Browsing by Subject "simulointi"

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  • Pukkala, Timo; Karsikko, Jari; Kolström, Taneli (Suomen metsätieteellinen seura, 1992)
  • Kellomäki, Seppo; Hänninen, Heikki; Kolström, Taneli; Kotisaari, Ahti; Pukkala, Timo (Suomen metsätieteellinen seura, 1987)
  • Bhattacharjee, Joy; Rabbil, Mehedi; Fazel, Nasim; Darabi, Hamid; Choubin, Bahram; Khan, Md. Motiur Rahman; Marttila, Hannu; Haghighi, Ali Torabi (Elsevier, 2021)
    Science of the Total Environment 797 (2021), 149034
    Lake water level fluctuation is a function of hydro-meteorological components, namely input, and output to the system. The combination of these components from in-situ and remote sensing sources has been used in this study to define multiple scenarios, which are the major explanatory pathways to assess lake water levels. The goal is to analyze each scenario through the application of the water balance equation to simulate lake water levels. The largest lake in Iran, Lake Urmia, has been selected in this study as it needs a great deal of attention in terms of water management issues. We ran a monthly water balance simulation of nineteen scenarios for Lake Urmia from 2003 to 2007 by applying different combinations of data, including observed and remotely sensed water level, flow, evaporation, and rainfall. We used readily available water level data from Hydrosat, Hydroweb, and DAHITI platforms; evapotranspiration from MODIS and rainfall from TRMM. The analysis suggests that the consideration of field data in the algorithm as the initial water level can reproduce the fluctuation of Lake Urmia water level in the best way. The scenario that combines in-situ meteorological components is the closest match to the observed water level of Lake Urmia. Almost all scenarios showed good dynamics with the field water level, but we found that nine out of nineteen scenarios did not vary significantly in terms of dynamics. The results also reveal that, even without any field data, the proposed scenario, which consists entirely of remote sensing components, is capable of estimating water level fluctuation in a lake. The analysis also explains the necessity of using proper data sources to act on water regulations and managerial decisions to understand the temporal phenomenon not only for Lake Urmia but also for other lakes in semi-arid regions.
  • Calderón, Silvia M.; Tonttila, Juha; Buchholz, Angela; Joutsensaari, Jorma; Komppula, Mika; Leskinen, Ari; Hao, Liqing; Moisseev, Dmitri; Pullinen, Iida; Tiitta, Petri; Xu, Jian; Virtanen, Annele; Kokkola, Harri; Romakkaniemi, Sami (Copernicus Publ., 2022)
    Atmospheric chemistry and physics
    We carried out a closure study of aerosol-cloud interactions during stratocumulus formation using a large eddy simulation model UCLALES-SALSA and observations from the 2020 cloud sampling campaign at the Puijo SMEAR IV station in Kuopio, Finland. The unique observational setup combining in situ and cloud remote sensing measurements allowed a closer look into the aerosol size-composition dependence of droplet activation and droplet growth in turbulent boundary layer driven by surface forcing and radiative cooling. UCLALES-SALSA uses spectral bin microphysics for aerosols and hydrometeors and incorporates a full description of their interactions into the turbulent-convective radiation-dynamical model of stratocumulus. Based on our results, the model successfully described the probability distribution of updraft velocities and consequently the size dependency of aerosol activation into cloud droplets, and further recreated the size distributions for both interstitial aerosol and cloud droplets. This is the first time such a detailed closure is achieved not only accounting for activation of cloud droplets in different updrafts, but also accounting for processes evaporating droplets and drizzle production through coagulation-coalescence. We studied two cases of cloud formation, one diurnal (24 September 2020) and one nocturnal (31 October 2020), with high and low aerosol loadings, respectively. Aerosol number concentrations differ more than 1 order of magnitude between cases and therefore, lead to cloud droplet number concentration (CDNC) values which range from less than 100cm-3 up to 1000cm-3. Different aerosol loadings affected supersaturation at the cloud base, and thus the size of aerosol particles activating to cloud droplets. Due to higher CDNC, the mean size of cloud droplets in the diurnal-high aerosol case was lower. Thus, droplet evaporation in downdrafts affected more the observed CDNC at Puijo altitude compared to the low aerosol case. In addition, in the low aerosol case, the presence of large aerosol particles in the accumulation mode played a significant role in the droplet spectrum evolution as it promoted the drizzle formation through collision and coalescence processes. Also, during the event, the formation of ice particles was observed due to subzero temperature at the cloud top. Although the modeled number concentration of ice hydrometeors was too low to be directly measured, the retrieval of hydrometeor sedimentation velocities with cloud radar allowed us to assess the realism of modeled ice particles. The studied cases are presented in detail and can be further used by the cloud modellers to test and validate their models in a well-characterized modelling setup. We also provide recommendations on how increasing amount of information on aerosol properties could improve the understanding of processes affecting cloud droplet number and liquid water content in stratiform clouds.
  • Nikinmaa, Eero (The Society of Forestry in Finland - The Finnish Forest Research Institute, 1992)
  • Kareinen, Timo; Nissinen, Ari; Ilvesniemi, Hannu (The Society of Forestry in Finland - The Finnish Forest Research Institute, 1998)
    In this study we analyze how the ion concentrations in forest soil solution are determined by hydrological and biogeochemical processes. A dynamic model ACIDIC was developed, including processes common to dynamic soil acidification models. The model treats up to eight interacting layers and simulates soil hydrology, transpiration, root water and nutrient uptake, cation exchange, dissolution and reactions of Al hydroxides in solution, and the formation of carbonic acid and its dissociation products. It includes also a possibility to a simultaneous use of preferential and matrix flow paths, enabling the throughfall water to enter the deeper soil layers in macropores without first reacting with the upper layers. Three different combinations of routing the throughfall water via macro- and micropores through the soil profile is presented. The large vertical gradient in the observed total charge was simulated succesfully. According to the simulations, gradient is mostly caused by differences in the intensity of water uptake, sulfate adsorption and organic anion retention at the various depths. The temporal variations in Ca and Mg concentrations were simulated fairly well in all soil layers. For H+, Al and K there were much more variation in the observed than in the simulated concentrations. Flow in macropores is a possible explanation for the apparent disequilibrium of the cation exchange for H+ and K, as the solution H+ and K concentrations have great vertical gradients in soil. The amount of exchangeable H+ increased in the O and E horizons and decreased in the Bs1 and Bs2 horizons, the net change in whole soil profile being a decrease. A large part of the decrease of the exchangeable H+ in the illuvial B horizon was caused by sulfate adsorption. The model produces soil water amounts and solution ion concentrations which are comparable to the measured values, and it can be used in both hydrological and chemical studies of soils.
  • Niemi, Jorma (Vesihallitus, 1979)
    Vesientutkimuslaitoksen julkaisuja 28
    Tiivistelmä: Simulointimallin soveltaminen Pohjois-Päijänteellä
  • Korhonen, Kari T. (Suomen metsätieteellinen seura, 1992)
  • Manninen, Terhikki; Jääskeläinen, Emmihenna; Siljamo, Niilo; Riihelä, Aku; Karlsson, Karl-Göran (Copernicus Publications, 2022)
    Atmospheric measurement techniques
    This paper describes a new method for cloudcorrecting observations of black-sky surface albedo derived using the Advanced Very High Resolution Radiometer (AVHRR). Cloud cover constitutes a major challenge for surface albedo estimation using AVHRR data for all possible conditions of cloud fraction and cloud type with any land cover type and solar zenith angle. This study shows how the new cloud probability (CP) data to be provided as part of edition A3 of the CLARA (CM SAF cLoud, Albedo and surface Radiation dataset from AVHRR data) record from the Satellite Application Facility on Climate Monitoring (CM SAF) project of EUMETSAT can be used instead of traditional binary cloud masking to derive cloud-free monthly mean surface albedo estimates. Cloudy broadband albedo distributions were simulated first for theoretical cloud distributions and then using global cloud probability (CP) data for 1 month. A weighted mean approach based on the CP values was shown to produce very-high-accuracy black-sky surface albedo estimates for simulated data. The 90 % quantile for the error was 1.1 % (in absolute albedo percentage) and that for the relative error was 2.2 %. AVHRR-based and in situ albedo distributions were in line with each other and the monthly mean values were also consistent. Comparison with binary cloud masking indicated that the developed method improves cloud contamination removal.
  • Pukkala, Timo; Kolström, Taneli (Suomen metsätieteellinen seura, 1987)
  • Hämäläinen, Heikki; Aroviita, Jukka; Jyväsjärvi, Jussi; Kärkkäinen, Salme (Ecological Society of America, 2018)
    Ecological Applications 28 (5): 1260-1272
    The ecological assessment of freshwaters is currently primarily based on biological communities and the reference condition approach (RCA). In the RCA, the communities in streams and lakes disturbed by humans are compared with communities in reference conditions with no or minimal anthropogenic influence. The currently favored rationale is using selected community metrics for which the expected values (E) for each site are typically estimated from environmental variables using a predictive model based on the reference data. The proportional differences between the observed values (O) and E are then derived, and the decision rules for status assessment are based on fixed (typically 10th or 25th) percentiles of the O/E ratios among reference sites. Based on mathematical formulations, illustrations by simulated data and real case studies representing such an assessment approach, we demonstrate that the use of a common quantile of O/E ratios will, under certain conditions, cause severe bias in decision making even if the predictive model would be unbiased. This is because the variance of O/E under these conditions, which seem to be quite common among the published applications, varies systematically with E. We propose a correction method for the bias and compare the novel approach to the conventional one in our case studies, with data from both reference and impacted sites. The results highlight a conceptual issue of employing ratios in the status assessment. In some cases using the absolute deviations instead provides a simple solution for the bias identified and might also be more ecologically relevant and defensible.
  • Pukkala, Timo; Kolström, Taneli (Suomen metsätieteellinen seura, 1991)
  • Sofieva, Svetlana; Asmi, Eija; Atanasova, Nina S.; Heikkinen, Aino E.; Vidal, Emeline; Duplissy, Jonathan; Romantschuk, Martin; Kouznetsov, Rostislav; Kukkonen, Jaakko; Bamford, Dennis H.; Hyvärinen, Antti-Pekka; Sofiev, Mikhail (Copernicus Publications, 2022)
    Atmospheric measurement techniques
    A new bubble-generating glass chamber with an extensive set of aerosol production experiments is presented. Compared to the experiments described in the literature since the ground-setting works of Edward C. Monahan et al. in 1980s, the current setup is among the medium-sized installations allowing for accurate control of the air discharge, water temperature, and salinity. The size and material of the chamber offer a variety of applications due to its portability, measurement setup adjustability, and sterilization option. The experiments have been conducted in a cylindrical bubbling tank of 10 L volume that was filled by ∼ 30 %–40 % with water of controlled salt content and temperature and covered with a hermetic lid. The chamber was used to study the characteristics of aerosols produced by bursting bubbles under different conditions. In line with previous findings, the sea spray aerosol production was shown to depend linearly on the surface area covered by the bubbles, which in turn is a near-linear function of the air discharge through the water. Observed dependencies of the aerosol size spectra and particle fluxes on water salinity and temperature, being qualitatively comparable with the previous experiments, substantially refined the existing parameterizations. In particular, the bubble size was practically independent from the air discharge through the water body, except in the case of very small flows. Also, the dependence of aerosol spectrum and amount on salinity was much weaker than suggested in some previous experiments. The temperature dependence, to the contrary, was significant and consistent, with a transition in the spectrum shape at ∼ 10 ◦C. Theoretical analysis based on the basic conservation laws supported the main results of the experiments but also highlighted the need for a better understanding of the aerosol production from a cold water surface.
  • Pursiainen, Tero (Helsingfors universitet, 2013)
    The long-run average return on equities shows a sizable premium with respect to their relatively riskless alternatives, the short-run government bonds. The dominant explanation is that the excess return is compensation for rare but severe consumption disasters which result in heavy losses on equities. This thesis studies the plausibility of this explanation in a common theoretical framework. The consumption disasters hypothesis is studied in the conventional Lucas-tree model with two assets and with constant relative risk aversion preferences, captured by the power utility function. The thesis argues that this oft-used model is unable to account for the high premium, and a simulation experiment is conducted to find evidence for the argument. The consumption process is modelled by the threshold autoregressive process, which offers a simple and powerful way to describe the equity premium as a result of a peso problem. Two statistics, the arithmetic average and the standard deviation, are used to estimate the long-run average and the volatility of the returns. The simulated data is analyzed and compared to the real world financial market data. The results confirm that the potential for consumption disasters produces a lower equity premium than the case without disasters in the Lucas-tree model with power utility. The disaster potential lowers the average return on equity instead of increasing it. This result comes from the reciprocal connection between the coefficient of relative risk aversion and the elasticity of intertemporal substitution, and from the special nature of the equity asset, which is a claim on the consumption process itself. The risk-free asset remains unaffected by the disaster potential. The equity premium remains a puzzle in this framework. The advantage of the threshold autoregressive consumption process is to show this result with clarity. Breaking the link between aversion to risk and intertemporal substitution is indeed one possible direction to take. Changing the assumptions about expected consumption or about the equity asset might offer another way forward. Another form of utility or another model is needed if the equity premium is to be explained in financial markets that are free of frictions.
  • Tanner, Merja (2005)
    Raportteja Espoosta ; 4/2004
    Tutkimuksen tavoitteena oli löytää Espoon tulevalle väestönkehitykselle minimi- ja maksimiarvot ajanjaksolle 2003-2020. Erityisesti haluttiin tutkia, miten erilaiset muuttoliikerakenteet vaikuttavat väestön määrään ja rakenteeseen. Ennusteisiin sisältyvää epävarmuutta tutkittiin simuloimalla ennustejakauma yhdelle ennusteista. Laaditut ennusteet ja skenaariot pohjautuvat erilaisille muuttoliikeoletuksille. Kuolleisuuden arvioinnissa käytettiin kaikille vuosien 1996-2000 kuolleisuuslukujen keskiarvoa. Hedelmällisyyden arvioinnissa käytettiin vuoden 2002 hedelmällisyyslukuja. Ennustemenetelmänä käytettiin Leslien matriisimallista kehitettyä sovellusta. Leslien matriisimalli on yksi maailman käytetyimmistä väestöennustemenetelmistä. Se on kehitetty 1940-luvulla. Varsinaisia ennusteita tehtiin kaksi. Ne pohjautuivat menneisyydessä tapahtuneeseen kehitykseen. Katsottiin mitä tapahtuisi, jos tiettynä vuonna vallinneet väestönmuutostekijät pysyisivät muuttumattomina koko ennusteajanjakson ajan. Vuodet, joiden pohjilta ennusteet laadittiin, olivat 1998 ja 2002. Huolimatta erilaisista lähtötiedoista tulokset olivat lähes samanlaiset. Haluttujen erojen aikaansaamiseksi tehtiin skenaarioita, joiden lähtöolettamukset ja -tiedot tehtiin selkeästi erilaisiksi. Skenaarioita tutkimuksessa tehtiin kolme: Sulkeutunut Espoo pohjautuu Espoon omavaraiseen väestönkasvuun ja Nuorekas Espoo perhepainotteiseen muuttoliikkeeseen. Ikääntyvä Espoo puolestaan kuvaa tilannetta, jossa ikääntyvät jäävät viettämään eläkepäiviään Espooseen. Siinä 55 vuotta täyttäneiden muuttoliike nollattiin. Sulkeutunut Espoo antaa alarajan Espoon väestön tulevalle määrälle. Ennuste johtaa ikärakenteeseen, joka painottuu vanhempiin ikäluokkiin, jopa 17 % väestöstä on eläkeikäisiä. Väestö ei pystyisi olemaan enää elinvoimainen, vaan väestön määrä alkaisi laskea. Nuorekas Espoo tuottaa ylärajan Espoon väestön tulevalle määrälle. Lasten ja työikäisten osuus kasvaa ja ennuste tuottaa alhaisimman osuuden eläkeikäisten määrälle, 12 %. Huoltorasitus tulee kuitenkin kasvamaan osaksi lasten määrän lisäyksenkin takia. Ikääntyvä Espoo johtaa puolestaan tilanteeseen, jossa lasten osuus laskee hieman ja ikääntyneiden osuus kasvaa. Huoltorasitus kasvaisi, mutta ei niin paljon kuin muissa laadituissa skenaarioissa. Kaikille skenaarioille on yhteistä, että ikääntyneiden palveluiden määrän tarve lisääntyy. Tämän lisäksi Espoo tulee tarvitsemaan myös lisää päivähoito- ja koulupaikkoja. Väestöennusteet sisältävät aina epävarmuutta. Tässä työssä ennusteiden sisältämää epävarmuutta tuotiin esille ennustejakauman avulla. Sovellus tehtiin vuoteen 2002 pohjautuvalle ennusteelle. Väestön määrä simuloitiin 100 kertaa aikavälille 2004-2020. Vaihtelu simulointeihin luotiin satunnaislukugeneraattorilla arvotuilla satunnaisluvuilla, joiden oletettiin noudattavan normaalijakaumaa. Jakauman varianssi määriteltiin menneisyyden vaihteluiden avulla. Simuloinnin tuloksena saatiin ennustejakauma, jonka mediaani antoi todennäköisimmän ennusteen ja kvartiilit kuvasivat väestönkehityksen epävarmuutta. Simulointituloksia verrattiin Changing Population of Europe: Uncertain Future - projektin tuloksiin. Kaupunkien ja kuntien ennusteet ovat epävarmempia kuin valtioiden väestöennusteet, koska kuntien ja kaupunkien rajat ylittävä liikkuvuus on runsaampaa kuin valtioiden rajat ylittävä muuttoliike.
  • Huard, David; Fyke, Jeremy; Capellán‐Pérez, Iñigo; Matthews, H. Damon; Partanen, Antti‐Ilari (John Wiley & Sons, 2022)
    The climate scenarios that form the basis for current climate risk assessments have no assigned probabilities, and this impedes the analysis of future climate risks. This paper proposes an approach to estimate the probability of carbon dioxide (CO2) concentration scenarios used in key climate change modeling experiments. It computes the CO2 emissions compatible with the concentrations prescribed by Coupled Model Intercomparison Project Phase 5 (CMIP5) and CMIP6 experiments. The distribution of these compatible cumulative emissions is interpreted as the likelihood of future emissions given a concentration pathway. Using Bayesian analysis, the probability of each pathway can be estimated from a probabilistic sample of future emissions. The approach is demonstrated with five probabilistic CO2 emission simulation ensembles from four Integrated Assessment Models (IAM), leading to independent estimates of the likelihood of the CO2 concentration of Representative Concentration Pathways (RCP) and Shared Socioeconomic Pathways (SSP). Results suggest that SSP5-8.5 is unlikely for the second half of the 21st century, but offer no clear consensus on which of the remaining scenarios is most likely. Estimates of likelihoods of CO2 concentrations associated with RCP and SSP scenarios are affected by sampling errors, differences in emission sources simulated by the IAMs, and a lack of a common experimental framework for IAM simulations. These shortcomings, along with a small IAM ensemble size, limit the applicability of the results presented here. Novel joint IAM and the Earth System Model experiments are needed to deliver actionable probabilistic climate risk assessments.
  • Bettencourt da Silva, Ricardo J.N; Saame, Jaan; Anes, Bárbara; Heering, Agnes; Leito, Ivo; Näykki, Teemu; Stoica, Daniela; Deleebeeck, Lisa; Bastkowski, Frank; Snedden, Alan; Camões, M. Filomena (Elsevier, 2021)
    Analytica Chimica Acta 1182 (2021), 338923
    The use of the unified pH concept, pHabsH2O, applicable to aqueous and non-aqueous solutions, which allows interpreting and comparison of the acidity of different types of solutions, requires reliable and objective determination. The pHabsH2O can be determined by a single differential potentiometry measurement referenced to an aqueous reference buffer or by a ladder of differential potentiometric measurements that allows minimisation of inconsistencies of various determinations. This work describes and assesses bottom-up evaluations of the uncertainty of these measurements, where uncertainty components are combined by the Monte Carlo Method (MCM) or Taylor Series Approximation (TSM). The MCM allows a detailed simulation of the measurements, including an iterative process involving in minimising ladder deviations. On the other hand, the TSM requires the approximate determination of minimisation uncertainty. The uncertainty evaluation was successfully applied to measuring aqueous buffers with pH of 2.00, 4.00, 7.00, and 10.00, with a standard uncertainty of 0.01. The reference and estimated values from both approaches are metrologically compatible for a 95% confidence level even when a negligible contribution of liquid junction potential uncertainty is assumed. The MCM estimated pH values with an expanded uncertainty, for the 95% confidence level, between 0.26 and 0.51, depending on the pH value and ladder inconsistencies. The minimisation uncertainty is negligible or responsible for up to 87% of the measurement uncertainty. The TSM quantified measurement uncertainties on average only 0.05 units larger than the MCM estimated ones. Additional experimental tests should be performed to test these uncertainty models for analysis performed in other laboratories and on non-aqueous solutions.