Investigation of how observed methane concentrations in Ny-Ålesund are influenced by atmospheric flow patterns

Abstract. Long-range atmospheric transport to Svalbard has been studied with a compilation of 4 years of daily trajectories to determine how the atmospheric flow patterns influence the observed methane (CH₄) at Mt. Zeppelin station (475 m.a.s.l.) in Ny-Ålesund (78°54' N, 11°53' E). The flow patterns were determined through cluster analysis of 5-day back-trajectories arriving at Ny-Ålesund twice a day (00:00 and 12:00 UTC) for the period 2000–2003. Eight cluster patterns were obtained and used in the analysis of the continuous methane measurements at Mt. Zeppelin station. The analysis shows a shift in frequencies eastward into the Arctic compared to identical studies of transport for 1992–2001.

Higher concentrations of methane are mainly seen in clusters with transport from Europe and Russia in contrast to air following transport pathways within the Arctic Basin. The vertical motion of the trajectories has been investigated and shows that it has an effect on the methane concentration at the Mt. Zeppelin station. This is consistent with previous similar studies of CO₂ and of other anthropogenic species. Seasonal variation in trajectory frequency can be seen, like for instance more trajectories from Europe and Siberia during winter, and short trajectories from the Arctic region in summer. The identified seasonal and indications of decadal shifts in transport pathways translate into shifts in source areas sampled by a single station. To determine shifts in regional source (and sink) strengths it is necessary to correct for transport pathway shifts when interpreting time series data.