EGU24-12943, updated on 09 Mar 2024
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Links between boreal forest and clouds inferred from long-term atmospheric observations

Ekaterina Ezhova1, Aino Aarne1, Antti Arola2, Antti Liponen2, Anna Lintunen1, Taina Yli-Juuti3, Jaana Bäck1, Harri Kokkola2,3, Veli-Matti Kerminen1, Tuukka Petäjä1, Annele Virtanen3, and Markku Kulmala1
Ekaterina Ezhova et al.
  • 1INAR - Institute for Atmospheric and Earth system research, University of Helsinki, Helsinki, Finland (
  • 2Atmospheric Research Centre of Eastern Finland, Finnish Meteorological Institute, Kuopio, Finland
  • 3Department of Technical Physics, University of Eastern Finland, Kuopio, Finland

Clouds play a vital role in the Earth's radiation budget, with low-level clouds having a net cooling effect. Evidence shows that forests alter low-level clouds' formation and physical properties (e.g., [1-3]). In their turn, clouds modify radiation transfer, influencing near-surface variables and forest carbon uptake. Shallow cumulus clouds can enhance photosynthesis due to the diffuse fertilization effect, and the relative increase in photosynthesis is most significant in boreal forests compared to other ecosystems [4]. All this evidence suggests a strong atmosphere-biosphere link for boreal forests. 

We use long-term observations at SMEAR II station in Finland and satellite data sets to study how air mass transformation over boreal forests changes the optical properties of low-level clouds. Further, we assess the dynamics of photosynthesis and net ecosystem exchange in response to changing cloud properties and near-surface variables under different low-level clouds. We show that stratus clouds dampen photosynthesis, and the effect is amplified with the time spent by an air mass over a forest. Oppositely, cumulus clouds enhance photosynthesis compared to the clear sky conditions. If an air mass is exposed to the boreal forest for several days, and cumulus clouds form during the daytime, photosynthesis is efficient, and clouds' transmittance somewhat decreases. Our results suggest that shallow cumulus clouds formed in an air mass interacting with boreal forest can become more reflective. At the same time, these clouds provide ideal conditions for enhanced boreal forest carbon uptake.


[1] Teuling, A. J., Taylor, C. M., Meirink, J. F., Melsen, L. A., Miralles, D. G., van Heerwaarden, C. C., Vautard, R., Stegehuis, A. I., Nabuurs, G.-J., and de Arellano, J. V.-G.: Observational evidence for cloud cover enhancement over western European forests, Nat. Commun., 8, 14065, 2017. 

[2] Yli-Juuti, T., Mielonen, T., Heikkinen, L., Arola, A., Ehn, M., Isokääntä, S., Keskinen, H.-M., Kulmala, M., Laakso, A., Lipponen, A., Luoma, K., Mikkonen, S., Nieminen, T., Paasonen, P., Petäjä, T., Romakkaniemi, S., Tonttila, J., Kokkola, H., and Virtanen, A.: Significance of the organic aerosol driven climate feedback in the boreal area, Nat. Commun., 12, 5637,  2021. 

[3] Petäjä, T., Tabakova, K., Manninen, A., Ezhova, E., O'Connor, E., Moisseev, D., Sinclair, V. A., Backman, J., Levula, J., Luoma, K., Virkkula, A., Paramonov, M., Räty, M., Äijälä, M., Heikkinen, L., Ehn, M., Sipilä, M., Yli-Juuti, T., Virtanen, A., Ritsche, M., Hickmon, N., Pulik, G., Rosenfeld, D., Worsnop, D. R., Bäck, J., Kulmala, M., and Kerminen, V.-M.: Influence of biogenic emissions from boreal forests on aerosol–cloud interactions, Nat. Geosci., 15, 42–47,  2022. 

[4] Zhou, H., Yue, X., Lei, Y., Zhang, T., Tian, C., Ma, Y., & Cao, Y.: Responses of gross primary productivity to diffuse radiation at global FLUXNET sites. Atmospheric Environment, 244, 117905, 2021.

How to cite: Ezhova, E., Aarne, A., Arola, A., Liponen, A., Lintunen, A., Yli-Juuti, T., Bäck, J., Kokkola, H., Kerminen, V.-M., Petäjä, T., Virtanen, A., and Kulmala, M.: Links between boreal forest and clouds inferred from long-term atmospheric observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12943,, 2024.