Ilmatieteen laitos: Recent submissions

Now showing items 1-20 of 144
  • Tuononen, Minttu (2019)
    Finnish Meteorological Institute Contributions 155
    Synoptic situation and different meteorological phenomena can highly affect renewable energy production. Investigating different phenomena will give new information on the occurrence and characteristics of specific phenomena and their impacts on renewable energy applications. Different observational data sets and numerical models can be widely used in different phases of renewable energy projects; from planning of the project to help with the operation and the maintenance of the existing wind or solar field. In this thesis a meteorological phenomena, a low-level jet, is investigated. Thesis comprises analysis of the climatological occurrence of low-level jets, their characteristics and forcing mechanisms, as well as numerical model capability to capture the phenomena. In addition, solar radiation forecasts obtained from the operational numerical weather prediction model are evaluated and the role of cloud cover forecast skill in solar radiation forecast error is investigated. Long data sets of observational data: mainly Doppler wind lidar, ceilometer, and solar radiation observations, are used, in addition to reanalysis and operational numerical weather prediction model data. A low-level jet is a wind phenomenon that can affect wind energy production. Nighttime low-level jets are a commonly known boundary-layer phenomenon occurring during stably stratified conditions over flat terrain. In this thesis, new information on the occurrence, characteristics, and forcing mechanisms of a low-level jet was gained in different conditions: in Northern Hemisphere mid-latitude and polar regions based on reanalysis data and at two different sites in Finland and Germany based on long-term Doppler lidar observations. The low-level jet identification algorithms developed in these studies can be used to repeat the studies by using different models covering different areas or at any site operating a Doppler lidar. The low-level jet identification algorithm for Doppler lidar data can also be applied to operationally detect low-level jets, which is useful information for example from wind energy point-of-view. Solar radiation and cloud cover forecasts were evaluated at one site in Finland based on long time-series of solar radiation and ceilometer observations. The role of cloud cover forecast in solar radiation forecast error is investigated. The solar radiation and cloud cover forecasts were obtained from operational numerical weather prediction model that can be used to predict the expected power production at solar field day-ahead. It was found that there is a positive bias in the forecast incoming solar radiation even if the cloud cover forecast is correct. The study can guide model improvements as the bias is likely due to underestimation in the forecast cloud liquid water content or incorrect representation of cloud optical properties. The methods created in this study can be applied to hundreds of sites globally. In addition, the algorithms developed in this study can be further used in different applications in the field of renewable energy, for example to detect potential in-cloud icing conditions.
  • Karsisto, Virve (2019)
    Finnish Meteorological Institute Contributions 153
    Wintertime weather conditions can be hazardous for road traffic. Icy roads and poor visibility caused by snowfall increase the accident risk. Accurate forecasting of road conditions is important, because reliable and precise forecasts help the road maintenance personnel to plan their operations accordingly. Well timed maintenance operations increase safety and enable economical savings as unnecessary actions can be avoided. Drivers can also adjust their route plan and driving behaviour appropriately when warnings of hazardous conditions are given well beforehand. Road conditions are forecasted in the Finnish Meteorological Institute (FMI) with specialized road weather model. Before executing the actual forecast, the model is first initialized by feeding it with observation data. The quality of this data is essential for forecast accuracy, as the forecast is greatly dependent of the initial model state. Road weather stations have traditionally been one of the main sources of information, but their density is sparse especially in rural areas. Road surface temperature can vary considerably across the road network, so observations should be done in dense enough spatial scale. Nowadays it is possible to gather real time information from vehicles. Mobile sources provide observations with high spatial density and thus facilitate detecting the road stretches most prone to freezing. However, the quality of mobile observations should be assessed before implementing them to the road weather forecasting systems. This dissertation aims to answer to two research questions. Firstly, it has been studied how to best use available surface temperature observations in the road weather model initialization. Secondly , it has been studied how differences in two road weather models’ physics affect to the surface temperature forecast accuracy. A method called coupling was implemented to the FMI road weather model. The main idea of the method is to adjust the incoming radiation flux so that the modelled surface temperature fits to the last observed value. The results show that this method improves considerably the short range surface temperature forecasts. Mobile surface temperature observations done with Teconer RTS411 were compared to road weather station measurements to assess the mobile data quality. According to the results, the mobile observations were on average 0.62 °C warmer than the road weather station measurements at 0 °C and in dry conditions. It was found out that the difference between mobile observations and road weather station measurements was dependent on the road status. A calibration equation for mobile observations was developed using linear mixed models to get mobile observations more in line with road weather station measurements. The effect of the mobile observations to the road surface temperature forecast accuracy was studied. According to the results, using the mobile observations calibrated with the developed equation improved the accuracy of road surface temperature forecasts compared to a theoretical situation where there would not be other surface temperature observations available. However, for an area with a dense road weather station network the accuracy of forecasts assimilating mobile observations with correction were on par with the accuracy of forecast assimilating interpolated surface temperature values. Studying model physics and comparing behaviour of different models is beneficial for model development. In this work, the verification results of the FMI’s and the Royal Netherlands Meteorological institute’s (KNMI) road weather models were compared to each other. In addition, the model physics were studied to find out the reasons for differences in the surface temperature forecasts. The forecasts of the KNMI model were found to be slightly more accurate than the forecasts of the FMI model. Although the core physics of the models were rather similar, there were large differences in some physical parameters and the number and the thickness of the ground layers. Individual reason for the better performance of the KNMI model could not be found, as the effects of different physical properties eventually sum up to surprisingly similar modelled surface temperature values.
  • Venäläinen, Ari; Ruosteenoja, Kimmo; Lehtonen, Ilari (2019)
    Raportteja – Rapporter – Reports 2019:3
    This report deals with projected climatic changes in four areas of operation of the UPM-Kymmene company: Finland, southern Germany, Uruguay and eastern China. The implications of the projected changes for forestry, including forest growth and productivity and possible climate change induced disturbances, are discussed as well. Climate projections have been derived from the output of 28 global climate models. Analyses focus on the RCP4.5 greenhouse gas scenario that represents an alternative of moderately large emissions. Mainly, projections calculated for the period 2040–2069 (relative to 1971–2000) have been examined. All the models analyzed simulate higher temperatures for the future. However, the degree of warming varies quite a lot among the models. For many other climate variables, like precipitation and incident solar radiation, even the sign of the future change can be uncertain. Even so, in the regions examined mean precipitation is more likely to increase than decrease, except for southern Germany in summer and early autumn, Uruguay in Southern Hemisphere winter and spring and China in late autumn. Rising temperatures enhance evaporation and increase drought risks despite modest increases in precipitation. In some seasons, both the intense rainfall events and dry periods are projected to become more severe. In recent decades, forest resources have been increasing in Europe. Especially in Northern Europe, forests have benefitted from the warmer climate and increased CO2 concentration in the atmosphere. During the coming decades, this positive development may at least partly be cancelled due to potentially increasing disturbances for the forest growth. For example, drought, fire and insect pests may cause damage. The role of forests as a carbon sink is an important aspect in the context of climate change mitigation activities, and vivid discussion on the most beneficial and sustainable use of forest resources is foreseen to continue. If global climate policy proves to be successful, it is possible that future changes in climate will be weaker than those based on the RCP4.5 scenario discussed in this report. However, this requires rapid restrictions of the greenhouse gas emissions globally.
  • Susiluoto, Jouni (2019)
    Finnish Meteorological Institute Contributions 154
    Climate change is one of the most important, pressing, and furthest reaching global challenges that humanity faces in the 21st century. Already affecting daily lives of many directly and everyone indirectly, changes in climate are projected to have many catastrophic consequences. For this reason, researching climate and climate change is needed. Studying complex geoscientific phenomena such as climate change consists of a patchwork of challenging mathematical, statistical, and computational problems. To solve these problems, local and global process models and statistical models are combined with both small in situ observation data sets with only few observations, and equally well with enormous global remote sensing data products containing hundreds of millions of data points. This integration of models and data can be done in a Bayesian inverse modeling setting if the algorithms and computational methods used are chosen and implemented carefully. The methods used in the four publications on which this thesis is based range from high-dimensional Bayesian spatial statistical models and Markov chain Monte Carlo methods to time series modeling and point estimation via optimization. The particular geoscientific problems considered are: finding the spatio-temporal distribution of atmospheric carbon dioxide based on sparse remote sensing data, quantifying uncertainties in modeling methane emissions from boreal wetlands, analyzing and quantifying the effect of climate change on growing season in the boreal region, and using statistical methods to calibrate a terrestrial ecosystem model. In addition to analyzing these problems, the research and the results help to understand model performance and how modeling uncertainties in very large computational problems can be approached, also providing algorithm implementations on top of which future efforts may be built.
  • Nurmi, Väinö (2019)
    Finnish Meteorological Institute Contributions 152
    This thesis applies cost-benefit analysis (CBA) to certain environmental questions and through its results contributes to both the theoretical literature on CBA in environmental economics and practical issues in the application of CBA to environmental problems. The work comprises an introduction and four articles, which address three common thematic areas: 1) distributional issues, 2) climate change adaptation, and 3) urban ecosystem services. Article I contributes to the literature through analyses that i) provide a connection between the income effect and distributional issues; ii) compare weighting schemes both theoretically and empirically; iii) show how weights could be incorporated into a CBA in practice; and iv) demonstrate that results are sensitive not only to whether weights are applied, but also to the choice of the inequality parameter and spatial resolution. Article II analyzes whether over-investment in disaster risk reduction and climate change adaptation is a legitimate economic concern and examines how the public reacts to major infrastructure investments. The results constitute a contribution to both the theoretical and empirical literature on the economics of climate change adaptation. Article III evaluates how potential innovations in weather services can reduce weather sensitivity and, consequently, decrease the negative effects of climate change on transport, particularly in the road transport sector. The article illustrates how innovations in the provision and use of weather and climate information can be beneficial for adapting to the changing climate and contributes to the empirical literature on the economics of climate change adaptation. Article IV presents a CBA of a relatively novel feature in the urban green portfolio: green roofs. The specific objectives of the research are i) to facilitate benefit-transfer of ecosystem services from one urban area to another by providing detailed information on valuation methods and the role of different assumptions and parameter values and ii) to include scenic values as a benefit item based on a formal and trackable analysis rather than on a guess. The article contributes to the empirical literature related to both the cost-benefit analysis of urban ecosystem services and the economics of climate change adaptation. *** Tässä tutkielmassa sovelletaan kustannushyötyanalyysiä (KHA) ympäristöön liittyviin kysymyksiin. Tulokset vievät eteenpäin sekä KHA-analyysin teoreettista kirjallisuutta että käytännön sovellettavuutta ympäristökysymyksiin. Työ koostuu neljästä artikkelista, joissa on kolme poikkileikkaavaa teemaa: 1) tulojakauma-kysymykset, 2) ilmastonmuutokseen sopeutuminen ja 3) urbaanit ekosysteemipalvelut. Artikkeli I pääkontribuutio kirjallisuuteen on i) luoda yhteys tulovaikutuksen ja tulojakauma-kysymyksen välille, ii) vertailla eri painotustapoja teoreettisesti ja empiirisesti, iii) osoittaa, miten painotukset voidaan käytännössä sisällyttää KHA:n, iv) näyttää tulosten herkkyys paitsi siihen, painotetaanko hyötyjä vai ei, myös siihen, mikä painotustapa valitaan ja mitä maantieteellistä tarkkuutta käytetään. Artikkeli II analysoi esimerkin avulla, onko liiallinen panostaminen ilmastonmuutokseen sopeutumiseen ja onnettomuusriskien vähentämiseen todellinen huolenaihe. Liiallinen panostus määritellään taloudellisen tehokkuuden avulla. Tulokset myötävaikuttavat ilmastonmuutokseen liittyvän taloustieteen teoreettiseen ja käytännön kirjallisuuteen. Artikkelissa III arvioimme, miten sääpalveluihin liittyvät innovaatiot voivat vähentää yhteiskunnan sääherkkyyttä ja vähentää ilmastonmuutoksen tuomia negatiivisia vaikutuksia tieliikenteelle. Artikkelissa näytetään, miten sääpalveluiden jakeluun ja käytettävyyteen liittyvät innovaatiot ovat hyödyllisiä ilmastonmuutokseen sopeutumiselle. Tulokset myötävaikuttavat ilmastonmuutokseen liittyvän taloustieteen käytännön kirjallisuuteen. Artikkeli IV käsittelee viherkattojen kustannushyötyanalyysiä. Tämän tutkimuksen päätavoitteet ovat: i) mahdollistaa tulosten siirtäminen toiselta urbaanilta alueelta toiselle antamalla mahdollisimman tarkat tiedot tutkimuksessa käytetyistä menetelmistä ja parametreista, ii) sisällyttää viherkattojen maisemahyödyt yhtenä hyötylajina mukaan. Tulokset myötävaikuttavat sekä ekosysteemipalveluihin liittyvän KHA:n käytännön kirjallisuuteen että ilmastonmuutokseen liittyvän taloustieteen käytännön kirjallisuuteen.
  • Lehtonen, Ilari; Ruosteenoja, Kimmo; Mäkelä, Antti (2019)
    Raportteja – Rapporter – Reports 2019:2
    Meneillään olevan ihmiskunnan aiheuttaman ilmastonmuutoksen vaikutukset ovat havaittavissa jo nyt: esimerkiksi Suomen keskilämpötila on noussut 1800-luvun puolivälistä yli kaksi astetta. Lämpeneminen on ollut Suomessa noin kaksi kertaa nopeampaa kuin maapallolla keskimäärin. Tulevaisuuden muutokset erilaisten sääilmiöiden esiintymisessä riippuvat vahvasti kasvihuonekaasupäästöjen määrästä: mitä tehokkaammin kasvihuonekaasujen päästöjä onnistutaan rajoittamaan, sitä vähäisemmiksi ilmastonmuutoksen vaikutukset jäävät. Ilmakehään jo päässeen hiilidioksidin suhteellisen pitkästä viipymäajasta johtuu, että ilmasto joka tapauksessa vielä lämpenee seuraavina vuosikymmeninä, vaikka fossiilisten polttoaineiden käytöstä aiheutuvia kasvihuonekaasupäästöjä onnistuttaisiin leikkaamaan nopeastikin. Tässä tutkimuksessa käsitellään ilmastonmuutoksen vaikutusta sähköverkkoliiketoiminnan kannalta oleellisiin sääilmiöihin. Keskeisimmät tähän mennessä havaitut ja kuluvan vuosisadan puoliväliin mennessä odotettavissa olevat muutokset on koottu sääilmiöittäin sisällysluettelon edellä olevaan taulukkoon. Selvimmin havaittavat muutokset liittyvät lämpötilan nousuun. Esimerkiksi kasvukaudet pidentyvät kesällä ja lumipeite vähenee talvella. Sen sijaan esimerkiksi myrskyisyydessä ei välttämättä tapahdu merkittäviä muutoksia, mutta lämpenemisestä johtuva roudan väheneminen todennäköisesti lisää talviaikaisia tuulituhoja. Vastaavasti esimerkiksi jokien talvitulvien odotetaan selvästi yleistyvän, vaikka sademäärä ei talvella kasvaisikaan enempää kuin noin 10–20 %. Tämä johtuu siitä, että lämpötilan noustessa entistä suurempi osa sateesta tulee vetenä. Muutokset eivät myöskään ole yleensä kovin suuria, jos tarkastelu ulotetaan vain noin 30–40 vuoden päähän. Kuluvan vuosisadan puoliväliin mennessä ilmasto lämpenee todennäköisesti suunnilleen yhtä paljon kuin se on tähän mennessä lämmennyt 1970–1980-lukuihin verrattuna. Tällöin 2050-luvun ilmasto olisi jo selkeästi erilainen kuin 1970–1980-lukujen ilmasto, vaikka muutos nykyhetken ilmastoon verrattuna olisi melko maltillinen. Lämpenemisestä huolimatta samat sääilmiöt tuottavat meillä harmia tulevaisuudessa kuin nykyisinkin. Myrskyt säilyvät merkittävimpänä laajoja ja äkillisiä metsätuhoja aiheuttavana sääilmiönä. Kesäisin esiintyy tuhoisia ukkosmyräköitä, eivätkä lumeen ja pakkaseen liittyvät ongelmat katoa talvella. Suomen ilmastolle tyypillinen suuri vuosienvälinen vaihtelu jatkuu yhä myös tulevaisuudessa.
  • Salmi, Jatta; Saari, Helena; Latikka, Jenni; Komppula, Birgitta; Vestenius, Mika; Wemberg, Antti; Laukkanen, Emmi (2019)
    Raportteja - Rapporter - Reports 2019:4
    Tässä työssä on selvitetty ilmanlaadun mittausasemien edustavuuden arvioinnin nykytilaa. Tällä hetkellä mittausasemien edustavuuden arvioinnille ei anneta ohjeita EU-lainsäädännössä eikä Suomen kansallisessa ilmanlaatulainsäädännössä. Kun ilmanlaadun mittaustuloksia raportoidaan EU:lle, tulee kiinteiltä mittausasemilta raportoida myös edustavan alueen alueellinen laajuus ja edustavuuden arviointi. Näiden tietojen raportointi on pakollista, mutta määritellyn referenssimenetelmän puuttuessa on toistaiseksi ollut sallittua jättää tieto raportoimatta. Eri EU-mailla on olemassa laaja kirjo erilaisia menetelmiä, joilla ne arvioivat mittausasemiensa edustavuutta. FAIRMODE järjesti vuonna 2016 mittausasemien edustavuuden arvioinnista käytännön harjoituksen, johon Suomikin osallistui. Harjoituksen tarkoituksena oli vertailla käytössä olevien erilaisten lähestymistapojen vahvuuksia ja heikkouksia. Harjoituksessa ei saatu aikaan yhtenäistä linjausta mittausaseman edustavuuden arvioimiseksi johtuen eri maiden menetelmien suurista eroavaisuuksista. Harjoituksen loppuraportissa suositeltiin jatkotoimenpiteiksi mittausaseman edustavuuden määritelmän ja kriteerien tarkentamista ja vasta tämän jälkeen yhtenäisen menetelmän kehittämistä keskipitkällä aikavälillä. Edustavuuden arviointia tullaan käsittelemään edelleen AQUILA:n ja FAIRMODE:n yhteistyön puitteissa. Tässä työssä esitetyllä menetelmällä pyritään kannustamaan mittausverkkoja arvioimaan mittausasemien edustavuusalueita. Menetelmässä on kuvattu täsmällisemmin Suomen FAIRMODE:n harjoituksessa käyttämää asiantuntija-arviota, joka perustuu olemassa olevaan monipuoliseen tietoaineistoon. Edustavuuden arviointimenetelmä jakaantuu kahteen vaiheeseen: ensimmäisessä vaiheessa arvioidaan pitoisuuksia ja toisessa vaiheessa pitoisuuksia aiheuttavia samankaltaisia syitä. Edustavuutta voivat arvioida ilmanlaadun arviointeihin hyvin perehtyneet henkilöt, joilla on ymmärtämystä ilman epäpuhtauksien päästöistä ja niihin vaikuttavista seikoista, eri päästölähteiden aiheuttamista pitoisuuksista sekä paikallisista olosuhteista. Mieluiten edustavuuden arviointi tehdään useamman asiantuntijan ryhmätyönä, mikä vähentää yksittäisen asiantuntijan näkemyksen liiallista korostumista.
  • Pajunpää, Kari; Häkkinen, Lasse; Laitinen, Tiera (2019)
    Raportteja – Rapporter – Reports 2019:1
    The magnetic yearbook of the magnetic recordings at the Nurmij¨arvi observatory contains tables, figures of hourly, monthly, and yearly means of the magnetic field components X, Y and Z as well as magnetic activity indices (K, Ak) in 2016. Magnetic isolines describing the distribution of geomagnetic field components in Finland 2017.0 are shown by a series of maps.
  • Anttila, Kati (2019)
    Finnish Meteorological Institute Contributions 149
    The topic of this dissertation is the seasonal snow surface roughness and albedo. These are studied using optical satellite data and terrestrial laser scanning. The use of remote sensing data requires knowledge on the optical properties of the measured surface. For snow, these properties are affected by surface roughness. In this dissertation, two different methods for measuring snow surface roughness were validated and used in the field. One of them is based on plate photography. It is easy to use in the field and able to study surface features in sub-millimeter scale. The other method is based on mobile laser scanning and is able to produce 3D surface descriptions of large areas. The plate-photography-based method was used in the field to gather 669 profiles of the snow surface. The profiles were analyzed using multiscale parameters. The validation of satellite data requires observations at the surface. This validation data typically consists of pointwise measurements, whereas the satellite data observations cover larger areas. Laser scanning provides data that cover larger areas, thus more in line with the satellite data. This could in the future be used for satellite data validation. The usability of laser scanning data on snow surfaces was improved by studying the incidence angle dependency of the laser scanning intensity data on different snow types. A function for correcting the incidence angle effect on all measured snow types was developed. The backscattering of laser beam on snow surface was found to take place at the very surface for dry snow, and within 1cm depth for wet snow. The final part of this dissertation studies the changes in surface albedo prior to melting and the timing of the melt season in Northern Hemisphere land areas between 40°N and 80°N. The albedo prior to melt had changed significantly in the boreal forest area, but not in the tundra. The direction of change is different in different areas. The melt season takes place at the same time of year for most of the study area, but for Central Siberian Plane the melt season takes place earlier. In Northern Canadian Rocky Mountains and in the area around the borders of Russia, China and Mongolia the melt starts earlier and ends later, thus resulting in longer melt seasons. The changes observed in the pre-melt albedo are related to vegetation, whereas the melt season timing is more related to the climatic parameters. The results of this dissertation can be used in developing remote sensing data and climate models through improved understanding of seasonal snow surface roughness and albedo. *** Tämä väitöskirja käsittelee kausittaisen lumipeitteen pinnan karkeutta ja kirkkautta hyödyntäen optista satelliittiaineistoa ja laserkeilausta. Maan pinnan kaukokartoitus tarvitsee tietoa maan pinnan säteilyominaisuuksista. Lumipinnat heijastavat suurimman osan auringosta tulevasta säteilystä takaisin ilmakehään ja avaruuteen. Kausittainen lumipeite kattaa laajan alueen pohjoisen pallonpuoliskon maaalasta. Alueellisen kattavuutensa ja kirkkautensa vuoksi sillä on merkittävä vaikutus maapallon energiataseeseen ja siten ilmastoon. Lumipinnan heijastusominaisuudet, kuten esimerkiksi pinnan karkeus, vaikuttavat suoraan lumipinnan kirkkauteen. Tässä väitöskirjassa on tarkasteltu kahta lumen pinnan karkeuden mittausmenetelmää. Ensimmäinen näistä tekniikoista perustuu lumeen asetetun mustan levyn valokuvaamiseen. Levystä ja lumipinnasta otetusta kuvasta etsitään automaattisesti lumipinnan profiili. Tämä tekniikka on helppokäyttöinen ja luotettava myös kenttäolosuhteissa. Sillä saadaan kerättyä tietoa lumen pinnan karkeudesta alle millimetrin tarkkuudella. Toisessa mittausmenetelmässä laserkeilainta liikutetaan moottorikelkalla. Näin saadaan katettua laaja alue, josta syntyy 3D havaintoja. Pinnan karkeutta kuvaavien suureiden arvoihin vaikuttaa analysoidun profiilin pituus tai alueen laajuus. Kaukokartoituksen kannalta on oleellista mitata pinnankarkeutta kaikissa sovellukselle oleellisissa mittakaavoissa. Maan pinnan sirontamallit käyttävät pinnan karkeuden kuvaamiseen vain yhtä suuretta. Siten tämän suureen tulisi sisältää tietoa useista mittakaavoista. Tässä väitöskirjassa kerättiin Sodankylän alueelta 669 lumiprofiilia levymenetelmää käyttäen. Nämä profiilit analysoitiin käyttäen suureita, jotka kuvaavat profiilin korkeusvaihtelun riippuvuutta mitatusta matkasta ja sisältävät siten tietoa useista mittakaavoista. Käyttämällä näitä suureita kyettiin erottelemaan eri lumipintoja niiden iän ja lumityypin mukaan. Satelliittien instrumentit mittaavat kerralla laajoja alueita. Maan pinnalla tehtävillä pistemäisiä alueita kuvaavilla havainnoilla selvitetään, kuinka laadukkaita satelliittituotteet, kuten lumi- ja albedotuotteet, ovat. Koska pintahavaintojen ja satelliittihavaintojen kattamat alueet eivät ole samat, itse ahavainnotkaan eivät täysin vastaa toisiaan. Laserkeilausaineistot kattavat laajempia alueita kuin perinteisin menetelmin tuotetut havainnot ja ovat siten lupaavia satelliittiaineistojen arviointiin. Tämän väitöskirjan sisältämä tutkimus lasersäteen käyttäytymisestä lumipinnoilla edistää laserkeilausaineistojen käytettävyyttä lumeen liittyvässä tutkimuksessa ja satelliittiaineistojen laadun määrittämisessä. Tulosten mukaan kuivasta lumesta lasersäde heijastuu takaisin aivan lumen pinnasta, kun taas märässä lumessa se heijastuu noin 1 cm syvyydestä. Takaisin heijastuneen lasersäteen kirkkaus riippuu tulokulmasta samalla tavalla erityyppisillä lumipinnoilla. Siten tulokulman vaikutus laserhavainnon kirkkauteen voidaan korjata samalla tavalla kaikilla mitatuilla lumipinnoilla. Tämän väitöskirjan viimeisessä osassa tutkittiin kausittaisen lumipeitteen peittämien alueiden pinnan kirkkauden (albedon) ja sulamiskauden ajankohdan muutoksia vuosina 1982-2015 pohjoisen pallon puoliskon maa-alueilla leveyspiirien 40°N ja 80°N välillä. Tutkimus keskittyi sulamiskautta edeltävään pinnan kirkkauteen, joka oli muuttunut huomattavasti boreaalisen metsävyöhykkeen alueella. Muutos oli erisuuntaista eri alueilla. Tundralla sulamista edeltävä pinnan kirkkaus ei ollut muuttunut. Sulamiskausi oli aikaistunut Keski-Siperian ylängöllä ja pidentynyt Kiinan, Mongolian ja Venäjän rajaa ympäröivällä alueella sekä Kanadan Kalliovuorten pohjois-osissa. Pinnan kirkkauden muutokset olivat sidoksissa kasvillisuuden muutoksiin, kun taas sulamiskauden ajankohdan muutoksiin vaikuttivat enemmän ilmastolliset tekijät. Tämä väitöskirja parantaa kausittaisen lumipeitteen pinnan sirontaominaisuuksien ymmärtämistä ja sen tuloksia voidaan käyttää kaukokartoitusaineistojen ja ilmastomallien kehittämisessä.
  • Strahlendorff, Mikko; Veijola, Katriina; Gallo, Jason; Vitale, Vito; Hannele, Savela; Smirnov, Alexander; Tanaka, Hajime; Sueyoshi, Tetsuo; Nitu, Rodica; Larsen, Jan René (2019)
    Raportteja - Rapporter - Reports 2019:3
    This report describes the first instance to employ the international assessment framework for arctic observations developed by SAON and IDA STPI in 2017. Earth Observation (EO) inputs like SYNOP station measurements of physical atmosphere and in other stations ocean variables were linked to key products/outcomes/services like numerical weather prediction and through groups like in this case weather service connected to key objectives of the assessment framework. Representative yearly unit costs of EO inputs and modelling components were estimated by station experts or estimated based on European Union projects or Copernicus program tenders. The WMO OSCAR database for satellite and surface observation systems north of 60°N was used for numbers of the different station and mission categories in the Arctic. The total yearly value of this observation system including EO inputs and modeling is over 204 million €. Compared to the observing system estimated costs in the area 30°N to 60°N this is only about a fifth. The value tree can now follow and combine the value invested in these components as it flows towards services. The key objectives have been connected by SAON/AMAP project members in a workshop to the services to build the first full value tree for a certain kind of observations. These observations are mainly produced by national meteorological and marine institutes in an operational mode. The yearly value invested in the observation can now be distributed between the 12 Societal Benefit Areas and their sub areas identified in the assessment framework. The value tree is presented at a web page by FMI and Spatineo (2019) with a browser that can highlight single components to analyze which inputs and which SBA targets its being used for. This can help to more holistically support the whole observation system for optimal impact on societal benefit. The value tree tool will be available for further work to address the many more EO domains like atmospheric composition or biodiversity. All in all this report can hopefully start a continuous action to update and improve the value tree. EO inputs are not static, the network changes, the costs are fluctuating and as the Arctic is becoming more accessible, it would be important to extend the observation system accordingly.
  • Takala, Matias (2018)
    Finnish Meteorological Institute Contributions 151
    Hemispheric snow extent and snow mass are two important parameters affecting the water cycle, carbon cycle and the radiation balance in particular at the high latitudes. In this dissertation these topics have been investigated focusing on the mapping of snow clearance day (melt-off day) and Snow Water Equivalent (SWE) by applying spaceborne microwave radiometer instruments. New algorithms have been developed and existing ones have been further advanced. Specific attention has been paid to estimate snow in boreal forests. This work has resulted in Climate Data Records (CDRs) of snow clearance day and daily values of SWE. Data are available for the entire Northern Hemisphere covering more than three decades. The developed CDRs are relevant for climate research, for example concerning the modeling of Earth System processes. CDR on snow clearance day can be used to map the CO2 balance between the biosphere and atmosphere in the case of boreal forests, which is demonstrated in the thesis. Further, methodologies to assess snow mass in terms of SWE for hemispherical and regional scales have been developed. The developed methodologies have also resulted in the establishment of new Near-Real-Time (NRT) satellite data services for hydrological end-use. In hydrology SWE data are used to enhance the performance of river discharge forecasts, which is highly important for hydropower industry and flood prevention activities.
  • Hooda, Rakesh (2019)
    Finnish Meteorological Institute Contributions 150
    Atmospheric aerosol particles are linked to visibility reduction and adverse health effects, and radiation balance of the Earth— directly by reflecting and absorbing solar radiation and indirectly by influencing the cloud properties and processes and, possibly, by changing the heterogeneous chemistry of reactive gaseous species. Atmospheric aerosols are the most uncertain driver of global climate change. The South‒Asian region has been increasingly recognized as one of the global hotspots of aerosols; and Indo Gangetic Plains (IGP) is one among them with complex geography, heterogeneity in sources and varying atmospheric dynamics. These factors make IGP’s aerosol and pollution very difficult to characterize. So far, long-term regional observations of aerosol properties have been scarce in this region, but argued necessary in order to bring the knowledge of regional and global distribution of aerosols further. In this context, regional studies of aerosol properties their dynamics and atmospheric processes are very important areas of investigation to better estimate the climatic importance of submicron aerosol particles. Moreover regional studies over IGP-Himalayas domain are inevitable to know how trans-Himalayan valleys are acting as conduits for aerosol and pollution transport from the plains to the Himalayas. Therefore, in this thesis we studied these issues by applying basic to state-of-the-art instrumentation in two different environments, plains—Gual Pahari, and Himalayan foothills— Mukteshwar; to obtain physical and optical properties of submicron particles. Additionally, we used meteorological parameters, emissions and process modelling to determine local and regional scale transport of atmospheric aerosols. The work carried out as part of the thesis infers four main conclusions, 1) Simultaneous long-term measurements at both the environments in Northern India region are useful to establish linkages between sub-urban environment and high altitude sites. One site represents a source region, while another characterize as a receiver site of atmospheric pollutants; 2) A distinct cycle of aerosol properties, both seasonal and diurnal, is present and provides information of driving factors of aerosol variability at both the sites; 3) The contribution of regional sources seem to dominate over the local /sub-urban sources, in the IGP region boundary layer; 4) Aerosol properties and specific humidity “passive tracer” based analysis clearly reveal that the mountainous terrain sites are under the influence of air from the plains due to convective transport processes enhanced by local and mesoscale topography. The results presented in this thesis are particularly useful, first, when examining the linkages of aerosol properties variability between two different environments. The second, in determining for instance local versus regional influences, and pollutants reaching high altitude sites which can be explained by boundary layer dynamics processes, especially in the mountain terrain where the modelled mixing layer depths have uncertainties. This work outlines future direction of multi-points measurements on vertical profile of atmospheric particles and local boundary layer over mountainous terrain where the atmospheric structure becomes much more complicated. Additionally, investigations including isotope-based analysis and modelling work over the Himalayan region are desirable to be able to describe better the transport of atmospheric aerosols from IGP to high altitudes and further up to Himalayan ice-pack and glaciers where aerosol deposition could have serious environmental impacts.
  • Waldén, Jari; Vestenius, Mika (2018)
    Raportteja - Rapporter - Reports 2018:2
    The Air Quality Directive, AQD, (2008/50/EC), set up the rules concerning the reference methods (RM) for the measurements of e.g. mass concentration of particulate matter in air. A member state (MS) can use any other method, which it can demonstrate to display a consistent relationship with the reference method. Demonstration of equivalence (DoE) for automated continuous monitoring systems (AMS) for determination of the PM2.5 and PM10 mass concentration of suspended particulate matter was conducted in Finland at the city of Kuopio during 2014-15 (Walden et al., 2017). The tested AMS were used in Finland at the local air quality networks for controlling the limit values for PM2.5 and PM10 mass concentration measurements. The purpose of the verification exercise was to demonstrate whether the AMS tested and approved during the DoE study in Kuopio are applicable elsewhere in Finland. The comparison of the AMS of the local network (site) with the RM was performed in various parts of Finland (south and north, east and west) to see if the AMS, which was approved as equivalence method still fulfills the suitability criteria elsewhere in Finland. Verification campaigns took place at eight measurement sites of different local air quality networks in Finland either for PM2.5 or PM10 measurements. AMS whose DoE was approved were: FH62-IR, Grimm model 180, MP101 CPM, Osiris, SHARP model 5030 and TEOM 1405. Additionally TEOM 1405D and APM-2 were tested for verification, though they did not participate in the DoE tests in Kuopio, but are used at some of the networks. The test strategy was modified from the relevant EN-standard for using the AMS for measurements of PM2.5 and PM10 concentrations in ambient air. This strategy enabled to include more sites and tested instruments into the study but with lack of less seasonality than would have been needed by following the guide accurately. As a result of the verification study the calibration factors achieved at DoE in Kuopio are applicable for the same model of AMS tested in Kuopio in different locations in Finland with few limitations. The FH62-IR made better performance by using the calibration factor obtained in this study in Helsinki than based on the DoE in Kuopio. Osiris passed the test for PM10 but not for PM2.5 measurements just like in Kuopio. APM-2 has been tested by Rheinland Energie und Umwelt GmbH, TÜV that is accredited testing laboratory and found to be equivalent with the reference method both for PM2.5 and for PM10 measurements. Based on the test results by TÜV and the verification results achieved in this study, the APM-2 can be used for PM2.5 and for PM10 measurements in Finland, but applying the calibration factors obtained in this study. TEOM 1405D has not been tested for DoE and cannot be claimed equivalent to reference method. Therefore calibration factors obtained in this study cannot be used for TEOM 1405D.
  • Saarnio, Karri; Kyllönen, Katriina; Laurila, Sisko; Lusa, Kaisa; Waldén, Jari (2018)
    Raportteja - Rapporter - Reports 2018:1
    Neljäs kaasumaisten yhdisteiden vertailumittauskampanja sekä mittausasemien kenttä- ja laatujärjestelmä-auditointi suoritettiin Suomen ilmanlaadun mittausverkoille vuoden 2017 aikana. Vertailumittauksessa kaasu-komponentit olivat rikkidioksidi (SO2), typpimonoksidi (NO) ja otsoni (O3). Vertailupitoisuudet eri komponenteille koostuivat kahdesta eri pitoisuudesta, joista toinen edusti alhaista pitoisuutta ja toinen korkeahkoa pitoisuutta. Lisäksi kullekin komponentille suoritettiin nollatason mittaus. Mittaustulosten raportointi vertailuun osallistuneilta tahoilta edellytti korjatut tulokset jokaisesta vertailumittauksesta sekä arvion mittaustulosten epävarmuudesta. Vertailu-mittauksiin osallistui 21 mittausverkkoa 31:stä ilmanlaadun seurantaa suorittavasta mittausverkosta. Näissä vertailu-mittauksia suoritettiin yhteensä 80 mittausta 28:lla eri mittausasemalla. Pitoisuusvertailujen ohessa suoritetussa kenttä- ja laatujärjestelmäauditoinnissa pyrittiin selvittämään mittausverkon laatujärjestelmän laajuus ja toimivuus. Pääpaino oli erityisesti mittausmenetelmää kuvaavien standardien vaatimusten toteutuminen kentällä tehtävissä laadunvarmennus-toimissa. Auditoinnissa tarkasteltiin kaasumaisten komponenttien mittausten lisäksi ulkoilman hiukkasmittauksia. Tässä raportissa esitetään vertailumittausten sekä kenttä- ja laatujärjestelmäauditoinnin tulokset sekä johtopäätökset. Raportoiduista SO2-tuloksista 22 tulosta 24:stä oli hyväksyttäviä. NO:n osalta 38 tulosta 40:stä oli hyväksyttäviä. O3:n osalta 14 tulosta 16:sta oli hyväksyttäviä. SO2:n, NO:n ja O3:n osalta yhteensä 92,5 % tuloksista oli hyväksyttäviä, mutta korjaavien toimenpiteiden jälkeen kaikki mittausverkot tuottivat hyväksyttävän vertailutuloksen. Mittausepävarmuusarvion oli laatinut noin 86% osallistuneista mittausverkoista. Laatujärjestelmä- ja kenttäauditointien tulokset olivat ylipäätään hyviä. Mittausverkot ovat laatineet menetelmäohjeita mittausaseman sijoittamisesta, mittausmenetelmistä, laadunvarmennustoimista, tulosten käsittelystä ja raportoinnista. Laatujärjestelmiä on kehitetty viime auditoinnin jälkeen. Mittausverkkojen ylläpitämistä laatu-järjestelmistä 16 oli kattavia, neljä oli rakenteilla ja kahdella mittausverkolla laatujärjestelmä oli pääasiallisesti dokumentoitu, mutta se ei ollut aktiivikäytössä. Kaikissa verkoissa oli toimivat tietojen keruu- ja käsittelyohjelmistot. Ilmanlaatumittausten tulokset oli jäljitetty kansalliseen vertailulaboratorioon joko suoraan mittausverkkojen ylläpitämillä tai välillisillä kalibroinneilla, joskin kalibrointivälit eivät aina täyttäneet EN-menetelmästandardeja (EN 14211, EN 14212, EN 14625). Välillisistä kalibroinneista suurin osa oli ulkoistettu yhdelle konsultille, jonka jäljitettävyys kansalliseen vertailulaboratorioon oli ylläpidetty säännöllisillä kalibroinneilla. Kaasumittausten laadunvarmennustoimet olivat pääasiallisesti em. EN-menetelmästandardien mukaisia, joskin poikkeuksiakin oli. Hiukkasmittausten osalta laadunvarmennustoimissa tavattiin eniten vaihtelevuutta eri verkkojen välillä ja tätä on syytä kehittää.
  • Westerlund, Antti (2018)
    Finnish Meteorological Institute Contributions 145
    Circulation and surface layer dynamics are of significant importance, for example, when considering how hazardous substances or nutrients are transported in the sea. The earliest studies mapping circulation patterns in the northern Baltic Sea were done before the Second World War and were based on lightship observations. Although the number of available observation points was low, these studies showed that there is a cyclonic long-term surface circulation pattern in the northern subbasins. Even today, there are considerable research gaps and uncertainties in knowledge. For example, observational data still has insufficient coverage, descriptions of processes in numerical models need tuning to the conditions of the Baltic Sea and model forcing data can have large uncertainties. With modern analysis methods and new observational datasets, gaps in the current understanding of Baltic Sea circulation patterns can be identified and analyzed. In this thesis, circulation dynamics were investigated in the northern Baltic Sea with numerical hydrodynamic modelling. The complex dynamics of the brackish Baltic Sea put hydrodynamic models to the test. Several different model configurations were applied and developed further, including a high-resolution configuration of the NEMO (Nucleus for European Modelling of the Ocean) model for the Gulf of Finland (GoF). Methods such as machine learning algorithms, new data from automated observational platforms and ensemble forecasting were applied. Circulation patterns in the GoF were investigated with the self-organizing map (SOM) algorithm. The cyclonic circulation pattern visible in earlier studies was not seen in the GoF in the overall means calculated from the model results for the studied periods 2007–2013 and 2012–2014. SOM analysis of currents in the GoF revealed that they are highly variable and complex. There was significant inter-annual and intra-annual variability in the circulation patterns. A connection between wind forcing and the characteristic patterns from the SOM analysis was found. Analysis emphasized the estuary-like nature of the GoF. The results showed that circulation in the GoF changes rapidly between normal estuarine circulation and reverse estuarine circulation. The fact that the dominant wind direction is from the southwest supports this reversal. The cyclonic mean circulation pattern seems to appear only if the normal estuarine circulation is common enough for it to emerge during the averaging period. Small changes to wind direction distribution can have a significant effect on the longterm circulation patterns. Upwelling events on a timescale of days to weeks can also affect long-term circulation patterns. The NEMO model proved to be a suitable tool for the studies of circulation in the northern sub-basins of the Baltic Sea. It quality seems comparable to other models commonly used in the GoF and Bothnian Sea. The GoF is still a challenging environment for circulation modelling. Salinity gradients in the GoF are still not reproduced in a satisfactory manner by the models. More information is required on how well the models reproduce true circulation patterns and, for example, upwelling frequency and intensity. The need for accurate model inputs, especially wind forcing, was demonstrated. The value of observations (especially the better spatial coverage of current measurements) was once again emphasized. Furthermore, the results highlighted that care must be taken to make sure that models and observations represent the same thing when they are compared.
  • Välisuo, Ilona (2018)
    Finnish Meteorological Institute Contributions 148
    Polar ice sheets, glaciers, and ice shelves, referred to as land ice in this document, are under transition in the changing climate. Observations show that glaciers have retreated and melt water discharge from land ice has increased together with the warming climate. Decreasing volume of land ice is reflected to the whole Earth system via changes in surface radiation balance, sea level rise, and water balance in inland watersheds. Warming and melting land ice creates positive feedback loops that further increase melting. The study of polar land ice in changing climate is challenging due to lack of observations from the remote areas. Large interannual variability of climate, rapid changes in temperature and ice conditions, and short observational timeseries further complicate the research. This Ph.D. thesis concentrates on the aspects of melting land ice in the polar regions. The focus is on the interannual variability of surface melt and weather conditions on two of the Antarctic Peninsula Ice Shelves (Larsen C and Wilkins) and the Greenland Ice Sheet. Surface melt is addressed through the surface energy balance and other direct measures of melt. Furthermore, the changes in surface accumulation and ablation patterns have been modelled on a small Arctic valley glacier, Midtre Lovénbreen. This modelling study presents for the first time a method that allows to produce high resolution maps of accumulation and ablation, using only a glacier flow model and the digital elevation models of the glacier surface. Surface energy balance controls the melt of snow and ice. The effect of atmospheric moisture or clouds on the surface energy balance was important in the Antarctica Peninsula region and on the Greenland Ice Sheet. Cloud cover fraction was related to the wintertime surface net heat flux on Larsen C Ice Shelf. A multi-regression model, including the cloud cover fraction as one of the explanatory variables, explained up to 80% of the interannual variation of the surface net heat flux in June-August. On the Greenland Ice Sheet the vertically integrated total column water was positively correlated with the summertime surface melt. Local near surface winds (at 10 m height above ground level) were important in explaining the surface net heat flux on Larsen C Ice Shelf in summer, autumn, and winter. In Greenland, the wind components correlated locally with the number of melt days. The positive correlation was likely related to the adiabatic heating of descending air on the lee side of the ice sheet and, in other locations, to the advection of warm air from lower latitudes. The number of melt days on the Greenland Ice Sheet were also correlated with positive North Atlantic Oscillation Index and Greenland Blocking Index, indicating that these large scale patterns contribute in creating conditions that favour melt. The large scale atmospheric conditions that increase humidity or advect warm air to the polar regions are likely to increase surface melt in Greenland or Antarctic Peninsula region. Nevertheless, explaining the high resolution melt patterns requires understanding of the local conditions and topographic features. This Ph.D. thesis contributes in understanding local surface melt as part of the large scale climate system.
  • Ruuhela, Reija (2018)
    Finnish Meteorological Insitute Contributions 147
    Human beings are able to adapt to their climatic normal conditions, but weather extremes may pose a substantial health risks. The aims of this dissertation were to model the dependence of all-cause mortality on thermal conditions in Finland, and to assess changes in the relationship over the decades and regional differences in the relationships between hospital districts. Another aim was to assess impacts of weather and climate on committed and attempted suicides Finland. Various methods were applied in these studies. Time series of all-cause mortality in three age groups in Helsinki-Uusimaa hospital district were made stationary, and thus the weather impacts were comparable over the 43-year long time period regardless of changes in population and life-expectancy. The increase in relative mortality due to hot extreme was more than due to cold extreme, when compared to seasonally varying expected mortality. However, a decrease in relative mortality in extreme temperatures over the decades was found in all age-groups, even among the 75 years and older, indicating decreased sensitivity to thermal stress in the population. Regional differences in temperature‒mortality relationships between 21 hospital districts were studied using distributed lag non-linear models (DLNM), and the differences were assessed by meta-regression with selected climatic and sociodemographic covariates. Regional differences in the relationships were not statistically significant indicating that the same temperature-mortality relationship can be applied in different parts of the country. On the other hand, the meta-regression suggested that the morbidity indices and population in the hospital districts could explain part of the small heterogeneity in the temperature‒mortality relationships. The study on committed suicides on the basis of 33-year long time series showed a significant negative association between suicides and solar radiation in the period from November to March, thus, a lack of solar radiation would increase suicide risk in winter. Men appeared to be more sensitive to variation in solar radiation than women. The study on weather dependence of attempted suicides in Helsinki on the basis of two shorter periods showed another difference between genders. The risk of suicide attempts of men increased with decreasing atmospheric pressure, while the risk of suicide attempts of women increased with increasing pressure. The outcomes of this thesis can be utilized e.g. in preparedness to weather extremes in health sector and in further studies on impacts of climate change on human health.
  • Thölix, Laura (2018)
    Finnish Meteorological Insitute Contributions 146
    Ozone and water vapour are important trace gases in the atmosphere, where both play an important role in radiative and chemical processes. Ozone protects the Earth's biosphere, humans and materials from the harmful ultraviolet (UV) radiation. The distributions and changes of ozone and water vapour are thus important to understand. Restrictions on the production and use of ozone depleting substances (ODS) within the Montreal Protocol have stopped the growth of the ozone loss, even signs of recovery of the ozone layer have been seen. However, many ODSs are long lived in the atmosphere and it will take decades before they are removed. Stratospheric water vapour influences the polar ozone loss by controlling the formation of polar stratospheric clouds (PSC). The climate change will cool the stratosphere, which could favour the formation of PSCs. This could cause significant ozone depletion despite the lower chlorine loadings in the future stratosphere. Atmospheric models are needed for studying these phenomena, because the number of observations is limited. Also the prediction of future ozone loss requires models. In this study simulations of the middle atmosphere have been made using the FinROSE chemistry transport model (FinROSE-CTM). It is an off-line 3-dimensional model, covering the altitude range of ca. 10–80 km, including the stratosphere. The model can be used for short term case studies, as well as for decadal simulations. The FinROSE-CTM needs pre-calculated winds, temperature and surface pressure, and then calculates the chemistry and transport using the meteorology. In this study ECMWF reanalysis data and climate model data have been used. Model results have been compared to ground based and satellite observations, and the model has been shown to be suitable for polar stratospheric ozone and water vapour studies. When running the model with climate model data also future conditions can be predicted. Both observations and simulations show an increase in the water vapour concentration in the Arctic stratosphere after 2006, but around 2012 the concentration started to decrease. Model calculations suggest that this increase in water vapour is mostly explained by transport-related processes. The increase in water vapour in the presence of the low winter temperatures in the Arctic stratosphere led to more frequent occurrence of ICE PSCs in the Arctic vortex. In a recent study, we studied the effect of changes in the water vapour concentration in the tropical tropopause on Arctic ozone depletion. A change in the tropical tropopause water vapour concentration resulted in a corresponding change in the Arctic stratosphere. We found that the impact of water vapour changes on ozone loss in the Arctic polar vortex depends on the meteorological conditions. The strongest effect was in intermediately cold conditions, when added water vapour resulted in more ozone loss due to the additional PSCs and associated chlorine activation on their surface. The effect was less pronounced in cold winters because cold conditions persisted long enough for a nearly complete chlorine activation even with observed water vapour. The results show that the simulated water vapour concentration in the tropical tropopause has a significant impact on the Arctic ozone loss and deserves attention, and therefore needs to be well simulated in order to improve future projections of ozone layer recovery.
  • Kontu, Anna (Finnish Meteorological Institute, 2018)
    Finnish Meteorological Insitute Contributions 144
    Remote sensing using microwave radiometry is an acknowledged method for monitoring various environmental processes in the cryosphere, atmosphere, soil, vegetation and oceans. Several decades long time series of spaceborne passive microwave observations can be used to detect trends relating to climate change, while present measurements provide information on the current state of the environment. Unlike optical wavelengths, microwaves are mostly insensitive to atmospheric and lighting conditions and are therefore suitable for monitoring seasonal snow in the Arctic. One of the major challenges in the utilization of spaceborne passive microwave observations for snow measurements is the poor spatial resolution of instruments. The interpretation of measurements over heterogeneous areas requires sophisticated microwave emission models relating the measured parameters to physical properties of snow, vegetation and the subnivean layer. Especially the high contrast in the electrical properties of soil and liquid water introduces inaccuracies in the retrieved parameters close to coastlines, lakes and wetlands, if the subnivean water bodies are not accounted for in the algorithm. The first focus point of this thesis is the modelling of brightness temperature of ice- and snow-covered water bodies and their differences from snow-covered forested and open land areas. Methods for modelling the microwave signatures of water bodies and for using that information in the retrieval of snow parameters from passive microwave measurements are presented in this thesis. The second focus point is the effect of snow microstructure on its microwave signature. Even small changes in the size of scattering particles, snow grains, modify the measured brightness temperature notably. The coupling of different modelled and measured snow microstructural parameters with a microwave snow emission model and the application of those parameters in the retrieval of snow parameters from remote sensing data are studied.
  • Gregow, Erik (2018)
    Finnish Meteorological Institute Contributions 142
    Observations have been and are an important part of today's meteorological developments. Surface observations are very useful as they are, providing weather information for a point location. ough they do not give much information, if any, on what happens between the stations across a larger area. With models one can create an analysis of the meteorological situation, i.e. calculate and estimate what happens between these fixed observation points. Remote-sensing data, such as radar and satellite, are being processed and the output is given over a domain as an analysed product of their measurements. For example, radar gives a plot of where the rain is located, i.e. an analysis of the current precipitation. With a series of radar images, a human (subjectively) or a computer objectively) can process this information to estimate where the rain will move and be located within the next few minutes (even hours), i.e. a short forecast also called "nowcast". is applies to some extent also for other observations, such as satellite data (cloud propagation). But for most quantities (such as temperature, wind, etc) it is significantly harder to make such a nowcast, since these are influenced by many other factors and there is no linear development of them. Therefore, there are forecast models that solve physical and dynamic equations, so that one can estimate the future weather for the coming hours and days. A prerequisite for generating a forecast of high quality is to capture the initial weather conditions as best as possible. This is done using observations and they are introduced into the forecast model through different techniques, where the model creates its own analysis as the initial step. There remain problems since forecast models often are affected by physical disagreements, as the dynamic conditions are not in balance. This results in the model having a spin-up effect, where the meteorological quantities are not yet in balance with each other and the resulting weather conditions are not always reliable during the first hours. Hence, a lot of research is spent on how to reduce this spin-up effect and on the use of nowcast models, in order to deliver the best model results for the first few hours of the forecast period. In this dissertation, the research work has been to improve the meteorological analysis, algorithms and functionality, using the Local Analysis and Prediction System (LAPS) model. Different kinds of observations were used and their interdependencies have been studied, in order to combine and merge information from variousinstruments. Primarily focus has been to improve the estimation of precipitation accumulation and meteorological quantities that affect wind energy. The LAPS developments have been used for several end-users and nowcasting applications, and experimentally as initial conditions for forecast modelling. The studies have been concentrated on Finland and nearby sea areas, with the available datasets for this domain. By combining surface-station measurements, radar and lightning information, one can improve the precipitation-amount estimations. The use of lightning data further improves the estimates and gives the advantage of having additional data outside radar coverage, which can potentially be very useful for example over sea areas. In addition, the improved LAPS analyses (cloud-related quantities) and a newly developed model (LOWICE), calculating the electricity production during wintertime (taking into account the icing of wind turbine rotor blades which reduces efficiency), have shown good results.