The influence of mid-latitude cyclones on European background surface ozone

The relationship between springtime mid-latitude cyclones and background ozone (O3) is explored using a combination of observational and reanalysis data sets. First, the relationship between surface O3 observations at two rural monitoring sites on the west coast of Europe – Mace Head, Ireland, and Monte Velho, Portugal – and cyclone track frequency in the surrounding regions is examined. Second, detailed case study examination of four individual mid-latitude cyclones and the influence of the associated frontal passage on surface O3 is performed. Cyclone tracks have a greater influence on the O3 measurements at the more northern coastal European station, Mace Head, located within the main North Atlantic (NA) storm track. In particular, when cyclones track north of 53° N, there is a significant relationship with high levels of surface O3 (> 75th percentile). The further away a cyclone is from the NA storm track, the more likely it will be associated with both high and low (< 25th percentile) levels of O3 at the observation site during the cyclone's life cycle. The results of the four case studies demonstrate (a) the importance of the passage of a cyclone's cold front in relation to surface O3 measurements, (b) the ability of mid-latitude cyclones to bring down high levels of O3 from the stratosphere, and (c) that accompanying surface high-pressure systems and their associated transport pathways play an important role in the temporal variability of surface O3. The main source of high O3 to these two sites in springtime is from the stratosphere, either from direct injection into the cyclone or associated with aged airstreams from decaying downstream cyclones that can become entrained and descend toward the surface within new cyclones over the NA region.

Validation of gas phase chemistry in the WRF-Chem model over Europe

This work presents the evaluation of the WRF-Chem model applied for a European domain over the year 2008 and employing two different chemical modules. Airbase European station data and E-OBS database are used for validation of the simulated meteorological conditions as well as concentrations of NO2, SO2 and ozone. In both experiments, underestimation of the amplitude of temperature daily cycle (by about 1 °C) and precipitation overestimation (by about 25 %) were found, with possible impact on chemistry processes due to increased removal via wet deposition. The modelled ozone concentrations match the observations quite well, while the simulated concentrations of other gases show highly negative bias.

The influence of mid-latitude cyclones on European background surface ozone

The relationship between springtime mid-latitude cyclones and background ozone (O3) is explored using a combination of observational and reanalysis data sets. First, the relationship between surface O3 observations at two rural monitoring sites on the west coast of Europe – Mace Head, Ireland and Monte Velho, Portugal – and cyclone track frequency in the surrounding regions is examined. Second, detailed case study examination of four individual mid-latitude cyclones and the influence of the associated frontal passage on surface O3 is performed. Cyclone tracks have a greater influence on the O3 measurements at the more northern coastal European station, Mace Head, located within the main North Atlantic (NA) storm track. In particular, when cyclones track north of 53° N, there is a significant relationship with high levels of surface O3 (> 75th percentile). The further away a cyclone is from the NA storm track, the more likely it will be associated with both high and low (

Regional differences in modelled net production and shallow remineralization in the North Atlantic subtropical gyre

We used 5-yr concomitant data of tracer distribution from the BATS (Bermuda Time-series Study) and ESTOC (European Station for Time-Series in the Ocean, Canary Islands) sites to build a 1-D tracer model conservation including horizontal advection, and then compute net production and shallow remineralization rates for both sites. Our main goal was to verify if differences in these rates are consistent with the lower export rates of particulate organic carbon observed at ESTOC. Net production rates computed below the mixed layer to 110 m from April to December for oxygen, dissolved inorganic carbon and nitrate at BATS (1.34±0.79 mol O2 m−2, −1.73±0.52 mol C m−2 and −125±36 mmol N m−2) were slightly higher for oxygen and carbon compared to ESTOC (1.03±0.62 mol O2 m−2, −1.42±0.30 mol C m−2 and −213±56 mmol N m−2), although the differences were not statistically significant. Shallow remineralization rates between 110 and 250 m computed at ESTOC (−3.9±1.0 mol O2 m−2, 1.53±0.43 mol C m−2 and 38±155 mmol N m−2) were statistically higher for oxygen compared to BATS (−1.81±0.37 mol O2 m−2, 1.52±0.30 mol C m−2 and 147±43 mmol N m−2). The lateral advective flux divergence of tracers, which was more significant at ESTOC, was responsible for the differences in estimated oxygen remineralization rates between both stations. According to these results, the differences in net production and shallow remineralization cannot fully explain the differences in the flux of sinking organic matter observed between both stations, suggesting an additional consumption of non-sinking organic matter at ESTOC.

Regional differences in modelled net production and shallow remineralization in the North Atlantic subtropical Gyre

We used 5-year concomitant data of tracers distribution from the BATS (Bermuda Time-series Study) and ESTOC (European Station for Time-Series in the Ocean, Canary Islands) sites to build a 1-D tracer model conservation including horizontal advection and compute net production and shallow remineralization rates at both sites. Net production rates computed below the mixed layer to 110 m from April to December for oxygen, dissolved inorganic carbon and nitrate at BATS (1.34 ± 0.79 mol O2 m−2, −1.73 ± 0.52 mol C m−2 and −125 ± 36 mmol N m−2) showed no statistically significant differences compared to ESTOC (1.03 ± 0.62 mol O2 m−2, −1.42 ± 0.30 mol C m−2 and −213 ± 56 mmol N m−2). Shallow remineralization rates between 110 and 250 m computed at ESTOC (−3.9 ± 1.0 mol O2 m−2, 1.53 ± 0.43 mol C m−2 and 38 ± 155 mmol N m−2) were statistically higher for oxygen compared to BATS (−1.81 ± 0.37 mol O2 m−2, 1.52 ± 0.30 mol C m−2 and 147 ± 43 mmol N m−2). Lateral advection, which was more significant at ESTOC, was responsible for the differences in estimated oxygen remineralization rates between both stations. Due to the relevance of the horizontal transport at ESTOC, we cannot assert that the differences in shallow remineralization rates computed for both stations can explain the observed descrepancies in the flux of sinking organic matter.