Browsing by master's degree program "Ilmakehätieteiden maisteriohjelma (Atmospheric Sciences)"
Now showing items 41-58 of 58
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(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.
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(2024)Maaperän keskilämpötila on noussut viime vuosikymmeninä pohjoisilla alueilla kahdesta kuuteen kertaa muita leveysasteita nopeammin, ja muuttuvien lämpö- ja kosteusolosuhteiden myötä myös kasvihuonekaasupäästöissä on havaittu muutoksia. Erityisesti pohjoisten soiden päästöt ovat ajankohtainen tutkimusaihe. Viimeaikainen tutkimus korostaa suon pieneliöiden vaikutusta hiilipäästöihin ja ehdottaa, että eliöyhteisöjen muutoksilla voi olla aiemmin ymmärrettyä tärkeämpi merkitys päästöjen synnyssä. Tässä opinnäytetyössä tutkin kahden eliöyhteisön, sammalpunkkien ja kuoriamebojen, yhteyksiä suon vedenpinnan korkeuteen, lämpötilaan ja happipitoisuuteen sekä hiilidioksidi- ja metaaninvoihin. Erottelen mittauskammioiden vierestä ottamistani pintanäytteistä punkki- ja amebaesiintymät, ja vertaan niiden runsautta ja lajirikkautta ympäristö- ja kaasumuuttujiin. Tutkimuksessa huomaan, että kahden vierekkäisen suon lajisto ja ympäristö- sekä kaasumuuttujat ovat huomattavan erilaisia. Vertailen myös punkkien ja amebojen sopivuutta näiden muuttujien prokseiksi eli epäsuoriksi indikaattoreiksi. Amebat ovat paleoekologisessa tutkimuksessa vakiintuneempi eliöryhmä, mutta tutkimukseni pohjalta näyttää siltä, että myös punkkiyhteisöt voivat kertoa meille nykyisistä ja menneistä elinympäristöstä ja hiilipäästöistä. Punkkiyhteisöjen korrelaatio vedenpinnan korkeuden kanssa on liki samaa luokkaa kuin amebojen ja vedenpinnan korkeuden. Erityisesti kuivemman ja ravinneköyhemmän suotyypin metaanivoiden ja sammalpunkkiyhteisön välillä on merkittävä korrelaatio, ja tätä yhteyttä olisi jatkossa mielenkiintoista tutkia tarkemmin. Johtopäätöksenä esitän, että sammalpunkkien käyttö ympäristömuuttujien ja hiilivoiden proksina ja siirtofunktioiden kehittäminen punkkiyhteisöille voisi laajentaa paleoekologisen tutkimuksen näkökulmaa ja tuoda lisätietoa pieneliöyhteisöjen merkityksestä kasvihuonepäästöjen synnyssä.
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(2023)Ozone, an important and ubiquitous trace gas, protects lives from harm of solar ultraviolet (UV) radiation in the stratosphere but behaves as a toxic compound in the troposphere to living organisms. Also, tropospheric ozone is a vital oxidant or source of daytime oxidant (i.e., OH radical) for e.g., different volatile organic compounds (VOCs). Affecting global radiation balance directly or indirectly by acting as cloud condensation nuclei and having negative impact to human health, aerosols are widely studied for over a century. Highly oxygenated organic molecules (HOM) were proved to be a large source of secondary organic aerosol (SOA) and their oxidation formation pathways from VOCs can also trigger the production of ozone once involving NOx (=NO+NO2) and UV light. The highly nonlinear relationship among ozone, NOx, and VOCs (O3-NOx-VOC sensitivity or O3 formation sensitivity) has been researched since last century. The complex system was recently reflected during COVID-19 lockdowns: reduction of NOx increased the ozone production. This is because the system was in VOC-limited regime, where reducing VOCs is the most efficient way to reduce O3. However, the determination of O3 formation regimes (either VOC-limited or NOx-limited) is challenging in different environmental conditions. The intrinsic connection between HOM and O3 formation provide a new insight: the proportions of VOCs and NOx not only affect the O3 formation regimes but also impact the distribution of HOM species. Therefore, in this study, we try to unveil the indicating role of HOM species on the O3 formation sensitivity by chamber experimental works with a nitrate chemical ionization mass spectrometer (CI-APi-TOF) and gas monitors. Injected NOx and VOCs step by step, the experiments were designed to make the atmosphere-mimicking system change between those two regimes. The ratio between HOM-dimers and HOM organic nitrate monomers was selected as the indicator for O3 formation sensitivity due to their closely connected chemical reactions, involving peroxy radicals. Furthermore, a simple box model was developed for simulating chamber results and obtaining O3 isopleths to visually show the O3 formation regimes. Through experimental and model results, it can be inferred that ratios below 0.2 consistently correspond to the VOC-limited regime, whereas ratios above 0.5 consistently correspond to the NOx-limited regime. This study demonstrates that the ratio based on HOM species could additionally indicate the O3 formation sensitivity of ambient air when we use CI-APi-TOF to investigate the chemical compounds and aerosol formation, helping to elaborate the O3 pollution in the real troposphere.
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(2024)Supercells are thunderstorms characterized by a persistently rotating updraft, which is separated from, and in quasi-steady state with the downdraft. The structure of a supercell allows for long-lived thunderstorms, capable of producing severe weather such as significant hail (hail with a diameter >5 cm) and tornadoes. Despite their relative rarity, supercells are responsible for a disproportionate share of thunderstorm related hazards and damage. Although uncommon at high latitudes, supercells do occur in Finland, where documented cases have led to severe weather events and substantial damage. The goal of this study is to improve our understanding on the meteorological environment in which supercells in Finland occur. Specifically, we aim to discriminate between the meteorological environment of supercell thunderstorms and ordinary thunderstorms in Finland. This is done by examining how kinematic and thermodynamical parameters from proximity soundings between both groups differ. Additionally, we inspect the difference in meteorological environments of significant hail-producing supercells (acronym HAIL) and tornado-producing supercells (acronym TOR) environments. The results indicate that bulk wind shear in various levels, as well as effective bulk wind shear (the bulk wind shear over the unstable layer), are strong discriminators between supercell and ordinary thunderstorm environments in Finland. Composite parameters such as the Energy Helicity Index (EHI) and Supercell Composite Parameter (SCP) also show some utility in distinguishing supercell and ordinary thunderstorm environments. Equilibrium Level (EL) and low-level Convective Available Potential Energy (CAPE) stand out as significant discriminators between significant hail-producing and tornado-producing supercell environments, while Lifting Condensation Level (LCL) and low-level humidity appear to show critical threshold values that may help distinguishing significant hail-producing supercell and tornado-producing supercell environments. Interestingly, the ratio of low-level CAPE to CAPE discriminates very strongly between significant hail-producing supercell and tornado-producing supercell environments. Composite parameters and Storm Relative Helicity (SRH) exhibit very limited utility in differentiating between significant hail and tornado-producing supercell environments in Finland.
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(2023)Norway spruce (Picea abies (L.) Karst.) is one of the economically most important tree species in Finland. It is known to be drought-sensitive species and expected to suffer from the warming climate. In addition, warmer temperatures benefit pest insect Eurasian spruce bark beetle (Ips typographus L.) and pathogen Heterobasidion parviporum, which both use Norway spruce as their host and can make the future of Norway spuce in Finland even more difficult. In this thesis, adult Norway spruce mortality was studied from false colour aerial photographs taken in years between 2010 and 2021. Dead trees were detected from the photos by visual inspection, and mortality was calculated based on the difference in the number of dead trees in the photos from different years. The aim was to find out if Norway spruce mortality in Finland had increased over time, and what were the factors that had been driving tree mortality. The results indicate that tree mortality was the highest in the last third of the studied 10-year period, so it was concluded that tree mortality had increased over time. Various possible tree mortality drivers were analysed and found to be connected to tree mortality. Each driver was analysed individually by testing correlation with tree mortality. In addition, linear regression analysis and segmented linear regression with one breakpoint were used with the continuous variables. Increased tree mortality correlated with higher stand mean age, mean height, mean diamater, and mean volume, supporting the findings in earlier research. Mortality was connected to the proportion of different tree species in the stand: the higher the proportion of spruce, the higher the mortality, and the higher the proportion of deciduous trees, the lower the mortality. Of different fertility classes, tree mortality was the highest in the second most fertile class, herb-rich heat forest, and mortality decreased with decreasing fertility. Dead trees were also found to be located closer to stand edges than the stand centroid. Increased temperature resulted in increased mortality. Increased vapour pressure deficit (VPD) and drought, which was analysed with Standardized Precipitation Evapotranspiration Index (SPEI) of different time scales, were also connected with increased tree mortality. Further research is required for understanding and quantifying the joint effect of all the interacting mortality drivers. Nevertheless, it seems that for Norway spruce, the warmer future with increased mortality is already here, and it should be taken into consideration in forest management. Favouring mixed stands could be one of the solutions to help Norway spruce survive in the warming climate.
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(2022)Sea-ice dynamics is becoming increasingly essential for the modelling warming climate as the extent and thickness of the ice cover are decreasing along with increasing drift speeds and mechanical weakening. The description of the sea-ice dynamics involves an enormous variety of spatial and temporal scales from meters to the scale of the Arctic Basin and from seconds to years in the geophysical approaches. The complex coupled spatio-temporal scaling laws prohibit the commonly utilized procedures for scale linkage of ice mechanics. Currently, deformation scaling presents one of the principal open questions in sea ice dynamics for which the thesis aims to provide observational analysis. The high-resolution ship-radar imagery gathered during the MOSAiC expedition from October 2019 to September 2020 for which deformation component rates were calculated to generate a seasonal deformation time series. Current research of deformation scaling commonly relies on satellite imagery and drift buoys for which the spatial and temporal resolutions often tend to be considerably lower than for the ship-radar data. The formerly observed dominant deformation mode of shear and the strong spatial correlation of divergence and shear in the Arctic sea ice were confirmed with no signs of seasonal variation. The temporally averaged deformation variations were found to coincide with satellite derived deformation events rather poorly. A strong length scale dependence of deformation was confirmed in the ship-radar data. The spatial scaling law exponents were found to show unexpectedly high values with the behaviour of both spatial and temporal scaling law exponents disobeying the previously observed large-scale characteristics. The seasonal variation of both scaling law exponents were found to exhibit the commonly observed trends following the progression of total deformation rate. The obtained results showed unexpected values and behaviour for the deformation scaling law exponents, which was suggested to be due to the technical faults in the ship-radar data. The faults were often spatially local and lasted merely for a single time step leading to a possible increase in the localization and intermittency of the deformation rates. Additionally, the new ice conditions of the Arctic Ocean and drift route along the Transpolar Drift were suggested as a possible physical source of the unexpected results. Further studies with different methodologies were suggested for the verification and possible the dismissal of the unexpected results.
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(2024)Fog has a significant impact on society, by making transportation and aviation industries difficult to operate as planned due to reduced visibility. Studies have estimated that 32 % of marine accidents, worldwide, and 40 %, in the Atlantic Ocean, took place during dense sea fog. Therefore forecasting fog accurately, and allowing society to function, would help mitigate financial losses associated with possible accidents and delays. However, forecasting the complex fog with numerical weather prediction (NWP) models remains difficult for the modelling community. A NWP model typically operates in the resolution of kilometres, when the multiple processes associated with fog (turbulence, cloud droplet microphysics, thermal inversion) have a smaller spatial scale than that. Consequently, some processes need to be simplified and parametrised, increasing the uncertainty, or more computational power is needed to be allocated for them. One of these NWP models is HARMONIE-AROME, which the Finnish Meteorological Institute develops in collaboration with its European colleague institutes. To improve the associated accuracy, a brand new, more complex and expensive, option for processing aerosols in HARMONIE-AROME, is presented. This near-real-time (NRT) aerosol option integrates aerosol concentrations from Copernicus Atmospheric Monitoring Services' NRT forecast into HARMONIE-AROME. The statistical performance of the model's sea fog forecast in the Baltic Sea was studied in a case study using marine observations. The quantitative metric, proportion score, was studied. As a result, a forecast using the NRT option showed a slight deterioration in visibility (0.52 versus 0.59), a neutral improvement in cloud base height (0.52 versus 0.51), and a slight deterioration in 2-meter relative humidity (0.73 versus 0.76) forecasts with respect to the reference option. Furthermore, the score in general remained weak against observations in the case of visibility and cloud base height. In addition, based on qualitative analysis, the spatial coverage of the forecasted sea fog in both experiments was similar to the one observed by the NWCSAF Cloud Type-product. In total, the new aerosol option showed neutral or slightly worse model predictability. However, no strong conclusions should be made from this single experiment sample and more evaluations should be carried out.
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(2024)Pohjois-Suomen tuntureilla tapahtuu useita lumivyöryjä vuosittain. Ihmishenkiä menetetään kuitenkin harvoin. Vuosituhannen vaihteessa kaksi henkilöä kuoli ja yksi loukkaantui vakavasti lumivyöryonnettomuuksissa Pohjois-Suomessa. Tämän seurauksena Ilmatieteen laitoksella kehitettiin lumivyöryennuste, jota on laadittu Pohjois-Suomeen talvisin vuodesta 2003 lähtien. Vuoden 2024 tammikuussa kaksi hiihtovaeltajaa eksyi huonossa säässä lumivyörymaastoon ja menehtyi lumivyöryssä. Viimeisten vuosikymmenien aikana lumivyöryennustusmenetelmiä on kehitetty maailmalla aktiivisesti. Lumivyörypalveluiden tarve on lisääntynyt luontoliikunnan ja vapaalaskun voimakkaan lisääntymisen seurauksena. Myös muuttuva ilmasto aiheuttaa tarvetta lumivyörypalveluiden kehittämiselle. Suomi liittyi mukaan eurooppalaiseen lumivyöryvaroituspalveluun (EAWS) vuonna 2018 sitoutuen samalla tavoittelemaan yhtenäistä, tuoreeseen tutkimustietoon perustuvaa lumivyörypalvelua. Ilmatieteen laitoksen lumivyöryennusteen suhteen tämä ei ole toteutunut toivotulla tavalla. Tutustumalla Ruotsin ja Norjan lumivyörypalveluiden toimintaan, tarkastelemalla lumivyöryjen laukeamiseen vaikuttavien säätapahtumien toistuvuutta Lapissa sekä keskustelemalla alan asiantuntijoiden kanssa kartoitin, miten Ilmatieteen laitoksen lumivyöryennuste saataisiin vastaamaan nykyaikaisia tavoitteita. Suurin puute nykyisessä Ilmatieteen laitoksen lumivyöryennusteessa on maastohavaintojen vähäisyys. Analysoimalla säähavaintoja arvioin, että havaintokierroksia lumivyörymaastossa on tehtävä lumivyörykaudella keskimäärin 3 kertaa viikossa. Merkittävin lumivyörymaaston olosuhteita muuttava tekijä on tuuli ja sen kuljettama lumi. Muutaman tunnin tuisku voi lisätä kuormaa lumipeitteen päällä jopa yli 500 kg/m². Yhteistyössä FINLAV- ja CAA-koulutettujen (Suomen lumivyörykoulutusja Canadian Avalanche Association) lumivyöryasiantuntijoiden kanssa Ilmatieteen laitoksen meteorologit voisivat laatia EAWS-tavoitteiden mukaisen lumivyörytiedotteen. Yhteistyöllä Pohjoismaiden kanssa voitaisiin löytää Suomen oloihin parhaimmat työkalut maastohavaintojen keruuseen, analysointiin, mallintamiseen ja tiedon jakoon. Lopputuloksena saataisiin Pohjoismaihin yhtenevät lumivyörypalvelut, mikä tekisi talvisessa erämaassa liikkumisen turvallisemmaksi niin kotimaassa kuin ulkomaillakin. Rahoituskysymystä tarkastelin Liikenne- ja viestintävirasto Traficomin ihmishengen hinnan arvion pohjalta. Liikenneturvallisuutta lisäävä hanke katsotaan kannattavaksi, jos 2,4 miljoonan euron panos tuksella pelastetaan yksikin ihmishenki. Tämä tarkoittaisi vastaavasti, että 240000 euron rahoitus lumivyörypalveluun vuosittain kannattaa, jos sillä pelastetaan yksikin ihmishenki 10 vuoden aikana.
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(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.
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(2024)The planetary boundary layer (PBL) is a layer of the atmosphere directly influenced by the presence of Earth's surface. In addition to its importance to the weather and climate systems, it plays significant role in controlling the air pollution levels and low-level heat conditions, thereby directly influencing the general well-being. While the modification of the boundary layer conditions by varying atmospheric forcings has been widely studied and discussed, it remains unknown what the dominant states of the PBL variation in response to this modification are. In this study, the dominant boundary layer types in both daytime and nighttime layers are examined. To understand the factors contributing to the development of these layers, weather regimes in the northern Atlantic-European region are considered. Machine learning techniques are utilized to study both the boundary layer and the large-scale flow classes, with an emphasis on unsupervised learning methods. It was found that the boundary layers in Helsinki, Finland, can be categorized into four daytime and three nighttime boundary layers, each characterized by the dominant turbulence production mechanism or the absence thereof. During the daytime, layers driven by both mechanical and buoyant turbulence are observed in summer, autumn, and spring, while individually buoyancy-driven layers occur in summer and winter, and individually mechanically-driven layers emerge in autumn, winter, and spring. Additionally, a layer characterized by overall reduced turbulence production is present throughout all seasons. During the nighttime, all three boundary layer types---individually buoyancy-driven, individually mechanically-driven, and stable layer---are observed in all seasons. Each boundary layer type exhibits season-specific variations, whereas daytime and nighttime boundary layers driven by the same mechanisms reflect the diurnal cycle of their relative intensities. The analysis revealed that the weather regimes producing cyclonic and anticyclonic flow anomalies over southern Finland collectively influence the boundary layer conditions, whereas the impact of individual weather regimes remains relatively small. Large-scale flow variation is associated with changes in the boundary layer dynamics through alterations in surface radiation budget (cloudiness) and wind conditions, thereby influencing the relative intensities of mechanical and buoyant turbulence production. However, inconsistencies in the analysis suggest that additional mechanisms, such as mesoscale phenomena, must also contribute to the development of the observed boundary layer types.
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(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.
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(2023)Zooplankton are an important link in marine pelagic food webs as they transfer energy from primary producers to higher trophic levels such as planktivorous fish. They migrate vertically in the water column, ascending to feed near the surface at night and descending to hide from visual predators for the day (diel vertical migration, DVM). Zooplankton are detected with Acoustic Doppler Current Profilers (ADCPs). These devices were developed for measuring water currents using acoustic pulses, a technique which requires particles such as zooplankton in the water column to scatter the sound. As a by-product of the velocity measurements, it provides information of these scatterers as echo intensity. This method has been used in researching zooplankton DVM, however, not in the northern Baltic Sea prior to this study. In this thesis, the data processing steps required to analyze echo intensity were examined for the specific environment of the Finnish Archipelago Sea. A one-year-long time-series was processed and averaged seasonally to investigate different patterns in zooplankton DVM. Vertical velocity data were used in estimating migration speed, and available reference measurements were combined to the data to examine the environmental factors affecting zooplankton DVM. Synchronized DVM was observed especially in autumn, however, indications of other migration patterns such as unsynchronized and reverse migration were detected during summer and winter, respectively. The primary cue behind zooplankton DVM was light, but additional contributing factors such as phytoplankton and currents were identified and discussed. The maximum migration speeds detected were approximately 10 cm/s downwards and 4 cm/s upwards. ADCP data are a good indicator of zooplankton migration in the northern Baltic Sea and in the future, it could prove beneficial in zooplankton monitoring and biomass estimates.
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(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.
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(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.
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(2024)Due to its long lifetime and relatively low variability compared with its background values, it is of great significance to precisely measure the concentration of CO2 in the atmosphere. In the high latitude regions, permafrost and boreal forest serve as large carbon reservoirs. Capturing the carbon concentration there helps us understand the process of climate change and provide accurate data to the carbon flux models. However, the measurement there is facing significant challenges. Sparse observation coverage and low-quality data are still major problems to be solved. In this thesis, we are looking into these problems from satellite-based OCO-2 XCO2 retrievals in high latitude regions. XCO2 data acquired above 45°N were used to compare the version updates, validate the results with ground-based TCCON site data and come up with a colocation method for boreal areas trying to tackle the issue caused by slant solar radiation. The comparison of version 10 and version 9 datasets shows improvements of version 10 in data volume and precision level. Yet the changes are not as significant for sites near polar areas. It also reveals that the current advances mainly focus on reducing systematic errors. In the validation with TCCON data, from OCO-2 displays lower seasonal fluctuations. The quality filters are shown to be too tight for boreal sites in filtering lower values. It provides information for new approaches when adjusting the filters. The global distribution of averaged XCO2 reveals that standard deviation is higher for nadir mode land observation in mountain areas. This might be lowered with an improved surface pressure correction method. Averaging kernel correction is applied when comparing with TCCON to standardize the sensitivity profile. It enhances the accuracy of the results and also stresses the significance of integration scheme. A new colocation method is implemented for better locating of TCCON observations in high latitudes but did not return good results. Further adjustments for the algorithm and tests in more areas are needed.
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Variability in carbon dioxide and heat fluxes in Minneapolis determined using land surface modelling (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.
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(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.
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(2023)Antarctic Bottom Water (AABW), a water mass that sinks to form the deepest limb of the meridional overturning circulation (MOC), is a key control on the ventilation of the Southern Ocean as well as global exchanges of heat, freshwater, and carbon. Sources of this water mass include latent heat polynyas found in Prydz Bay, East Antarctica, which expose the Southern Ocean to the colder atmosphere and are important sources of high salinity shelf water (HSSW). This water mass is the precursor to Dense Shelf Water (DSW) which can be exported from the continental shelf to form Antarctic Bottom Water (AABW). In this study, Lagrangian particle tracking of water masses within Prydz Bay was used to investigate the roles of seasonality, bathymetry, and the presence of other water masses on the mechanisms of water mass transformation (WMT), a series of key processes in the MOC. Online particles were released weekly within the Prydz Bay polynya region in a 10 km resolution simulation of the Whole Antarctic Ocean Model (WAOM10) and their forward trajectories were tracked for one year. Results highlight the export of Prydz Bay water along the westward Antarctic Slope Current (ASC). Cluster analysis of the results shows a winter signal for bottom water forming particles. When advected beneath the ice shelf, polynya water can mix with fresh meltwater, becoming less dense and forming ice shelf water (ISW). After this polynya-originating water departs the ice shelf again, its increased buoyancy can make future AABW formation less likely. This study confirms that the presence of modified circumpolar deep water (mCDW) can play a controlling factor in rates of DSW export as bottom water. Results show export of DSW from the Prydz Channel and Cape Darnley, mixing either along or across isopycnals depending on the influence of other water masses and cross-slope flow. Interactions with the ASC and major topographic features including the Enderby Land projection and several underwater canyons appear to influence the export of water to the deep ocean. WAOM10 finds realistic ratios of AABW formation as compared with observational data and shows greater low-density water formation than other models.
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