Bestimmung der Tagesgänge kurzlebiger chemischer Substanzen aus MIPAS-B Spektren und Vergleich mit Simulationen eines Box-Modells

Abstract

The balloon-borne cryogenic Fourier transform spectrometer MIPAS-B2 (Michelson Interferometer for Passive Atmospheric Sounding), has been developped at the IMK (Institut fur Meteorologie und Klimaforschung) in Karlsruhe (Germany) for atmospheric composition measurements. It allows the detection of the emittance of molecules in the wavenumber range from about 660 cm -1 up to 2400 cm -1 . Here limb-sounding provides the ability to obtain vertical profiles. The analyses covered in this work comprise the measurements of two flights performed at the edge of the arctic polar vortex. The altitude dependence of the dynamic tracers N 2 O and CH 4 reveals the influence of the polar vortex on the observed air masses. To obtain a more detailed estimation of the origin of air masses, computations of backward trajectories with respect to the tangent points of the measurements are very helpful. Comparisons of potential vorticity values at the measurment points with those at the edge of the vortex confirm the dynamic connections. The main focus of this work is the diurnal variation of trace gases, mainly species of the NO y -family. The comparison of daytime and night-time sequences of the first evaluated flight in February 2002 reveals the diurnal variation in the NOy-chemistry. Special measurements during sunset, which aimed especially at the evolution of NO x , show growing column densities of NO 2 with increased shading in the middle and upper stratosphere. The importance of good a-priori-knowledge above the flight level is clearly shown here. In a second flight, temporally high resolved measurements have been performed during sunrise. These measurements possess a high capability for the characterisation of the continuously changing NO y -partitioning with rising or setting sun. This continuous change appears in the evaluation of the gases NO 2 , N 2 O 5 , and, by considering NLTE conditions, also of NO. Other NOy-gases with lower reactiveness and, as supplement to ClONO 2 , further chloric gases have been analysed. These long-living species evince the characteristic dynamical and chemical conditions at the edge of the arctic polar vortex that evolve during longer timescales. The modelling of the chemical conditions along the backward trajectories initialised with a global chemistry and transport model, serves as a mutual check between the implemented chemistry and the measured profiles. Possibilities for improvements both on sides of the modelling and the measurements result from this comparison and from the difficulties concretely shown in particular during the analysis of the gas NO.