Urban Meteorology Research

The observational part of the group is largely based on measurements carried out at the SMEAR III station located in Helsinki. Currently we have two active sites, where the fluxes of CO2, H2O, heat and particles are measured using the eddy covariance (EC) technique (Figure 1). The two sites represent different land uses: The semi-urban Kumpula site (blue) has been running since 2004 (Vesala et al. 2008, Järvi et al. 2009) and the urban site, Hotel Torni (red), was started in 2009 in the city centre and it represents a highly built-up land cover (Nordbo et al. 2013, Kurppa et al. 2015). Within the approximate footprint of the Kumpula measurement site, half of the surface is covered with vegetation, whereas in city centre the fraction is only 22%. Kumpula is also ICOS (Integrated Carbon Observation System) associated ecosystem station. In addition to the long-term measurements, we have conducted several EC measurement campaigns related to other compounds like VOCs, CO and N2O.

With the aid of the observations, we try to understand how different urban land uses affect the surface exchange processes with particular emphasis on the role of vegetation. The observations are also used in urban land surface model development .

The current and past projects are

  • Pan-Eurasian Experiment (PEEX), 2015 - present
  • Integrated Carbon Observations System (ICOS), 2008 - present
  • The exchange of carbon dioxide, heat and water in urban areas, PI: Leena Järvi, The Academy of Finland post-doctoral fellow, 2010 - 2013
  • The FP7 project BRIDGE (sustainaBle uRban plannIng Decision support accountinG for urban mEtabolism), PI: Timo Vesala, 2007 - 2011
  • Micrometeorology and air quality in urban areas, PI: Leena Järvi, Maj and Tor Nessling Foundation, 2007 - 2010

Figure: The locations of the two eddy covariance (EC) stations in Helsinki (Karsisto et al. 2015). The 1 km circular areas around the station approximate the source areas for the EC measurements.

We actively participate to the development of the Surface Urban Energy and Water Balance Scheme SUEWS (Järvi et al. 2011, Ward et al. 2016) in close collaboration with the Prof. Sue Grimmond a the University of Reading. The model simulates the energy and water balance components through the use of commonly measured meteorological variables and information on the surface cover in a neighborhood scale. The model is also part of the Urban Multi-Scale Environmental Prediction Tool (UMEP, Lindberg et al. 2017). Besides model development, we use SUEWS to examine both long- and short-term behavior of the surface balances in different urban areas. Current study interests are long-term hydrological changes in in urban areas using re-analysis data as forcing, urban surface energy and water balances in cold climate regions and include carbon dioxide as one of the simulated components. The current and past research projects are

  • Modelling of the surface energy and water balances in high-latitude cities, PI: Leena Järvi, Maj and Tor Nessling foundation, 2014 - 2017
  • The exchange of carbon dioxide, heat and water in urban areas, PI: Leena Järvi, The Academy of Finland post-doctoral fellow, 2010 - 2013

Figure: Modelled energy balance at the urban site (Rl) in Montreal
during (a) cold snow, (b) warm snow and (c) snow-free periods in 2007-2008 using SUEWS (Järvi et al. 2014).

We develop and use the Large Eddy Simulation model PALM in collaboration with Finnish Meteorological Institute and University of Hannover to examine the flow fields and air quality in above realistic Helsinki. The current work covers the calculation of footprints for our EC measurement sites and examination of the sensitivity of the model system to model boundary conditions. We are also adding sectional aerosol particle model (SALSA) to be part of the model so that it can be used to simulate aerosol particle size distribution within complex urban landscapes. We also use the model (with and without aerosol particle dynamics) to examine how new neighbourhoods in Helsinki metropolitan region should be built so that the air quality within would be as good as possible. Current and past reseach projects are

  • Hienon resoluution ilmanlaatumallinnus kaupunkisuunnittelun tukena (Fine resolution air quality modelling as support of urban planning), PI: Leena Järvi, Helsinki Metropolitan Region Urban Research Program, 2017-2018
  • Towards reliable prediction of urban climate using novel methodology development, PI: Mikko Auvinen, Maj and Tor Nessling foundation, 2017-2018
  • Modelling air quality and ventilation inside city blocks using large-eddy simulations, PI: Mona Kurppa, Doctoral School in Atmospheric Sciences of the UHEL, 2017-2020
  • Effect of building structures on the ventilation of Helsinki city boulevards, PI: Antti Hellsten (FMI), Helsinki City Planning Department, 2016
  • Large eddy simulations of a realistic urban surface, PI: Timo Vesala, CSC Grand Challenge, 2014 - 2015

Figure: Flow field in central Helsinki as simulated using PALM model using detailed surface model (M. Auvinen).

 

Our group collaborates with several research groups both nationally and internationally. The main collaborators for the current research topics are

  • Prof. Sue Grimmond, University of Reading, UK
  • Prof. Siegfried Raasch, Leibniz University Hannover, Germany
  • Prof. Prashant Kumar, University of Surrey, UK
  • Adj. Prof. Liisa Pirjola, Metropolia, University of Applied Sciences, Finland
  • Dr Topi Rönkkö, Tampere University of Technology, Finland
  • Dr Ari Karppinen, Finnish Meteorological Institute, Finland
  • Dr Antti Hellsten, Finnish Meteorological Institute, Finland
  • Prof. Andreas Christen, University of Freiburg, Germany
  • Prof. Huizi Liu, Chinese Academy of Sciences, China
  • Dr Carl Fortelius, Finnish Meteorological Institute, Finland
  • Dr Helen Ward, University of Innsbruck, Austria
  • Ass. Prof. Joe Mcfadden, University of Santa Barbara, California, USA