Browsing by master's degree program "Ilmakehätieteiden maisteriohjelma (Atmospheric Sciences)"

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.

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.

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.

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.

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.

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.

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.

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.

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.

After 2013, the environmental protection department in China has significantly reduced on-road emission through the upgrade of emission standards, the improvement of fuel quality and economic tools. However, the specific effect of the control policies on emission and air quality is still difficult to quantify. This is mainly due to the data shortage on vehicle emission factors and vehicle activities. In this research, we developed the 2008-2018 on-road emissions inventory based on Emission Inventory Preparation Guide (GEI) and existing vehicle activity database. Our estimates suggest that CO and PM2.5 showed a relatively significant decrease, by 66.2% and 58.8%. However, the trend of NOx (5.8%) and NMVOC (-4.8%) was relatively stable. The Beijing-Tianjin-Hebei (BTH), Yangtze River Delta (YRD), Pearl River Delta (PRD) and Sichuan Basin (SCB) regions all showed a uniform trend especially in NOx. For Beijing-Tianjin-Hebei, the significant decline in NOx might be caused by earlier implementations in emission standard and fuel quality. In addition to this, we designed additional evaporation emission scenarios to verify the application of GEI in quantify emission impact on secondary pollutant (PM2.5 and O3). The results indicate that evaporation emission contributed to Maximum Daily Average 8-hour (MDA8) O3 concentration by about 3.5%, for Beijing, Shanghai and Nanjing. This value can reach up to 5.9%, 5.3% and 7.3%, but the impact on PM2.5is extremely limited. Our results indicate the feasibility of GEI in improving and lowering the technical barrier of on-road emission inventory establishment at the same time and its further application in quantifying on-road emission contribution to air quality. Besides that, it shows a strong potential in on-road policy environmental assessment and short-term air quality assessment.