Elsevier

Atmospheric Environment

Volume 89, June 2014, Pages 482-490
Atmospheric Environment

Effects of teleconnection patterns on the atmospheric routes, precipitation and deposition amounts in the north-eastern Iberian Peninsula

https://doi.org/10.1016/j.atmosenv.2014.02.057Get rights and content

Highlights

  • WeMO index better describes winter precipitation in the NE Iberian Peninsula than NAO.

  • Element deposition was correlated with NAO and WeMO depending on air provenance.

  • Few studies have analyzed the relationship between rain chemistry vs. NAO and WeMO.

Abstract

The North Atlantic Oscillation (NAO) has been identified as one of the atmospheric patterns which mostly influence the temporal evolution of precipitation and temperature in the Mediterranean area. Recently, the Western Mediterranean Oscillation (WeMO) has also been proposed to describe the precipitation variability in the eastern Iberian Peninsula. This paper examines whether the chemical signature and/or the chemical deposition amounts recorded over NE Iberian Peninsula are influenced by these climatic variability patterns. Results show a more relevant role of the WeMO compared to NAO in the deposition of either marine (Cl, Na+, Mg2+) or anthropogenic pollutants (H+, NH4+, NO3 and SO42−). A cluster classification of provenances indicated that in winter (December to March) fast Atlantic air flows correspond to positive WeMO indices, while negative WeMOi are associated to Northeastern and Southwestern circulations. The negative phase of WeMO causes the entry of air masses from the Mediterranean into the Iberian Peninsula, that are enriched with marine ions and ions of anthropogenic origin (NH4+, NO3 and SO42−). For these later, this suggests the advection over the Mediterranean of polluted air masses from southern Europe and the scavenging and deposition of this pollution by precipitation during the WeMO negative phases. This will carry transboundary pollutants to the NE Iberian Peninsula. However, local pollutants may also contribute, as precipitation events from the Mediterranean and the Atlantic (associated to both WeMO phases) may incorporate emissions that accumulate locally during the winter anticyclonic episodes typical of the region.

Introduction

The chemical composition of precipitation is strongly influenced by the predominant atmospheric transport patterns, which affect the scavenging of pollutants depending on the pollution climate encountered. Also, the precipitation amount is important as it influences the dilution and amount of pollutants. The Iberian Peninsula (IP) is located in the south-western corner of the European continent, with the Atlantic Ocean to the west and the Mediterranean to the east, the industrialised Europe to the north and the arid Africa to the south, thus it is in a crossroads influenced by pollutant sources differing strongly in strength and character, which will affect the precipitation chemistry. The levels of atmospheric particulate matter (PM) in this area and its chemical composition has been shown to depend on the origin of air masses (Pérez et al., 2008, Querol et al., 2009, Pey et al., 2009, Pey et al., 2010, Cusack et al., 2012) and the chemical composition of precipitation as well (Àvila and Alarcón, 1999, Àvila and Alarcón, 2003, Izquierdo et al., 2012). African events have been found to be related with the specific position of cyclonic lows in the western or southern flank of the IP or the permanence of high pressures over North Africa in summer (Escudero et al., 2005, Escudero et al., 2011). A higher contribution of African precipitation events for particular years significantly affects the acidity/alkalinity balance of precipitation and the contribution of crustal components (Àvila et al., 1997, Àvila et al., 2007, Àvila and Rodà, 2002, Pulido-Villena et al., 2006, Morales-Baquero et al., 2013). Furthermore, the region is subject to a large load of anthropogenic emissions from the intense activity of large cities such as Marseille, Barcelona and Tarragona and their industrial surroundings and of the heavy traffic along the eastern coast of IP. The pollutant climate in this area is further modulated by a marked seasonality. In winter, the frequent entry of Atlantic relatively clean air fluxes induces the replacement of air masses, thus reducing the levels of atmospheric pollutants that may have accumulated during periods of anticyclonic stability (Rodríguez et al., 2003, Escudero et al., 2007). In contrast, the synoptic scenario in summer is characterised by very weak pressure gradients in the western Mediterranean which produce local circulations enhancing the regional accumulation of pollutants (Millán et al., 1991, Millán et al., 1997, Rodríguez et al., 2003).

In the Mediterranean area, a year to year variability in the amount of precipitation (Xoplaki et al., 2004; Lionello et al., 2006, Mariotti and Dell'Aquila, 2012) and dust transport (Moulin et al., 1997, Gionux et al., 2004, Pey et al., 2013) has been related to the atmosphere–ocean interaction defined as the North Atlantic Oscillation (NAO). The NAO strongly influences the atmospheric circulation and the hydrological cycle in the Northern hemisphere (Hurrell, 1995, Wallace, 2000, Hurrell et al., 2004, Hurrell and Deser, 2010). An intensification of NAO (producing more westerly winds across the North Atlantic and into Eurasia) has been observed over the past few decades (Hurrell, 1995). This intensification would bring an increase in precipitation in mid-latitude zones in Europe. Although many models suggest that such a change might be the result of anthropogenic greenhouse warming (Carnell and Senior, 2002, Zhang et al., 2007, Min et al., 2011), most models seem to underestimate the magnitude of this circulation change in central Europe (Gillett et al., 2005). In the Mediterranean, Barkhordarian et al. (2013) indicate that changes in atmospheric greenhouse gas and sulphate concentrations are not the dominant forcing process affecting precipitation changes in this area. Additional anthropogenic forcing agents potentially have a larger effect on regional scale precipitation. The emission of aerosols related to traffic and industry and/or forcing from land-use changes such as deforestation are missing in current climate models and need to be incorporated.

Recently, the Western Mediterranean Oscillation (WeMO) climatic variability has been proposed to describe the synoptic framework of the western Mediterranean basin (Martín-Vide and Lopez-Bustins, 2006). The WeMO index is calculated as the difference between the standardised surface pressure values recorded at Padua (45.40°N, 11.48°E) in northern Italy, an area with a relatively high barometric variability due to the influence of the central European anticyclone, and San Fernando (Cádiz) (36.28°N, 6.12°W) in south-western Spain, an area often influenced by the Azores anticyclone (Fig. 1). This regional pattern strongly determines the variability of rainfall in the eastern façade of the IP (Martín-Vide and Lopez-Bustins, 2006, Gonzalez-Hidalgo et al., 2009). As in most of the variability patterns of the Northern Hemisphere, WeMO shows its most relevant dynamics during the winter (Martín-Vide and Lopez-Bustins, 2006). The WeMO positive phase has been shown to trigger air masses from the Atlantic to move into the IP, while its negative phase is associated to flows from the Mediterranean (Martín-Vide and Lopez-Bustins, 2006, Lopez-Bustins et al., 2008). Thus, it can be foreseen that part of the precipitation variability and precipitation chemical signature in Northeastern Spain may be related to the WeMO pattern. The effects of the WeMO on precipitation amounts in NE Spain has been recently explored (Lopez-Bustins et al., 2008, Gonzalez-Hidalgo et al., 2009), but to our knowledge, no studies have been focused on the analysis of its influence on the precipitation chemical composition.

We explore here whether the chemical signature and/or the chemical deposition amounts reaching a site in Catalonia (NE Iberian Peninsula) is influenced by these climatic variability patterns. This is studied by comparing winter bulk precipitation chemistry data at a locality in Catalonia (La Castanya) and the NAO and WeMO indexes for a long-time series of weekly precipitation chemical data from 1984 to 2012. Thus, this study covers a 3-decade period where changes in emissions have taken place in Europe in response to emission abatement strategies agreed under the Convention on Long-range Transboundary Air Pollution (UNECE, available at http://www.unece.org/env/lrtap/). The aim here is to discern the influence of the main circulation patterns as represented by NAO and WeMO on precipitation amounts and the chemical loads of precipitation.

Section snippets

Study site

La Castanya station (LC, 41°46′N, 2°21′E, 700 m) is located in the Montseny mountains of the Pre-litoral Catalan Range. Long-term biogeochemical studies have been undertaken since the 1970s in a forest plot close to the atmospheric sampling site (Rodà et al., 1999). The site is amidst extensive holm-oak (Quercus ilex L.) forests in the Montseny Natural Park, 40 km to the N–NE from Barcelona and 25 km from the Mediterranean coast (Fig. 1). The climate in Montseny is meso-Mediterranean sub-humid,

Annual atmospheric circulation patterns and precipitation regime

Back-trajectory clusters obtained from the annual database were classified in seven main provenances: 1) Northern flows, 2) North-Western, 3) Western, 4) North-Eastern, 5) Mediterranean, 6) Iberian Peninsula and 7) Regional/Local recirculation.

The annual NAOi was negatively correlated with Northern (R = −0.40 p < 0.05) and positively with Mediterranean (R = 0.39 p < 0.05) annual precipitation amount, but no correlation was found between annual NAOi and the frequency, the number of rainy days,

The influence of NAO and WeMO on the annual atmospheric circulation patterns and precipitation amount

There is a general interest regarding the effects of the atmospheric dynamics, especially in a context of climate change. We analysed the influence of NAO and WeMO on the atmospheric transport routes and precipitation amount. The NAO is a large-scale oscillation in atmospheric mass, with centres of action near Iceland and over subtropical Atlantic (Visbeck et al., 2001). WeMO is a pattern of low-frequency variability defined as an alternative to the NAO for explaining the precipitation

Conclusions

This study has shown that the influence of the NAO index is lower than an index describing the Mediterranean variability, the WeMOi, at a site in the northeast of the Iberian Peninsula. Consistently with other works in the west Mediterranean, winter precipitation amount was inversely correlated with winter WeMOi and NAOi. The relationship between element deposition and indices of climatic variability has not been usually explored in the literature for Europe, other than a few studies in the

Acknowledgements

We acknowledge the financial support from the Spanish Government (CGL2012-39523-C02-02, CGL2009-13188-C03-01, CGL2009-11205, CSD2008-00040-Consolider Montes and CSD 2007-00067-Consolider GRACCIE). Javier Martín-Vide and Joan Albert López-Bustins from the Group of Climatology (University of Barcelona) are thanked for WeMOi data, and Mirna Lopez for assistance with back-trajectory analysis.

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