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Energetics of interannual temperature variability.

Jouni Räisänen, Climate Dynamics, https://link.springer.com/article/10.1007/s00382-018-4306-0

The paper analyzes the energetics of interannual temperature variability in two reanalysis data sets using a method that attributes temperature anomalies to variations in the atmospheric energy budget.

Sensitivity of idealised baroclinic waves to mean atmospheric temperature and meridional temperature gradient changes

Rantanen, M., Räisänen, J., Sinclair, V.A. and Järvinen H. (2018). Climate Dynamics https://doi.org/10.1007/s00382-018-4283-3

We studied how the dynamics of idealised mid-latitude cyclones changes with three different temperature forcings. The forcings were based on temperature changes which are expected to occur in the Northern Hemisphere with climate change: (1) uniform temperature increase, (2) decrease of the lower level meridional temperature gradient, and (3) increase of the upper level temperature gradient.

Validation of GMI Snowfall Observations by Using a Combination of Weather Radar and Surface Measurements.

von Lerber, A., D. Moisseev, D.A. Marks, W. Petersen, A. Harri, and V. Chandrasekar (2018). J. Appl. Meteor. Climatol., 57, 797–820,
https://doi.org/10.1175/JAMC-D-17-0176.1

In this study we have evaluated performance of the NASA Global Precipitation
Mission snowfall product using observations collected at the Hyytiälä SMEAR
II station and FMI weather radar located in Ikaalinen. We show that while
probability of snowfall detection is better than 0.9, the precipitation
intensity is underestimated.

Measurement–model comparison of stabilized Criegee intermediate and highly oxygenated molecule production in the CLOUD chamber

Sarnela, N., Jokinen, T., Duplissy, J., Yan, C., Nieminen, T., Ehn, M., Schobesberger, S., Heinritzi, M., Ehrhart, S., Lehtipalo, K., Tröstl, J., Simon, M., Kürten, A:, Leiminger, M., Lawler,M. J., Rissanen, M. P., Bianchi, F., Praplan, A. P., Hakala, J., Amorim, A., Gonin, M., Hansel, A., Kirkby, J., Dommen, J., Curtius, J., Smith, J. N., Petäjä, T., Worsnop, D. R., Kulmala, M., Donahue, N. M. and Sipilä M. (2018) Atmospheric chemistry and physics, 18, 2363-2380,
doi:10.5194/acp-18-2363-2018

In this paper we studied the formation of sulfuric acid and highly oxygenated
molecules, the key compounds in atmospheric new particle formation, in
chamber experiments and introduced a way to simulate these ozonolysis
products of α-pinene in a simple manner.
Temporal variation of VOC fluxes measured with PTR-TOF above a boreal forest

Schallhart, S., Rantala, P., Kajos, M. K., Aalto, J., Mammarella, I., Ruuskanen, T. M., and Kulmala, M.: Temporal variation of VOC fluxes measured with PTR-TOF above a boreal forest, Atmos. Chem. Phys., 18, 815-832, https://doi.org/10.5194/acp-18-815-2018, 2018.
Emissions of volatile organic compounds (VOCs) have impact to air quality, human health and climate. We investigated the development of VOC exchange in a boreal forest between April and June 2013. VOC exchange and diversity increased towards summer, but over 75 % of the biogenic net exchange was driven by methanol, monoterpenes and acetone only. The boreal forest emitted less than 0.2 % carbon in form of VOCs in relation to the carbon uptake.

Kulmala M. 2018. Build a global Earth observatory. Science doi: 10.1038/d41586-017-08967-y

 
Applicability of open rainfall data to event-scale urban rainfall-runoff
modelling.

Niemi, T., L. Warsta, M. Taka, B. Hickman, S. Pulkkinen, G. Krebs, D. Moisseev, H. Koivusal, and T. Kokkonen (2017). . J. Hydrol.,
10.1016/j.jhydrol.2017.01.056.

Rainfall-runoff simulations in urban environments require meteorological
input data with high temporal and spatial resolutions. The availability of
precipitation data is constantly increasing due to the shift towards more
open data sharing. However, the applicability of such data for urban runoff
assessments is often unknown. Here, the feasibility of Finnish Meteorological
Institute’s open rain gauge and open weather radar data as input sources
was studied by conducting Storm Water Management Model simulations at a very
small (33.5 ha) urban catchment in Helsinki, Finland. In addition to the open
data sources, data were also available from two research gauges, one of them
located on-site, and from a research radar.
Secondary Ice Production: Current State of the Science and Recommendations
for the Future.

Field, P.R., R.P. Lawson, P.A. Brown, G. Lloyd, C. Westbrook, D. Moisseev, A. Miltenberger, A. Nenes, A. Blyth, T. Choularton, P. Connolly, J. Buehl, J. Crosier, Z. Cui, C. Dearden, P. DeMott, A. Flossmann, A. Heymsfield, Y. Huang, H. Kalesse, Z.A. Kanji, A. Korolev, A. Kirchgaessner, S. Lasher-Trapp, T. Leisner, G. McFarquhar, V. Phillips, J. Stith, and S. Sullivan (2017).
Meteorological Monographs, 58, 7.1–7.20, doi:
10.1175/AMSMONOGRAPHS-D-16-0014.1.

Measured ice crystal concentrations in natural clouds at modest supercooling
(temperature ~>−10°C) are often orders of magnitude greater than the
number concentration of primary ice nucleating particles. Therefore, it has
long been proposed that a secondary ice production process must exist that is
able to rapidly enhance the number concentration of the ice population
following initial primary ice nucleation events. Secondary ice production is
important for the prediction of ice crystal concentration and the subsequent
evolution of some types of clouds, but the physical basis of the process is
not understood and the production rates are not well constrained.
Thunderstorm hail and lightning detection parameters based on
dual-polarization Doppler weather radar data.
Voormansik, T. P. Rossi, D. Moisseev, P. Post (2017). Meteorological Applications. doi: 10.1002/met.1652.
Four years (2011–2014) of the summer period (May–September)
dual-polarization Doppler C-band weather radar data for Sürgavere, Estonia,
were examined to determine the best indicator for cloud-to-ground lightning
activity. Furthermore, the legacy radar-derived hail indicator probability of
hail and the storm maximum reflectivity were compared with the polarimetric
hydrometeor classification algorithm (HCA) to establish a link between them
and ensure data continuity.
Quantifying the effect of riming on snowfall using ground-based observations

Moisseev, D., A. von Lerber, and J. Tiira (2017). J. Geophys. Res.
Atmos., 122, doi:10.1002/2016JD026272.

Ground-based observations of ice particle size distribution and ensemble mean
density are used to quantify the effect of riming on snowfall. Given the
current interest on sensitivity of precipitation to aerosol pollution, which
could inhibit riming, the importance of riming for surface snow accumulation
is investigated. It is found that riming is responsible for 5% to 40% of
snowfall mass. The study is based on data collected at the University of
Helsinki field station in Hyytiälä during U.S. Department of Energy
Biogenic Aerosols Effects on Clouds and Climate (BAECC) field campaign and
the winter 2014/2015.
Microphysical Properties of Snow and Their Link to Ze–S Relations during BAECC 2014.

von Lerber, A., D. Moisseev, L.F. Bliven, W. Petersen, A. Harri, and V. Chandrasekar (2017). Microphysical Properties of Snow and Their Link to Ze–S Relations during BAECC 2014. J. Appl. Meteor.
Climatol., 56, 1561–1582, https://doi.org/10.1175/JAMC-D-16-0379.1

This study uses observations of snow events from the Biogenic
Aerosols–Effects on Clouds and Climate (BAECC) 2014 campaign to investigate
the connection between properties of snow and radar observations. The general
hydrodynamic theory is applied to video-disdrometer measurements to retrieve
masses of falling ice particles. From the derived microphysical properties,
event-specific relations between the equivalent reflectivity factor Ze and
snowfall precipitation rate S are determined.
Collocated observations of cloud condensation nuclei, particle size distributions, and chemical composition

Schmale, J.; Henning, S.; Henzing, B.; Keskinen, H.; Sellegri, K.; Ovadnevaite, J.; Bougiatioti, A.; Kalivitis, N.; Stavroulas, I.; Jefferson, A.; Park, M.; Schlag, P.; Kristensson, A.; Iwamoto, Y.; Pringle, K.; Reddington, C.; Aalto, P.; Äijälä, M.; Baltensperger, U.; Bialek, J.; Birmili, W.; Bukowiecki, N.; Ehn, M.; Fjæraa, A. M.; Fiebig, M.; Frank, G.; Fröhlich, R.; Frumau, A.; Furuya, M.; Hammer, E.; Heikkinen, L.; Herrmann,
E.; Holzinger, R.; Hyono, H.; Kanakidou, M.; Kiendler-Scharr, A.; Kinouchi, K.; Kos, G.; Kulmala, M.; Mihalopoulos, N.; Motos, G.; Nenes, A.; O’Dowd, C.; Paramonov, M.; Petäjä, T.; Picard, D.; Poulain, L.; Prévôt, A. S. H.; Slowik, J.; Sonntag, A.; Swietlicki, E.; Svenningsson, B.; Tsurumaru, H.;
Wiedensohler, A.; Wittbom, C.; Ogren, J. A.; Matsuki, A.; Yum, S. S.; Myhre, C. L.; Carslaw, K.; Stratmann, F.; Gysel, M. (2017). Scientific Data, 4,
170003.

This "data descriptor" presents harmonized data records of cloud condensation nuclei (CCN) number concentrations, submicrometer particle number size
distributions and particle chemical composition from 11 stations around the world (including Hyytiälä).
OZO v.1.0: software for solving a generalised omega equation and the
Zwack–Okossi height tendency equation using WRF model output

Rantanen, M., Räisänen, J., Lento, J., Stepanyuk, O., Räty, O., Sinclair,
V. A., and Järvinen, H. (2017). Geoscientific Model Development, 10,
827-841, doi:10.5194/gmd-10-827-2017.

This paper describes new software OZO, which is a meteorological tool for
both studying and research purposes. OZO can be used for investigating
physical mechanisms affecting the development of extratropical cyclones. The
software is an open-source tool and the distribution is supported by the
authors. OZO will be used as a part of the author's PhD, in which the changes
in cyclone dynamics due to warmer climate are studied.
Occupational health risk assessment and exposure to floor dust PAHs inside an educational building.

Androniki Maragkidou, Sharif Arar, Afnan Al-Hunaiti, Yuning Ma, Stuart Harrad, Omar Jaghbeir, Dina Faouri, Kaarle Hämeri, Tareq Hussein. (2016).
Science of The Total Environment, Volume 579, 1 February 2017, Pages 1050-1056,
http://dx.doi.org/10.1016/j.scitotenv.2016.11.055

In the paper, PAHs concentrations in floor dust were reported and their exposure and health risk inside the Department of Physics of the University of Jordan were evaluated.
Factors affecting atmospheric vertical motions as analyzed with a generalized
omega equation and the OpenIFS model.

Stepanyuk, O., J. Räisänen, V. A. Sinclair, and H. Järvinen, 2017: Tellus
A, 69:1, 1271563

The causes of atmospheric vertical motions are studying by applying a generalized omega equation to a one-year simulation with the OpenIFS atmospheric model. The results show the general dominance of vorticity advection and thermal advection in extratropical latitudes in winter, the increasing importance of diabatic heating towards the tropics, and the significant role of friction in the lowest troposphere. There is also a clear increase in the relative importance of diabatic heating in the Northern Hemisphere midlatitudes from the winter to the summer, particularly over the continents.
Hydroxyl radical-induced formation of highly oxidized organic compounds

Berndt, T., Richters, S., Jokinen, T., Hyttinen, N., Kurtén, T., Otkjær, R.
V., Kjaergaard, H. G., Stratmann, F., Herrmann, H., Sipilä, M., Kulmala, M., & Ehn, M. (2016). Hydroxyl radical-induced formation of highly oxidized organic compounds. [Article]. Nature Communications, 7, 13677. doi:10.1038/ncomms13677

This paper shows how OH-initiated oxidation of alpha-pinene is able to form
many more highly oxidized (O/C > 0.6) product molecules (HOM) than previously
thought. Earlier studies had used nitrate ion-based chemical ionization mass
spectrometry (CIMS), which were found to underestimate HOM byt a factor of 40
compared to less sensitive CIMS methods.
Airborne laser scan data: a valuable tool with which to infer weather radar partial beam blockage in urban environments.

Cremonini, R., Moisseev, D., and Chandrasekar, V. (2016). Atmos. Meas. Tech., 9, 5063-5075, doi:10.5194/amt-9-5063-2016, 2016.

Although high-spatial-resolution resolution weather radar observations are of
primary relevance for urban hydrology, weather radar siting and
characterization are challenging in an urban environment. Buildings, masts
and trees cause partial beam blockages and clutter that seriously affect the
observations. For the first time, this paper investigates the benefits of
using airborne laser scanner (ALS) data for characterizing performance of
weather radars in a metropolitan area.
Ensemble mean density and its connection to other microphysical properties of falling snow as observed in Southern Finland

Jussi Tiira, Dmitri N. Moisseev, Annakaisa von Lerber, Davide Ori, Ali Tokay, Larry F. Bliven, and Walter Petersen (2016). Atmospheric Measurement Techniques 9, 4825-4841, doi:10.5194/amt-9-4825-2016, 2016.

In this study winter measurements collected in Southern Finland are used to
document microphysical properties of falling snow. It is shown that a new
video imager can be used for such studies. Snow properties do vary between
winters.
How dual-polarization radar observations can be used to verify model representation of secondary ice

Sinclair V.A., D. Moisseev, and A. vonLerber (2016), J. Geophys. Res., 121, doi:10.1002/2016JD025381.
http://onlinelibrary.wiley.com/doi/10.1002/2016JD025381/full

Ice particles exist in much higher concentrations than can be explained by
primary ice production: secondary ice production methods such as rime
splintering (Hallet-Mossop process) are responsible. In this paper we analyse
dual-polarization radar, microwave radiometer, radiosonde sounding and
surface mircophysical observations made at Hyytiälä during the Biogenic
Aerosols on Clouds and Climate (BAECC) campaign to identify secondary ice
production. We show that bands of specific differential phase (Kdp) in the
temperature range ‐3 to ‐8 C can be linked to secondary ice. We use these
observation of Kdp bands to verify numerical weather prediction model
representation of secondary ice. We find that secondary ice production is not
well represented in high‐resolution (1 km grid spacing) Weather Research
and Forecasting (WRF) model simulation of a high‐latitude wintertime
frontal cloud band. This potentially impacts the forecast of precipitation.
An energy balance perspective on regional CO2-induced temperature changes in CMIP5 models

Räisänen, J. (2015). Climate Dynamics, doi:10.1007/s00382-016-3277-2

The paper conducts an energy balance decomposition of temperature changes in CMIP5 climate models. The global annual mean warming is dominated by enhanced clear-sky greenhouse effect due to increased CO2 and water vapour, but other energy balance terms strongly modify the geographical and seasonal patterns of the change. The three most important terms for intermodel differences in warming are the changes in the clear-sky greenhouse effect, clouds, and the net surface energy flux, making the largest contribution in 34, 29 and 20 % of the world, respectively. The magnitude of warming over Greenland and Antarctica is substantially controlled by heat transport from the surrounding sea areas.
Anthropogenic and biogenic influence on VOC fluxes at an urban background site in Helsinki, Finland.

Rantala P., Järvi L., Taipale R., Laurila T. K., Patokoski J., Kajos M. K., Kurppa M., Haapanala S., Siivola E., Petäjä T., Ruuskanen T. M. and Rinne J. (2016). Atmospheric Chemistry Physics 16, 7981-8007, doi:10.5194/acp-16-7981-2016.

 
Continental anthropogenic primary particle number emissions.

Paasonen, P., Kupiainen, K., Klimont, Z., Visschedijk, A., Denier van der Gon, H. A. C., and Amann, M.: Continental anthropogenic primary particle number emissions, Atmos. Chem. Phys., 16, 6823-6840,doi:10.5194/acp-16-6823-2016, 2016.

In this paper we show the first results of size-segregated anthropogenicparticle number emissions from the GAINS emission scenario model. The sharesof different sources and their predicted changes from 2010 to 2030 aredescribed, showing clear difference in sources dominating the particle numberand mass emissions. We also point out the main uncertainties in numberemissions. The GAINS particle number emissions can be applied in improvingthe evaluation of aerosol climate and health effects.
Canopy-scale flux measurements and bottom-up emission estimates of volatile organic compounds from a mixed oak and hornbeam forest in northern Italy

Acton, W. J. F., Schallhart, S., Langford, B., Valach, A., Rantala, P.,Fares, S., Carriero, G., Tillmann, R., Tomlinson, S. J., Dragosits, U.,Gianelle, D., Hewitt, C. N., and Nemitz, E., Atmos. Chem. Phys., 16,7149-7170, doi:10.5194/acp-16-7149-2016, 2016.

Volatile organic compounds (VOCs) represent a large source of reactive carbonin the atmosphere and hence have a significant impact on air quality. It istherefore important that we can accurately quantify their emission. In thispaper we use three methods to determine the fluxes of reactive VOCs from awoodland canopy. We show that two different canopy-scale measurement methodsgive good agreement, whereas estimates based on leaf-level-based emissionunderestimate isoprene fluxes.
Characterization of total ecosystem-scale biogenic VOC exchange at a Mediterranean oak–hornbeam forest

Schallhart, S., Rantala, P., Nemitz, E., Taipale, D., Tillmann, R., Mentel,T. F., Loubet, B., Gerosa, G., Finco, A., Rinne, J., and Ruuskanen, T. M.,Atmos. Chem. Phys., 16, 7171-7194, doi:10.5194/acp-16-7171-2016, 2016.

We present ecosystem exchange fluxes from a mixed oak–hornbeam forest inthe Po Valley, Italy. Detectable fluxes were observed for 29 compounds,dominated by isoprene, which comprised over 60 % of the upward flux.Methanol seemed to be deposited to dew, as the deposition happened in theearly morning. We estimated that up to 30 % of the upward flux of methylvinyl ketone and methacrolein originated from atmospheric oxidation ofisoprene.
Kieloaho, A.-J., Pihlatie, M., Dominquez Carrasco, M., Kanerva, S., Parshintsev, J., Riekkola, M.-L., Pumpanen, J., Heinonsalo, J. (2016). Soil Biology and Biochemistry, 96, 97-106, doi:10.1016/j.soilbio.2016.01.013 There is link between forest trees and soil organic matter degrading processing and the presence of plant have same effect on soil nitrogen pool than enzymes alone. It was also shown that simple organic nitrogen compounds, e.g. alkylamines are in the same range as nitrate in the soil.
Sources of long-lived atmospheric VOCs at the rural boreal forest site, SMEAR II.Patokoski J., Ruuskanen T. M., Kajos M. K., Taipale R., Rantala P., Aalto J., Ryyppö T, Nieminen T, Hakola H., and Rinne J. (2015). Atmospheric Chemistry and Physics, 15, 13413-13432, doi: 10.5194/acp-15-13413-2015.  
Dual-polarization radar signatures in snowstorms: Role of snowflakeaggregation

Moisseev, D., S. Lautaportti, J. Tyynela, and S. Lim. (2015). J. Geophys. Res. Atmos., 120, 12644–12655, doi:10.1002/2015JD023884.

In this article a potential role of snowflake growth by aggregation onformation of dual-polarization radar signatures in winter storms isdiscussed. The bands of increased specific differential phase are caused byhigh number concentrations of oblate relatively dense ice particles and takeplace in regions where an ice phase “seeder-feeder” process is active.Furthermore, based on surface observations of snowflakes, it is determinedthat early aggregates, consisting of a small number of ice crystals, areoblate. These oblate particles could contribute to the reporteddual-polarization radar signatures in snow,
Seasonal surface urban energy balance and wintertime stability simulated using three land-surface models in the high-latitude city Helsinki

Karsisto P., Fortelius C., Demuzere M., Grimmond C.S.B., Kouznetsov R., Masson V. and Järvi L. (2015). Q. J. Roy. Met. Soc., doi:10.1002/qj.2659. http://onlinelibrary.wiley.com/doi/10.1002/qj.2659/abstract

The performance of three urban land surface schemes is examined in Helsinki, Finland. The simulated net all-wave radiation, turbulent fluxes of sensible and latent heat, and snow depth are compared against observations at two sites with different surface cover fractions. In general the models perform well, but the thermal model parameters need to be revisited in cold climateregions and the description of vegetation needs to be improved in order to realistically simulate the surface forcing for numerical weather prediction, climate and air quality models.
Ambient measurements of aromatic and oxidized VOCs by PTR-MS and GC-MS:intercomparison between four instruments in a boreal forest in Finland.

Kajos M.K., Rantala P., Hill M., Hellén H., Aalto J., Patokoski J., Taipale R., Hoerger C.C., Reimann S., Ruuskanen T.M., Rinne R., and Petäjä T. (2015). Atmos. Meas. Tech., 8, 4453-4473, doi:10.5194/amt-8-4453-2015.

 
Annual cycle of volatile organic compound exchange between a boreal pine forest and the atmosphere.Rantala P., Aalto J., Taipale R., Ruuskanen T. M. and Rinne J. (2015). Biogeosciences 12, 5753-5770,doi: 10.5194/bg-12-5753-2015.  
Structures, Hydration, and Electrical Mobilities of Bisulfate Ion-Sulfuric Acid-Ammonia/Dimethylamine Clusters: A Computational Study

Narcisse T. Tsona, Henning Henschel, Nicolai Bork, Ville Loukonen, and Hanna Vehkamäki (2015). Journal of Physical Chemistry A, 119, 9670-9679, DOI: 10.1021/acs.jpca.5b03030

 
Satellite observations of changes in snow-covered land surface albedo duringspring in the Northern Hemisphere.

Atlaskina, K., Berninger, F., and de Leeuw, G (2015). The Cryosphere, 9,1879-1893, doi:10.5194/tc-9-1879-2015.

Snow cover explained most of the spring surface albedo changes in the Northern Hemisphere in the years 2000−2012. However, there are vast areas where albedo changed up to ±0.2 under full snow-covered conditions. We found that if in these areas, the mean monthly air temperature exceeds a value between -15°C and -10°C, depending on the region, albedo decreases with an increase of the temperature. The complexity of processes involved in surface albedo changes is discussed.
Lintunen, A., Paljakka, T., Riikonen, A., Lindén, L., Lindfors, L., Hölttä, T., Nikinmaa, E. 2015. Irreversible diameter change of branches correlates with other methods for estimating frost tolerance of living cells in freeze- thaw experiment: a case study with seven urban tree species in Helsinki. Annals of Forest Science, doi: 10.1007/s13595-015-0516-3. We assessed tree frost tolerance using electrolyte leakage and a method based on irreversible diameter change of branches. It was shown that irreversible diameter change correlates with electrolyte leakage and USDA hardiness rating and is a good indicator of frost tolerance.
Sulphuric acid and aerosol particle production in the vicinity of an oil refinery

Sarnela, N., Jokinen, T., Nieminen, T., Lehtipalo, K., Junninen, H., Kangasluoma, J., Hakala, J., Taipale, R., Schobesberger, S., Sipilä, M., Larnimaa, K., Westerholm, H., Heijari, J., Kerminen, V.-M., Petäjä, T. and Kulmala, M. (2015) Atmospheric Environment 119, 156-166,http://dx.doi.org/10.1016/j.atmosenv.2015.08.033

One month in-situ measurements were conducted close to a large oil refinery. We observed elevated concentrations of H2SO4 and nano-particles from oil refinery. SO2, H2SO4 and particle concentrations showed source dependentbehaviour. Large fraction of the particle growth could be accounted to sulphuric acid.
Footprint evaluation for flux and concentration measurements for anurban-like canopy with coupled Lagrangian stochastic and large-eddysimulation models.

Hellsten A., Luukkonen S.M., Steinfeld G., Kanani-Suhring F., Markkanen T.,Järvi L., Vesala T. and Raasch S. (2015), Boundary-Layer Meteorology, DOI10.1007/s10546-015-0062-4.

Calculations of flux and concentration footprint of passive scalar over anurban-like canopy using coupled Lagrangian stochastic and Large EddySimulation (LES) models are made. The local heterogeneity of the flow has aconsiderable impact on flux and concentration footprints. As expected,footprints for flux measurements within and right above the canopy layer showcomplex and completely different footprint shapes compared to the ellipsoidalshape obtained from conventional footprint models that assume horizontalhomogeneity of the turbulent flow as well as the sources of passive scalars.
Effect of seasonal variability and land use on particle number and CO2exchange in Helsinki, Finland.

Kurppa M., Nordbo A., Haapanala S. and Järvi L. (2015). Urban Climate 13, 94- 109, doi:10.1016/j.uclim.2015.07.006.

Turbulent fluxes of particles and CO2 at two sites (Kumpula and city centre)in Helsinki were studied. CO2 flux was larger in the city centre than at thesuburban site whereas particles were emitted with a similar strength from asingle large road as from the city centre. Particle flux had the largest netfluxes in winter and the smallest in summer, whereas seasonal variability inFc was minor. Partly this can be explained by increasing particle emissionsin colder temperatures.
Kalman Filtering-Based Probabilistic Nowcasting of Object-Oriented TrackedConvective Storms

Rossi, Pekka, V. Chandrasekar, Vesa Hasu, and Dmitri Moisseev, (2015). J.Atmos. Oceanic Technol., 32, 461-477.doi: 10.1175/JTECH-D-14-00184.1

The weather radar–based object-oriented convective storm tracking is astandard approach for analyzing and nowcasting convective storms. However,the majority of current storm-tracking algorithms provide nowcasts only in adeterministic fashion with limited ability to estimate the relateduncertainties. This paper proposes a method for probabilistic nowcasting ofconvective storms that addresses the issue of uncertainty of nowcasts. Theapproach first utilizes a two-dimensional radar-based storm identificationand tracking algorithm in conjunction with the Kalman filtering of noisymeasurements of storm centroid. The verification of the method shows that thealgorithm is applicable in both deterministic and probabilistic manner.Moreover, the forecast probabilities are consistent with observed frequenciesof the storms, especially with 20- and 30-min nowcasts.
Identification and suppression of nonmeteorological echoes using spectral polarimetric processing Alku, L., D. Moisseev, T. Aittomaki and V. Chandrasekar, (2015). IEEE Trans. Geosci. Remote Sens., 53, 3628-3638, doi: 10.1109/TGRS.2014.2380476 The presence of nonmeteorological radar signals, such as sea clutter, birds, and chaff, is a continuous challenge for meteorological services in different regions. In this paper, we assign membership functions to these signals using spectral decompositions of copolar correlation coefficient, differential reflectivity, and differential phase. Additionally, we apply the dual-polarization spectral decomposition technique to identify and suppress nonmeteorological echoes present in radar observations. The performance of the polarimetric spectral filter is illustrated in observations from the C-band Helsinki University Kumpula radar. The results show that the spectral polarimetric filter may be a suitable solution for the mitigation of these nonmeteorological signals.
Observed relations between snowfall microphysics and triple-frequency radar measurements Kneifel, S., A. von Lerber, J. Tiira, D. Moisseev, P. Kollias, and J. Leinonen (2015). J. Geophys. Res. Atmos., 120, 6034–6055. doi: 10.1002/2015JD023156. Until recently, no in situ observations have been available to investigate links between microphysical snowfall properties and their scattering properties. In this study, we investigate for the first time relations between collocated ground-based triple-frequency observations with in situ measurements of snowfall at the ground. The three analyzed snowfall cases obtained during a recent field campaign in Finland cover light to moderate snowfall rates with transitions from heavily rimed snow to open-structured, low-density snowflakes. The observed triple-frequency signatures agree well with the previously published findings from airborne radar observations. A rich spatiotemporal structure of triple-frequency observations throughout the cloud is observed during the three cases, which often seems to be related to riming and aggregation zones within the cloud.
Nordbo A., Karsisto P., Matikainen L., Wood C.R. an Järvi L. (2015). Urban surface cover determined with airborne lidar at 2 m resolution–Implications for surface energy balance modelling. Urban Climate 13, 52-72, doi:10.1016/j.uclim.2015.05.004. The surface cover fractions for central Helsinki were calculated with airborne lidar at 2 m resolution and the effect of horizontal resolution on surface energy balance modelling was examined. An aggregation of the surface-cover map from 2 to 100 m reduced the fraction of vegetation by two thirds resulting in 16% increase in simulated sensible heat and 56% reduction in latent heat flux.
Tuija Jokinen, Torsten Berndt, Risto Makkonen, Veli-Matti Kerminen, Heikki Junninen, Pauli Paasonen, Frank Stratmann, Hartmut Herrmann, Alex B. Guenther, Douglas R. Worsnop, Markku Kulmala, Mikael Ehn and Mikko Sipilä: Production of extremely low volatile organic compounds from biogenic emissions: Measured yields and atmospheric implications, Proc. Natl. Acad. Sci., doi/10.1073/pnas.1423977112, 2015.

http://www.pnas.org/content/early/2015/05/20/1423977112.abstract

Investigations of extremely low volatile organic compound (ELVOC) production from different biogenic precursors suggest that ozonolysis of endocyclic monoterpenes have a major role in global ELVOC budget while hydroxyl radica reaction is less important. Furthermore, study shows that oxidation of exo- or acyclic monoterpenes and isoprene are not as significant source of ELVOC.ELVOCs are important constituents of secondary organic aerosol and they have been shown to explain particle growth from cluster sizes to cloud condensation nuclei in forested environments.
Optical modeling of volcanic ash particles using ellipsoids. Merikallio, S., Muñoz, O., Sundström, A-M., Virtanen, T.H., de Leeuw, G., and Nousiainen, T. (2015). J. Geophys. Res. Atmos., 120,doi:10.1002/2014JD022792. In this work the single-scattering properties of volcanic ash particles are modeled by using ellipsoidal shapes. To assess the performance of the ellipsoidal particle models, the results are compared with measured single-scattering optical properties of ash particles from several volcanoes across the globe, including previously unpublished measurements from the Eyjafjallajökull and Puyehue volcanoes.
Characterization of satellite-based proxies for estimating nucleation modeparticles over South Africa. Sundström, A.-M. , Nikandrova, A., Atlaskina, K., Nieminen, T., Vakkari,V., Laakso, L. , Beukes, J. P., Arola, A., van Zyl, P. G., Josipovic, M.,Venter, A. D., Jaars, K., Pienaar, J. J., Piketh, S., Wiedensohler,A., Chiloane, E. K., de Leeuw, G. and Kulmala, M. (2015). Atmos. Chem.Phys., 15, 4983-4996, doi:10.5194/acp-15-4983-2015.  
Exposure to Airborne Particles and Volatile Organic Compounds from Polyurethane Molding, Spray Painting, Lacquering, and Gluing in a Workshop. Molgaard, B., Viitanen, A-K., Kangas, A., Huhtiniemi, M., Larsen, S. T., Vanhala, E., Hussein, T., Boor, B. E., Hämeri, K. & Koivisto, A. J. 04.2015 In : International Journal of Environmental Research and Public Health. 12, 4, p. 3756-3773 18 p.  
Chemistry and the Linkages between Air Quality and Climate Change. Erika von Schneidemesser, Paul S. Monks, James D. Allan, Lori Bruhwiler, Piers Forster, David Fowler, Axel Lauer, William T. Morgan, Pauli Paasonen, Mattia Righi, Katerina Sindelarova, and Mark A. Sutton (2015). Chemical Reviews, DOI: 10.1021/acs.chemrev.5b00089.  
Räisänen, J., 2015: Twenty-first century changes in snowfall climate in Northern Europe in ENSEMBLES regional climate models. Climate Dynamics, DOI 10.1007/s00382-015-2587-0.  Available at: Changes in snowfall in northern Europe are analysed from 12 regional model simulations of 21st century climate. The models suggest a decrease in the winter total snowfall in nearly all of northern Europe. In the middle of the winter, however, snowfall generally increases in the coldest areas. High extremes of daily snowfall remain nearly unchanged, except for decreases in the mildest areas.
Joint control of terrestrial gross primary productivity by plant phenology and physiologyXia J, Niu S, Ciais P, Janssens IA, Chen J, Ammann C, Arain A, Blanken BD, Cescatti A, Bonal D, Buchmann N, Curtis PS, Chen S, Dong J, Flanagan LB, Frankenberg C, Georgiadis T, Gough CM, Hui D, Kiely G, Lia J, Lund M, Magliulo V, Marcolla B, Merbold L, Montagnani L, Moors EJ, Olesena JE, Piao S, Raschi A, Roupsard O, Suyker AE, Urbaniak M, Vaccari FB, Varlagin A, Vesala T, Wilkinson M, Weng E, Wohlfahrt G, Yan L, Luo Y (2015) PNAS doi: 10.1073/pnas.1413090112 Terrestrial gross primary productivity (GPP), the total photosynthetic CO2 fixation at ecosystem level, fuels all life on land. However, its spatiotemporal variability is poorly understood, because GPP is determined by many processes related to plant phenology and physiological activities. In this study, we find that plant phenological and physiological properties can be integrated in a robust index—the product of the length of CO2 uptake period and the seasonal maximal photosynthesis—to explain the GPP variability over space and time in response to climate extremes and during recovery after disturbance.
Modeling Attenuation of Radio Waves by a Low Melting Layer at C-band von Lerber, A., D. Moisseev, J. Lenonen, J. Koistinen and M. Hallikainen(2015). IEEE Trans. Geosci. Remote Sens. 53, 724-737, doi: 10.1109/TGRS.2014.2327148. In Finland radar observations could be affected by attenuation of radio waves while propagating through wet snow. This attenuation was not quantified previously. In this paper first quantitative analysis of this effect is presented. A simple relation between radar observations and expected attenuation has been derived.
Use of 2D-Video Disdrometer to Derive Mean Density-Size and Ze-SR Relations: Four Snow Cases from the Light Precipitation Validation ExperimentHuang, G.-J., V.N. Bringi, D. Moisseev, W.A. Petersen, L. Bliven and D. Hudak (2015). Atmos. Research, 153, 34-48, doi:10.1016/j.atmosres.2014.07.013. Snowfall data from Light Precipitation Validation Experiment that took place in 2010 is analyzed. It is shown that a relation between radar reflectivity and a snowfall rate can be established by using observations of snowflake fall velocity. It was also found that the current FMI relation overestimates snowfall rate by about factor of 2.
What do triple-frequency radar signatures reveal about aggregate snowflakes?Leinonen, J., and Moisseev D. (2015). J. Geophys. Res. Atmos., 120, 229–239, doi:10.1002/2014JD022072. The triple-frequency radar signature of aggregate snowflakes was studied. It was found that the signature is not sensitive to the type of ice crystals in the aggregate, but the size of the constituent crystals does have a measurable effect.
Brief communication: Light-absorbing impurities can reduce the density of melting snowO. Meinander, A. Kontu, A. Virkkula, A. Arola, L. Backman, P. Dagsson-Waldhauserová, O. Järvinen, T. Manninen, J. Svensson, G. de Leeuw, and M. LeppärantaThe Cryosphere, 8, 991-995, 2014 In this paper, we hypothesize that BC may decrease the liquid-water retention capacity of melting snow, and present our first data, where both the snow density and elemental carbon content were measured. In our experiments, artificially added light-absorbing impurities decreased the density of seasonally melting natural snow. No relationship was found in case of natural non-melting snow. We also suggest three possible processes that might lead to lower snow density.
Trends in the average temperature in Finland, 1847–2013Mikkonen S., Laine M., Mäkelä H. M., Gregow H., Tuomenvirta H., Lahtinen M., Laaksonen A. (2015)Stochastic Environmental Research and Risk Assessment, In Press, doi:10.1007/s00477-014-0992-2. Over the past 166 years, the average temperature in Finland has risen by more than two degrees. During the observation period, the average increase was 0.14 degrees per decade, which is nearly twice as much as the global average. Read the article here: http://link.springer.com/article/10.1007%2Fs00477-014-0992-2
Räisänen J, Ylhäisi JS. 2014. CO2-induced climate change in northern Europe: CMIP2 versus CMIP3 versus CMIP5. Climate Dynamics. doi: 10.1007/s00382-014-2440-x This paper compares the simulation of CO2-induced climate change in northern Europe between three ensembles of global climate models: CMIP2 (~1999), CMIP3 (~2005) and CMIP5 (~2011). The systematic differences between the three ensembles are generally small compared with the differences between the individual models. An energy and water balance based analysis of the simulated temperature and precipitation changes is also presented. Read the article here:
Sundström A-M, Arola A, Kolmonen P, Xue Y, de Leeuw G, Kulmala M. 2015. On the use of a satellite remote-sensing-based approach for determining aerosol direct radiative effect over land: a case study over China. Atmos. Chem. Phys. 15: 505-518. doi:10.5194/acp-15-505-2015. A satellite-based approach to derive the aerosol direct shortwave (SW) radiative effect (ADRE) at the top of the atmosphere (TOA) was studied in an environment with highly variable aerosol conditions over eastern China. The method combines coincident observations from two different satellite instruments. The results showed that the satellite-based clear-sky estimates for median instantaneous and diurnally averaged ADRE over the study area were -8.8 W/m² and -5.1 W/m², respectively. Over heavily industrialized areas, the cooling at TOA was 2 to more than 3 times stronger, and associated with high AODs (>0.5). read the article here: http://adsabs.harvard.edu/abs/2014ACPD...1415113S
Bork N, Loukonen V, Kjaergaardb HG, Vehkamäki H. 2014. Resolving the anomalous infrared spectrum of the MeCN–HCl molecular cluster using ab Initio molecular dynamics. Phys. Chem. Chem. Phys. 16: 24685-24690. A front cover -paper published in Physical Chemistry Chemical Physics by Bork, Loukonen, Kjærgaard and Vehkamäki. Acetonitrile–hydrogen chloride cluster is one of the best model systems for atmospheric acid–base clustering studied by IR spectroscopy to date. They have shown that the highly unusual spectral shape associated with the fundamental H–Cl stretch mode in this complex is due to the dynamics of the N–H–Cl angle, not captured by the conventional static minimum energy picture of the cluster. Read the article here: http://pubs.rsc.org/en/Content/ArticleLanding/2014/CP/C4CP03828B#!divAbstract
Onset of photosynthesis in spring speeds up monoterpene synthesis and leads to emission bursts.

Aalto J., Porcar-Castell A., Atherton J., Kolari P., Pohja T., Hari P., Nikinmaa E., Petäjä T. and Bäck J. (2015) Plant, Cell & Environment, DOI: 10.1111/pce.12550

Long-term monitoring showed that Scots pine shoots are expressing exceptionally high monoterpene emissions in early spring, suggesting a strong link between photosynthetic spring recovery and monoterpene synthesis. The finding challenges the current concept of constant emission capacities and has potentially implications on studies concerning seasonal changes in atmospheric chemistry and physics. 

 

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