Aerosol climatology and planetary boundary influence at the Jungfraujoch analyzed by synoptic weather types

Abstract

Abstract. Fourteen years of meteorological parameters, aerosol variables (absorption and scattering coefficients, aerosol number concentration) and trace gases (CO, NO x , SO 2 ) measured at the Jungfraujoch (JFJ, 3580 m a.s.l.) have been analyzed as a function of different synoptic weather types. The Schüepp synoptic weather type of the Alps (SYNALP) classification from the Alpine Weather Statistics (AWS) was used to define the synoptic meteorology over the whole Swiss region. The seasonal contribution of each synoptic weather type to the aerosol concentration was deduced from the aerosol annual cycles while the planetary boundary layer (PBL) influence was estimated by means of the diurnal cycles. Since aerosols are scavenged by precipitation, the diurnal cycle of the CO concentration was also used to identify polluted air masses. SO 2 and NO x concentrations were used as precursor tracers for new particle formation and growth, respectively. The aerosol optical parameters and number concentration show elevated loadings during advective weather types during the December-March period and for the convective anticyclonic and convective indifferent weather types during the April-September period. This study confirms the consensus view that the JFJ is mainly influenced by the free troposphere during winter and by injection of air parcels from the PBL during summer. A more detailed picture is, however, drawn where the JFJ is completely influenced by free tropospheric air masses in winter during advective weather types and largely influenced by the Correspondence to: M. Collaud Coen (martine.collaud@meteoswiss.ch) PBL also during the night in summer during the subsidence weather type. Between these two extreme situations, the PBL influence at the JFJ depends on both the time of year and the synoptic weather type. The fraction of PBL air transported to the JFJ was estimated by the relative increase of the specific humidity and CO.

A synthesis of cloud condensation nuclei counter (CCNC) measurements within the EUCAARI network

“…Being located high in the mountains (3580 m a.s.l. ), the station is far from local sources of pollution and is, in fact, in the free troposphere most of the time; hence, it is considered a continental background site and aerosol concentrations are very low (Collaud Coen et al, 2011). However, particularly during the summer months, the Jungfraujoch site is frequently influenced by the injections of more polluted air from the planetary boundary layer, driven by thermal convection (Jurányi et al, 2010Kammermann et al, 2010a).…”

Surface-to-mountaintop transport characterised by radon observations at the Jungfraujoch

“…Following a different approach entirely, previous investigations (Collaud Coen et al, 2011;Lugauer et al, 1998) have found that circulation-pattern classifications (Huth et al, 2008) are useful for explaining the occurrence of anabatic conditions at Jungfraujoch. Many schemes have been developed (Demuzere et al, 2011;Philipp et al, 2010); for comparison with the radon-based method we selected the CAP9 scheme, a nine-class objective scheme based on mean sea level pressure in a domain centred on the Alps and implemented by MeteoSwiss (MeteoSwiss, 2012).…”

“…Thermally driven boundary-layer growth and anabatic mountain winds (Henne et al, 2004(Henne et al, , 2005Collaud Coen et al, 2011;De Wekker et al, 2004;Weigel et al, 2006;Kossmann et al, 1999;Zellweger et al, 2000).…”

“…Previous studies made use of in situ measurements of surface-emitted tracers with a strong concentration contrast between the boundary layer and the free troposphere, such as aerosols (Collaud Coen et al, 2011), volatile organic compounds (VOCs) (Prévôt et al, 2000), CO (Forrer et al, 2000) and moisture (Henne et al, 2004(Henne et al, , 2005, while others have incorporated back-trajectories (Balzani Lööv et al, 2008;Kossmann et al, 1999;Cui et al, 2011). While back-trajectories have proven to be effective during the winter months, they are less able to resolve anabatic mountain winds due to the small-scale nature of these processes.…”

“…Consequently, meteorological, statistical or time-of-day filters (Andrews et al, 2011;Brooks et al, 2012;Zellweger et al, 2003) have been used to avoid periods influenced by anabatic winds. Yet another approach is to relate synoptic weather classifications to the occurrence of vertical transport (Collaud Coen et al, 2011). Data augmenting in situ measurements has included lidar, used to de-tect the top of aerosol layers Gallagher et al, 2012;Ketterer et al, 2014), and radiosondes, which are launched from near the mountain and used to define the unperturbed free troposphere (Weiss-Penzias et al, 2006).…”