Ilmatieteen laitos

Nyligen publicerat

  • Hoilijoki, Sanni (Finnish Meteorological Institute, 2017)
    Contributions 132
    This thesis investigates interactions between solar wind and the magnetosphere of the Earth using two global magnetosphericsimulation models, GUMICS-4 and Vlasiator, which are both developed in Finland. The main topic of the thesis is magnetic reconnection at the dayside magnetopause, its drivers and global effects. Magnetosheath mirror mode waves and their evolution, identification and impacts on the local reconnection rates at the magnetopause are also discussed. This thesis consists of four peer-reviewed papers and an introductory part. GUMICS-4 is a magnetohydrodynamic model solving plasma as a single magnetized fluid. Vlasiator is the world’s first global magnetospheric hybrid-Vlasov simulation model, which solves the motion of ions by describing them as velocity distribution functions, whereas electrons are described as a charge neutralizing fluid. Vlasiator is able to solve ion scale physics in a global scale simulation. However, it is computationally heavy and the global simulations are currently describing Earth’s magnetosphere only in two spatial dimensions, whereas the velocity space is three dimensional. This thesis shows that magnetic reconnection at the dayside magnetopause is controlled by several factors. The impact of dipole tilt angle and sunward component of the interplanetary magnetic field on magnetopause reconnection is investigated with a set of GUMICS-4 simulations. Using Vlasiator simulations, this thesis shows that local reconnection rate is highly variable even during steady solar wind and correlates well with an analytical model for 2D asymmetric reconnection. It is also shown that the local reconnection rate is affected by local variations in the magnetosheath plasma. Fluctuations in the magnetosheath parameters near X-lines are partly generated by mirror mode waves that are observed to grow in the quasi-perpendicular magnetosheath. These results show that that the local reconnection rate at the X-lines is affected not only by the fluctuations in the inflow parameters but also by reconnection at nearby X-lines. Outflow from stronger X-lines pushes against the weaker ones and might ultimately suppress reconnection in the weaker X-lines. Magnetic islands, 2D representations of FTEs, form between X-lines in the Vlasiator simulations. FTEs propagate along the dayside magnetopause driving bow waves in the magnetosheath. The bow waves propagate upstream all the way to the bow shock causing bulges in the shock, from which solar wind particles can reflect back to the solar wind causing local foreshocks. The overall conclusion of this thesis is that the ion scale kinetic physics is important to accurately model the solar wind – magnetosheath – magnetopause interactions. Vlasiator results show a strong scale-coupling between ion and global scales: global scale phenomena have an impact on the local physics and the local phenomena may have unexpected impacts on the global dynamics of the magnetosphere. Neglecting the global scales in local ion scale simulations and vice versa may therefore lead to incomplete description of the solar wind – magnetosphere interactions.
  • Jääskeläinen, Emmihenna; Manninen, Terhikki; Tamminen, Johanna; Laine, Marko (Finnish Meteorological Institute, 2017)
    Raportteja - Rapporter - Reports 2:2017
    In the Satellite Application Facility on Climate Monitoring (CM SAF) project, financially supported by EUMETSAT, the 34-year long (1982-2015) broadband albedo time series CLARA-A2 SAL (the Surface ALbedo from the CM SAF cLoud, Albedo and RAdiation data record, second version) was produced from Advanced Very High Resolution Radiometer (AVHRR) measurements. CLARA-A2 SAL data record uses a Simplified Method for Atmospheric Correction algorithm SMAC for correcting for atmospheric effects. Aerosol optical depth (AOD) is the main input of the algorithm. Because there were no global AOD time series for the whole needed time period (1982-2015), the AOD-related time series were constructed, and the method for calculating it is described in this report.
  • Suomi, Irene (Finnish Meteorological Institute, 2017)
    Finnish Meteorological Institute Contributions 134
    Wind gusts, which are short duration (typically 3 s) wind speed maxima, are representative of the extreme wind conditions. They are very important for human activity, because the strongest gusts associated with storms are the most significant single cause of natural hazards. The impact of wind gusts on different structures depends on the characteristics of each structure. For example for wind energy, it is important to know both the probability of extreme maximum gusts in time scales of decades for the design of power plants and in the shorter term to support wind turbine operations. For wind gust forecasting it is essential to have reliable wind gust observations. Traditionally, observations have only been available from weather stations here the wind is usually measured at a reference height of 10 m. For wind energy, information is needed at greater heights, as the hub heights of the largest turbines extend even above 150 m. The main aim of this work has been to investigate wind gusts across the entire atmospheric boundary layer based on observations from tall meteorological masts as well as applying new measurement methods developed in this dissertation. The novel methods are based on turbulence measurements taken onboard a research aircraft and by a Doppler lidar. The research aircraft can fly long distances in a short time, so the measured wind speeds do not represent wind speed variation in time but they are a function of flight distance. The new method developed in this dissertation to compare temporal and spatial scales allows the measurement of wind gusts from a research aircraft. Then, observations can be obtained from places where traditional weather stations or meteorological masts cannot be deployed. Applying the new method, the observed wind gusts from the marine Arctic matched well with those observed at a meteorological mast in the Baltic Sea, although also differences were observed between these environments. Doppler lidar provides radial wind speed measurements along a laser beam transmitted by the instrument. When data from at least three lines of sight are combined, the three-dimensional wind vector can be derived. However, the measurements from multiple lines of sight take several seconds, and the different beams represent different measurement volumes. For these reasons, the measured wind speed maxima from the Doppler lidar used in this work were higher than the corresponding wind gusts from the nearby meteorological mast. In this dissertation, we developed a new theoretical method that significantly reduced this positive bias. Wind gust measurements are usually prone to measurement errors, called outliers. The use of a spike removal algorithm typically applied in traditional turbulence measurements, resulted in significantly improved Doppler lidar data quality. The method performed even better than the traditional data quality assurance methods based on carrier-to-noise ratio, by removing the unrealistic outliers present in the time series. Based on the above wind gust measurements, it was found that in the lowest part of the atmospheric boundary layer the ratio of the wind gust speed and the mean wind speed, called the gust factor, decreases strongly with measurement height. The higher the aerodynamic roughness of the surface, the greater is the change. Moreover, the static stability of the atmosphere affects the gust factor: the decrease of the gust factor with height is clearly smaller in unstable than in stable conditions. The gust parameterizations used in numerical weather rediction models were originally designed for the reference measurement height of 10 m. A new parameterization was developed that takes into account not only the effects of surface roughness and atmospheric stability but also the height above the surface. Based on meteorological mast and research aircraft measurements, the new parametrization yielded better results than previous methods.
  • Lehtonen, Ilari (Finnish Meteorological Institute, 2017)
    Finnish Meteorological Institute Contributions 133
    The aim of this work was to study the climate change impact on two specific abiotic risks affecting forests in Finland: fires and heavy snow loads. Approximately 1000 forest fires occur annually in Finland, but thanks to effective fire suppression, the average size of fires is only about 0.5 ha. Occasionally, heavy snow loading causes forest damage, which reduces stand quality in boreal forests experiencing cold winters. In Finnish forests, snow damage occurs most commonly in the eastern and northern parts of the country. The basic tools used in this work to evaluate the climate change impact were climate models. In addition, observational weather data and fire statistics were used. In evaluating the forest fire risk, the Canadian Fire Weather Index (FWI) system was used. Snow load amounts were estimated mainly by applying a snow load model developed at the Finnish Meteorological Institute (FMI). The results indicate that forest fire risk will most likely increase in the future due to increasing temperature and enhanced evaporation. However, there is large uncertainty regarding the rate of change, which originates from the differences between climate model responses to the same radiative forcing. Moreover, an increase in forest fire risk will at the same time increase the risk of onflagrations. Crown snow loads were projected to become heavier in northern Finland and in the regions of Kainuu and North Karelia next to the Russian border. In southern and western Finland the risk of snow damage is expected to decrease. The largest decrease in the risk is projected to occur in coastal areas. In the areas expected to experience increased risk of snow damage, conditions favouring oth heavy wet snow loading and rime accretion were predicted to become more common. The results of this work can be utilized when considering climatically-driven risks in forest management.
  • Vazquez, L; Harri, A-M; Genzer, M (Finnish Meteorological Institute, 2017)
    Raportteja – Rapporter – Reports 2017:5
    The “ExoMars Atmospheric Science and Missions” Workshop served as a forum for general discussions on Martian atmospheric science with a focus on the assessment of the results and instrumentation development cycle of the ExoMars 2016 mission. These led to presentations and discussions of the atmospheric investigation plans and strategies for the ESA ExoMars-2020 mission in particular and for forthcoming Mars missions in general. The workshop gave overviews of the ExoMars atmospheric investigations through invited talks by Exomars scientists. The ExoMars atmospheric results and planned investigations were covered by individual scientific presentations. The workshop engaged early career scientists, inclusiveness states and scientific and technological cooperation in the European planetary science community. The Workshop provided a forum for discussion and debate on the outstanding scientific topics of the Martian atmosphere, and on how to integrate and network the scientific teams with providers of instruments and technical systems. Thus the workshop also contributed to international cooperation in the field of Martian atmospheric science and technology.
  • Verronen, Pekka (Finnish Meteorological Institute, 2017)
    Raportteja - Rapporter - Reports 4:2017
    The 13th International Workshop on Greenhouse Gas Measurements from Space (IWGGMS) will be held on 6-8 June, 2017, at the University of Helsinki in Helsinki, Finland. The workshop is organised by the Finnish Meteorological Institute with support from the University of Helsinki. The workshop gathers together more than 160 scientists from the EU, USA, Japan, China, Australia, Canada, and Russia. This report is the official abstract book of the workshop. Background. Success in space-based global measurement of greenhouse gases, such as carbon dioxide and methane, is critical for advancing the understanding of carbon cycle. The recent developments in observations and in interpreting the data are very promising. Space-based greenhouse gas measurement, however, poses a wide array of challenges, many of which are complex and thus demand close international cooperation. The goal of the workshop is to review the state of the art in remote sensing of CO 2 , CH 4 , and other greenhouse gases from space including the current satellite missions, missions to be launched in the near future, emission hot spots on regional and global scales, process studies and interactions of carbon cycle and climate, pre-flight and on-orbit instrument calibration techniques, retrieval algorithms and uncertainty quantification, validation methods and instrumentation, related ground-based, shipboard, and airborne measurements, and flux inversion from space based measurements. The workshop is part of the programme for the centenary of Finland's independence in 2017. The workshop is also one of the activities arranged by the Finnish Meteorological Institute to support Finland's chairmanship of the Arctic Council, 2017 - 2019. The workshop is sponsored by the Finnish Meteorological Institute, the University of Helsinki, the European Space Agency, the City of Helsinki, the Federation of Finnish Learned Societies, and ABB Inc.
  • Laakia, Jaakko (Finnish Meteorological Institute, 2017)
    Finnish Meteorological Institute Contributions 131
    This thesis covers two aspects of utilisation of advanced separation technology together with mass spectrometry: 1. Drift tube ion mobility spectrometry – mass spectrometry (IMS-MS) studies of the behaviour of ions in the gas phase and 2. Comprehensive two dimensional gas chromatography – time-offlight mass spectrometry (GC×GC-TOF-MS) studies for characterization of crude oil samples. In IMS studies, the focus was on the separation of isomeric compounds. For example, [M-H]- ions of 2,4-di-tert-butylphenol (2,4-DtBPh) and 2,6-di-tert-butylphenol (2,6-DtBPh) were separated. It was also observed that shielding of the charge site by the functional groups of a molecule has a large effect on the separation of the isomeric compounds. For example, amines with a shielded charge site were separated from those with a more open charge site, while some of the isomeric amines studied were not separated. Different kinds of adduct ions were observed for some of the analytes. Dioxygen adducts were seen for 2,4-DtBPh [M+O2]-, 2,6-di-tert-butylpyridine (2,6-DtBPyr) [M+O2]+· and 2,6-di-tert-butyl-4-methylpyridine (2,6-DtB-4MPyr) [M+O2]+·. The adduct formation increases the total mass of the analyte ion, and therefore, for example the 2,4-DtBPh [M+O2]- ion could be separated from its isomeric compound 2,6-DtBPh [M-H]-, which did not from the dioxygen adduct ion. In the case of 2,6-DtBPyr and 2,6-DtB-4MPyr, the [M]+ ions formed dioxygen adduct [M+O2]+· ions. The both ions, [M]+ and [M+O2]+·, shared the same drift time which was longer than their [M+H]+ ion species. This work demonstrates that measuring with IMS the mobility of different ion structures of the same molecule, especially dioxygen adducts, results in a better understanding of the role of adduct ions in the IMSseparation process. In GC×GC-TOF-MS studies, the focus was on detailed characterization of crude oil samples. For instance, oils from the Recôncavo Basin were classified to two different groups by using minor oil components. The GC×GC-TOF-MS data showed the correlation between 2D retention time and the number of carbons in a ring for several hydrocarbons as known from the literature. This information was used to achieve more structural information about eight new tetracyclic compounds, some of them similar to nor-steranes, detected during analysis. Some of these new compounds could be used as maturity indicators. This study demonstrated how GC×GC-TOF-MS can be used to separate geochemically interested isomers, identify minor geochemical differences between oils and achieve structural information about unknown biomarkers.
  • 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.