Regional responses of surface ozone in Europe to the location of high-latitude blocks and subtropical ridges
This paper analyses for the first time the impact of high-latitude blocks and subtropical ridges on near-surface ozone (O<sub>3</sub>) in Europe during a 15-year period. For this purpose, a catalogue of blocks and ridges over the Euro–Atlantic region is used together with a gridded datas...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-02-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/17/3111/2017/acp-17-3111-2017.pdf |
| Summary: | This paper analyses for the first time the impact of high-latitude blocks and
subtropical ridges on near-surface ozone (O<sub>3</sub>) in Europe during a 15-year period.
For this purpose, a catalogue of blocks and ridges over the Euro–Atlantic
region is used together with a gridded dataset of maximum daily 8 h running
average ozone (MDA8 O<sub>3</sub>) covering the period 1998–2012. The response of
ozone to the location of blocks and ridges with centres in three longitudinal
sectors (Atlantic, ATL, 30–0° W; European, EUR, 0–30° E;
Russian, RUS, 30–60° E) is examined. The impact of blocks on ozone
is regionally and seasonally dependent. In particular, blocks within the EUR
sector yield positive ozone anomalies of ∼ 5–10 ppb over large parts
of central Europe in spring and northern Europe in summer. Over 20 and
30 % of the days with blocks in that sector register exceedances of the
90th percentile of the seasonal ozone distribution at many European locations
during spring and summer, respectively. The impacts of ridges during those
seasons are subtle and more sensitive to their specific location, although
they can trigger ozone anomalies above 10 ppb in northern Italy and the
surrounding countries in summer, eventually exceeding European air quality
(AQ) targets. During winter, surface ozone in the north-west of Europe presents
completely opposite responses to blocks and ridges. The anticyclonic
circulation associated with winter EUR blocking, and to a lesser extent with
ATL blocking, yields negative ozone anomalies between −5 and −10 ppb
over the UK, northern France and the Benelux. Conversely, the enhanced zonal
flow around 50–60° N during the occurrence of ATL ridges favours
the arrival of background air masses from the Atlantic and the ventilation of
the boundary layer, producing positive ozone anomalies of ∼ 5 ppb in
an area spanning from the British Isles to the northern half of Germany. We
also show that multiple linear models on the seasonal frequency of occurrence
of these synoptic patterns can explain a considerable fraction of the
interannual variability in some winter and summer ozone statistics (mean
levels and number of exceedances of the 90th percentile) over some regions of
western Europe. Thus, this work provides the first quantitative assessments
of the remarkable but distinct impacts that the anticyclonic circulation and
the diversion of the zonal flow associated with blocks and ridges exert on
surface ozone in Europe. The findings reported here can be exploited in the
future to evaluate the modelled responses of ozone to circulation changes
within chemical transport models (CTMs) and chemistry–climate models (CCMs). |
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| ISSN: | 1680-7316 1680-7324 |