WeatherBlog 8 2016/17 | Snow and air pollution?

Current situation and outlook

The permanent high pressure soup has started to move a little and at least in the southwest it has also snowed quite heavily in the last few days. In the Mediterranean countries (both north and south of the Mediterranean!) it is generally quite wet and in the last few days there have even been a few snowflakes in the Sahara. The Mediterranean low, which also triggered the current alarm, is responsible for this, as is the rear of the low there and the cold air behind it further to the east (in this case east in the sense of Turkey, not east in the sense of Salzburg).

A bird's eye view of the Mediterranean low:
via GIPHY

It remains dry in the northern Alps and the last two days have been foehn-like in many places thanks to the Mediterranean low. Today (Wednesday) and tomorrow should be very sunny in the entire Alpine region (above the high fog), then a few clouds will approach from the north, from which a few flakes may fall in the Eastern Alps - but this is still uncertain and it is not the longed-for northern dust dump anyway. The Christmas holidays (Sunday/Monday) will be exciting in the British Isles. An impressive low-pressure system is approaching here, which should make for very turbulent conditions. The whole thing will probably also touch northern Germany in some form or another, with the Alps currently looking mainly like north föhn. It is unclear what will happen afterwards: recently it looked as if the Atlantic would set the tone for a little longer, but now there are signs of a tough high-pressure situation again

The higher aerosol content has an effect on cloud formation, among other things: clouds tend to consist of more and smaller droplets the more aerosols there are. This makes them brighter and in turn reflects more incoming radiation back into space. This results in an overall dampened temperature, with less pronounced diurnal temperature fluctuations due to less nocturnal cooling. The cooler temperatures caused by dimming were also responsible for the fairly widespread glacier advances in the 1980s. Since the reversal to brightening, glacier melting has increased sharply. According to some studies, the (areal) snow cover in the winter months of the northern hemisphere also began to shrink with the brightening. Cooler temperatures are of course conducive to the formation and persistence of snow cover.

It is not really clear how increased aerosol levels due to air pollution affect snowfall (and precipitation in general), but over the year and globally, most studies assume a decrease in precipitation, as evaporation decreases at lower temperatures and there is generally less water in the air. Locally, this may be different and in some regions there are contrary trends (increase in precipitation), some of which correlate with pollutant concentrations, but here some things can also be explained by other factors (e.g. accumulation of certain weather conditions). It is difficult to make general statements here, as the type and size of the aerosols and the altitude at which they are located also play a role.

Conclusion:

The WeatherBlog is not convinced that higher air pollution necessarily leads to more snowfall and is against corresponding experiments with car tire bonfires or similar.

Literature:

Li, Guohui, et al. "Increased winter precipitation over the North Pacific from 1984-1994 to 1995-2005 inferred from the Global Precipitation Climatology Project." Geophysical Research Letters 35.13 (2008).

Stjern, Camilla W., Andreas Stohl, and Jón Egill Kristjánsson. "Have aerosols affected trends in visibility and precipitation in Europe?." Journal of Geophysical Research: Atmospheres 116.D2 (2011).

Wild, Martin. "Global dimming and brightening: A review." Journal of Geophysical Research: Atmospheres 114.D10 (2009).