The coupling of the Earth's surface and the overlying atmosphere through mass and energy fluxes has an important role in atmospheric chemistry and physics in addition to boundary layer meteorology and ecosystem research. Our research group aims at increasing the fundamental understanding of atmosphere-biosphere coupling for different ecosystems and surfaces and to apply the gained information for practical applications and purposes. Our research areas are:

• Fluxes and Ecosystems:
  • Forests
  • Wetlands
  • Croplands
  • Lakes
• Urban Meteorology
• Boundary Layer and Turbulence
• Atmos-Bios Interactions in Global Models

Projects

ABBA (COST Action ES0804: Advancing the Integrated Monitoring of Trace Gas Exchange between Biosphere and Atmosphere)
BRIDGE (sustainaBle uRban plannIng Decision support accountinG for urban mEtabolism)
DEFROST (Nordic Centre of Excellence)
GHG-Europe (Greenhouse gas management in European land use systems)
ICOS (Integrated Carbon Observation System)
ICOS-Finland
IMECC (Infrastructure for Measurements of the European Carbon Cycle)
Nitroeurope (Integrated European research into the nitrogen cycle)
Nordflux (A Nordic research network supporting the study of greenhouse gas exchange from northern ecosystems)
TTORCH (Promoting science on greenhouse gas observations)

People

Left, back: Ivan Mammarella, Samuli Launiainen (now in METLA), Annika Nordboooo, Sami Haapanala, Maarit Raivonen, Pavel Alekseychik
Left, front: Timo Vesala, Leena Järvi, Sampo Smolander
Not in photo:  Petri Keronen, Marin Tomasic, Mei-Kuei Tu (Sofia), Olli Peltola,Sigrid Dengel, Joni Kujansuu

Professor
Timo Vesala (publications in the University of Helsinki research database TUHAT)

Postdocs
Sigrid Dengel (publications)
Leena Järvi (publications)
Joni Kujansuu (publications)
Ivan Mammarella (publications)
Maarit Raivonen (publications)
Sampo Smolander (publications)
Marin Tomasic (publications)
Sami Haapanala (publications)
Annika Nordbo (publications)

Doctoral students
Pavel Alekseychik (publications)
Petri Keronen (publications)
Olli Peltola (publications)
Mei-Kuei Tu (Sofia) (publications)

Undergraduate students
Jouni Heiskanen

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Background

Meteorological research can be divided into three groups according to the size of the phenomenon in concern. Global meteorology studies global scale phenomena, synoptic meteorology looks into phenomena the size of weather systems and micrometeorology aims at the understanding of phenomena near the ground with sizes ranging from a couple of hundred kilometers to less than a millimeter. Despite their small scale, micrometeorological phenomena play an important role for instance in global climate models and numerical weather prediction models as the models are still lacking the contribution of the small scale phenomena. Micrometeorological phenomena occur in the atmospheric boundary layer, the 10-2000 meter high atmospheric layer close to the ground. In this layer, air flow is almost always turbulent, that is, the flow field consists of chaotic, three dimensional swirls of motion. Consequently, the physical understanding of boundary layer process! es is exceptionally challenging.

The atmosphere and the surface are coupled to each other through turbulence-induced vertical flows (fluxes) of momentum, mass and energy. The surface, in this context, includes the surface itself, its vegetation and potentially also buildings. Momentum flux becomes apparent for instance as shear stress when the wind bends trees. Mass flux, on the other hand, can be thought as a vertical flux of air pollutants or green house gases such as methane and water vapor. Such a flux can be caused e.g. by a methane flow from a fen to the atmosphere or by transpiration of a tree. In the latter case, the flux is closely connected to tree physiology. A heat flux composes of a sensible heat flux and a latent heat flux where the energy is "hidden" in the phase and will be released in phase transition. An example of a heat flux could be sensible heat rising from a warmer lake to the overlying colder air. The fluxes between the surface and the atmosphere depen! d largely on the surface type and thus research concerning different land use types is needed.

The largest portion of Finland's surface area is covered by forestry land (metsätalousmaa) (77%, 26milj. ha) from which one third is covered by wetlands. The success of trees is partly based on their capability to interact with the surrounding air. The boreal forest is the most widespread vegetation type in the northern hemisphere: the forests of Eurasia cover 900milj. hectares of land. Lakes comprise a much smaller area of Finland (10%) and the boreal zone (7%). The contribution of urban areas in Finland is very minimal but it must be kept in mind that currently half of the world's population lives in cities and by 2050 the portion may have risen to 70%.

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Fluxes and Ecosystems

The biosphere and the atmosphere form a complex, interactive and non-linear system whose dynamics are governed by the exchange of energy and mass. Our research group is dealing with the atmospheric coupling at different ecosystems:

• Forests
• Wetlands
• Croplands
• Lakes

Forests

Ivan Mammarella, Petri Keronen, Timo Vesala

The measurements of energy and mass between a forest ecosystem and the atmosphere are carried out since 1996 at our Forestry Field Station for Measuring Ecosystem-Atmosphere Relationship (SMEAR II) located in Hyytiälä, southern Finland. The measurements cover, among others, fluxes monitoring of carbon dioxide, water, ozone, etc. The fluxes are determined applying micrometeorological techniques, including gradient method, eddy covariance method and chamber method for soil, woody-tissue and shoot components. The station has a vast selection of aerosol and voltaic organic compounds (VOCs) measurements. SMEAR II forms a unique facility for soil-tree- atmosphere continuous measurements that have been used in several international projects and during field courses and summer schools.

Figure 2 shows the weekly average net ecosystem exchange (NEE) of the Scots pine forest at SMEAR II. The grey bars represent the weekly mean in 1996-2006. Three dry years are shown separately - the pines responses to drought by closing the stomata which reduces photosynthesis in late summer when the soil water availability is limited. For details of the carbon balance and its variability at the site see Kolari et al. (2009).

Selected publications

L. Kulmala, J. Pumpanen, P. Hari and T. Vesala: Photosynthesis of ground vegetation in different aged pine forests: Effect of environmental factors predicted with a process-based model. J. Vegetation Science 22, 96-110, 2011

Mammarella, I., P. Kolari, T. Vesala and J.Rinne, 2007, Determining the contribution of vertical advection to the net ecosystem exchange at Hyytiälä forest, Finland, Tellus 59B, 900-909

Mammarella I., S. Launiainen, T. Gronholm, P. Keronen, J. Pumpanen, Ü. Rannik, T. Vesala, 2009, Relative humidity effect on the high frequency attenuation of water vapour flux measured by a closed-path eddy covariance system, Journal of Atmospheric and Oceanic Technology, 26(9), 1856-1866

Van Gorsel, E., ........I. Mammarella et al., 2009, Estimating nocturnal ecosystem respiration from the vertical turbulent flux and change in storage of CO2. Agricul. and Forest Meteorol., 149, 1919-1930

Ilvesniemi H.! , J., Pumpanen, R., Duursma, P., Hari, P., Keronen, P., Kolari, M., Kulmala, I. Mammarella, E., Nikinmaa, Ü., Rannik, T., Pohja, E., Siivola, and T., Vesala, 2010. Water balance of a boreal Scots pine forest. Boreal Environ. Research. In Press.

Ü. Rannik, I. Mammarella, P. Keronen and T. Vesala, 2009, Vertical advection and nocturnal deposition of ozone over a Boreal pine forest, Atmospheric Chemistry and Physics, 9, 2089-2095

Ü. Rannik, I. Mammarella, P. Aalto, P. Keronen, T. Vesala and M. Kulmala, 2009, Long-term aerosol particle flux observations Part I: Uncertainties and time-averaged statistics. Atmospheric Environment, 43(21), 3431-3439

Wetlands

Sami Haapanala, Olli Peltola, Timo Vesala

The coupling of a fen ecosystem and the atmosphere has been studied at Siikaneva from summer 2004 onwards. The fluxes of carbon dioxide, water vapor and methane are determined by the eddy covariance method. In addition, the methane flux has been measured with the chamber technique. The Siikaneva research station also operates as the intercomparison site of methane instrumentation in the ICOS project (Integrated Carbon Observation System). Northern wetlands are usually sinks of carbon but they also act as the largest natural source of methane. Figure 4 shows the annual cycle of the methane flux at Siikaneva fen.

Figure 4: Methane flux at Siikaneva fen in March 2005.February 2006. Figure from Rinne et al., 2007.

Selected publications

Riutta, T., Laine, J., Aurela, M., Rinne, J., Vesala, T., Laurila, T., Haapanala, S., Pihlatie, M., and Tuittila, E.-S., 2007: Spatial variation in plant community functions regulates carbon gas dynamics in a boreal fen ecosystem. Tellus, 59B, 838-852.

Aurela, M., Riutta, T., Laurila, T., Tuovinen, J.-P., Vesala, T., Tuittila, E.-S., Rinne, J., Haapanala, S., and Laine, J., 2007: CO2 exchange of a sedge fen in southern Finland - the impact of a drought period. Tellus, 59B, 826-837.

Rinne, J., Riutta, T., Pihlatie, M., Aurela, M., Haapanala, S., Tuovinen, J.-P., Tuittila, E.-S., and Vesala, T., 2007: Annual cycle of methane emission from a boreal fen measured by the eddy covariance technique. Tellus, 59B, 449-457.

Haapanala, S., Rinne, J., Pystynen, K.-H., Hellén, H., Hakola, H., and Riutta, T., 2006:
Measurements of hydrocarbon emissions from a boreal fen using the REA technique.
Biogeos., 3, 103-112.

Croplands

Sami Haapanala, Joni Kujansuu, Timo Vesala

A campaign to measure the greenhouse gas exchange between a cropland and the atmosphere was conducted in Yuncheng, Shanxi, China. The fluxes of N₂O and CO₂ were measured by eddy covariance and automatic chamber techniques on an intensively managed cotton field from January to December 2009. The aim of the work has been to quantify greenhouse gas emissions, especially N₂O, from a typical cropland in China with several parallel measurement techniques and perform method comparisons.

An inter-comparison campaign of instrumentation for eddy covariance flux measurements of N2O is carried out on a perennial bioenergy crop . reed canary grass (Phalaris arundinaceae, L) plantation. The site is located on the rural area of Maaninka, Eastern Finland (Figure 6). The campaign is conducted in collaboration with the Department of Environmental Science, University of Eastern Finland since April 2011.  At Maaninka site different techniques and instrumentation for N2O flux measurements are applied parallel. Concentrations and fluxes retrieved from four different instruments using laser spectroscopy (Pulsed and continuous wave quantum cascade laser systems, Aerodyne Research, Inc., USA; Tunable diode laser absorption spectroscopy, Campbell Scientific, Ltd., USA; and Off-axis integrate cavity output spectroscopy, Los Gatos Research, Inc., USA) are compared. Moreover, the chamber technique and the soil profi! le sampling technique are used for N2O fluxes. The goals of this study are to compare the available equipment for N2O measurements and their reliability; and to determine the magnitude and dynamics of N2O fluxes during the growing season of reed canary grass.

Figure 6: Maaninka measurement station (Photo: Sami Haapanala).

Figure 7: The daily mean N2O fluxes measured by eddy covariance and automatic chamber techniques.

Selected publications

Liu C, Zheng X, Zhou Z, Han S, Wang Y, Wang K, Liang W, Li M, Chen D, Yang Z, 2010. Nitrous oxide and nitric oxide emissions from an irrigated cotton field in Northern China. Plant and Soil 332, 123-134.

Liu C, Wang K, Meng S, Zhou Z, Han S, Chen D, Yang Z, Zheng X, 2011. Effects of irrigation, fertilization and crop straw management on nitrous oxide and nitric oxide emissions from a wheat-maize rotation field in northern China. Agriculture, Ecosystems and Environment, 140, pp.226-233.

Partners

• Mari Pihlatie
• Chunyan Liu
• Huizhi Liu
• Xunhua Zheng
• University of Eastern Finland (Narasinha Shurpali, Saara Lind, Niina Hyvönen)

Lakes

Sami Haapanala, Jouni Heiskanen, Joni Kujansuu, Annika Nordbo, Timo Vesala

The coupling between a lake ecosystem and the atmosphere was studied at Lake Valkea-Kotinen, Lammi, from 2002 to fall 2009. The fluxes of carbon dioxide, water vapor, heat and momentum were measured on a raft with the eddy covariance technique. In addition, the water temperature profile was measured continuously to determine the changes in heat storage of the lake, and the carbon dioxide profile of the lake was measured in order to determine the CO2 flux using the profile method. In summer 2009, lake measurements were also started at Lake Kuivajärvi in Hyytiälä. The fluxes between a lake and the atmosphere depart much from those observed between a forest and the atmosphere. Lake Valkea-Kotinen is on average a carbon dioxide source (0.2 μmolm-1s-1) during its open water period. The capability of the lake to store large amounts of heat leads to a heat flux from the atmosohere to the lake in spring and summer and a heat release ! in fall and early winter. The constantly wet surface causes the channeling of available energy to latent heat flux whereas the sensible heat flux remains smaller.

Figure 8: Sensible and latent heat fluxes at Lake Valkea-Kotinen during the open-water period of 2003. Figure from Vesala et al., 2006.

Selected publications

A. Nordbo, S. Launiainen, I. Mammarella, M. Leppäranta, J. Huotari, A. Ojala and T. Vesala: Long-term energy flux measurements and energy balance over a small boreal lake using eddy covariance technique. J. Geophys. Res. 116, DOI: 10.1029/2010JD014542, 2011.

Vesala T., Huotari J., Rannik Ü., Suni T., Smolander S., Sogachev A., Launiainen S. and Ojala A. (2006). Eddy covariance measurements of carbon exchange and latent and sensible heat fluxes over a boreal lake for a full open-water period. J. Geophys. Res., 111, D11101, doi:10.1029/2005JD006365.

Nordbo, A., S. Launiainen, I. Mammarella, M. Leppäranta, J. Huotari, A. Ojala, and T. Vesala (2011). Long-term energy flux measurements and energy balance over a small boreal lake using eddy covariance technique, J. Geophys. Res., 116, D02119, doi:10.1029/2010JD014542.

Partners

• Department of Forest Sciences, University of Helsinki
• Finnish Meteorological Institute
• University of Kuopio
• Finnish Environment Institute
• University of Lund
• University of Copenhagen
• CEA, France
• University of Viterbo, Italy
• University of Edinburgh

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Urban Meteorology

Leena Järvi, Annika Nordbo, Sami Haapanala, Petri Keronen, Ivan Mammarella, Timo Vesala

Daily updated online data can be viewed here.

The mass, energy and momentum fluxes observed in an urban site differ much from those in natural surroundings. The reason lies in the significant changes in land use and the anthropogenic sources of heat and pollutants. The changes in heat fluxes have led to a heat island effect, i.e. the urban areas are warmer than their surrounding suburban areas. Particle and greenhouse gas fluxes, on the other hand, effect air quality and contribute to the climate change.

The coupling of an urban ecosystem and the atmosphere is studied at three sites in Helsinki (Figure 7). The oldes station is SMEAR III that has been running since 2004. The setup includes eddy covariance measurements (Figure 8) of the fluxes of carbon dioxide, water vapor, particles and heat, and the station is the north most urban station with long-term flux measurements done using the eddy covariance technique. The flux measurements done from the mast represent an area consisting of three sectors: urban, road and vegetation. Consequently, one station can gather data from three different urban land use types. Figure 9 shows the average diurnal cycle of the carbon dioxide flux for all three sectors. Furthermore, profile measurements are additionally utilized for the determination of the fluxes of heat and momentum, and auxiliary meteorological data has been collected since 2003.  The SMEAR III station has also tree measurements done in ! cooperation with the Department of Forest Ecology. 

In June 2010 an eddy covariance setup was also installed to the Fire Station tower in central Helsinki and another station was installed in September to Hotel Tower (Figure 7). The former was operational until the end of January 2011 and the latter is intended to provide long-term measurements.

Figure 9: Average diurnal cycle of carbon dioxide at SMEAR III in winter and summer and for three different wind direction sectors.

Selected publications

J.T. Koskinen, J. Poutiainen, D.M. Schultz, S. Joffre, J. Koistinen, E. Saltikoff, E. Gregow, H. Turtiainen, W.F. Dabberdt, J. Damski, N. Eresmaa, S. Göke, O. Hyvärinen, L. Järvi, A. Karppinen, J. Kotro, T. Kuitunen, J. Kukkonen, M. Kulmala, D. Moisseev, P. Nurmi, H. Pohjola, P. Pylkkö, T. Vesala and Y. Viisanen: The Helsinki Testebed. A mesoscale measurement, research, and service platform. Bull. American Meteorolog. Society 92, 325-342, 2011.

Vesala, T., L. Järvi, S. Launiainen, A. Sogachev, Ü. Rannik, I. Mammarella, E. Siivola, P. Keronen, J. Rinne, A. Riikonen, and E. Nikinmaa (2008). Surfaceatmosphere interactions over complex urban terrain in Helsinki, Finland. Tellus Series B-Chemical and Physical Meteorology 60 (2): 188-199.

Järvi, L., H. Hannuniemi, T. Hussein, P. Aalto, R. Hillamo, T. Mäkelä, P. Keronen, E. Siivola, T. Vesala, and M. Kulmala (2009). The urban measurement station SMEAR! III: Continuous monitoring of air pollution and surface-atmosphere interactions in Helsinki, Finland. Boreal Environment Research 14 (Suppl. A), 86-109.

Järvi, L., I. Mammarella, W. Eugster, A. Ibrom, E. Siivola, E. Dellwik, P. Keronen G. Burba, and T. Vesala (2009). Comparison of net CO2 fluxes measured with open- and closed-path infrared gas analyzers in urban complex environment. Boreal Environment Research 14 (4): 499-514.

Järvi, L., Ü. Rannik, I. Mammarella, A. Sogachev, P. P. Aalto, P. Keronen, E. Siivola, M. Kulmala, and T. Vesala (2009). Annual particle flux observations over a heterogeneous urban area. Atmospheric Chemistry and Physics 9(3): 13407-13437.

Partners

• prof. Eero Nikinmaa, Department of Forest Sciences
• Tareq Hussein
• Prof. Sue Grimmond, King's College London
• Finnish Meteorological Institute

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Boundary Layer and Turbulence

Ivan Mammarella, Annika Nordbo, Pavel Alekseychik, Mei-Kuei Tu (Sofia), Timo Vesala

The main scope of boundary layer physics is to determine the momentum, energy and mass fluxes in a wide range of atmospheric boundary layer (ABL) regimes from stable and neutral to convective. One of the most challenging part of ABL physics is to understand flows close to and within tall vegetation. Vegetation canopy flows show several unique features (Finnigan 2000) like coherent structures, counter-gradient transport and the aerodynamic drag creating turbulence. Local equilibrium condition between production and destruction/dissipation of turbulence is not achieved inside and just above the canopy (Finnigan 2000), and large coherent eddies, which have length scales proportional to the canopy height, dominate the transport of momentum, heat and mass through the canopy layer. The region where these eddies dominate defines the roughness sub-layer (RSL), and depending on stand density, it can extend several canopy heights in the vertical direction.

Recent studies of our research group focused on the following aspects of atmospheric turbulent motions above and within forest canopies:

• The effect of atmospheric stratification on vertical profiles of turbulent statistics was recently studied by using data collected during a measurement campaign at SMEAR II station (see figure below). Measurements of RSL flow statistics down to the canopy floor are essential, in order to improve turbulence parameterization in numerical models.
• The canopy thermal stability often shows a different diurnal cycle compared to the surface layer stability (especially for the very dense canopy). Observations of night time turbulence in the Scots pine forest of Hyytiälä, Finland (Launianen et al. 2007, Mammarella et al. 2007) indicates thermal decoupling situations within the canopy layer. In such conditions non-local processes (advective fluxes) can influence the energy budget and the CO2 net ecosystem exchange (Mammarella et al. 2007), as well as modifies the nocturnal chemical conversion of gases such as NO and O3 to NO2, which can subsequently be removed by dry deposition (Rannik et al. 2009).
• Experimental evaluation of shear stress and turbulent kinetic energy budgets highlighted how the pressure and turbulent transport terms are mainly responsible of the absence of local equilibrium condition inside the RSL (Mammarella et al. 2008).
• Recently we are investigating several methods to filter out the eddy covariance CO2 flux data measured during low turbulent mixing conditions (e.g. night-time measurement problem). The traditional filtering criterion, based on the friction velocity, although commonly used in the Fluxnet community, it is subjected to several drawbacks. For example, when the air flows above and below canopy are decoupled, the friction velocity measured above the canopy (at the same level of EC flux) fails to represent the degree of turbulent mixing within the canopy. In fact in some cases, while the turbulence above canopy can still be maintained, the mixing in the subcanopy layer is suppressed. Moreover the sub-canopy wind direction tends to follow the local terrain slope, regardless of the above canopy flow (Mammarella et al. 2007).

Finally our research group has a long time experience on modeling flux/concentration footprint, which is defined as the relative contribution from each element of the surface area source/sink to the vertical flux or concentration measured for example by an eddy covariance system located on a micrometeorological tower. The footprint area is a complex function of the observation level, surface roughness length and canopy structure together with meteorological conditions (wind speed and direction, turbulence intensity and atmospheric stability) (for a review see Vesala et al. 2008).

Selected publications

G. Katul, S. Launiainen, T. Grönholm and T. Vesala: The effects of the canopy medium on dry deposition velocities of aerosol particles in the canopy sub-layer above forested ecosystems. Atmospheric Environment 45, 1203-1212, 2011.

Ü. Rannik, I. Mammarella, P. Keronen and T. Vesala. 2009. Vertical advection and nocturnal deposition of ozone over a Boreal pine forest, Atmospheric Chemistry and Physics, 9, 2089-2095.

Vesala, T., N. Kljun, Ü. Rannik, J. Rinne, A. Sogachev, T. Markkanen, K. Sabelfeld, T. Foken, M.Y. Leclerc. 2008. Flux and concentration footprint modelling: State of the art. Environmental Pollution, 152, 653-666.

Mammarella, I., E. Dellwik and N.O. Jensen. 2008. Turbulence spectra, shear stress and turbulent kinetic energy budgets above two beech forest sites in Denmark. Tellus 60B, 2, 179-187.

Launiainen S., T. Vesala, M. Molder, I. Mammarella, S. Smo! lander, P. Kolari, Ü. Rannik, P. Hari and A. Lindroth. 2007. Vertical variability and effect of stability in turbulent characteristics and fluxes down to the floor of a pine forest. Tellus 59B, 919-936.

Mammarella, I., P. Kolari, T. Vesala and J.Rinne. 2007. Determining the contribution of vertical advection to the net ecosystem exchange at Hyytiälä forest, Finland. Tellus 59B, 900-909.

Partners

• Prof. Gaby Katul (Duke University)
• Prof. Sergej Zilitinkevich (Finnish Meteorological Institute)
• Dr. Andrei Sogachev (Risø National Laboratory for Sustainable Energy, Wind Energy Division, Denmark)

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Atmos-Bios Interactions in Global Models

Maarit Raivonen, Sampo Smolander, Marin Tomasic, Timo Vesala

A major enterprise conducted at the international level is the development of complex Earth System Models (ESM). Such models integrate our knowledge regarding the atmosphere, ocean, cryosphere and biosphere, accounting for the couplings between physical and biogeochemical processes in these components of the Earth System. We are a part of COSMOS, a project for community ESM, led by Max Planck Institute in Hamburg. We have the COSMOS ESM code and can readily modify and run it, which makes the implementation of the newest results in the model convenient. The most recent findings in the biogeochemistry taking place in the boreal region are applied in parameterizations of carbon, water and nitrogen cycles.

We are currently working on models for:

• Methane production, transport and emissions in peatlands
• Biogenic Volatile Organic Compounds (BVOC's) production and emissions from vegetation

to be icluded in the JSBACH global vegetation model, part of the COSMOS Earth System Models network.

Selected publications

T. Thum, P. Räisänen, S. Sevanto, M. Tuomi, C. Reick, T. Vesala, T. Raddatz, T. Aalto, H. Järvinen, N. Altimir, K. Pilegaard, Z. Nagy, S. Rambal, and J. Liski: Soil carbon model alternatives for ECHAM5/JSBACH climate model: Evaluation and impacts on global carbon cycle estimates. J. Geophys. Res., 116, G02028, 2011.

Partners

• Global Vegetation Modelling Group, Max Planck Institute for Meteorology, Hamburg
• Almut Arneth, Lund University
• Finnish Meteorological Institute
• Finnish Environment Institute

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Last update: Feb 08 2012, Annika Nordbo