Wache, Sebastian (2010) Transport of trace gases measured in the marine boundary layer in the tropical West Pacific during the TransBrom-Sonne campaign . (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 100 pp.

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Abstract

This thesis describes the TransBrom-Sonne cruise and the evaluation of the transport of three different atmospheric trace gases, which were measured during the cruise. The campaign started in Tomakomai, Japan (42°N 141°E), sailed through the Western Pacific, and ended in Townsville, Australia (19°S 146°E). Because of their role in ozone depletion methyl iodide and bromoform as natural trace gases are investigated. Additionally methane as an anthropogenic trace gase is investigated as well. To chase these air masses 5 day backward trajectories are calculated. First two independent trajectory models (Hybrid Single Lagrangian Integrated Trajectory [HySplit], British Atmospheric Data Centre [BADC]) using different meteorological input data (National Centers for Environmental Prediction - Global Data Assimilation System [NCEP-GDAS], operational European Centre of Medium-Range Weather Forecasts [opECMWF]) are compared with each other. Both models generally agree, although, the HySplit trajectories have a larger spread than BADC trajectories. The comparison of the whole cruise track reveals a good qualitative agreement, however, the BADC trajectories are often longer than the HySplit trajectories, which is due to higher wind speeds in the meteorological input data. Furthermore the onboard measured wind speeds and wind directions are used other way around to verify the high resolution opECMWF wind data. Overall, the opECMWF data show a good agreement to the observed wind fields. However, the maxima in wind speed, especially during storm/typhoon events, are underestimated in the opECMWF data. For the investigation of source regions the HySplit trajectories are used. The whole cruise and its adjacent regions are classified into 10 boxes based on their open ocean or mainland/island characteristics. The main difference is the separation due to anthropogenic and natural source regions. Additionally a separation is done by classification of different meteorological regimes. On the one hand three meteorological regimes were identified on the other hand 8 source regimes were used due to the observed bromoform characteristics during the cruise. The first part of the cruise was mainly influenced by northerly winds and mainland of Japan, East Russia and China leading to high concentrations of the three measured gases. Especially, the tropical storm events lead to high correlation of wind speed and methyl iodide concentration (coefficient of 0.56). Methane and bromoform show no such correlation with wind speed. In the middle part of the cruise weak easterly winds and the open ocean source lead to a steady concentration of the trace gases. The last part of the cruise was influenced by trade and southerly winds and coastal regions. Thus the amounts of bromoform and methyl iodide reach their maxima with 4 ppt respectively 1 ppt. In contrast, over the whole cruise, methane shows the typical global distribution with a gradient between the northern (NH) and southern hemisphere (SH) with 1860 ppb respectively 1750 ppb, due to more mainl and hence more anthropogenic influences on the NH.

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