The sky in August: lots of cirrus clouds in the smoke of the upper troposphere

Leipzig, 19.08.2025 – Albert Ansmann

In these times of climate change, nothing is the same anymore as we Lidar people measured the atmosphere over Leipzig (Central Europe) from 1995 to 2017.

In June and July 2025, we had the thick smoke clouds from Canada, which drifted over us  and Germany, and then, especially in August, with the now prevailing south winds, the forest fire aerosols, mainly from Portugal, Spain, and France, joined in, and ... when the air mass transport then swings further to the southeast ... smoke particles from the Balkan region (including Albania!) and Greece (...probably not from Cyprus) etc. were added.

Now to the facts: Our trusty and expensive, upgraded MARTHA (now with a fluorescence spectrometer and additional fluorescence channel), the 'super light' (LIDAR) in Europe , is operated by the doctoral students and postdocs of our Lidar team in a self-sacrificing manner as often as possible at night from 9 p.m. to 3 a.m. Only at night can we obtain a very detailed picture of the aerosol conditions , but then also up to an altitude of 30-40 km. Cristofer Jimenez and Benedikt Gast coordinate everything and also take most of the measurements. We also often launch radiosondes at night to record the actual state of the meteorological parameters around the lidar beam with super-high accuracy.

What do we see? In August, we see many fluorescent layers of Saharan dust unusual! This is! How is this possible, experts will ask? ...  Mineral dust hardly fluoresces at all. This is because the dust is mixed with forest fire aerosols .... We are seeing such layers this August mainly between 2-6 km altitude, but further layers often up to 8 km altitude. Everything else above 8 km altitude probably comes from Canada... or is forest fire aerosol that has been circulating. around the globe for weeks. Once around the globe at our latitude takes about 2-3 weeks (and not 80 days). The troposphere is quite full of aerosol up to the tropopause this summer. This is now the new NORMAL , at least since 2022-2023.

The smoke particles absorb sunlight and rise continuously to the tropopause, where they accumulate... as predicted by Kevin Ohneiser in his doctoral thesis (there is an ACP paper on this in 2023 – see https://acp.copernicus.org/articles/23/2901/2023/ ). You can always see this tropopause layer enriched with smoke. But the rise continues... (in very thin layers)...

The Canadian aerosol from early June (my first report discussed this – see https://www.tropos.de/aktuelles/science-blog/beitrag/kanadischer-rauch-zu-pfingsten-ueber-deutschland ) has now reached an altitude of 19 km during its multiple trips around the globe. All this can only be seen with a really powerful LIDAR like the one we have at TROPOS. We can see the fluorescence up to an altitude of 20 km with this great MARTHA and therefore know exactly that it is smoke and not volcanic sulphate aerosol... That's cool!

What we also see: A large number of cirrus clouds are forming in the smoke in the upper troposphere (10-12 km altitude) ... I would say that the cirrus cloud cover has increased significantly... and with it the greenhouse effect... compared to times with a clear and clean troposphere above 8-10 km altitude.

Incidentally, TROPOS is also significantly involved in ESA's EarthCARE work (LIDAR in SPACE). There was a special report on the Canadian fires (EarthCARE, IMAGE of the MONTH, see https://earth.esa.int/eogateway/success-story/earthcare-sees-canadian-wildfire-smoke-spreading-over-the-northern-hemisphere ), pushed by our 10-15-strong EarthCARE team at TROPOS. The smoke now dominates the free troposphere throughout the entire northern North hemisphere..., i.e. north of approximately 40-50 degrees north.

Best regards from the forest fire observer

Albert Ansmann