January 2017: freezing temperatures and snow in Central and Southern Europe
19 January 2017 12:00 UTC
Freezing temperatures and snow hit Central and Southern Europe in January 2017.
11 November 2022
19 January 2017
By Jochen Kerkmann (EUMETSAT) and Mike Fromm (US Naval Research Laboratory)
High pressure situation leads to high pollution (fine dust) in Central Europe. Easterly winds push highly polluted air out on the eastern Atlantic, as seen in Meteosat-10 RGB imagery. Due to a large-scale pressure pattern (a high over Western and Central Europe and a low over Mediterranean) Europe was in an easterly flow with quite cold, dry air in early-mid January, as can be seen on the Natural Colour RGB which has the ECMWF 850hPa map overlaid (Figure 1).
Large areas in Europe were snow covered; the cold air invaded Spain and Portugal, and flowed further west out on the Atlantic where it met warmer, maritime air.
Because of the four-pressure configuration (two highs and two lows) the boundary between the European airmass (cold, polluted) and the Atlantic maritime airmass (warm, moist, clean) was very clear as it stretched along the deformation zone that ran from south of Iceland down to Madeira, as shown in the Airmass RGB (Figure 2).
In the Day Microphysics RGB product (Figure 3), observe the colour difference of the stratocumulus clouds across the deformation zone over the Atlantic, west of Europe — from nice yellow, indicating small droplets and polluted air, to magenta showing large droplets and clean air.
Due to the persistent high pressure weather, the fine dust values in Germany rose above the permitted limits for a number of days. In Stuttgart and Nuremberg the values even rose to unprecedented heights. On 16 January at the Neckartor in Stuttgart, 188 micrograms fine dust per cubic meter of air was recorded — setting new record. At the highly frequented Von-der-Tann-Straße in Nuremberg, the peak value was 232 micrograms — four times higher than the European-wide limit of 50 micrograms.
These high fine dust values were caused by the lack of winds and the high pressure. The cooling of air layers near the grounded results in an inversion. The warmer air at the top acts as a cover, so that the pollutants near the ground can not spread over the entire atmosphere. Since this 'barrier' was only 150m above the Stuttgart Talkessel (a 2–3km wide hollow in the Keuperbergland) the low mist was full of toxic pollutants.
Mike Fromm, of the US Naval Research Laboratory (NRL), investigated the levels of pollution within the airmass. Using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) data from NASA's Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite.
On the daytime pass from 19 January (see zip file) stratocumulus clouds can be seen north of Spain, then some adjacent boundary layer liquid particles to the north, then a little 'clear' air, then more aerosol and stratocumulus clouds north of Ireland.
Research paper Extensive closed cell marine stratocumulus downwind of Europe — A large aerosol cloud mediated radiative effect or forcing? , Tom Goren and Daniel Rosenfeld