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The long-term monitoring of the cosmogenic 7Be activity concentrations has been used to better understand the influence of large-scale atmospheric circulation dynamics in the troposphere. With an aim, this study analyzes weekly 7Be data from 15 sampling stations in Europe over 2005–2014. We first define peak (or extremely high) events in each station as those activity concentrations above the 90th percentile, and then investigate their temporal and spatial variability. These events are most frequent in the spring and summer seasons, with a notable latitudinal variability in their number. Next, we use back-trajectory cluster analysis to identify the main advection pathways associated with these high concentrations. To achieve this, persistent periods, i.e., sampling periods over which at least 60% of the calculated backward trajectories arriving at a given site correspond to the same airflow pattern, are taken as reference. This method reveals large differences in the association between the airflow patterns observed at different stations in connection with the 7Be peaks. A comparison between stations shows no clear spatial pattern, which suggests a further influence of mesoscale/local physical processes on the surface 7Be activity concentrations. Finally, the main airflow pattern at each sampling site and the associated 7Be peaks, are related to the main teleconnection patterns of large scale and regional climate variability in Europe: North Atlantic Oscillation, Arctic Oscillation, East Atlantic, East Atlantic/Western Russia, Scandinavian pattern and Western Mediterranean Oscillation. The results point out the connection between the negative phases of NAO and We-MO, and the positive phase of EA with the spatial and temporal variability and occurrence of the 7Be peak activity concentrations. These results show a latitudinal division between northern and southern sites, with similar influence of teleconnection patterns, while those located in the central part of Europe present larger variability in the impact of teleconnection patterns.

The components and the periodicity characterising airborne 7Be monthly concentration collected in Granada (SE Spain) between 2000 and 2018 are studied. These 19 years of measurements are particularly significant for the 7Be analysis as they cover the complete 24th solar cycle, 2008–2018. A Time Series Decomposition (TSD) technique has been applied to determine the different components present in the dataset: the trend, seasonal and irregular components. Then, the atmospheric parameters (Precipitation (Pp), Relative Humidity (RH), Temperature (Temp), Wind speed (WS), Total Cloudiness (TC), Low Cloudiness (LC)), teleconnection indices and the solar activity (Sun Spot Number, SSN) were used to justify the variability of each component. SSN and the teleconnection indices (Western Mediterranean Oscillation (WeMO), Atlantic Multidecadal Oscillation (AMO) and Quasi Biennial Oscillation (QBO)) are found to have a major impact on the trend component of 7Be. In turn, all the atmospheric parameters were found to have strong impact on the seasonal component. In order to observe the change in the impact of the parameters from the 24th solar cycle (from 2008 to 2018) to the complete time series (starting in 2000), the comparison between the two periods has been carried out. The results show that, over the 24th solar cycle, the SSN impacted predominantly on the trend component, whereas atmospheric parameters showed a slightly higher impact on the seasonal component. In addition, some atmospheric factors (Temp, RH, Pp, TC, LC) appeared to partially affect the irregular component. The analysis of the two phases of the 24th solar cycle shows that the influence of SSN is higher during the descending phase than during the ascending one. This behaviour is opposed to the one found for the 23rd solar cycle, which clarifies the special characteristics of the 24th cycle. Besides that, the Continuous Wavelet Transform (CWT) analysis was applied in order to extract the possible periodicities characterising 7Be data. The analysis revealed three sets of periodicities. Then, the Wavelet Coherence Analysis (WCA) method was particularly useful to study coherences between 7Be data and teleconnection indices. The 7Be concentrations in the large period (11–14 years) detected by CWT was found to be mainly modulated by WeMO, AMO and QBO, while the NAO modulates the smaller periods.

The long-term contemporary 210Pb time series acquired during the period 2004–2011 at two distant sites of different altitude in the Mediterranean basin, El Arenosillo (40 m a.s.l. in southwestern Spain) and Mt. Cimone (2165 m a.s.l. in northern Italy), are analyzed and compared. Besides being considered a tracer of continental air masses, 210Pb radionuclide is also a proxy of fine stable aerosol. For this reason, the measurements of PM10 mass concentrations collected at the same time and the corresponding 210Pb/PM10 ratio at the two sites are considered to gain better insights into the origin and size of the particles. Three statistical trajectory methods are applied to identify and characterize the 210Pb source regions at the two sites. The three methods yield similar outcomes in the source identification, which strengthens the robustness of our results. In addition to the importance of the transport from areas of continental Europe, this study highlights the relevant role of the Mediterranean Sea as a major 210Pb reservoir layer associated to the aged air masses that accumulate in the western Mediterranean basin. The analysis of the sources points out the significant influence of northern Africa to 210Pb increases at both sites as well, even though the most intensive episodes are not of Saharan origin.

Relationships between the beryllium-7 activity concentrations in surface air and meteorological parameters (temperature, atmospheric pressure, and precipitation), teleconnection indices (Arctic Oscillation, North Atlantic Oscillation, and Scandinavian pattern) and number of sunspots are investigated using two multivariate statistical techniques: hierarchical cluster and factor analysis. The beryllium-7 surface measurements over 1995–2011, at four sampling sites located in the Scandinavian Peninsula, are obtained from the Radioactivity Environmental Monitoring Database. In all sites, the statistical analyses show that the beryllium-7 concentrations are strongly linked to temperature. Although the beryllium-7 surface concentration exhibits the well-characterised spring/summer maximum, our study shows that extremely high beryllium-7 concentrations, defined as the values exceeding the 90th percentile in the data records for each site, also occur over the October–March period. Two types of autumn/winter extremes are distinguished: type-1 when the number of extremes in a given month is less than three, and type-2 when at least three extremes occur in a month. Factor analysis performed for these autumn/winter events shows a weaker effect of temperature and a stronger impact of the transport and production signal on the beryllium-7 concentrations. Further, the majority of the type-2 extremes are associated with a very high monthly Scandinavian teleconnection index. The type-2 extremes that occurred in January, February and March are also linked to sudden stratospheric warmings of the Arctic vortex. Our results indicate that the Scandinavian teleconnection index might be a good indicator of the meteorological conditions facilitating extremely high beryllium-7 surface concentrations over Scandinavia during autumn and winter.

The FRESA (“Impacto de las intrusiones de masas de aire con polvo aFRicano y de masas de aire EStratosférico en la Península Ibérica. Influencia de El Atlas”) Spanish national project aims to study the interaction between upper level disturbances and the Atlas Mountains in promoting low-level instability and cyclone formation in the lee of the Atlas Mountains, responsible of dust uplift over the Sahara Desert and also of upper tropospherelower stratosphere (UT-LS) to troposphere transport. This work presents an overview of the results obtained during a preliminary campaign of the FRESA project (June-October 2016) at Sierra Nevada (Granada) (37.096 N, 3.387 W, 2550 m a.s.l.) analysing weekly samples of 7Be, 210Pb (tracers of UTLS and continental origin, respectively) and PM10, as well as hourly particle number size distribution from a Grimm OPC. 96-hour 3D backward trajectories starting every 6 h (00, 06, 12, and 18Z) were calculated using the HYSPLIT4 model with the meteorological input from the ERA-Interim 0.5 deg meteorological dataset. Moreover, potential vorticity (PV) data was associated to each of the 96 trajectory endpoints by performing a 3D nearest-neighbour interpolation to the 27 isobaric levels between 100 and 1000 hPa of the ERA-Interim reanalysis. During this pre-campaign, 12 Saharan dust and 14 stratospheric intrusions days were identified analysing back-trajectories, BSC-DREAM model, particle number concentrations and synoptic charts: the meteorological situation leading to these outbreaks will be further studied in detail. The analysis of the source-receptor relationship for 7 Be, 210Pb and PM10 shows the influence of the Sahara Desert and of air parcels which passed over the North Sea with strong subsidence and then at lower heights over the western Mediterranean basin on all the three parameters. The analysis also shows that the Atlantic air masses are more associated to 7 Be than 210Pb increases. The fine and coarse fractions (smaller and larger than 1 µm in diameter) were analysed on both a weekly and 6-hourly basis. Locations to the south of the Atlas and the western Mediterranean were identified as important sources of the coarse fraction while the origin of the fine fraction was quite similar to that of 7 Be, probably because of the attachment of 7 Be nuclide to accumulation-mode aerosols soon after its production. The comparison between 7 Be/210Pb potential sources with those of high PV crossing shows that the Atlas is connected both to events of high PV values and to a strong PSCF probability of the 7 Be/210Pb ratio. This result suggests that the high PV areas located around the Atlas Mountains are not linked to friction and turbulence over the mountains themselves, but are rather associated to tropopause crossing and Stratosphere-TroposphereExchange (STE) occurring in the leeward side of mountain ranges, in agreement with the recent work of Brattich et al. (submitted). This work was supported by the Spanish MINECO under grant CGL2015-70741-R (FRESA). Brattich et al. (submitted to JGR), Influence of stratospheric air masses on radiotracers and ozone over the central Mediterranean.

The interaction between upper-level disturbances and major orographic features in north-western Africa is a key element for cyclogenesis and the development of convective storms, which promote instability at lower levels and lead to dust mobilization. It may also induce stratospheric to tropospheric exchange. The analysis of these processes and their subsequent impact over the Iberian Peninsula (IP) is the objective of the FRESA (“Impacto de las intrusiones de masas de aire con polvo aFRicano y de masas de aire EStratosférico en la Península Ibérica. Influencia de El Atlas”) research project. After a long term (2004-2016) analysis of jet streams in NW Africa and the analysis of a number of representative cases, in this work we present a description of the largescale meteorological processes leading to massive dust mobilization in NW Africa and transport to the IP after passing over the Saharan Atlas for three episodes (October 2008, September 2007, and February 2016). The three events had a strong impact either at the ground level or in the vertical. Contrarily to most of African events over the IP, none of these events occurred during the summertime, when African dust outbreaks are more common but the jet streams are by far less frequent over the study area. The interaction of upperlevel troughs and cut-off lows with the Atlas Mountains as well as the interaction of tropical plumes and/or the subtropical jet with the Hoggar Massif were the largescale relevant processes, but the precise location of the meteorological features is found to be crucial as indicated by the differences among the three episodes. In the case of October 2008, a cut-off low moving westwards over the Atlas was the cause of both dust mobilization (cold pool and density current formation, leading to a haboob that ran parallel to the SE slope of the Atlas) and transport to the IP. On September 2007, a low to the SW of St. Vincent Cape in combination with the North African high advected dust to the IP at mid-low tropospheric altitude after mobilization due to moist convection produced to the SW and N of the Hoggar. On February 2016, three main synoptic features at midupper levels were involved: a cut-off low to the SW of St. Vincent Cape, which was mostly responsible for the dust advection to the IP during the first part of the event; a tropical moist plume accompanied by an intense southwesterly subtropical jet streak that interacted with the Hoggar and triggered the instability at low levels; and the North African high (extended to the north when the trough was cut-off and the polar front jet retreated northwards) which advected the dust laden air masses to the east of the IP in the second part of the event. The analysis of back-trajectories calculated at multiple heightsfor the event of February 2016 in connection with aerodrome present-weather reports and satellite observations shows the orographic uplifting of the dust laden flows in the southern slope of the Saharan Atlas and their entrance into the IP at mid-low levels, in good agreement with the backscatter coefficient profiles of the CEAMA (Granada) ceilometer (Cazorla et al., submitted). This work was supported by the Spanish MINECO under grant CGL2015-70741-R (FRESA). Cazorla et al. (submitted to ACP), Near real time processing of ceilometer network data: characterizing and extraordinary dust outbreak over the Iberian Peninsula.