Abstract
Abstract. Events of very high concentrations of 7Be cosmogenic radionuclide have been recorded at low-elevation surface stations in the subpolar regions of Europe during the cold season. With an aim to investigate the mechanisms responsible for those peak 7Be events, and in particular to verify if they are associated with the fast descent of stratospheric air masses occurring during sudden stratospheric warming (SSW) events, we analyze 7Be observations at six sampling sites in Fennoscandia during January–March 2003 when very high 7Be concentrations were observed and the Arctic vortex was relatively unstable as a consequence of several SSW events. We use the GEOS-Chem chemistry and transport model driven by the MERRA-2 meteorological reanalysis to simulate tropospheric 7Be over northern Europe. We show that the model reasonably reproduces the temporal evolution of surface 7Be concentrations observed at the six sampling sites. Our analysis of model simulations, surface 7Be observations, atmospheric soundings of ozone and temperature and surface ozone measurements indicates that the 7Be peak observed in late February 2003 (between 20 and 28 February 2003) at the six sampling sites in Fennoscandia was associated with downward transport of stratospheric vortex air that originated during an SSW that occurred a few days earlier (between 18 and 21 February 2003).
Highlights
Beryllium-7 (7Be) is a cosmogenic radionuclide widely monitored and analyzed around the world (e.g., Tositti et al, 2004, 2014; Gourdin et al, 2014; Sýkora et al, 2017)
Our analysis of model simulations, surface 7Be observations, atmospheric soundings of ozone and temperature and surface ozone measurements indicates that the 7Be peak observed in late February 2003 at the six sampling sites in Fennoscandia was associated with downward transport of stratospheric vortex air that originated during an stratospheric warming (SSW) that occurred a few days earlier
As indicated by Ajticet al. (2018) and Bianchi et al (2019), the winter of 2003 offers a good opportunity to investigate a possible link between SSW events and extreme surface concentrations of 7Be detected in northern Europe
Summary
Beryllium-7 (7Be) is a cosmogenic radionuclide widely monitored and analyzed around the world (e.g., Tositti et al, 2004, 2014; Gourdin et al, 2014; Sýkora et al, 2017). The variability of the 7Be activity concentration in surface layers is driven by both static and dynamic factors, e.g., geographical location of the monitoring sites (e.g., Hernández-Ceballos et al, 2015), seasonal atmospheric processes driving transport of carrier aerosols (Lal and Peters, 1967), stratosphere–troposphere air mass exchange (Cristofanelli et al, 2003, 2009; Putero et al, 2016; Brattich et al, 2017a), synoptic influences E. Brattich et al.: High-7Be concentration events at the surface in northern Europe et al, 2009), downward transport in the troposphere (Lee et al, 2007), solar activity, and dry and wet deposition (e.g., Hernández-Ceballos et al, 2015, 2016; Ioannidou and Papastefanou, 2006). A recent study by SalminenPaatero et al (2019), who used potential vorticity analysis to gain insights into stratosphere-to-troposphere transport of radionuclides at Rovaniemi (Finnish Lapland) indicated that the transfer of stratospheric air into the upper troposphere was at its maximum in March followed by descent to the ground level during late spring and early summer
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