Ilmatieteen laitos

Recent Submissions

  • Pfau-Kempf, Yann (Finnish Meteorological Institute, 2016)
    Vlasiator – From local to global magnetospheric hybrid-Vlasov simulations Contributions 127
    The Sun is the source of the solar wind, a continuous stream of electrically charged particles and magnetic fields pervading the Solar system. Its interaction with the magnetic field of the Earth, in and around the region called the magnetosphere, controls the flow of matter and energy in near-Earth space. A fundamental understanding of the physical processes at play is crucial for the building of forecasting and warning systems, as the influence of the solar wind during space storms can harm life and technology in space and on the ground. These effects, collectively known as space weather, are one of the biggest albeit least understood natural threats to society. The research effort needed includes the development of observational methods as well as theories and models, to first describe and later predict the mechanisms and consequences of space weather. This doctoral thesis, comprising an introduction and four peer-reviewed articles, presents the hybrid-Vlasov model Vlasiator developed at the Finnish Meteorological Institute. Based on a detailed description of proton physics in space plasmas, Vlasiator allows to simulate both local contexts and the Earth’s magnetosphere on global scales. This unprecedented capability is only accessible by harnessing the power of modern supercomputers. The aim of this work is threefold. The current version of Vlasiator is documented considering physical and computational aspects, the correctness of the simulations is demonstrated by comparing to analytical theories and spacecraft observations, and new scientific results gained with this model are presented.
  • Vira, Julius (Finnish Meteorological Institute, 2017)
    Finnish Meteorological Institute Contributions 130
    Atmospheric chemistry and transport models are used for a wide range of applications which include predicting dispersion of a hazardous pollutants, forecasting regional air quality, and modelling global distribution of aerosols and reactive gases. However, any such prediction is uncertain due to inaccuracies in input data, model parametrisations and lack of resolution. This thesis studies methods for integrating remote sensing and in-situ observations into atmospheric chemistry models with the aim of improving the predictions. Techniques of data assimilation, originally developed for numerical weather prediction, are evaluated for improving regional-scale predictions in two forecast experiments, one targeting the photochemical pollutants ozone (O3) and nitrogen dioxide (NO2), the other targeting sulphur dioxide (SO2). In both cases, assimilation of surface-based air quality monitoring data is found to initially improve the forecast when assessed on monitoring stations not used in assimilation. However, as the forecast length increased, the forecast converged towards the reference simulations where no data assimilation was used. The relaxation time was 6-12 hours for SO2 and NO2 and about 24 hours for O3. An alternative assimilation scheme was tested for SO2. In addition to the initial state of the forecast, the scheme adjusted the gridded emission fluxes based on the observations within the last 24 hours. The improvements due to adjustment of emissions were generally small but, where observed, the improvements persisted throughout the 48 hour forecast. The assimilation scheme was further adapted for estimating emission fluxes in volcanic eruptions. Assimilating retrievals of the Infrared Atmospheric Sounding Interferometer (IASI) instrument allowed reconstructing both the vertical and horizontal profile of SO2 emissions during the 2010 eruption of Eyjafjallaj¨okull in Iceland. As a novel feature, retrievals of plume height were assimilated in addition to the commonly used column density retrievals. The results for Eyjafjallaj¨okull show that the plume height retrievals provide a useful additional constraint in conditions where the vertical distribution would otherwise remain ambiguous. Finally, the thesis presents a rigorous description and evaluation of a numerical scheme for solving the advection equation. The scheme conserves tracer mass and non-negativity, and is therefore suitable for regional and global atmospheric chemistry models. The scheme is particularly adapted for handling discontinuous solutions; for smooth solutions, the scheme is nevertheless found to perform comparably to other state-of-art schemes used in atmospheric models.
  • Votsis, Athanasios (Finnish Meteorological Institute, 2016)
    Finnish Meteorological Institute Contributions 129
    As the adaptation of cities to climate change is increasingly overlapping sustainable urban development, the necessity to harmonize climate-proofing with economic objectives becomes ever clearer. Climate-sensitive ecological risks and amenities, and their role in markets and urban planning, are central in this issue. This research explores the reaction of urban housing markets to changes related to green amenities and flood risks; deepens the understanding of complex spatial processes, in housing markets and urban growth, that relate to the implementation of sustainable adaptation strategies; and develops advanced spatial modelling methodology that renders urban economic analysis better suitable to address questions of sustainable and climate-proof urban planning. The results demonstrate that physical or behavioral planning interventions surrounding climate-sensitive ecological risks and amenities generate economic benefits via multiple channels, when attuned with market mechanisms. This is an important building block in synchronizing climate-proofing with economic development objectives, therefore facilitating urban adaptation that is also sustainable. The synchronization requires an evidence-based understanding of the effects linked to particular interventions, at concrete locations and spatiotemporal scales. The overall message is that, while trade-offs are unavoidable, if green cities maintain agglomeration benefits, ensure increased information flows about ecological risks and amenities, while implementing amenities in a spatially parameterized manner, they are able to achieve both climate-proofing and sustainability objectives. The thesis consists of five quantitative analysis articles, while the introductory chapter synthesizes the results in the context of urban planning, spatial economics, and climate change adaptation. The first three articles apply empirical microeconometric methodologies (spatial hedonic and difference-in-differences analysis) to explore the response of housing markets to changes in green infrastructure and to policy instruments related to flood risk information. The fourth and fifth articles apply spatial complexity methods (cellular automata, fractal geometry) to extend the intuitions of microeconometric estimations into dynamic spatial processes in housing prices and urban growth. The five articles use environmental-economic datasets developed by this dissertation research, covering the urban region of Helsinki (Helsinki, Espoo, and Vantaa) and the cities of Pori and Rovaniemi.
  • Waldén, Jari; Waldén, Tuomas; Laurila, Sisko; Hakola, Hannele (Finnish Meteorological Institute, 2017)
    Raportteja - Rapporter - Reports 1:2017
    Euroopan Yhteisön CAFÉ-direktiivin (2008/50/EY) määrittää mm. hiukkasmittausten vertailumenetelmän, mikä perustuu hiukkasmassan gravimetriseen määritykseen. Jäsenmaa voi käyttää muuta menetelmää vertailumenetelmän sijasta, mikäli se voi osoittaa, että tulokset ovat yhteneviä vertailumenetelmän antamien tulosten kanssa. Tällaisella menetelmällä saatuja tuloksia on tarvittaessa korjattava, jotta saataisiin vertailumenetelmää käyttämällä saatavia tuloksia vastaavat tulokset. Hiukkasmittausten osalta vertailumenetelmä PM2.5 ja PM10 massapitoisuuden määrittämiseksi ulkoilmassa perustuu gravimetriseen määritysmenetelmään. Tässä tutkimuksessa testattiin eräiden jatkuvatoimisten hiukkasmittalaitteiden yhdenvertaisuutta vertailumenetelmää vastaan noudattaen komission ohjetta. Vertailumittaukset tehtiin Kuopiossa ja ne käsittivät hiukkasten aerodynaamiselta halkaisijaltaan olevat alle 2.5 μm:n ja alle 10 μm:n kokoiset hiukkasmittaukset. Vertailuun osallistuivat kaikkiaan kahdeksan eri jatkuvatoimista hiukkasanalysaattorimallia: BAM 1020, DustTrak 8535, FH 62 I-R, Grimm 180, MP101 CPM, Osiris, SHARP 5030 ja TEOM 1405. Vertailumittausohjelma toteutettiin komission ohjeen mukaisesti. Ohje määrittelee mm. pitoisuustasoista niin, että 20 % havainnoista tulee ylittää alimman arviointikynnykset (UAT) sekä PM2.5 että PM10 massapitoisuuksille. Havaintoaineistosta osoittautui, että PM2.5 massapitoisuudet eivät ylittäneet sille asetettua UAT arvoa, 17 µg/m3, yli asetetun kriteerin, vaan tästä jäätiin selvästi alle. Verrattaessa Suomessa mitattuja PM2.5 pitoisuuksia, voidaan todeta, että hyvin harvoin mittauksissa ylitetään UAT-arvo PM2.5 pitoisuuksissa. PM10 pitoisuuksissa sen sijaan ylempi arviointikynnys, 30 µg/m3, ylitettiin useammin kuin vaadittava määrä. Vertailumittaustulokset analysoitiin komission ohjeen mukaan ja sen perusteella esitetään jokaiselle vertailtavalle hiukkasanalysaattorille kalibrointikertoimet sekä PM2.5- että PM10-mittauksille. Raportissa osoitetaan myös kaikki poikkeamat, mitä esiintyi sallituista kriteereistä. Tulosten perusteella voidaan todeta, että yksi vertailtava analysaattori, DustTrak 8535, ei täyttänyt vaadittavia kriteerejä sekä PM2.5- että PM10-mittauksille. Osiris täytti vaatimukset PM10-mittauksille, mutta ei PM2.5-mittauksille. Sen sijaan kaikki muut testatut hiukkasanalysaattorit, FH 62 I-R, Grimm 180, MP101 CPM, SHARP 5030, TEOM 1405 ja BAM 1020 täyttivät vertailumenetelmälle asetetut vaatimukset sekä PM2.5- että PM10-mittauksille.
  • Prank, Marje (Finnish Meteorological Institute, 17-0)
    Finnish Meteorological Institute Contributions 128
    Atmospheric composition has strong influence on human health, ecosystems and also Earth's climate. Among the atmospheric constituents, particulate matter has been recognized as both a strong climate forcer and a significant risk factor for human health, although the health relevance of the specific aerosol characteristics, such as its chemical composition, is still debated. Clouds and aerosols also contribute the largest uncertainty to the radiative budget estimates for climate projections. Thus, reliable estimates of emissions and distributions of pollutants are necessary for assessing the future climate and air-quality related health effects. Chemistry-transport models (CTMs) are valuable tools for understanding the processes influencing the atmospheric composition. This thesis consists of a collection of developments and applications of the chemistry-transport model SILAM. SILAM's ability to reproduce the observed aerosol composition was evaluated and compared with three other commonly used CTM-s in Europe. Compared to the measurements, all models systematically underestimated dry PM10 and PM2.5 by 10-60%, depending on the model and the season of the year. For majority of the PM chemical components the relative underestimation was smaller than that, exceptions being the carbonaceous particles and mineral dust - species that suffer from relatively small amount of available oservational data. The study stressed the necessity for high-quality emissions from wild-land fires and wind-suspended dust, as well as the need for an explicit consideration of aerosol water content in model-measurement comparison. The average water content at laboratory conditions was estimated between 5 and 20% for PM2.5 and between 10 and 25% for PM10. SILAM predictions were used to assess the annual mortality attributable to short-term exposures to vegetation-fire originated PM2.5 in different regions in Europe. PM2.5 emitted from vegetation fires was found to be a relevant risk factor for public health in Europe, more than 1000 premature deaths per year were attributed to vegetation-fire released PM2.5. CTM predictions critically depend on emission data quality. An error was found in the EMEP anthropogenic emission inventory regarding the SOx and PM missions of metallurgy plants on the Kola Peninsula and SILAM was applied to estimate the accuracy of the proposed correction. Allergenic pollen is arguably the type of aerosol with most widely recognised effect to health. SILAM's ability to predict allergenic pollen was extended to include Ambrosia Artemisiifolia - an invasive weed spreading in Southern Europe, with extremely allergenic pollen capable of inducing rhinoconjuctivitis and asthma in the sensitive individuals even in very low concentrations. The model compares well with the pollen observations and predicts occasional exceedances of allergy relevant thresholds even in areas far from the plants' habitat. The variations of allergenicity in grass pollen were studied and mapped to the source areas by adjoint computations with SILAM. Due to the high year-to-year variability of the observed pollen potency between the studied years and the sparse observational network, no clear geographic pattern of pollen allergenicity was detected.
  • Mäkelä, Antti; Lehtonen, Ilari; Ruosteenoja, Kimmo; Jylhä, Kirsti; Tuomenvirta, Heikki; Drebs, Achim (Finnish Meteorological Institute, 2016)
    Raportteja - Rapporter - Reports 2016:8
    Ilmasto on jo muuttunut ihmiskunnan kasvihuonekaasupäästöjen seurauksena. Ilmastomalleihin perustuvien arvioiden mukaan lämpeneminen jatkuu ja sen suuruus ja vaikutukset riippuvat päästöjen määrän kehityksestä eli niiden rajoittamisen tehokkuudesta. Koska ilmakehään jo tähän mennessä päässeet kasvihuonekaasupäästöt vaikuttavat siellä vielä vuosikymmeniä, muuttuviin olosuhteisiin varautuminen esimerkiksi kaupungeissa on joka tapauksessa välttämätöntä. Tuoreimpien arvioiden mukaan pääkaupunkiseudun ilmasto lämpenee kaikkina vuodenaikoina, talvella enemmän kuin kesällä. Mikäli päästöjen hillinnässä onnistutaan tyydyttävästi, vuoteen 2100 mennessä tammikuun keskilämpötila on arvioiden mukaan reilut 5°C korkeampi kuin nykyään, ja vastaavasti heinäkuussa ero on noin 3°C. Äärimmäisen alhaiset lämpötilat harvinaistuvat voimakkaasti. Vuorokauden korkeimmat lämpötilat kesäisin kohoavat samaa tahtia keskilämpötilan kohoamisen kanssa. Talvella sataa selvästi nykyistä enemmän ja aurinkoa nähdään harvemmin. Keskimääräiset ja suurimmat sademäärät sekä sadepäivien määrä kasvavat. Kesällä rankkasateiden arvioidaan voimistuvan runsaat 10 % sadassa vuodessa. 1900-luvun loppuvuosikymmeninä noin kerran 20 vuodessa havaittu rankkasade koetaan 2000-luvun lopulla hiukan useammin kuin kerran kymmenessä vuodessa, ja kerran sadassa vuodessa esiintynyt rankkasade noin kerran 30 vuodessa. Keskimääräiset tuulen voimakkuudet pysyvät likimain ennallaan. Merenpinnan keskimääräinen korkeus Helsingin edustalla noussee muutamia kymmeniä senttimetrejä. Merellä jäät keskimäärin ohenevat ja jään pinta-ala pienentyy. Kuitenkin yksittäisiä runsasjäisiäkin talvia esiintyy vielä lähivuosikymmeninä. Vaikka ilmastonmuutoksen vaikutuksista osan voidaan ajatella olevan Suomessa suotuisia (lämmitystarpeen pieneneminen, pidempi kasvukausi), maailmanlaajuisesti suurin osa vaikutuksista on ihmiskunnan ja maapallon eliöstön kannalta erittäin epäsuotuisia (entistä voimakkaammat äärisääilmiöt, kuivuus, nälänhätä, pakolaisuus). Koska päästöt eivät tunne valtakuntien rajoja, päästöjen hillinnästä on sovittava kansainvälisesti. Kansainvälisistä sopimuksista tuorein on Pariisin ilmastosopimus vuodelta 2015, jota tarkastellaan myös lyhyesti tässä raportissa. Tähän raporttiin on koostettu viimeisin tieto ilmastonmuutoksen vaikutuksista pääkaupunkiseudulla perustuen IPCC:n 5. arviointiraportin RCP-kasvihuone-kaasupäästöskenaarioihin. Raportti siten päivittää aiempia pääkaupunki-seudulle tehtyjä vastaavia arviointeja.
  • Seitola, Teija (Finnish Meteorological Institute, 16-1)
    Finnish Meteorological Institute Contributions 126
    The ability of climate models to simulate the climate variability is of great importance when considering the reliability of, for instance, multiannual or longerterm predictions. The aim of this thesis is to study the 20th century lowfrequency variability patterns in the Earth system and how these patterns are represented by the current modelling systems. Another, equally important objective is to enable efficient spatiotemporal analysis of highdimensional climate data sets. Decadal scale variability and predictability, from the point of view of the Nordic region, is also summarised in this study. The work is based on the nearsurface temperature of two 20th century reanalyses, obtained from the NOAA/OAR/ESRL and ECMWF, and historical climate model simulations from the coupled model intercomparison project 5 (CMIP5) data archive. In addition, a millennial Earth system model simulation is analysed. The analysis relies on a powerful dimensionality reduction method, called random projection (RP), which is introduced as a preprocessing for highdimensional climate data sets to enhance or enable the analysis. The spectral decomposition of the data sets is based on randomised multichannel singular spectrum analysis (RMSSA), which is one of the main achievements of this thesis. It is shown that dimensionality reduction obtained by RP preserves the main spatial and temporal patterns with high accuracy. In addition, RMSSA is shown to provide an efficient tool for identifying different variability modes in highdimensional climate data sets. This study shows that the 20th century variability patterns in the two reanalysis data sets are very similar. It is also shown that none of the studied climate models can closely reproduce all the variability modes identified in the reanalyses, although many aspects are simulated well. Taking into account the rapidly accumulating amount of data and increasing dimensionality of data sets, RP is a promising method for dimensionality reduction. The results of the model evaluation can be useful in model development due better understanding of the deficiencies in representing the lowfrequency modes. In addition to nearsurface temperature, it would be a natural extension to include more variables in the analysis, especially because RP allows efficient data compression.
  • Ruosteenoja, Kimmo; Kämäräinen, Matti; Aņiskeviča, Svetlana; Pirinen, Pentti; Mäkelä, Antti (Finnish Meteorological Institute, 2016)
    Raportteja - Rapporter- Reports 2016:7
    This report examines climatic changes projected for Latvia during the 21st century. Climate projections are based on a wide ensemble of state-of-the-art CMIP5 global climate models; that set of models was utilized in compiling the 5th Assessment Report of the Intergovernmental Panel on Climate Change. Projections have been elaborated separately for three greenhouse gas cenarios, the RCP2.6 scenario representing small, RCP4.5 medium and RCP8.5 large emissions. By the late 21st century, the following changes (expressed relative to the mean of the period 1971-2000) are projected: • In winter, mean temperatures are projected to increase by 1-4 °C under RCP2.6, 2-6 °C under RCP4.5 and 4-9 °C under RCP8.5. In summer, anticipated warming is weaker: 1-3 °C under RCP2.6, 1-4 °C under RCP4.5 and 2-7 °C under RCP8.5. In winter, warming appears to be somewhat larger in the eastern part of the country while in summer the geographical differences are small. • Diurnal temperature range would diminish in winter by 0-50 % and incident solar radiation by 0-30 %. In summer, changes in these quantities are most likely positive but fairly small. • Mean winter precipitation increases by 0-20 % under RCP2.6, 0-30 % under RCP4.5 and 10-50 % under RCP8.5. In summer, the sign of change is uncertain, but in southern Latvia it is somewhat more likely that precipitation decreases slightly rather than increases. • Ice days (with a maximum temperature below zero) become substantially less frequent while the count of summer days (maximum temperature above 25 °C) increases. • Thermal growing season would lengthen by up to two months and the degree day sum would nearly double (under RCP8.5). • According to the best estimate (multi-model mean), wind speeds would remain nearly unchanged throughout the year. Even so, scatter among the individual model projections is large, and in winter even changes larger than ± 20% are possible. When studying projections for a less distant future, the sign of change is the same as what is projected for the late 21st century but the magnitude is smaller. The above uncertainty intervals of projected changes reflect mainly the inter-model differences but the contribution of natural unforced variability has also been taken into account. In the course of the project, several data files have been delivered into Latvia to be used for additional analyses. These files include, for instance, the time series of 30-year running monthly mean changes and bias-corrected daily model output, both given for five climate variables and represented on a 10 x 10 km grid.
  • Meinander, Outi (Finnish Meteorological Institute, 2016)
    Finnish Meteorological Institute Contributions 125
    Light-absorbing impurities in the cryosphere are of hydrological, environmental and climatic importance. The wet and dry deposition of black carbon (BC), organic carbon (OC), and dust particles affect the optical properties and melt of snow and ice. In the Arctic region, the climatic effects are amplified, and surface albedo feedback is often cited as the main contributor. The aim of this thesis is to fill in some of the gaps in our knowledge of the effects of BC, OC, and Icelandic dust on snow in the European Arctic through a series of field and laboratory experiments and an analysis of the resulting data, including modeling. The thesis presents a new hypothesis on the snow density effects of light-absorbing impurities, an important quantity for climate modeling and remote sensing. Three processes are suggested to explain the proposed ”BC density effect”. Experimental results show that dirty snow releases melt water quicker than cleaner snow. The albedo of natural seasonally melting snow in Sodankylä, north of the Arctic Circle, is found to be asymmetric with respect to solar midday, thus indicating a change in the properties of the snow. The radiative transfer modeling results show that the observed solar zenith angle asymmetry results in a 2–4 % daily error for satellite snow albedo estimates. Surface albedo model results indicate that the biggest snow albedo changes due to BC are expected in the ultraviolet (UV) part of the electromagnetic spectrum. The albedo of natural seasonal snow measured in Sodankylä, is found to be lower than expected. Solar UV and visible (VIS) albedo values of 0.6–0.8 in the accumulation period and 0.5–0.7 during melting are observed. The low albedo values are explained to be due to large snow grain sizes up to ∼3 mm in diameter, meltwater surrounding the grains and increasing the effective grain size, and absorption caused by impurities in the natural snow (87 ppb BC and 2894 ppb OC). The BC contents of the surface snow layer at the Sodankylä Arctic Research Center, Finland, is higher than expected. Increased BC in spring time suggests surface accumulation of hydrophobic BC during snow melt. Some of the high BC concentrations are related to anthropogenic soot transported from the Kola Peninsula, Russia. The origin of OC can be anthropogenic or natural, and may include pollen, seeds, lichens, natural litter or microorganisms that reside in snow and ice. Iceland is the most important Arctic dust source, but a scientific assessment of its impacts on the cryosphere is currently unavailable and scientific results are urgently needed to investigate the role of Icelandic dust in Iceland and elsewhere, in the past, present and future. Experimental results on Icelandic volcanic ash show that a thin layer increases the snow and ice melt but that an ash layer exceeding a certain critical thickness causes insulation. The Arctic results of this thesis have relevance to the assessment of Arctic climate change, including modeling and satellite applications.
  • Harjanne, Atte; Haavisto, Riina; Tuomenvirta, Heikki; Luhtala, Sanna; Mäkelä, Antti; Gregow, Hilppa; Halonen, Mikko; Raivio, Tuomas; Hildén, Mikael; Parjanne, Antti; Jakkila, Juho; Juhola, Sirkku; Räsänen, Aleksi; Haanpää, Simo; Jurgilevich, Alexandra; Peltonen-Sainio, Pirjo; Lanki, Timo; Miettinen, Ilkka; Zacheus, Outi; Kollanus, Virpi (Finnish Meteorological Institute, 2016)
    Raportteja - Rapporter - Reports 2016:6
    Raportissa kuvaillaan sää- ja ilmastoriskien hallintaa ja siihen liittyvien tietolähteiden käyttöä Suomessa. Raportti perustuu kolmeen erilliseen, mutta toisiaan tukevaan työvaiheeseen. Ensimmäinen työvaihe koostui kahdesta verkkokyselystä, joista toinen oli suunnattu kunnille ja toinen suomalaisille organisaatioille yleisesti. Kyselyillä kartoitettiin vastaajien kokemuksia sää- ja ilmastoriskeistä, niiden hallintaa ja käytettyjä tietolähteitä. Toisen työvaiheen muodosti sidosryhmätyöpaja, jonka tavoitteena oli vahvistaa kyselyn pääpiirteiset tulokset ja kerätä ajatuksia sää- ja ilmastoriskien hallinnan ja sitä tukevien palveluiden kehittämiseen. Kolmas työvaihe koostui kirjallisuusperustaisesta toimialakartoituksesta, jossa koottiin yhteen tietoa sää- ja ilmastoriskeistä ja niiden hallinnasta valituilla yhteiskunnan aloilla (vesivarat, vesihuolto, energia, maatalous, liikenne, matkailu, kuntasektori ja finanssiala). Kukin kolmesta työvaiheesta tuloksineen on esitelty raportissa erikseen. Tulokset viittaavat siihen, että vaikka säällä ja ilmastolla on merkittäviä vaikutuksia yhteiskunnan eri aloille ja toimijoille, on niiden aiheuttamien riskien hallinta vaihtelevaa. Yhteistyö eri muodoissaan koetaan tärkeäksi parannettaessa kykyä sää- ja ilmastoriskien hallintaan. Raportti perustuu ELASTINEN-hankkeessa tehtyyn työhön. Tämä julkaisu on toteutettu osana valtioneuvoston vuoden 2015 selvitys- ja tutkimussuunnitelman toimeenpanoa.
  • Gao, Yao (2016)
    Finnish Meteorological Institute Contributions 124
    Interactions between the land surface and climate are complex as a range of physical, chemical and biological processes take place. Changes in the land surface or the climate can affect the water, energy and carbon cycles in the Earth system. This thesis discusses a number of critical issues that concern land-atmospheric interactions in the boreal zone, which is characterised by vast areas of peatlands, extensive boreal forests and a long snow cover period. Regional climate modelling and land surface modelling were used as the main tools for this study, in conjunction with observational data for evaluation. First, to better describe the present-day land cover in the regional climate model, we introduced an up-to-date and high-resolution land cover map to replace the inaccurate and outdated default land cover map for Fennoscandia. Second, in order to provide background information for future forest anagement actions for climate change mitigation, we studied the biogeophysical effects on the regional climate of peatland forestation, which has been the dominant land cover change in Finland over the last century. Moreover, climate variability can influence the land surface. Although drought is uncommon in northern Europe, an extreme drought occurred in the summer of 2006 in Finland, and induced visible drought symptoms in boreal forests. Thus, we assessed a set of drought indicators with drought impact data in boreal forests in Finland to indicate summer drought in boreal forests. Finally, the impacts of summer drought on water use efficiency of boreal Scots pine forests were studied to gain a deeper understanding of carbon and water dynamics in boreal forest ecosystems. In summary, the key findings of this thesis include: 1) the updated land cover map led to a slight decrease in biases of the simulated climate conditions. It is expected that the model performance could be improved by further development in model physics. 2) Peatland forestation in Finland can induce a warming effect in the spring of up to 0.43 K and a slight cooling effect in the growing season of less than 0.1 K due to decreased surface albedo and increased evapotranspiration, respectively. Corresponding to spring warming, the snow clearance day was advanced by up to 5 days over a 15-year mean. 3) The soil moisture index SMI was the most capable of the assessed drought indicators in capturing the spatial extent of observed forest damage induced by the extreme drought in 2006 in Finland. Thus, a land surface model capable of reliable predictions of regional soil moisture is important in future drought predictions in the boreal zone. 4) The inherent water use efficiency (IWUE) showed an increase during drought at the ecosystem level, and IWUE was found to be more appropriate than the ecosystem water use efficiency (EWUE) in indicating the impacts of drought on ecosystem functioning. The combined effects of soil moisture drought and atmospheric drought on stomatal conductance have to be taken into account in land surface models at the global scale when simulating the drought effects on plant functioning.
  • Marnela, Marika (Finnish Meteorological Institute, 2016)
    Finnish Meteorological Institute Contributions 122
    The Arctic Ocean and its exchanges with the Nordic Seas influence the north-European climate. The Fram Strait with its 2600 m sill depth is the only deep passage between the Arctic Ocean and the other oceans. Not just all the deep water exchanges between the Arctic Ocean and the rest of the world's oceans take place through the Fram Strait, but also a significant amount of cold, low-saline surface waters and sea ice exit the Arctic Ocean through the strait. Correspondingly, part of the warm and saline Atlantic water flowing northward enters the Arctic Ocean through the Fram Strait bringing heat into the Arctic Ocean. The oceanic exchanges through the Fram Strait as well as the water mass properties and the changes they undergo in the Fram Strait and its vicinity are studied from three decades of ship-based hydrographic observations collected from 1980-2010. The transports are estimated from geostrophic velocities. The main section, comprised of hydrographic stations, is located zonally at about 79 °N. For a few years of the observed period it is possible to combine the 79 °N section with a more northern section, or with a meridional section at the Greenwich meridian, to form quasi-closed boxes and to apply conservation constraints on them in order to estimate the transports through the Fram strait as well as the recirculation in the strait. In a similar way, zonal hydrographic sections in the Fram Strait and along 75 °N crossing the Greenland Sea are combined to study the exchanges between the Nordic Seas and the Fram Strait. The transport estimates are adjusted with drift estimates based on Argo floats in the Greenland Sea. The mean net volume transports through the Fram Strait are averaged from the various approaches and range from less than 1 Sv to about 3 Sv. The heat loss to the atmosphere from the quasi-closed boxes both north and south of the Fram Strait section is estimated at about 10 TW. The net freshwater transport through the Fram Strait is estimated at 60-70 mSv southward. The insufficiently known northward transport of Arctic Intermediate Water (AIW) originating in the Nordic Seas is estimated using 2002 Oden expedition data. At the time of data collection, excess sulphur hexafluoride (SF6) was available, a tracer that besides a background anthropogenic origin derives from a mixing experiment in the Greenland Sea in 1996. The excess SF6 can be used to distinguish AIW from the upper Polar Deep Water originating in the Arctic Ocean. It is estimated that 0.5 Sv of AIW enters the Arctic Ocean. The deep waters in the Nordic Seas and in the Arctic Ocean have become warmer and in the Greenland Sea also more saline during the three decades studied in this work. The temperature and salinity properties of the deep waters found in the Fram Strait from both Arctic Ocean and Greenland Sea origins have become similar and continue to do so. How these changes will affect the circulation patterns will be seen in the future.
  • Tukiainen, Simo (Finnish Meteorological Institute, 2016)
    Finnish Meteorological Institute Contributions 123
    Measurements of the Earth's atmosphere are crucial for understanding the behavior of the atmosphere and the underlying chemical and dynamical processes. Adequate monitoring of stratospheric ozone and greenhouse gases, for example, requires continuous global observations. Although expensive to build and complicated to operate, satellite instruments provide the best means for the global monitoring. Satellite data are often supplemented by ground-based measurements, which have limited coverage but typically provide more accurate data. Many atmospheric processes are altitude-dependent. Hence, the most useful atmospheric measurements provide information about the vertical distribution of the trace gases. Satellite instruments that observe Earth's limb are especially suitable for measuring atmospheric profiles. Satellite instruments looking down from the orbit, and remote sensing instruments looking up from the ground, generally provide considerably less information about the vertical distribution. Remote sensing measurements are indirect. The instruments observe electromagnetic radiation, but it is ozone, for example, that we are interested in. Interpreting the measured data requires a forward model that contains physical laws governing the measurement. Furthermore, to infer meaningful information from the data, we have to solve the corresponding inverse problem. Atmospheric inverse problems are typically nonlinear and ill-posed, requiring numerical treatment and prior assumptions. In this work, we developed inversion methods for the retrieval of atmospheric profiles. We used measurements by Optical Spectrograph and InfraRed Imager System (OSIRIS) on board the Odin satellite, Global Ozone Monitoring by Occultation of Stars (GOMOS) on board the Envisat satellite, and ground-based Fourier transform spectrometer (FTS) at Sodankylä, Finland. For OSIRIS and GOMOS, we developed an onion peeling inversion method and retrieved ozone, aerosol, and neutral air profiles. From the OSIRIS data, we also retrieved NO2 profiles. For the FTS data, we developed a dimension reduction inversion method and used Markov chain Monte Carlo (MCMC) statistical estimation to retrieve methane profiles. Main contributions of this work are the retrieved OSIRIS and GOMOS satellite data sets, and the novel retrieval method applied to the FTS data. Long satellite data records are useful for trends studies and for distinguishing between anthropogenic effects and natural variations. Before this work, GOMOS daytime ozone profiles were missing from scientific studies because the operational GOMOS daytime occultation product contains large biases. The GOMOS bright limb ozone product vastly improves the stratospheric part of the GOMOS daytime ozone. On the other hand, the dimension reduction method is a promising new technique for the retrieval of atmospheric profiles, especially when the measurement contains little information about the vertical distribution of gases.
  • Mäkelä, Antti; Laurila, Terhi; Haapalainen, Jussi (Ilmatieteen laitos, 2016)
    Raportteja - Rapporter - Reports 2016:5
    Ilmatieteen laitos on koonnut ja julkaissut salamanlaskijoiden havainnot vuosilta 1960–1997. Vuodesta 1998 lähtien kaikki järjestelmälliset maasalamahavainnot perustuvat salamanpaikantimeen, jonka nykyinen malli aloitti toimintansa elokuussa 1997. Se käsitti 2015 kahdeksan anturia, pohjoisin Lokassa. Vuodesta 2002 mukana ovat olleet lisäksi Norjan ja Ruotsin anturit, joiden ansiosta koko Lappi on katettu ja suorituskyky on parantunut myös muualla Suomessa, sekä yksi anturi Virossa (mukaan vuonna 2005) ja kolme anturia Liettuassa (mukaan 2014). Laitteisto paikantaa maasalamoista erikseen jokaisen osaiskun ja ryhmittelee ne kokonaisiksi salamoiksi. Paikannettu salama voi sisältää 1-15 iskua; keskiarvo Suomessa on vajaa kaksi iskua/salama. Tilastoinnin pohjana käytetään salama- eikä iskumääriä, koska salama on ilmastollisesti edustavampi suure. Kesän 2015 aikana paikannettiin Suomen alueella ennätyksellisen vähän maasalamoita, noin 30 000, joka on vain viidennes keskimääräisestä (139 000). Suomen kesää pitkään hallinnut viileä säätyyppi ei suosinut rajuja ukkosia, ja elokuun lämmin ilmamassa estyi tuottamasta ukkospilviä korkeapainevoittoisen sään vuoksi. Kuukausista ainoastaan syyskuu ylsi hieman yli keskimääräisen.
  • Verronen, P.T. (editor) (Finnish Meteorological Institute, 16-0)
    Raportteja - Rapporter - Reports 2016:4
    Tervetuloa kuudenteen kansainväliseen HEPPA-SOLARIS-kokoukseen, jonka Ilmatieteen laitos järjestää 13.-17. kesäkuuta 2016 Helsingissä. Kokous jatkaa vuodesta 2008 järjestettyjen kokousten sarjaa, jonka aiheena on auringon säteilyn ja korkeaenergisen hiukkaspresipitaation vaikutukset ilmakehään ja ilmastoon. Kokoukseen osallistuu kansainvälinen joukko tutkijoita, jotka esittelevät sekä havaintoihin että tietokonemallinnukseen perustuvia tuloksiaan. Tämä raportti sisältää em. esitysten tiivistelmät. Kokouksen aihepiiri kattaa a) auringon säteilyn ja hiukkaspresipitaation vaihtelut ja näihin liittyvät ilmiöt, b) kemiallisten ja dynaamisten ilmakehävaikutusten mekanismit c) vaikutukset avaruudessa ja ilmakehässä sekä kytkennät ilmastoon, d) tutkimusta tukevat havainnot, tietokonemallit ja menetelmät nyt ja tulevaisuudessa. IAMAS/IUGG, VarSITI/SCOSTEP ja SPARC tukevat kokousta tieteellisesti ja taloudellisesti.