Air stagnation in the Euro-Mediterranean area from 1979 to 2016

Trabajo presentado en el AGU (American Geophysical Union) Fall Meeting: Advancing Earth and Space Science, celebrado en Washington D.C. (Estados Unidos), del 10 al 14 de diciembre de 2018
near-surface wind speed, which strongly depends on the local setting of the observational sites and the boundary layer parameterizations within the reanalysis model. There is considerable spatial heterogeneity in stagnation patterns (i.e. occurrence of stagnation days and events, duration of events) over the area of study. Therefore, we have used the k-means algorithm to regionalise the monthly frequency of stagnant days, obtaining five regions: Scandinavia (SCAN), Northern-Europe (NEU), Central-Europe (CEU), South-West (SW) and South-East (SE). The northern regions (SCAN and NEU) present low frequency of stagnation compared to the southern regions (SW and SE). We will present additional results from the temporal variability and synoptic patterns associated with air stagnation in these regions. Finally, we have assessed the impact of air stagnation on air quality. This is particularly strong over CEU. In this region, the anomalies of summer ozone and winter PM10 on stagnant vs. non-stagnant days exceed 20% and 50%, respectively. Persistent, widespread stagnation events have also been found to favour the build-up of these pollutants over most of the continent. We will discuss the distinct impacts of stagnation on both pollutants over the different regions, considering the main processes at play.