case of low S(IV) polluted area is not always in disfavor of HOx gaseous concentrations, as it is usually claimed

Numerical simulation of aqueous-phase atmospheric models : use of a non-autonomous rosenbrock method

International audienceWe present in this article an efficient numerical solver for the time integration of atmospheric multiphase chemical kinetics. This solver is based on a second-order Rosenbrock scheme, that has been proposed by Verwer et al. (SIAM J. Sci. Comput. 20 (4) (1999) 1456) for gas-phase chemical kinetics. We show that the stiff time dependence of cloudy events (through liquid water content) has to be solved by the numerical scheme and a non-autonomous version has to be used. We benchmark the non-autonomous ROS2 scheme with the classical LSODE solver for two kinetic schemes. For detailed schemes such as RADM2, the speed-up is of magnitude 5 for the same accuracy

Reduction of multiphase atmospheric chemistry

International audienceThe aim of this article is to investigate the dynamical behaviour of multiphase atmospheric chemical mechanisms. Reducing procedures are applied to a multiphase chemical box model including gas-phase reactions, aqueous-phase reactions and interfacial mass transfer. The lumping of species is computed in an automatic way using an efficient algorithm (APLA). The computed lumped species are related to the fast behaviour of chemical and microphysical processes such as Chapman cycle, ionic dissociations within the cloud drops and interfacial Henry's equilibria. Depending on some parameters (liquid water content, droplet radius) mixed lumped species (including both phases) may also be computed. We show the existence of hierarchical reduced models due to the existence of multiple timescales. We use a special algorithm (DAN2) in order to solve the reduced models. Such models are accurate and the relative error remains under the threshold of 1%. The speed-up is up to a factor 5 compared with a fully implicit method (Gear) for the same accuracy. The key point is that it provides a good qualitative understanding for the behaviour of the kinetic schem

Impact of two chemistry mechanisms fully couples with mesoscale model on the tropospheric pollutants distribution.

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Modeling of atmospheric multiphase chemistry: Numerical integration and sensitivity analysis

International audienceThe presence of clouds in the atmosphere can substantially modify the chemical kinetics and thus the rates of destruction and production of chemical species. Multiphase models are stiffer and rather more difficult to integrate than pure gas models. They contain moreover many physical and microphysical parametres whose values arc often known with poor accuracy. In this paper we focus on two major points. The first one is time integration. We propose the nonautonomous second-order Rosenbrock method in order to solve such heterogenous models. In the second part we focus on the sensitivity analysis of the model outputs with respect to the input parameters using an automatic differentiation tool (ODYSSEE)

Modelling aqueous phase chemistry : numerical integration and sensitivity analysis

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Interannual evolution of (sub)mesoscale dynamics in the Bay of Biscay

International audienceIn the north-east Atlantic Ocean, the Bay of Biscay is an intersection between a coastal constrained dynamics (wide continental shelf and shelf break regions) and an eastern boundary circulation system. In this framework, the eddy kinetic energy is 1 order of magnitude lower than in western boundary systems. To explore this coastal complex system, a high-resolution (1 km, 100 vertical sigma layers) model experiment including tidal dynamics over a period of 10 years (2001-2010) has been implemented. The ability of the numerical environment to reproduce main patterns over interannual scales is demonstrated. Based on this experiment, the features of the (sub)mesoscale processes are described in the deep part of the region (i.e. abyssal plain and continental slope). A system with the development of mixed layer instabilities at the end of winter is highlighted. Beyond confirming an observed behaviour of seasonal (sub)mesoscale activity in other regions, the simulated period allows exploring the interannual variability of these structures. A relationship between the winter maximum of mixed layer depth and the intensity of (sub)mesoscale related activity (vertical velocity, relative vorticity) is revealed and can be explained by large-scale atmospheric forcings (e.g. the cold winter in 2005). The first submesoscale-permitting exploration of this 3-D coastal system shows the importance of (sub)mesoscale activity in this region with its evolution implying a potentially significant impact on vertical and horizontal mixing

Analysis of the interactions taking place in the recognition site of a bimetallic Mg(II) Zn(II) enzyme, isopentenyl diphosphate isomerase. A parallel quantum-chemical and polarizable molecular mechanics study

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Sea Level Expression of Intrinsic and Forced Ocean Variabilities at Interannual Time Scales

International audienceThis paper evaluates in a realistic context the local contributions of direct atmospheric forcing and intrinsic oceanic processes on interannual sea level anomalies (SLAs). A ¼° global ocean-sea ice general circulation model, driven over 47 yr by the full range of atmospheric time scales, is quantitatively assessed against altimetry and shown to reproduce most observed features of the interannual SLA variability from 1993 to 2004. Comparing this simulation with a second driven only by the climatological annual cycle reveals that the intrinsic part of the total interannual SLA variance exceeds 40% over half of the open-ocean area and exceeds 80% over one-fifth of it. This intrinsic contribution is particularly strong in eddy-active regions (more than 70%-80% in the Southern Ocean and western boundary current extensions) as predicted by idealized studies, as well as within the 20°-35° latitude bands. The atmosphere directly forces most of the interannual SLA variance at low latitudes and in most midlatitude eastern basins, in particular north of about 40°N in the Pacific. The interannual SLA variance is almost entirely due to intrinsic processes south of the Antarctic Circumpolar Current in the Indian Ocean sector, while half of this variance is forced by the atmosphere north of it. The same simulations were performed and analyzed at 2° resolution as well: switching to this laminar regime yields a comparable forced variability (large-scale distribution and magnitude) but almost suppresses the intrinsic variability. This likely explains why laminar ocean models largely underestimate the interannual SLA variance