Browsing by master's degree program "Ilmakehätieteiden maisteriohjelma (Atmospheric Sciences)"
Now showing items 21-40 of 59
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(2022)To evaluate whether CMIP6 models provide good simulation in Arctic sea-ice extent, thickness, and motion, selected 6 CMIP6 models are EC-Earth3, ACCESS-CM2, BCC-CSM2-MR, GFDL-ESM4, MPI-ESM1-2-HR, NORESM2-LM. For CMIP6 models and observations, seasonal cycle and the annual variation from 1979-2014 of sea-ice extent were studied, for sea-ice thickness and sea-ice motion, the Arctic is separated into three regions, geographical distribution, inter-annual variation from 1979-2014, seasonal cycle, and trend were studied. Then student t-test is used to evaluate whether the model output has a significant difference from observation, to select the best model(s). For sea-ice extent, EC-Earth3 is overestimating sea-ice extent, especially in winter, BCC-CSM2-MR model underestimates sea-ice extent, ACCESS-CM2, MPI-ESM1-2-HR, NorESM2-LM models perform the best. For sea-ice thickness, BCC-CSM2-MR underestimates sea-ice thickness, EC-Earth3, ACCESS-CM2, and NORESM2-LM models are overestimating sea-ice thickness. GFDL-ESM4 and MPI-ESM1-2-HR have the best performance at sea-ice thickness simulation. For sea-ice motion, the MPI-ESM1-2-HR model overestimates sea-ice drifting speed all year round, ACCESS-CM2 model tends to overestimate sea-ice drifting speed in summer for region1 and region2, in region3 ACCESS-CM2 model mostly overestimate sea-ice motion except winter months. NorESM2-LM model has the best performance overall, and ACCESS-CM2 has the second-best simulation for region1 and region2. EC-Earth3 also has a satisfactory simulation for sea-ice motion. Models and observation also agree on common results for sea-ice properties: Maximum sea-ice extent occurs in March, and minimum sea-ice extent occurs in September. There's a decreasing trend of sea-ice extent. The Central Arctic and Canadian Archipelago always have the thickest sea ice, followed by the East Siberian Sea, Laptev Sea, and Chukchi Sea, Beaufort Sea. East Greenland Sea, Barents Sea, Buffin Bay, and the Kara Sea always have the thinnest sea ice. There's a decreasing trend for sea-ice thickness according to models, sea-ice is thicker in the Chukchi Sea and the Beaufort Sea than in Laptev and East Siberian seas. Winter sea-ice thickness is higher than in summer, and sea-ice thickness has a more rapid decreasing rate in summer than in winter. Laptev and the East Siberian Sea have the most rapidly sea-ice thinning process. Sea-ice thickness has seasonal cycle that maximum usually occurs in May, and minimum sea-ice thickness happens in October. For sea-ice motion, there's an increasing trend of sea-ice motion, and summer sea-ice motion has faster sea-ice motion than winter, Chukchi Sea, and the Beaufort Sea has faster sea-ice motion than Laptev and the East Siberian Sea. Corresponding with the comparatively faster-thinning in the Laptev and the East Siberian Seas simulated by models, there's also a faster increasing rate in the Laptev and the East Siberian Sea.
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(2023)The oxidation mechanisms of atmospheric organic compounds are an important puzzle piece for many atmospherically relevant topics, including but not limited to air quality and climate change. One poorly understood step in this oxidation process is peroxy radical recombination, in some conditions the most important sink reaction for peroxy radicals, which are formed in abundance due to gas phase reactions in the lower troposphere. After a few initial steps, the peroxy radical recombination reaction results in the ejection of O_2 leaving behind a pair of alkoxy radicals in close proximity. This reactive complex has three known reaction pathways: Hydrogen shift forming an alcohol and a carbonyl compound, radical recombination forming a ROOR dimer, and diffusive break-up forming two free alkoxy radicals. In this thesis, alkoxy bond scission followed by radical recombination resulting in the formation of a ROR is proposed as a fourth reaction pathway. To test the hypothesis, computational chemistry was used to determine alkoxy bond scission rates for radicals of atmospheric significance, and gas-phase oxidation experiments were realized on three peroxy radical precursor molecules to look for signs of ROR formation. More precisely, the Eyring equation was used to calculate the rate of alkoxy bond scission on a potential energy surface determined using density functionals, with corrections to electronic energy using coupled-cluster calculations. In the experiments, liquid phase alkenes were vaporized, and oxidized by O_3 in the gas phase, resulting in peroxy radical formation, after which the possible dimers were detected using a NO_3^- -atmospheric pressure chemical ionization time-of-flight mass spectrometer. A highly oxidized radical reaction partner was present in the chamber to improve the detectability of the formed dimers. The combined results of these two approaches suggest that the reaction pathway is possible in standard atmospheric conditions and may thus be important for a number of peroxy radicals.
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(2022)Tässä tutkielmassa tarkastellaan horisontaalisten gravitaatiovaihteluiden vaikutusta ilmakehän perusyhtälöihin sekä yksinkertaisen ilmakehämallin tuloksiin erilaisissa simulaatioissa. Työn motivointina oli tutkia putoamiskiihtyvyyden vaikutusta mallinnustarkkuuteen, koska se on yksi monista säänennustus- ja ilmastosimulaatioihin liittyvistä epätarkkuustekijöistä. Ilmakehän perusyhtälöt johdettiin aluksi uudelleen huomioimalla gravitaation vaihtelu vaakasuunnassa. Tämän jälkeen vastaavat yhtälömuutokset tehtiin SPEEDY-mallin lähdekoodiin, ja mallin avulla tehtiin simulaatioita gravitaatiovaihteluiden vaikutusten selvittämiseksi. Jotta tulosten analysointi olisi mahdollisimman helppoa, käytettiin simulaatioissa paljon yksinkertaistuksia. Näistä merkittävin oli mallimaapallon korvaaminen vesiplaneetalla. Yhtälömuutosten oikeellisuus mallissa verifioitiin yhden aika-askeleen kokeilla, minkä jälkeen muokatuille perusyhtälöille tehtiin suuruusluokka-analyysi. Analyysin perusteella gravitaatiovaihteluista aiheutuvat lisätermit olivat pääosin yhdestä kahteen kertaluokkaa yhtälöiden muita termejä pienempiä. Lopuksi tehtiin kymmenen vuoden simulaatioita, joissa tarkasteltiin niin sanotun normaaligravitaatiojakauman vaikutuksia mallin tuloksiin. Näissä kokeissa havaittiin, että meteorologisten suureiden anomaliat olivat pääosin maltillisia, mutta eivät merkityksettömän pieniä. Esimerkiksi tuulikentässä havaitut muutokset olivat suurimmillaan noin 2 m/s, kun taas lämpötila-anomaliat jäivät globaalisti alle puoleen asteeseen. Meridionaalisen kiertoliikkeen anomaliassa havaittiin puolestaan selkeä antisymmetria pallonpuoliskojen välillä: intertrooppinen konvergenssivyöhyke siirtyi päiväntasaajalta leveyspiirin 10°S tienoille, kun taas leveyspiirillä 5°N nousuliike heikkeni. Lisäksi länsituulet hidastuivat pohjoisen pallonpuoliskon keskileveysasteilla, mutta voimistuivat eteläisellä pallonpuoliskolla. Tulosten perusteella aiheen tutkimista kannattaa jatkaa myös tulevaisuudessa.
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(2023)Tässä työssä on karakterisoitu uudentyyppisen ilmaisimen toimintaa haihtuvien orgaanisten yhdisteiden vesimittauksissa. Karakterisointi tehtiin ilmaisimelle, jota on aikaisemmin hyödynnetty vain maaperämittauksissa. Ilmaisimen toimintaa tutkittiin kolmen haihtuvan orgaanisen yhdisteen (asetonin, isopreenin ja metanolin) muodostamien eri väkevyisten vesiliuosten avulla. Ilmaisimen avulla vesiliuoksesta erotetut molekyylit analysoitiin protoninsiirtoreaktio-lentoaikamassaspektrometrilla (PTR-TOF-MS), jonka tuottama data analysoitiin Origin-datankäsittelyohjelmalla. Tutkielmassa perehdytään haihtuviin orgaanisiin yhdisteisiin, ilmaisimen rakenteeseen ja funktionaalisuuteen, diffuusioon, Henryn lakiin ja tulosten tilastolliseen merkitsevyyteen ennen varsinaisia mittaustuloksia. Tuloksissa pohditaan muun muassa virtausnopeuden, lämpötilan ja molekyylikoon vaikutusta vesiliukoisten haihtuvien orgaanisten yhdisteiden mitattuun signaaliin. Lisäksi tuloksissa esitetään arviot tutkitun lampinäytteen asetoni- ja metanolipitoisuuksista kevättalvella. Tämän työn karakterisointitutkimustulosten mukaan ilmaisin toimii kvalitatiivisesti ja loogisesti vesiliukoisten haihtuvien orgaanisten yhdisteiden mittauksissa. Mittauslämpötila vaikuttaa merkittävästi tarkasteltavien yhdisteiden signaalien intensiteetteihin, sillä diffuusio ja haihtuminen ilmaisimessa ovat tehokkaita verrattain korkeassa lämpötilassa. Toisin kuin vesiliukoisten yhdisteiden, rasvaliukoisten yhdisteiden käyttäytymistä ilmaisimessa ei tässä työssä ymmärretty kokonaan.
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(2022)The legislation of the Paris Agreement obliges Finland to pursue actions that keep the global average temperature rise below 2°C and aim to limit the average temperature rise to 1.5°C. The current Finnish government has aligned the national goal of carbon neutrality by 2035. The role of municipalities in promoting or compensating carbon sinks has not yet been defined, although municipalities play an important role as a platform for climate work at local and regional levels. However, it is already known that the Finnish National Climate Act, which is being reformed at this moment, will be subject to an obligation to produce their own climate programs at municipal, regional or provincial level. Environmental competence and environmental development have been important in Lahti for several decades already. The City of Lahti has set its target for carbon neutrality for 2025 and it includes targets for reducing, compensating, and increasing carbon sinks. This work focused on the examination of carbon sequestration and sinks in an urban environment in Lahti, in the example area of approximately 82 hectares, through which a wider understanding of the city's potential to grow coal stocks and sinks in a tight urban structure within different land use classes and different ground cover between them. Based on the Finnish Environment Agency's CORINE land cover classification, the current potential of carbon sequestration for urban land use classes were calculated in this work and the actions to increase carbon sequestration capacity were identified. The work examined the availability of the finished spatial data and to supplement incomplete information, existing literature on the topic was used, as well as other existing spatial records of the city of Lahti and previously made surveys. The largest carbon sink was observed in forest areas, of which in mixed forests representing the largest forest type in the area. Through the calculations and literature carbon sinks and stocks in residential areas were also found to be significant in terms of vegetation, as well as in terms of soil based on the literature review. In planting street and park trees for the purpose of increasing the carbon sink, the most important thing was found to be the long lifetime of trees and securing it. Growing of carbon sinks is most effective in areas where carbon sequestration is already at a high level but increasing vegetation cover in all urban land covers will increase the carbon sink in the long run. One major conclusion of the work was that Lahti's current method of determining carbon sinks and stocks has been inadequate at least for the determining them in built areas, and future measures to maintain, preserve and increase carbon stocks and sinks would not be seen by the same calculation method in the computing. In general, the research data and methods are still largely based on observations and results from the operational processes of natural ecosystems, and these are utilized in urban planning, construction, and maintenance of urban green areas. An incomplete knowledge of the ecological processes in urban areas is a problem that produced challenges in this work as well. More research data is needed on carbon sinks in urban land use classes to gain a more secure understanding of carbon sinks and stocks, although the common importance of vegetation in urban areas is already clear. Although the work focused on carbon in an urban environment, it is necessary to remember the diversity of the urban environment and the other ecosystem services it produces. Land use planning, as well as the management of green spaces in the urban environment, can enhance both the size of carbon storages and sinks and biodiversity and they do not have to be entirely separate from each other.
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(2023)Numerical weather prediction models are the backbone of modern weather forecasting. They discretise and approximate the continuous multi-scale atmosphere into computable chunks. Thus, small-scale and complex processes must be parametrised rather than explicitly calculated. This introduces parameters estimated by empirical methods best fit the observed nature. However, the changes to the parameters are changing the properties of the model itself. This work quantifies the impact parameter optimisation has on ensemble forecasts. OpenEPS allows running automated ensemble forecasts in a scientific setting. Here, it uses the OpenIFS model at T255L91 resolution with a 20 min timestep to create 10-day forecasts, which are initialised every week in the period from 1.12.2016 to 30.11.2017. Four different experiments are devised to study the impact on the forecast. The experiments only differ in the parameter values supplied to OpenIFS, all other boundary conditions are held constant. The parameters for the experiments are obtained using the EPPES optimisation tool with different goals. The first experiment minimises the cost function by supplying knowledge regarding the ensemble initial perturbation. The second experiment takes a set of parameters with a worse cost function value. Experiments three and four replicate experiments one and two with the difference that the ensemble initial perturbations are not provided to EPPES. The quality of an ensemble forecast is quantified with a series of metrics. Root mean squared error, spread, and continuous ranked probability score are used with ERA5 reanalysis data as the reference, while the filter likelihood score is providing a direct comparison with observations. The results are summarised in comprehensive scorecards. This work shows that optimising parameters decreases the root mean square error and continuous ranked probability score of the ensemble forecast. However, if the initial perturbations are included in the optimisation the spread of the ensemble is strongly limited. It also could be shown that this effect is reversed if the parameters are tuned with a worse cost function. Nonetheless, when excluding the initial perturbations from the optimisation process, then a better model can be achieved without sacrificing the ensemble spread.
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Improved Integration of Ground-Based Low-Level Wind Shear Alert Systems Using a Grid-Based Approach (2022)Low-level wind shear is a significant aviation hazard. A sudden reduction in the headwind along an aircraft flight path can induce a loss of lift, from which an aircraft may not be able to recover when it is close to the ground. Airports therefore use low-level wind shear alert systems to monitor wind velocities within the airport terminal area and alert of any detected hazardous wind shear. There exist three ground-based sensor systems capable of independently observing low-level wind shear: a Doppler weather radar-based, a Doppler wind lidar-based, and an anemometer-based system. However, as no single sensor system is capable of all-weather wind shear observations, multiple alert systems are used simultaneously, and observations from each system are integrated to produce one set of integrated wind shear alerts. Algorithms for integrating Doppler weather radar and anemometer wind shear observations were originally developed in the early 1990s. However, the addition of the Doppler wind lidar-based alert system in more recent years warrants updates to the existing radar/anemometer integration algorithms. This thesis presents four different replacement candidates for the original radar/anemometer integration algorithms. A grid-based integration approach, where observations from different sensor systems are mapped onto a common grid and integrated, is found to best accommodate central integration considerations, and is recommended as the replacement to the original radar/anemometer algorithms in operational use. The grid-based approach is discussed in further detail, and a first possible implementation of the algorithm is presented. In addition, ways of validating the algorithm and adopting it for operational use are outlined.
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(2021)Accuracy and general performance of weather radar measurements are of great importance to society due to their use in quantitative precipitation estimation and its role on flood hazard risks prevention, agriculture or urban planning, among others. However, radars normally suffer from systematic errors such as attenuation, misscalibration in Z field or bias in Zdr field, or random errors such as clutter, beam blockage, noise, non-meteorological echoes or non-uniform beam filling, which affect directly the rain rate estimates or any other relevant product to meteorologists. Impact of random errors is reduced by exploiding the polarimetric properties of polarimetric radars by identifying and classifying measurements according to their signature and a classification scheme based on the available polarimetric variables, but systematic errors are more difficult to address as they require a ’’true’’ or reference value in order to be corrected. The reference value can either be absolute or obtained from another radar variable. In reality, an absolute reference value is not feasible because we normally do not know what we are observing with the radar. Therefore, a way of assesing this issue is by elaborating theoretical relations between radar variables based on their consistency when measuring a volume with hydrometeors of known characteristics such as size and concentration. This procedure is known as self-consistency theory and it is a powerful tool for checking radar measurements quality and correcting offsets causing bias, misscalibration or attenuation. The theoretical radar variables themselves can be simulated using available T-Matrix scattering algorithms, that estimate the scattered phase and amplitude for a given distribution of drops of a given size. Information of distribution of drops of a given size, commonly referred as drop size distributions, can be obtained, for instance, from gauge or disdrometer measurements. Once the theoretical relations among radar variables are established, it is possible to check the consistency of, for instance, measured differential reflectivity with respect to differential reflectivity calculated as function of measured reflectivity, assuming the latter has been filtered properly, and any discrepancy between the observed and theoretical differential reflectivity can be thus attributed to offsets in the radar. This work thus presents a methodology for the revision of radar measurements filtering and quality for their improvement by correcting bias and calibration, using theoretical relations between radar variables through self-consistency theory. Furthermore, as the aforementioned issues are easier to track and resolve in the liquid rain regime of precipitation, this work presents a detailed description of methodologies to exclude ice-phased hydrometeors such as the melting layer detection algorithm and its operational implementation along with other complementary filters suggested in the literature. Examples of the melting layer detection and filtering as well as self-consistency curves for radar measurement performance evaluation are also provided.
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(2024)Aerosol particles are a significant factor both environmentally and in terms of health. They can influence climate change in various ways: certain aerosol particles contribute to warming the atmosphere, while others may have a cooling effect. The concentration of secondary organic aerosol (SOA) in the atmosphere is significant, thus playing a crucial role in the climate. SOA can influence the temperature of the climate and the chemistry of the atmosphere. SOA are formed through the oxidation of volatile organic compounds (VOCs), creating a complex mixture of various less volatile organic compounds with diverse properties. Highly oxygenated organic molecules, products of VOC oxidation, are estimated to explain a substantial part of SOA formation. To assess the climate impacts accurately, it is essential to comprehend the characteristics of SOA in the atmosphere. The aim of the thesis was to investigate the influence of temperature and prefence of dimethyl sulfide (DMS) on the gas-phase oxidation products of VOCs, especially how temperature affects the formation of accretion products. The compounds and ozone reacted in a flow tube, and the resulting oxidation products were ionized by clustering them with reagent ions. The mass-to-charge ratio of the formed charged clusters was then measured with orbitrap mass spectrometer. Identifiable oxidation products were selected based on studies by Rissanen et al. [2014] and Tomaz et al. [2021], and the previously described products in these studies were followed using the Orbitool program. The starting materials used in this thesis were cyclohexene, deuterated cyclohexene, and limonene, which were oxidized in the presence of ozone. Several oxidation products were observed in the measurements that were expected to form based on literature. However, mass spectra also revealed that the reaction time with deuterated cyclohexene might have been too short. With a longer reaction time, the molecules could have undergone further oxidation, allowing better detection of oxidation products. In the thesis, it was observed that temperature influences the formation of oxidized products; as the temperature increases, oxidation reactions progress further in 2.7 s reaction time. Monomers that underwent more extensive oxidation could form more highly oxidized accretion products. DMS likely reacts with hydroxyl radicals, thereby influencing the oxidation of VOC compounds in the flow tube. Measurements conducted with DMS may result in the formation of more organic alkoxy radicals than organic peroxy radicals, which could undergo further oxidation.
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(2024)Ilmatieteen laitoksen ylläpitämä Suomen virallisten sademittarien havaintoverkko on harva ja sen laajentaminen vaatisi enemmän resursseja. Kansalaisten sadehavaintojen hyödyntäminen olisi yksi keino laajentaa havaintoverkkoa ja siten muun muassa parantaa sääennusteiden laatua. Tässä tutkielmassa selvitettiin kansalaisten Netatmo-kesäsadehavaintojen käyttökelpoisuutta Suomessa. Vuosien 2019–2022 kesä-, heinä- ja elokuun Netatmo-sadehavaintojen laatua tutkittiin vertailemalla niitä Ilmatieteen laitoksen automaattisadeasemien havaintoihin. Vertailua tehtiin tilastollisten suureiden, keskiarvon, korrelaation ja absoluuttisen keskivirheen, avulla. Ennen varsinaista analyysia pyrittiin rajauksilla selkeyttämään aineistoa sekä poistamaan siitä selvästi virheellisiä Netatmo-sadeasemia ja -havaintoja, kuten yli 150 mm:n tunti- ja yli 200 mm:n vuorokausisademäärät. Pääsääntöisesti Netatmo-sadehavainnot näyttävät tilastollisten suureiden valossa hyviltä, sillä esimerkiksi 75 % Netatmo- ja lähimpien Ilmatieteen laitoksen asemien välisistä vuorokausisateiden korrelaatioista oli vähintään 0.6. Netatmo-havaintojen välinen vaihtelu oli kuitenkin suurempi kuin Ilmatieteen laitoksen asemien havaintojen, mikä kertoo osan Netatmo-havainnoista olevan virheellisiä. Virheitä löytyi useita erilaisia. Yleisesti monien Netatmo-asemien havaittiin aliarvioivan sademäärää, koska keskimäärin Netatmo-asemat olivat mitanneet sateita vajaat 10 % vähemmän kuin niiden vertailuasemat. Lisäksi Netatmo-asemien havainnoissa oli huomattavasti enemmän pieniä 0.1 mm mittauksia kuin Ilmatieteen laitoksen vertailuasemilla eikä osa asemista ollut mitannut mitään 0.1 mm virhemittauksia lukuunottamatta. Jotkut Netatmo-asemat puolestaan mittasivat yksittäin tai jopa jatkuvasti virheellisiä hyvin suuria sademääriä. Osa asemista myös yliarvioi sademäärää, sillä asemien sateet korreloivat hyvin vertailuasemien sateiden kanssa ollen vain paljon suurempia. Toisaalta joidenkin Netatmo-asemien realistiset sadehavainnot oli mitattu eri aikoihin kuin vertailuasemien sateet, joten asemien koordinaatit voivat olla väärät. Välillä taas Netatmo-havaintojen laatu muuttui ajan myötä, sillä kyse on kansalaisten havainnoista. Asemat saattoivat ensin tuottaa hyviä havaintoja ja sitten huonoja tai päinvastoin. Kaikkiaan Netatmo-kesäsadehavainnot vaikuttavat käyttökelpoisilta, koska suurin osa havainnoista on hyviä. Netatmo-asemat myös saavat suuria sateita kiinni hyvin. Lisäksi huonoja havaintoja korrelaation perusteella tuottavat Netatmo-asemat ovat hajallaan eri puolilla Suomea ja hyviä asemia on kaikkialla enemmän. Koska virheellisiä Netatmo-asemia ja -havaintoja on silti varsin paljon, Netatmo-sadehavainnot tarvitsevat kattavaa laadun varmistusta ennen havaintojen hyödyntämistä. Laadun varmistusta voisi tehdä tämän tutkimuksen tavoin vertailemalla havaintoja tilastollisesti Ilmatieteen laitoksen asemien havaintoihin. Lisäksi Netatmo-havaintoja voisi verrata keskenään.
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(2023)The parameterization of deep convection is simulated poorly over the Central and East Pacific. This could lead to issues in predicting the annual total precipitation in the tropics, such as the existence of a double intertropical convergence zone over the equatorial Pacific. Resolving tropical deep convection instead of parameterization leads to the presence of more linear systems. Observations over Atlantic indicate that shear-perpendicular lines (squall lines) propagate faster than shear- parallel lines, mainly due to their connection with the low-level vertical wind shear (VWS). The study examines the different movement speeds of mesoscale convective systems (MCSs) over the East- and West Pacific to determine whether this could explain the reason why climate models have problems with predicting deep convection. A higher proportion of fast moving MCSs (squall lines) could contribute to the prediction problems in the tropics. The MCS motion is determined by the sum of the mean wind and propagation speed. In squall lines, the MCS motion is mainly influenced by the propagation, which is associated with the low-level VWS. Therefore, the effect of the low-level VWS on the fast- and slow moving MCSs is also investigated. The Global High-Resolution Mesoscale Convective System Database is used, which provides infor- mation about the time, location and movement of MCSs. Additionally, ERA5 wind data is used to obtain the mean wind and VWS. Two specific areas over the northern equatorial Pacific are chosen to compare the different types of MCSs. These areas are over the East Pacific (120°W - 140°W and 5°N - 12°N) and West Pacific (140°E - 160°E and 0°N - 7°N). The movement speed is used to categorize the MCSs into three groups: slow moving MCSs (< 3 m/s), moderate moving MCSs (3 m s−1 − 7 m s−1) and fast moving MCSs (> 7 m/s). The study reveals that the share of the fast moving MCSs is 9.8% over the East Pacific and 13.8% over the West Pacific. This is only a 4 percent point difference between the two areas. Therefore, it is not shown that the fast moving MCSs contribute to the existing issues that models have in predicting the annual total precipitation over the East Pacific. Moreover, approximately 85-90% are categorized as slow- to moderate moving MCSs. Hence, the influence of fast moving MCSs is relatively small when compared to the other types. A difference is seen in the mean wind and VWS over the East Pacific, but do not explain the MCS motion vector. Therefore, the difference between fast- and slow moving MCSs cannot be explained by only the monthly averaged mean wind and low-level VWS over the East Pacific. Over the West Pacific, the mean wind direction and VWS are about the same in direction and speed. Therefore, the difference between fast- and slow moving MCSs is not explained by the low-level VWS over the West Pacific.
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(2024)The purpose of this master's thesis is 1) to determine the meteorological structure and evolution of extra-tropical cyclones that develop in an idealized aqua-planet simulation, which utilizes a newly developed way to represent the large-scale initial state of the atmosphere; and 2) to examine the Lorenz energy cycle of this simulation. The simulation is run with the OpenIFS numerical weather model for 15 days, and the Lorenz energy cycle terms are computed for each time step of the simulation over a volume of the atmosphere, which extends from the 1000-hPa pressure surface to the 200-hPa pressure surface between 30 N and 75 N. The intensity of cyclones is evaluated with the TRACK program. In general, the simulation produces text-book type realistic cyclones whose structures resemble those of the Norwegian cyclone model. Cyclones which form upstream of the firstly developing original cyclone are smaller and less intense than the ones which form downstream of it. The most intense cyclone is the first cyclone which develops downstream of the original cyclone. None of the cyclones undergo their full life-cycle and therefore the simulation could be run for more than 15 days in the future. Over the course of the simulation, the available potential energy of the zonal mean flow decreases due to conversion to eddy available potential energy by a northward meridional heat flux. Vertical heat flux acts to inhibit this energy conversion, but its effect is minor. Eddy available potential energy is converted to eddy kinetic energy by the rising of warm air and the sinking of cold air within the developing cyclones and anticyclones. Eddy kinetic energy is converted to the kinetic energy of the zonal mean flow by momentum fluxes of the zonal wind component. The kinetic energy of the zonal mean flow is converted back to the available potential energy of the mean flow by the mean meridional overturning. In addition, friction dissipates the kinetic energy of the eddies and the zonal mean flow. Overall, the results of this thesis show that Lorenz energy cycle terms can be computed for an idealized aqua-planet simulation and that the computed terms can be used as diagnostics for evaluating the development of extra-tropical cyclones.
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(2023)Tutkielmassa on selvitetty lumensyvyyden muutoksia ERA5-Land-uudelleenanalyysin antamille tuloksille ajanjaksolla 1950-2021. Datan analyysi ja käsittely on toteutettu Pythonilla. ERA5-Land:n etuihin lukeutuu muun muassa parempi erotuskyky kuin ERA5-uudelleenanalyysiin, mikä parantaa aineiston tarkkuutta huomattavasti. ERA5-Land ei suoraan käytä havaintoarvoja vaan lumensyvyys lasketaan muitten sääsuureitten, kuten lämpötilan ja sademäärän, aikasarjoja hyödyntäen. Näin ollen tutkielmassa käsiteltyihin suureisiin on sisällytetty muitakin suureita kuin vain lumensyvyys jotta syitä lumensyvyyden muutoksiin olisi helpompaa hahmottaa. Tutkielmaan valikoitiin kolme tutkimusaluetta; Suomi kokonaisuudessaan, Fennoskandian alueelta Norjan, Ruotsin sekä Suomen yhteinen pinta-ala, sekä Japanista Hokkaidon ja Honshun saarten muodostama maa-alue. Aineiston pohjalta voidaan todeta varsin yksiselitteisesti lumensyvyyden kuukausikeskiarvojen olevan, varsinkin lumensyvyyden huippuarvokuukausina, vertailukaudelle 1991-2020 pienempiä kuin vertailukaudelle 1951-1980. Sama trendi näkyy myös vuotuisten keskiarvojen kehityksessä. Muutosten suuruus on jonkin verran sidoksissa alueellisiin erityispiirteisiin mutta päätrendi on kaikille alueille jokseenkin samansuuntainen; nykyisentyyppinen ilmastollinen kehitystrendi laskee lumensyvyyttä pitkällä aikatähtäimellä. Toisin sanoen ilmastonmuutos vähentää lumimäärää pohjoisella pallonpuoliskolla.
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(2023)The Differential Mobility Particle Sizer (DMPS) is a widely used instrument in the size distribution measurements of sub-micron aerosol particles. The particles are size classified based on their electrical equivalent diameter by a Differential Mobility Analyser (DMA) in the DMPS. Only charged particles can be measured with a DMPS. An aerosol charger is hence required since most ambient particles are neutral. An estimation of the size dependent charge distribution of the aerosol particles is required to reach a representative size distribution of the whole aerosol population from the raw measurement data. The charged fractions of the population are conventionally calculated by applying bipolar charging (i.e., an ion atmosphere including ions of both polarities charges aerosols by diffusion and ion attachment onto the particles) theories. Fixed charger ion properties have been used to derive approximation to these theories. The charger ion properties in ambient “real-world” measurements are, however, not fixed but proven to vary substantially. These variations may lead to significant differences when comparing to the approximations. A new method for aerosol charging that reduces the uncertainties that originate from unknown properties of the charger ions was tested in this thesis. The method consists of the introduction of a known trace compound (hereafter called doping) into the aerosol sample flow upstream of a bipolar charger. The effect of doping on charger ion mobility distribution was successfully tested in laboratory experiments. A possible enhancement of charging efficiencies of nanoparticles was studied. The charger ion doping was also tested in atmospheric measurements, where it showed an effect on charger ion properties.
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(2022)Mars-planeetan kaasukehä koostuu enimmäkseen hiilidioksidista, kun taas vesihöyryä on hyvin vähän. Kaasukehän lämpötila vaihtelee noin +10 ja -130 Celsius-asteen välillä ja pintapaine on vain noin sadasosa Maan ilmakehän paineesta. Marsin kaasukehässä on usein paljon hienojakoista pölyä, joka absorboi tehokkaasti auringonsäteilyä ja täten vaikuttaa kaasukehän toimintaan. Marsin pinnan reagoidessa erittäin nopeasti auringonsäteilyn määrän muutoksiin sekä kaasukehässä olevan pölyn vuoksi rajakerroksen mallinnuksessa käytettävissä malleissa säteilyn parametrisaatioiden täytyy olla mahdollisimman hyviä. Helsingin yliopisto ja Ilmatieteen laitos ovat kehittäneet Marsin kaasukehän tutkimukseen tarkoitetun 1-ulotteisen pylväsmallin. Malli on erittäin nopea ja helposti muokattavissa, joten sillä voidaan testata uusia ilmakehäfysiikan lainalaisuuksia ja algoritmeja, joita voidaan mahdollisesti lisätä kolmiulotteisiin Marsin kaasukehän malleihin. Tämä työ tehtiin osana Ilmatieteen laitoksen Marsin tutkimusryhmää ja työssä tutustutaan Marsin kaasukehän rajakerrokseen sekä pylväsmalliin. Lisäksi mallin antamia tuloksia esitellään ja verrataan Curiosity mönkijän (toiselta nimeltään Mars Science Laboratory, MSL) havaintoihin sekä tutkitaan mallin herkkyyttä sen alustusparametreihin. Mallin ennustamia lämpötilan, vesihöyryn tilavuuden sekoitussuhteen ja suhteellisen kosteuden vuorokausisyklejä verrattiin MSL:n havaintoihin eri vuodenaikoina. MSL laskeutui vuonna 2012 lähelle Marsin päiväntasaajaa Gale-kraatterin pohjalle ja se sisältää Ilmatieteen laitoksen suunnittelemat ja rakentamat mittalaitteet paineelle ja suhteelliselle kosteudelle. Mallin ennustamat vuorokausisyklit vastasivat hyvin mönkijän havaintoja ja tuloksista nähtiin myös lämpötilan suuri vuorokausivaihtelu kaasukehän reagoidessa nopeasti auringonsäteilyn muutoksiin. MSL:n paineen mittauksista (yli 3000 Marsin vuorokautta) nähtiin selvästi hiilidioksidin vuodenaikaiskierto etelänavalta pohjoisnavalle ja päinvastoin. Lisäksi vuoden 2018 globaali pölymyrsky näkyi monissa eri mittaustuloksissa. Mallin herkkyyttä tutkittiin muuttamalla neljää eri alustusparametria: pinnan lämpötilaa ja painetta, ilmapylvään vesisisältöä (PWC) sekä pölyn optista paksuutta (tau). Näiden testien perusteella mallin ennustamiin vuorokauden lämpötilaprofiileihin eniten vaikuttivat pinnan lämpötilan ja pölyn optisen paksuuden alustus, kun taas kosteusprofiileihin eniten vaikuttivat PWC:n ja pölyn optisen paksuuden alustus. Näistä parametreista pinnan paineen alustuksella oli vähiten vaikutusta mallin ennustamiin profiileihin.
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(2023)The mean temperature of Earth has been rising due to human-influenced climate change. Climate change has been mostly caused by the rise of greenhouse gases from anthropogenic sources. After carbon dioxide (CO2), the second most important anthropogenic greenhouse gas to climate change is methane (CH4). Approximately half of the methane emissions come from natural sources, including wetlands. The northern high latitude wetlands store large amounts of carbon in permafrost, and the thawing of permafrost could release more methane into the atmosphere. However, there is still much uncertainty related to the methane emissions from the northern high latitude wetlands. The emissions on these wetlands have an annual cycle related to the freezing and thawing of the soil with the highest emissions during summer and the lowest during winter. Climate change can affect the duration and timing of the freezing and thawing periods leaving the winter period shorter. In this thesis, the melting season for the northern high latitude wetlands was defined for four regions: non-permafrost, sporadic, discontinuous and continuous permafrost as well as two smaller regions: Hudson Bay lowlands and Western Siberian lowlands for the years 2011-2020. The melting period was defined with a new method of using the SMOS F/T soil thawing data, which has not been done before this study. The data includes daily information on the freezing state of the soil in the northern latitudes. The melting period methane emissions were defined from the inversion model Carbon Tracker Europe -CH4. The relationship between the emissions, melting period length and mean temperature was studied. Emissions during the spring melting season were detected in all the permafrost regions defined in this study. The fluxes grew stronger as spring progressed and the soil and snow melted. The melting period methane emissions were relatively small compared to the annual emissions (a few per cent of the annual budget). However, the emissions were a little larger than autumn emissions. To understand the melting season emissions better, different drivers in addition to air temperature, like the melting of the permafrost, should be studied in relation to the CH4 emissions.
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(2023)Clouds and aerosols are among the key components of Earth's energy budget, and a major source of uncertainty in climate models, affecting the predictability of the future climate. This thesis focuses on the microphysical processes governing cirrus clouds, wispy clouds composed of ice crystals. Understanding these processes is crucial due to the extensive global coverage of cirrus clouds and their potential warming effect on the atmosphere. The study investigates ice nucleation, the process by which ice crystals form in the atmosphere. Ice nucleation occurs via two main pathways: homogeneous freezing and heterogeneous nucleation. Homogeneous freezing is a process where droplets spontaneously freeze without an aid of an ice nucleating particle (INP). It occurs in highly supersaturated conditions and at cold temperatures below -38°C. Heterogeneous nucleation occurs when INPs act as surfaces to trigger freezing at temperatures below 0°C. The study is conducted using UCLALES-SALSA Large Eddy Simulation (LES) model, which offers high spatial and temporal resolution for atmospheric simulation. The aim is to investigate ice nucleation with five well-established parameterizations. Simulations produced with these parameterizations are compared with cirrus cloud properties measured during the MACPEX campaign. Among heterogeneous nucleation mechanisms, deposition ice nucleation is considered as a primary contributor to the formation of cirrus clouds in the upper troposphere and used as a mechanism to generate ice in the model study. Heterogeneous nucleation requires the presence of INPs which are assumed to be mineral dust is used as it known to dominate ice nucleation. Results show good agreement between modeled and measured data for ice concentration (Ni) and ice water content (IWC). The comparison between parameterizations revealed a relatively similar performance, with variations in Ni and IWC falling within the same order of magnitude. However, conclusive determination of the best-performing parameterization within the temperature and humidity ranges of the study was challenging. The study sheds light on the fundamental difficulties when using parameterizations with ice nucleation processes in cirrus clouds without accurate initial conditions and knowledge about the history of ice nucleation of the measured cirrus clouds. Also, the importance of proper validation of each parameterization by using different scenarios was emphasized.
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(2023)Thawing of permafrost is widely observed, and its rate is expected to be accelerated due to the global warming caused by anthropogenic climate change. Although permafrost thawing has been acknowledged in IPCC Assessment reports, uncertainties related to model-based estimates of its extent and magnitude in the future exist due to the challenges for the models to account for heterogeneous changes in permafrost under the changing climate. Various one-dimensional finite element conductive heat transfer model codes have been successfully used for simulating permafrost, while models created with the COMSOL multiphysics tool have seen little use. In this work, COMSOL version 5.6 was chosen for modelling the heat transfer in permafrost. COMSOLs' ability to accurately simulate thermal evolution in porous medium experiencing freezing was demonstrated using the Interfrost test case T1, which is a benchmark modelling problem adapted to use by the Intercomparison project for TH (Thermo-Hydro) coupled heat and water transfers in permafrost regions. Benchmark results agreed with Lunardini's analytical solution, although compared to the previous studies, the results had more deviation from the analytical solution. Discontinuous permafrost in North-Western Siberia is thawing. Based on the temperature measurements available from three boreholes located in the area (Nadym), and an observed increasing mean annual air temperature trend of 0.5\textdegree C per decade, the rate of thawing could be increasing. A one-dimensional heat transfer model for one of the boreholes was created and benchmarked against soil temperature measurements to form a basis for future estimates of the permafrost evolution. The temperature time series produced by the model agreed moderately with the measurements, but the need for further model improvements was identified. Adjustments proposed in this work and parameter changes indicated by the sensitivity analysis form a basis for further model development. Additionally, the results of the conducted sensitivity analysis showed the importance of using accurate soil properties in modelling works.
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(2023)The Arctic is warming approximately four times as fast as the rest of the planet, and the current and future changes may have drastic effects on the entire globe. However, the detailed processes of the Arctic climate have been studied to a small extent due to the remote and hard-to-reach location, and the representation of the Arctic in climate models has been inadequate. There are many uncertainties in climate models, and significant uncertainties concern aerosol-related information. Atmospheric aerosols have a large, yet not entirely understood and quantified effect on the climate. Aerosols affect the Earth’s radiative balance by scattering and absorbing incoming radiation, and they play a significant role in the cloud formation process. In order to improve the representation of the Arctic in climate models and tackle the unsolved questions about the Arctic atmosphere, sea ice, ocean, biogeochemistry and ecosystem, a one-year-long expedition called Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) was conducted in the central Arctic between September 2019 and October 2020. As secondary aerosol formation (new particle formation) produces more than 50% of the atmospheric cloud condensation nuclei, and iodic acid has been identified to be a significant compound for new particle formation in the Arctic pristine environments, the iodic acid concentrations during the full-year MOSAiC expedition was investigated. The main research objective was to quantify the seasonal cycle of iodic acid in the Arctic. The correlation with temperature, solar radiation and ozone were also studied. Together with ice dynamics, sea ice thickness and air mass back trajectory simulations, the possible sources of measured iodic acid were investigated. The participation in forming new particles was also studied. The measured iodic acid concentrations varied between 1e4 and 4e7 molecules/cm3 with a detection limit of 1.22e5 molecules/cm3, and the concentrations were in the same range with measured earlier in the Arctic. The highest concentrations were measured in April. An increased correlation of iodic acid concentration with temperature and radiation was observed during spring, and an anticorrelating trend was observed between iodic acid concentration and ozone during the period of high iodic acid, implying that iodic acid is partially responsible for ozone depletion in the arctic. Comparison with particle data showed that iodic acid concentrations measured during MOSAiC were sufficient to take part in the new particle formation. However, nucleation was not observed during the highest iodic acid concentration period in April.
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(2022)The effects of atmospheric aerosol particles on Earth’s radiative balance are mainly cooling, which is mostly due their indirect effects with clouds. In the Arctic more than half of the cloud condensation nuclei (CCN) production is originated from secondary aerosols, and to further the understanding of Arctic climate and its changes due to the global warming, it is necessary to better understand the secondary aerosol processes there. Highly oxygenated organic molecules (HOM) are known to be important for the formation and especially for the growth of newly formed secondary aerosols to climate relevant sizes. Because of the low volatilities of HOM, they can condense onto the smallest particles, which is crucial for the growth of the new particles. Volatile organic compounds (VOC), especially monoterpenes, are known to be sources of HOM in boreal forest, but in the Arctic where the vegetation is scarce the sources of HOM have not yet been identified. The processes related to secondary aerosol formation in the Arctic are still not fully understood. Especially the observations of HOM and their sources are lacking. Recent studies in Ny-Ålesund, Svalbard showed that multiple aerosol precursors are found to be present in the Arctic atmosphere, as well as contributing to the early stages of the formation of secondary particles. However, more molecular scale observations of aerosol precursors are still needed to form a full picture of the Arctic climate processes. In this thesis, the different aerosol precursors and their contributions to the new particle formations in high Arctic location Ny-Ålesund, Svalbard were analysed. Chemical compositions of HOM were identified for the first time from Arctic atmosphere, and their contributions to new particle formation in high Arctic location were investigated. Because of the high concentrations of HOM during the observed NPF events, it can be suggested that they were contributing to the nucleation of aerosol particles. Particle growth rate calculation shows that the HOM present in the study site were responsible for up to 50% of the total growth of the newly formed particles. VOC flux measurements done in same location were also analysed, and Arctic tundra in Svalbard was found out to be a source of at least four different VOC. Furthermore, the identified HOM were linked to the VOC flux measurements, suggesting a possible link between Arctic VOC and HOM.
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