Atmospheric sciences

The main research activities in atmospheric sciences are i) climate change research, ii) climate change and air quality interactions, iii) aerosol and environmental physics, (iv) micrometeorology and forest-atmosphere relations, and (v) dynamical meteorology.

The core of the research is the understanding of energy, mass and momentum transfer and phase transitions. Theoretical, modelling and experimental studies of nucleation, condensation/evaporation and atmospheric aerosol dynamics have continued in 2013. Studies of deposition and fluxes of atmospheric gases, cloud microphysics, atmospheric radiation, mesoscale meteorology, and climate and radar meteorology were performed.

Researchers operate together with the researchers of the Department of Forest Sciences at versatile field stations: SMEAR I (Station for Measuring Forest Ecosystem-Atmosphere Relations) station in Värriö (Lapland), SMEAR II station in Hyytiälä, and SMEAR III (urban SMEAR) in Kumpula Campus. Particularly SMEAR II has turned out to be a leading station in its research field due to its comprehensive research program and to its unique time series of fresh aerosol formation. The development and construction of novel weather radar techniques has been performed in collaboration with Vaisala Oyj. The research at the Division is also linked with the instrumental development work with international companies. The most important one has been Aerodyne Research, Inc. in the U.S.A. The co-operation concerns development of high-response greenhouse gas analyzers and the aerosol mass spectroscopy technique.

The Finnish Centre of Excellence in "Physics, Chemistry, Biology and Meteorology of Atmospheric Composition and Climate Change" started its operation in 2008. The international Master programme "Atmosphere-Biosphere Studies" has continued its operation together with the national graduate school. Three Nordic Centers of Excellence CRAICC (Cryosphere-Atmosphere Interactions in a Changing Arctic Climate, coordinated by Markku Kulmala), DEFROST (Impacts of a changing cryosphere - depicting eco-system-climate feedbacks from permafrost, snow and ice), and SVALI (The Stability and Variations of Arctic Land Ice) started in 2010, and will continue until 2015.

A project office "Integrated Land Ecosystem – Atmosphere Processes Study" (iLEAPS) has continued its work related to land-atmosphere interactions within the International Geosphere – Biosphere Programme (IGBP). The iLEAPS project aims at advancing new integrated experimental and modelling research approaches needed in the Earth System. We are also active in Future Earth initiative. The division is also in charge to establish national and European Integrated Carbon Observation System (ICOS). The PEEX initiative (Pan Eurasian Experiment) has continued to gather momentum during 2013.

The researchers have coordinated and participated in several international projects, and organized a number of international workshops, conferences, and measurement campaigns in Finland and abroad. The most visible of these was the aerial campaign of the PEGASOS project to measure aerosol particles and trace gases in the lowest layers of atmosphere up to about 1.5 km.

Highlights of research

First direct micrometeorological gas exchange measurement over a river

The importance of rivers in the global carbon cycle between the biosphere-atmosphere has appeared to be larger than thought in the past. The largest uncertainties in accurately resolving the role of rivers and streams in carbon cycling stem from difficulties in determining gas exchange between water and the atmosphere. So far, estimates for river-atmosphere gas exchange have lacked direct ecosystem-scale flux measurements not disturbing gas exchange across the air-water interface. We conducted the first direct riverine gas exchange measurements with the micrometeorological technique with continuous surface water CO2 measurements in a large boreal river (Kymijoki in Southern Finland) for 30 days. Our measured gas transfer velocity was clearly higher than the model estimates based on river channel morphology and water velocity. These results demonstrate that present estimates for riverine CO2 emissions are very likely too low. This result is also relevant to any other gases emitted, as their diffusive exchange rates are similarly proportional to gas transfer velocity.

Farewell lecture of Prof. Juhani Keinonen

The measuring platform in the middle of the River Kymijoki. The sonic anemometer to measure turbulence is on the right hand side of the platform towards the river flow. CO2/H2O analyzer together with the computer is in the gray metal box. Probes for radiation measurements are on the pole on the left hand side.

Reference:

Huotari, J., S. Haapanala, J. Pumpanen, T. Vesala, and A. Ojala (2013) Efficient gas exchange between a boreal river and the atmosphere, Geophys. Res. Lett., 40, doi:10.1002/2013GL057705.

Algorithmic tuning of numerical weather prediction and climate models

Ensemble prediction can be combined with parameter estimation to tune numerical weather prediction (NWP) model closure parameters. Here we tune the medium-range forecast skill of the ECHAM5 atmospheric general circulation model using an ensemble of medium-range prediction. Initial state uncertainty is represented by applying the initial state perturbations generated at the European Centre for Medium-range Weather Forecasts (ECMWF). Model uncertainty is represented in the emulator via parameter variations at the initial time. We vary four closure parameters related to parametrizations of subgrid-scale physical processes of clouds and precipitation. A summarizing conclusion is that the EPPES method is able to find ECHAM5 model closure parameter values that correspond to smaller values of the objective function. The forecast skill score improvements verify positively in dependent and independent samples. The main reason is the reduced temperature bias in the tropical lower troposphere. Moreover, the optimization improved the top-of-atmosphere radiation flux climatology of the ECHAM5 model, as verified against the Clouds and the Earth's Radiant Energy System (CERES) radiation data over a 6-year period, while the simulated tropical cloud cover was reduced, thereby increasing a negative bias as verified against the International Satellite Cloud Climatology Project (ISCCP) data.

Reference:

Ollinaho, P, Laine, M, Solonen, A, Haario, H, Järvinen (2013) NWP model forecast skill optimization via closure parameter variations. Q. J. R. Meteorol. Soc. 139, 1520-1532. doi:10.1002/qj.2044.

Direct observations of atmospheric nucleation

Atmospheric nucleation is the dominant source of aerosol particles in the global atmosphere and an important player in aerosol climatic effects. The key steps of this process occur in the sub–2 nanometer (nm) size range, in which direct size-segregated observations have not been possible until very recently. In Kulmala et al. (2013) we present detailed observations of atmospheric nanoparticles and clusters down to 1-nm mobility diameter for the first time. We identified three separate size regimes below 2-nm diameter that build up a physically, chemically, and dynamically consistent framework on atmospheric nucleation—more specifically, aerosol formation via neutral pathways. Our findings emphasize the important role of organic compounds in atmospheric aerosol formation, subsequent aerosol growth, radiative forcing and associated feedbacks between biogenic emissions, clouds, and climate.

Reference:

Kulmala, M., Kontkanen, J., Junninen, H., Lehtipalo, K., Manninen, H.E., Nieminen, T., Petäjä, T., Sipilä, M., Schobesberger, S., Rantala, P., Franchin, A., Jokinen, T., Järvinen, E., Äijälä, M., Kangasluoma, J., Hakala, J., Aalto, P.P., Paasonen, P., Mikkilä, J., Vanhanen, J., Aalto, J., Hakola, H., Makkonen, U., Ruuskanen, T.M., Mauldin III, R.L., Duplissy, J., Vehkamäki, H., Bäck, J., Kortelainen, A., Riipinen, I., Kurtén, T., Johnston, M.V., Smith, J.N., Ehn, M., Mentel, T.F., Lehtinen, K.E.J., Laaksonen, A., Kerminen, V.-M. and Worsnop, D.R. (2013) Direct observations of atmospheric nucleation, Science, 339, 943-946, doi:10.1126/science.1227385.

Molecular understanding of aerosol formation

Atmospheric aerosols formed by nucleation of vapors affect radiative forcing and therefore climate. However, the underlying mechanisms of nucleation remain unclear, particularly the involvement of amines and organic compounds. In Almeida et al. (2013) we show the importance of dimethyl amine and in Schobesberger et al. (2013) we underline the importance of organic vapors. The experiments were performed at the Cosmics Leaving Outdoor Droplets chamber (CLOUD) at the European Organization for Nuclear Research (CERN). Our measurements connect amines and oxidized organics directly, and in detail, with the very first steps of new particle formation and their growth between 1 and 2 nm in a controlled environment.

References:

Almeida, J., Schobesberger, S., Kürten, A., Ortega, I.K., Kupiainen-Määttä, O., Praplan, A.P., Adamov, A., Amorim, A., Bianchi, F., Breitenlechner, M., David, A., Dommen, J., Donahue, J.M., Downard, A., Dunne, E., Duplissy, J., Ehrhart, S., Flagan, R.C., Franchin, A., Guida, R., Hakala, J., Hansel, A., Heinritzi, M., Henschel, H., Jokinen, T., Junninen, H., Kajos, M., Kangasluoma, J., Keskinen, H., Kupc, A., Kurtén, T., Kvashin, A.N., Laaksonen, A., Lehtipalo, K., Leiminger, M., Leppä, J., Loukonen, V., Makhmutov, V., Mathot, S., McGrath, M.J., NIeminen, T., Olenius, T., Onnela, A., Petäjä, T., Riccobono, F., Riipinen, I., Rissanen, M., Rondo, L., Ruuskanen, T., Santos, F.D., Sarnela, N., Schallhart, S., Schnitzhofer, R., Seinfeld, J.H., Simon, M., Sipilä, M., Stozkov, Y., Stratmann, F., Tomé, A., Tröstl, J., Tsagkogeorgas, G., Vaattovaara, P., Viisanen, Y., Virtanen, A., Vrtala, A., Wagner, P.E., Weingartner, E., Wex, H., Williamson, C., Wimmer, D., Ye, P., Yli-Juuti, T., Carslaw, C.S., Kulmala, M., Curtius, J., Baltensberger, U., Worsnop, D.R., Vehkamäki, H. and Kirkby, J. (2013) Molecular understanding of sulphuric acid-amine particle nucleation in the atmosphere, Nature, doi: 10.1038/nature12663.

Schobesberger, S., Junninen, H., Bianchi, F., Lönn, G., Ehn, M., Lehtipalo, K., Dommen, J., Ehrhart, S., Ortega, I.K., Franchin, A., Nieminen, T., Riccobono, F., Hutterli, M., Duplissy, J., Almeida, J., Amorim, A., Breitenlechner, M., Downard, A.J., Dunne, E.M., Flagan, R.C., Kajos, M., Keskinen, H., Kirkby, J., Kupc, A., Kürten, A., Kurtén, T., Laaksonen, A., Mathot, S., Onnela, A., Praplan, A.P., Rondo, L., Santos, F.D., Schallhart, S., Schnitzhofer, R., Sipilä, M., Tomé, A., Tsagkogeorgas, G., Vehkamäki, H., Wimmer, D., Baltensperger, U., Carslaw, K.S., Curtius, J., Hansel, A., Petäjä, T., Kulmala, M., Donahue, N.M. and Worsnop, D.R. (2013) Molecular understanding of atmospheric particle formation from sulfuric acid and large oxidized organic molecules, PNAS, doi:/10.1073/pnas.1306973110.

Aerosol climate effects and feedback mechanisms

Atmospheric aerosol particles influence the climate system directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei. Apart from black carbon aerosol (Cappa et al. 2013), aerosols cause a negative radiative forcing at the top of the atmosphere and substantially mitigate the warming caused by greenhouse gases. In Paasonen et al. (2013) we analyzed long-term observations of concentrations and compositions of aerosol particles and their biogenic precursor vapors in continental mid- and high-latitude environments. Our results confirm a negative feedback mechanism between the continental biosphere, aerosols and climate: aerosol cooling effects are strengthened by rising biogenic organic vapor emissions in response to warming, which in turn enhance condensation on particles and their growth to the size of cloud condensation nuclei. We conclude that biosphere–atmosphere interactions are crucial for aerosol climate effects and can significantly influence the effects of anthropogenic aerosol emission controls, both on climate and air quality.

References:

Cappa, C.D., Onasch, T.B., Massoli, P., Worsnop, D.R., Bates, T.S., Cross, E.S., Davidovits, P., Hakala, J., Hayden, K., Jobson, B.T., Kolesar, K.R., Lack, D.A., Lerner, B.M., Li, S.-M., Mellon, D., Nuaaman, I., Olfert, J.S., Petäjä, T., Quinn, P.K., Song, C., Subramanian, R., Williams, E.J. and Zaveri, R.A. (2012) Response to Comment on "Radiative Absorption Enhancements Due to the Mixing State of Atmospheric Black Carbon", Science, 339, 393c.

Paasonen, P., Asmi, A., Petäjä, T., Kajos, M.K., Äijälä, M., Junninen, H., Holst, T., Abbatt, J.P.D., Arneth, A., Birmili, W., Denier van den Gon, H., Hamed, A., Hoffer, A., Laaksonen, A., Laakso, L., Leaitch, R., Plass-Dülmer, C., Pryor, S.C., Räisänen, P., Swietlicki, E., Wiedensohler, A., Worsnop, D.R., Kerminen, V.-M. and Kulmala, M. (2012) Warming-induced increase in aerosol number concentration likely to moderate climate change, Nature Geosci., doi: 10.1038/NGEO1800.