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Browsing by study line "Meteorology"

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  • Kröger, Anni (2019)
    Earth’s energy budget describes the balance between the net incoming and outgoing energy fluxes, and the energy balance approach can be used to better understand the basic physical mechanisms of climate change. Anthropogenic changes in the atmospheric composition, such as increases in greenhouse gases, drive changes in climate system which in turn can cause rising of the global temperatures. Various feedbacks, associated with increase in atmospheric water vapor content, changes in clouds and reduced snow/ice cover, affect the pattern of surface warming by altering the fluxes of energy. By studying the energy balance at the top of the atmosphere and at the surface, we gain useful information about the climate system’s response to changes in the atmospheric composition. In this thesis, data for 23 climate models in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) was used. The present-day distributions and future projections of the simulated changes (under RCP8.5 emission scenario, Representative Concentration Pathway) for 14 radiative and non-radiative energy budget components, along with the changes in surface temperature and cloud cover were studied, with baseline period of 1981-2010 and a comparison scenario period of 2071-2100. The geographical distributions of the multimodel mean changes and their global averages were analysed. Additionally, the intermodel consistency of the simulated changes was studied with the intermodel standard deviations and the ratio of multimodel mean change to the intermodel standard deviation. Furthermore, the intermodel correlation between the change in surface temperature and each energy budget variable was discussed. A general finding was that the multimodel mean surface temperature increases everywhere, more over land than oceans, and that the warming is amplified over the northern polar regions. The changes were largest for the thermal radiation fluxes, and the dominating contribution to the surface warming was concluded to be the change in clear- sky atmospheric re-radiation component. However, increase in absorbed shortwave radiation, presumably due to reduced ice/snow cover and increase in atmospheric water vapor content, was also found to be substantial, and there was a strong negative correlation between the clear-sky downward shortwave radiation flux and the change in temperature over the low-to-mid latitudes. The comparison of contribution of the changes in longwave and shortwave fluxes to global warming in the near-future and long-term climate model projections could be an interesting subject for future studies. Additionally, the changes in the surface energy fluxes were found to modify the pattern of surface warming.
  • Corner, Joona (2023)
    The aim of this work is to develop and optimise an atmospheric inverse modelling system to estimate local methane (CH4) emissions in peatlands. Peatlands are a major source of CH4 regionally in boreal areas and they have significance on a global scale as a soil carbon storage. Data assimilation in the inverse modelling system is based on an ensemble Kalman filter (EnKF) which is widely used in global and regional atmospheric inverse models. The EnKF in this study is an implementation of the EnKF used in the global atmospheric inversion model CarbonTracker Europe-CH4 (CTE-CH4) applied to local setting in the peatland. Consistency of the methodology with regional and global models means that it is possible to expand the system in scale. Siikaneva fen in Southern Finland is used as a testbed for the optimisation of the system. Prior natural CH4 fluxes in Siikaneva are acquired from the HelsinkI Model of MEthane buiLd-up and emIssion for peatland (HIMMELI) which simulates exchange of gases in peatlands. In addition to the peatland fluxes, anthropogenic fluxes at the site are estimated as well in the inversion. For the assimilation of atmospheric CH4 concentration observations, the CH4 fluxes are transformed into atmospheric concentration with a simple one-dimensional box model. The optimisation of the system was done by changing parameters in the model which affect the data assimilation. In model optimisation tests it was discovered that the performance of the modelling system is unstable. There was large variability in the produced estimates between consecutive model runs. Model evaluation statistics did not indicate improvement of the estimates after the inversion. No exact reason for the unstability was able to be determined. Posterior estimates of CH4 fluxes for years 2012–2015 did not differ much from prior estimates and they had large uncertainty. However, evaluation against flux measurements showed reasonable agreement and posterior concentration estimates were within the uncertainty range of the observed concentration.
  • Mahó, Sándor István (2021)
    This thesis analyses the alterations of vertically integrated atmospheric meridional energy transport due to polar amplification on an aqua planet. We analyse the energy transport of sensible heat, latent energy, potential energy and kinetic energy. We also cover the energy flux of the mean meridional circulation, transient eddies and stationary eddies. In addition, we also address the response of the zonal mean air temperature, zonal mean zonal wind, zonal mean meridional wind, zonal mean stream function and zonal mean specific humidity. Numerical model experiments were carried out with OpenIFS in its aqua planet configuration. A control (CTRL) and a polar amplification (PA) simulation was set up forced by different SST (sea surface temperature) patterns. We detected tropospheric warming and atmospheric specific humidity increase 15-90° N/S and reduction of the meridional temperature gradient throughout the troposphere. We also found reduced strength of the subtropical jet stream and slowdown of the mean meridional circulation. Important changes were identified in the Hadley cell: the rising branch shifted poleward and caused reduced lifting in equatorial areas. Regarding the total atmospheric vertically integrated meridional energy transport, we found reduction in case of the mean meridional circulation and transient eddies in all latitudes. The largest reduction was shown by the Hadley cell transport (-15%) and by midlatitude transient eddy flux (-23%). Unlike most studies, we did not observe that meridional latent energy transport increases by polar amplification. Therefore, it is stated that the increased moisture content of the atmosphere does not imply increased meridional latent energy transport, and hence there is no compensation for the decrease of meridional dry static energy transport. Lastly, we did not detect stationary eddies in our simulations which is caused by the simplified surface boundary (i.e. the water-covered Earth surface). The main finding of this thesis is that polar amplification causes decreasing poleward energy transport on an aqua planet.
  • Mikkola, Johannes (2020)
    Local mountain winds have a diurnal cycle of flowing up the slopes and valleys daytime and down nighttime. It is important to improve the understanding on these thermally driven winds, because they have a major role in pollution transport in mountain areas, which are highly sensitive for air-quality problems. This thesis determines if the slope and valley winds in the Khumbu valley, Himalayas, are driven by the textbook mechanisms. By the textbook mechanisms the slope and valley winds are driven by horizontal temperature differences caused by uneven heating over an area of complex terrain. Slope winds are driven by the horizontal air temperature difference in the slope surface vicinity when the slope surface is heated or cooled. Valley winds are driven by the uneven heating caused by the air volume difference between the valley and above an adjacent plain. If the valley slopes narrow and the floor is elevated towards the head of the valley, both the valley and slope wind mechanisms drive the winds along the valley. The slope and valley winds in the Himalayas are studied using Weather Research and Forecasting model (WRF), that is run for 5 days period in December 2014 with 1 kilometer horizontal grid spacing and 61 vertical levels. Earlier studies have shown that WRF is capable of simulating the thermally driven mountain winds on this resolution with the length scales of the Khumbu valley topography. Horizontal gradient of air temperature and slope wind component at the slope surface have a matching daily cycle in the lower and middle parts of the valley. The boundary layer air volume decreases from the mouth of the valley towards the middle parts of the valley indicating the valley wind mechanism. The daytime potential temperature profiles yield that also the slope wind mechanism drives the winds along the valley. The slope winds have a textbook daily cycle in the lower and middle parts of the valley and the analysis yields that they are driven by the slope wind mechanism. In the upper part of the valley the thermally driven slope winds are dominated by synoptic scale channelling and gravity wave developing into the valley. The daytime up-valley winds are driven by both valley wind mechanism and slope wind mechanism due to the valley narrowing and elevation towards the head of the valley, respectively. Nocturnal along-valley winds are weak less than 0.5 meters per second flowing up or down-valley. The wind patterns are similar to what is shown in earlier studies done in Khumbu valley.
  • Keränen, Tuukka (2021)
    A stably stratified layer is often observed to form near the surface during nighttime. If the terrain is not flat, cold air near the surface can start to flow down the slope despite the wind direction above the stable layer being different. This slope flow is called katabatic wind. Katabatic winds are challenging for eddy covariance measurements that are commonly used to calculate the fluxes of gases and energy between the soil and the atmosphere. If the measurement is done above the canopy, the katabatic wind may lead to significant advective transport of gas and energy not detected by the measurement. Therefore eddy covariance measurements might underestimate the fluxes by a significant amount. Therefore it is important to understand the mechanisms of katabatic flow so that the effects of it can be taken into account when eddy covariance measurements are used in sloping terrain. This thesis determines how the katabatic flow within a boreal forest canopy in Hyytiälä, Finland depends on the static stability and depth of the stable layer within the canopy. The measurements are also compared to a simplified theory to find out how well the existing formulations of katabatic flow within canopies describe the observed conditions. Wind measurements done with sonic anemometers and temperature measurements done with distributed temperature sensing system during June-October 2019 are analyzed in this thesis to form understanding of the vertical profiles of temperature and wind within the canopy layer at the measurement site. In addition to the wind and temperature measurements, solar radiation measurements are also used to find the dominant driver for the formation of the stably stratified canopy layer. The measurement site represents typical Finnish Scots pine forest and has sloping terrain with main slope of 2° in the north-south direction. This study found evidence of katabatic northerly flow forming at the measurement site during stable nights. However, this study could not find a relation between the depth of the stable layer and strength of the katabatic flow. The katabatic flow was observed to get stronger in the open trunk space with increasing static stability within the canopy layer. The results of this study suggest, that katabatic flow follows the simplified theory well within the upper part of the canopy, where the majority of the foliage is. At lower levels within the open trunk space, the simplified model greatly underestimates the flow speed.
  • Taurinen, Janina (2021)
    Maapallon keskilämpötila on ollut selkeässä nousussa jo noin sadan vuoden ajan ja nousun odotetaan jatkuvan tulevaisuudessakin. Suurimman osan eri kuukausien keskilämpötiloista on ennustettu nousevan ilmastollisiin vertailuarvoihin suhteutettuna normaalia korkeammiksi. Lämpeneminen vaikuttaa etenkin korkeiden leveysasteiden talviin. Muutos Suomen lämpötiloissa sekä pohjois- ja eteläosien välisessä lämpötilaerossa on huomattavasti suurempi talvisin kuin kesäisin. Talvi 2019-2020 oli Suomessa ennätyksellisen lämmin. Tässä tutkimuksessa pyrin kartoittamaan kuinka poikkeava talvi 2019-2020 oli lämpötilojen suhteen edellisten 30 talven muodostamaan vertailukauteen verrattuna. Tutkimuksessa tarkastellaan kuutta kuukautta, loka-maaliskuu, ja vertailukauden on valittu olevan tammikuusta 1989 – maaliskuuhun 2019. Lisäksi käsitellään korkeiden lämpötilojen todennäköisimpiä aiheuttajia tarkastelemalla valittuja perusmuuttujia; paine, geopotentiaalikorkeus, ominaiskosteus, ilmapilarin kokonaiskosteus ja yläilmakehän tuulen nopeus ja suunta. Lämpimimmät poikkeamat havaittiin joulu-helmikuussa, kun lounaasta puhaltava suihkuvirtaus toi mukanaan lämpimiä, kosteita ilmamassoja sekä voimakkaita matalapaineita. Tammikuu 2020 rikkoi monilla asemilla lämpöennätyksiä ja Etelä-Keski-Suomessa vertailukauden keskiarvot ylittyivät jopa 7-8 asteella. Helmikuu oli mittaushistorian toiseksi lämpimin. Loka-marraskuu sitä vastoin olivat vertailukautta noin asteen viileämpiä ja maaliskuun puolella poikkeuksellinen lämpimyys tasoittui lähelle vertailukautta. Runsaan matalapainetoiminnan sekä ilman korkean kosteussisällön vuoksi sadetta tuli läpi talven paikoin jopa kaksi-kolminkertaisesti verrattuna keskiarvoihin.
  • Hasu, Mikael (2022)
    This thesis investigates how the Lorenz model state sensitivity appears on the prior state error of the Extended Kalman Filter (EKF) process. The Lorenz model is a well-known ordinary differential equation system. Its simple nonlinear equations show that a chaotic system, like the atmosphere, does not have a single deterministic solution. Edward N. Lorenz also showed that the predictability of the state depends on the flow itself, and numerical weather prediction models, therefore, cannot always be trusted equally. For this reason, when computing a forecast, it is necessary to consider both the model and observations with their weight uncertainties to get the most probabilistic analysis state. The EKF is an algorithm that provides a powerful data assimilation method for nonlinear systems. Its operating principle is based on the evolution of prior state (model evolution) and observation updates. Each observation update calculates the most likely state based on the prior state and observation errors. The process continues from the new analysis state by evolving the model until the next observation update. In this study, I made the EKF utilizing the Lorenz model and sent ensembles from the analysis states on the Lorenz attractor. I calculated the variance of evolved ensembles and compared them to the magnitude of prior state error at the observation update time levels. The results showed that these two parameters are positively correlated. For the 18-timestep observation interval, Pearson’s correlation coefficient was 0.850, which indicates a very high correlation. Therefore, it can be concluded that when the prior state error is small, the ensemble on the Lorenz attractor indicates good predictability (i.e., dispersion of ensemble members is small) and vice versa.
  • Koskentausta, Juho (2023)
    Global warming is rapidly reducing the Arctic sea ice cover. Along with its major impacts in the Arctic, the sea ice loss is known to affect the climate in remote continental areas. In this thesis, the remote effects are studied by analysing data from experiments carried out using the ECHAM6 atmospheric general circulation model forced with simple sea ice concentration and sea surface temperature configurations. The European and Asian midlatitude winter responses of surface air temperature are investigated, together with anomalies of variables potentially affecting them: sea level pressure, thermal advection, adiabatic and diabatic heating and surface energy fluxes. Arctic sea ice loss was found to have contributed weakly to the European warming from the 1980s to the 2010s. With sea ice and sea surface temperature conditions projected for 2071–2100, the warming response was about 1 °C relative to the 1979–2008 climatology, despite a negative North Atlantic Oscillation phase response. In Asia, the model simulates slight cooling of about 0.5 °C east of the Urals in the past and in the eastern parts of the continent in the future. However, the cooling responses are overwhelmed by the warming effect of global forcings. The effects of internal variability are large, and the role of the thermodynamic processes and surface energy fluxes in the link between the Arctic and Eurasia is not very clear. However, the temperature responses are mostly consistent with previous research, even though the model does not capture the observed past changes well.
  • Strömberg, Jani (2021)
    Air temperatures are commonly higher in urban environments compared to rural ones. The energy input of solar radiation and its storage in urban surfaces changes the way the surface interacts with the atmosphere through turbulent fluxes and mixing processes. The complexity of radiative properties combined with the effect of urban geometry makes the magnitude of the effect radiation has on the dynamics of boundary layer flow an important area of study. The aim of this study is to understand and quantify how much the radiative processes alter the flow field and turbulence in a real urban street canyon in Helsinki. The model used is the large-eddy simulation (LES) model PALM, which solves for the flow and the most relevant atmospheric scales that describe interactions between the surface and atmosphere. An additional library called RRTMG (Rapid Radiative Transfer Model for Global Models) is used in this study to provide the radiation input impacting the boundary layer flow. Two embedded surface models in PALM, USM (Urban Surface Model) and LSM (Land-Surface Model) are used to solve the local conditions for radiative balance based on the output of RRTMG. Two model runs are made (RRTMG On & RRTMG Off), both identical in terms of the large-scale forcing boundary conditions and land-use data, but with additional radiation input in RRTMG On. The results show that radiation alters the low level stratification of potential temperature, which leads to more unstable conditions. Near-surface air temperatures within the canyon were increased by 3.9 C on average. Horizontal wind speeds increased by 76 % close to the ground compared to RRTMG Off. RRTMG On also showed a change in the structure of the topographically forced canyon vortex, as the low wind conditions enabled the radiative effects to have a stronger effect in its forcing. The center of the vortex changed in location more towards the center of the canyon and the vertical motions on opposing sides of the street were strengthened by 0.15 m/s in both vertical directions. Additionally both mechanical and thermal turbulence production increased with RRTMG On, while the thermal production remained smaller by one magnitude compared to mechanical production within Mäkelänkatu. Higher wind speeds and their variance gave rise to increased mechanical production of turbulence and radiative effects increased the thermal production. More research is however needed to determine thermal turbulence's role in situations with different meteorological conditions or in other cities.
  • Virta, Henrik (2020)
    TROPOMI eli TROPOspheric Monitoring Instrument on lokakuussa 2017 Sentinel-5 Precursor -satelliitin mukana laukaistu spektrometri, joka mittaa useiden eri ilmakehän hivenkaasujen pitoisuuksia, aerosoleja sekä pilviä. Se on samalla myös uusin ja resoluutioltaan tarkin typpidioksidin (NO2) pitoisuuksia mittaava satelliitti-instrumentti. NO2:ta havainnoivien satelliitti-instrumenttien mittaukset perustuvat ilmakehästä siroavaan auringon valoon, minkä perusteella niiden algoritmit laskevat ilmakehässä olevien NO2-molekyylien lukumäärän käyttäen apuna erilaisia syötetietoja. Saadussa tuloksessa on tämän vuoksi paljon erilaisia virhelähteitä, minkä vuoksi satelliitti-instrumenttien mittausten oikeellisuutta seurataan jatkuvasti vertaamalla niitä erilaisiin referenssiaineistoihin. Tällaista seurantaa kutsutaan myös instrumentin validoinniksi, ja se on erityisen tärkeää uusien instrumenttien kuten TROPOMIn tapauksessa. Tässä työssä validoidaan TROPOMIn NO2-mittaukset käyttäen Helsingin Kumpulassa sijaitsevan Pandora-referenssi-instrumentin mittauksia. Tämän lisäksi TROPOMIn herkkyyttä lähellä maanpintaa tapahtuville pitoisuusvaihteluille arvioidaan vertaamalla sen mittauksia Kumpulassa sijaitsevan in situ -ilmanlaatuaseman mittauksiin. Lopuksi arvioidaan TROPOMIn ja Pandoran mittausten ja niiden välisen vastaavuuden riippuvuutta rajakerroksen paksuudesta ja siellä vallitsevasta tuulesta. Tutkimus ajoittuu 19.4.–29.9.2018 väliselle ajalle. Vertailuissa tarkastellaan erityisesti instrumenttien mittausten välisiä eroja (TROPOMI – Pandora) ja niiden keskiarvoa, erojen suhteellisia arvoja (suhteessa Pandoraan) ja niiden mediaania, sekä mittausten välistä Pearsonin korrelaatiokerrointa. Näiden tunnuslukujen riippuvuutta ajasta tarkastellaan eripituisia aikavälejä kattavien aikasarjojen avulla. Tulosten mukaan TROPOMIn ja Pandoran mittausten välinen Pearsonin korrelaatiokerroin on 0,66 ja niiden välisten suhteellisten erojen mediaani 12,1 %. Tätä voidaan pitää hyvänä tuloksena, sillä TROPOMIlle asetettu suhteellisten erojen tavoite on enintään 30 %. Positiivinen arvo on kuitenkin epätyypillinen kaupungissa tehtävälle validoinnille, mikä voi tarkoittaa Kumpulan alueen edustavan pitoisuuksiltaan enemmän tausta-aluetta kuin tyypillistä kaupunkiympäristöä. Mittausten välisen korrelaation havaittiin riippuvan rajakerroksen paksuudesta, mikä voi johtua TROPOMIn tulkinta-algoritmin käyttämästä NO2:n pystyprofiilista tai paksussa rajakerroksessa tapahtuvasta voimakkaammasta sekoittumisesta. Asian selvittäminen edellyttää kuitenkin lisätutkimuksia. Lopuksi TROPOMIn todettiin olevan herkkä viikon- ja päivänsisäisille pitoisuusvaihteluille Pandora-instrumenttiin verrattuna, mikä on lupaava tulos TROPOMIn mahdollisten ilmanlaadun seurantaan liittyvien sovellusten kannalta. TROPOMIn parantuneen resoluution vaikutus on tutkimuksessa nähtävissä aiempiin instrumentteihin verrattuna parantuneena korrelaationa ja positiivisempina mittauseroina, sekä herkkyytenä päivänsisäisille pitoisuusvaihteluille. TROPOMIn voidaankin odottaa tulevaisuudessa lisäävän satelliittipohjaisten NO2-mittausten käyttökohteita.
  • Lobo, Hannah (2021)
    The lidar depolarisation ratio is used for aerosol categorisation as it is indicative of aerosol shape. Commonly, depolarisation ratio is measured in short term studies at short wavelengths such as 355 nm and 532 nm. The depolarisation ratio has a spectral dependency and so exploring values at longer wavelengths could be valuable for future studies. Here, aerosol depolarisation ratio at 1565 nm is measured across Finland’s ground based remote sensing network over a four year period. The Halo Photonics StreamLine Doppler lidars instruments were found to be stable over long time periods and cloud based calibration was used to correct for the bleed though. The depolarisation ratio of elevated aerosol layers was compared to boundary layer aerosol. A higher average depolarisation ratio was found for elevated aerosol with the exception of boreal forest sites in the summer months where values were similar. Elevated aerosols over Finland were found to originate mostly from the Arctic, Europe, Russia and North America using aerosol transport models. Four case studies were looked at in more detail: Saharan dust with a depolarisation ratio of 0.249 ± 0.018, pollen with a depolarisation ratio of 0.207 ± 0.013, anthropogenic pollution with a depolarisation ratio of 0.067 ± 0.009, and a mixed layer with a depolarisation ratio of 0.152 ± 0.019 thought to be pollen and smoke. Based on this study, Halo Doppler Lidar can be used to measure elevated aerosol at 1565 nm in the long term. Future studies could use 1565 nm depolarisation ratio alongside commonly used shorter wavelengths to aid aerosol categorisation.
  • Koivula, Kalle-Matti (2023)
    In this thesis we try to find the measurement accuracy of our dronebound wind measurement setup and if the quality of the measurements is high enough for operational usage. The thesis goes over the most important theoretical concepts concerning effects of wind in the boundary layer. In the thesis we analyze wind data gathered by a drone-bound anemometer, and introduce a direct method of measuring wind with a UAV. The data includes stationary wind data gathered at height of 30 metres, as well as vertical wind profiles to 500 metres above ground level. The data is compared to reference data from a 30 metre wind mast and automatic radiosoundings. The measurements were conducted in Jokioinen, Finland between the 2nd of September 2022 and 10th of October 2022. Total of 20 measurement flights were conducted, consisting of 14 stationary wind measurements and six wind profile measurements. We found out the stationary wind measurement quality to be comparable with earlier studies. The vertical wind profile measurements were found to be hard to analyze, as the reference measurement was not as compatible as we had hoped for. The difference between automatic radiosoundings and our profile measurements was distinctly greater than the difference between the stationary drone and wind mast measurements. Lastly some optimization and improvements to the measurement arrangement are discussed. The application of these improvements and modifications will be left as future endeavour for some willing individual.
  • Karvonen, Anni (2023)
    Growing population in cities increases the share of global greenhouse gas (GHG) emissions coming from urban areas. To understand the energy, water and GHG emission exchanges between urban surface and the atmosphere, modelling is a necessary tool. This is because measurements are not always available from all the different urban environments. In the case of carbon dioxide CO2 exchange, modelling is needed to provide new information on the different anthropogenic and biogenic components over various land uses. In this thesis, the aim was first to compare energy and CO2 fluxes from an urban land surface model called Surface Urban Energy and Water Balance Scheme (SUEWS) against measurements from suburban neighbourhood in Minneapolis, USA. The second aim was to study differences in the fluxes between years in the area. The model is parameterized with surface information about the study area, which is divided into two grids, residential and recreational area. The meterological forcing data are derived from ERA5. In the first part of the study, SUEWS is run in the area from June 2006 to April 2009, and the fluxes of latent QE and sensible QH heat and CO2 are compared against eddy covariance (EC) measurements conducted in the same area in the same time period. The diurnal cycles of CO2 show that the model is able to catch the daytime values well in every season for both study area grids, but night-time positive values are difficult especially for recreational area in autumn and winter. The model also underestimates the emissions in every season in the morning and evening rush hour peaks, which are caused by traffic. Overall, CO2 flux is simulated reasonably well. The model performs very well against QE measurements, but more poorly against QH. The second part of the study extended time period from January 1995 to April 2009 to analyze the long-term variation of fluxes. These were studied independently without the measurement comparisons. Annual cumulative sum of CO2 showed great variation between the years, and the highest value was emissions of 1135 gCm-2year-1 in 2001 and the lowest 600 gCm-2year-1 in 2005 from the residential area. Annual cumulative sums of QE did not show so much variation. The reason behind the differences between these two years was the great variation of photosynthesis. In 2001 air temperature restrained photosynthesis when surface conductance and its environmental factors were further studied. No statistical difference between the years 2001 and 2005 was though found.
  • Hamberg, Sanna (2023)
    Tutkielmassani tutkin Suomessa esiintyneiden voimakkaiden keski- ja puuskatuulien suunta- ja vuodenaikajakaumia vuosilta 2010-2019. Työssä käyttämäni tuulihavainnot keräsin 19 sääasemalta Suomesta, joista yhdeksän oli sisämaa-asemia, kahdeksan oli meri- tai rannikkoasemia ja kaksi oli tunturiasemia. Työni tavoitteena oli selvittää, mistä suunnasta ja milloin voimakkaimmat tuulet esiintyvät sekä onko voimakkailla tuulilla alueellisia yhtäläisyyksiä suunta- ja vuodenaikajakaumissa. Työssä tutkin aluksi jokaisen aseman tuulihavaintojen voimakkainta kahta prosenttia eli noin 1500-1750 havaintoa. Vuodenaikoja esitellessä käytin myös 100 ja 30 voimakastuulisinta päivää 10 vuoden havaintojaksolta, jotta pystyin vertailemaan vuodenaikajakaumia kaikista voimakkaimmissa tuulissa. Kuukausijakaumissa käytin 100 voimakastuulisinta päivää. Lopuksi vertailin suuntia eri vuodenaikoina, jolloin rajasin jokaisen aseman kunkin vuodenajan tuulihavainnot voimakkaimpaan prosenttin. Meri- ja rannikkoasemilla havaitsin eniten voimakkaita keskituulia syksyllä ja talvella, sisämaassa loppusyksystä ja alkukeväällä sekä Pohjois-Suomessa puolestaan talvella ja alkukeväällä. Nämä voimakkaat keskituulet aiheutuvat talven voimakkaista matalapaineista sekä keväällä voimistuvasta turbulenssista. Sisämaa-asemilla havaitsin myös kesäkuussa voimakkaita keskituulia, joiden aiheuttajana on saattanut olla edellä mainittujen sijasta mesoskaalan konvektiivinen ilmiö. Voimakkaiden tuulten suuntajakaumissa eniten tuulia puhalsi etelän ja lännen väliltä. Sisämaassa kaikkein voimakkaimmat tuulet puhalsivat siitä suunnasta, mistä puhalsi suurin osa kaikista voimakkaista tuulista. Meri- ja rannikkoasemilla kaikkein voimakkaimmat keski- ja puuskatuulet tulivat luoteesta ja idästä.
  • Viljamaa, Iiris (2019)
    Säätutkia käytetään sadealueiden liikkeiden ja sateen voimakkuuden arvioimisen. Säätutkan toimintaperiaate perustuu sille, että sen lähettämä mikroaaltopulssi siroaa ilmakehässä olevista partikkeleista kuten vesipisaroista ympäristöönsä, jolloin pieni osa lähetetystä pulssista heijastuu takaisin kohti tutkaa. Tutka vastaanottaa palanneen pulssin ja arvioi sen perusteella sadealueita. Säätutkat ovat mittalaitteita, jotka vaativat toimiakseen säännöllistä huoltoa ja mittaustulosten validointia. Säätutkan kalibrointi on monessa mielessä haasteellista. Tutka on kaukokartoituslaite, jonka keräämä data kattaa alueen aina 250 km säteelle tutkasta. Se ei mittaa suoraan sademäärää, kuten sademittarit yleensä, vaan arvio sen välillisesti tutkaheijastuvuuden kautta. Tämän tutkimuksen tarkoitus on tarkastella uutta mahdollista kalibrointimenetelmää. Uusi menetelmä käyttäisi pienoissadetutkaa MRR-2 vertailukohtana. Myös MRR-2 mittaa tutkaheijastuvuustekijää, joten se voisi olla hyvä vertailupari säätutkalle. Tasaisen sateen otoksessa vuosien 2015-2018 kesäsateissa säätutkan WRM200 ja pienoissadetutkan MRR-2 vertailupisteihin sovitetun suoran yhtälö on 𝑍(𝑊𝑅𝑀200) = 0.83 𝑍(𝑀𝑅𝑅−2) + 2.01, jossa 𝑍(𝑊𝑅𝑀200) on säätutkan ja 𝑍(𝑀𝑅𝑅−2) on pienoissadetutkan mittaama tutkaheijastuvuustekijä. Tasaisessa sateessa otoksen RMS-virhe on 3,36 dB. Konvektiivisen sateen otoksessa vastaava yhtälö on 𝑍(𝑊𝑅𝑀200) = 0.77 𝑍(𝑀𝑅𝑅−2) + 3.70 ja RMS-virhe 5,36 dB. Tasaisessa sateessa verrattavuus on konvektiivisessa sateessa tehtyä vertailua parempi. Tutkimus sisältää pohdintaa tuloksiin vaikuttavista tekijöistä sekä pohdintaa MRR-2:n soveltuvuudesta vertailulaitteeksi säätutkan kalibrointiin. Tutkimuksen pohjalta vaikuttaa siltä, että vaikka vertailunasettelu pyritään tehdä mahdollisimman vakaaksi, ei virhetekijöitä voida sulkea pois. Näin ollen tämän kaltaisella asettelulla ei voida suorittaa tarkkaa säätutkan kalibrointia.
  • Skyttä, Aurora (2021)
    Ilmakehän aerosolihiukkasilla on vaikutuksia maapallon säähän ja ilmastoon ja siksi niiden syntyä ja toimintaa pyritään tuntemaan yhä paremmin. Jos niiden rakenneosaset tunnetaan hyvin, voidaan myöskin aerosolihiukkasten ominaisuudet oppia tuntemaan paremmin. Mallinnusten ohella kokeelliset mittaukset ovat yksi keino saada lisää tietoa ilmakehän pienten rakenneosasten toiminnasta. Tässä työssä tutkin voidaanko differentiaalisella liikkuvuusanalysaattorilla (differential mobility analyzer, DMA) mitata α-pineenin hapetustuotteiden eri rakenteita. α-pineeni ja otsoni reagoivat virtausputkessa ja reaktioissa muodostuneet hapetustuotteet varattiin klusteroimalla ne elektrospraylla tuotettujen varattujen reagenssi-ionien kanssa. Näin syntyneiden varattujen klustereiden liikkuvuus ja massa-varaus-suhde mitattiin. Analysointiprosessissa käytin Matlab-pohjaista ToFTools-ohjelmaa ja INAR:in postdoc Lauri Ahosen tekemää Flat-DMA-analysointiohjelmaa. Tunnistin ToFToolsilla α-pineenin hapetustuotteista ja reagenssi-ionista koostuvien klustereiden kemiallisen koostumuksen niiden massan perusteella ja sovitin niiden liikkuvuusspektrin piikkien sisään Flat-DMA-analysointiohjelmalla piikkejä DMA:n maksimiresoluutiolla. Sovitettujen piikkien määrä kertoo siitä, kuinka monta rakennetta kullakin klusterilla mahdollisesti voisi olla. Mittauksissa havaittiin useita yhdisteitä, joita voitiin teorian perusteella olettaa syntyvän. Kuitenkin tunnistettiin myös sellaisia yhdisteitä, joita ei odotettu muodostuvan α-pineenin ja otsonin välisissä reaktioissa. On mahdollista, että yhdisteet on tunnistettu väärin tai mittauksiin on päässyt epäpuhtauksia. Näiden mittausten perusteella ei voida vielä varsinaisesti tehdä johtopäätöksiä siitä, miten monta isomeeria α-pineenin hapetustuotteilla on. Tulosten perusteella käytetty reagenssi-ioni vaikuttaa merkittävästi mitattujen rakenteiden määrään, joten jotta α-pineenin hapetustuotteiden rakenteita voitaisiin tutkia, täytyisi kunkin reagenssi-ionin vaikutus tuntea paremmin. Myöskin jotta rakenteiden määrää voitaisiin tutkia luotettavammin, täytyisi DMA:n resoluution olla huomattavasti nykyistä parempi. Nykyisellä resoluutiolla isomeerien määrän arviointi oli hankalaa eikä lopputuloksista voida olla varmoja.