Panos Hadjinicolaou

Variability of total ozone due to the NAO as represented in two different model systems

To explain regional trends and long time variability of ozone the understanding and quantie cation of dynamical mechanisms ine uencing the zonal asymmetry of ozone is essential. Therefore we assess here the relationship between total ozone variability and the North Atlantic Oscillation (NAO), one of the dominant modes of variability in the European sector using two different model systems in conjunction with the same simplie ed ozone chemistry. One model is the Met Ofe ce Unie ed Model, which is a comprehensive general circulation model forced by prescribed sea-surface temperatures only. The other model is the chemistry-transport model SLIMCAT, which is driven by meteorological observations and therefore includes observed meteorological trends. The simplie ed ozone chemistry is based on the Cariolle scheme with an additional parameterization of polar ozone loss, but with no allowance for changing chlorine or aerosol levels. It is shown that the NAO signal in ozone during mid-winter is well represented in both model systems. Geopotential height correlations are used to explain the spatial pattern. It is demonstrated that composites of total ozone derived from the model integrations are capable of capturing the observed spatial characteristics as seen in TOMS data. Implications are drawn for NAO induced long time variability/regional trends of ozone. Zusammenfassung

An efficient chemical systems modelling approach

Abstract Systems of stiff chemical reactions are often associated with atmospheric chemistry modelling, which plays a very important role in the studies of stratospheric ozone depletion, tropospheric air pollution problems, and future chemistry-climate feedbacks and interactions. This paper revisits an open-source stiff system solver SVODE and presents its efficient use in modelling different levels of complexity of a range of chemical systems. The chemical systems discussed here are the Lotka–Volterra (predator–prey) model, the Brusselator model, the Oregonator model, and the Lorenz model. The first two models consist of two variables, while the remaining two models consist of three variables. Finally, an application of this modelling approach to a generalised organic/NOx mechanism for characterising air pollution development is presented. Since the SVODE is an open-source code, and the simulations were run on a Linux PC (with g77 compiler), all results discussed in this paper can be easily reproduced. Most importantly, the approach shown here can be readily extended to other larger scale applications such as the three-dimensional air pollution modelling.

Generation of low particle numbers at the edge of the polar vortex

The Antarctic vortex plays a well-known role in stratospheric ozone depletion in the early southern spring. One key requirement for this phenomenon is the isolation of air from inside the vortex to that from mid-latitudes. This paper seeks a new way to present this separation leading to isolation process by integrating several Lagrangian methods: a flow following coordinate system that combines a contour advection technique, a Lagrangian particle model, and a vortex diagnostic method, with new ways of contour particle initializations, visualization, and interpretations. We found that there exists a distinctive area with low density of contour particle numbers in the vortex edge region, and this low particle density region separates high particle density areas inside the vortex from those in mid-latitudes. We demonstrated the existence of an area with low particle numbers surrounded by the high particle numbers to the north (inside the vortex) and to the south (mid-latitudes). We show that the polar night jet is (1) efficient in generating this low particle density plateau that separate particles from inside the vortex to that from outside the vortex. (2) The polar night jet can pull particles from outside the vortex to the vortex edge region, and maintaining these particles in the polar night jet and carrying them around the polar vortex. Hence, the existence of a proper polar night jet is the key process in separating particles from inside the vortex to those from mid-latitudes, and the meridional profile of zonal winds and their time-varying behaviour directly affect the distribution of particles both inside the vortex and at mid-latitudes.