Browsing by master's degree program "Magisterprogrammet i atmosfärsvetenskaper"

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.

Mixing processes under a seasonal ice cover in boreal lakes have received little attention from the physical limnological community. Even though the water is calm under the ice cover, many different phenomena are still able to cause mixing in the water column, which in turn affects the gas fluxes as well as physical and chemical properties of the water. Lakes in the boreal zone are very numerous. Understanding their behaviour helps us predict the effects of climate change in the boreal zone. In my thesis I present the various mechanisms that reign under the ice cover, and attempt to see these mechanisms in action in lake Kuivajärvi. Emphasis was placed on internal waves and the various components of the energy balance that can induce mixing. Data was collected with thermistor chains and a measurement raft between 24.1. – 3.5.2017. Two types of internal waves were observed during the ice-on season of 2016 – 2017. Short period barotropic seiches were observed during the whole ice-on season and transient long period baroclinic seiches were observed on two occasions. Other mixing processes seen in the lake were sediment heating in the dead of winter, penetrative convection caused by short wave radiation in the spring and diurnal stratification and mixing during spring caused by the daily heating and nightly cooling. Some mixing under the ice cover was found to depend on the meteorological conditions prevailing over the lake during the previous summer and just before the ice-on in late autumn, while others were more predictable. Long period internal waves and sediment heating are set in motion by meteorological conditions, while the spring mixing and overturn are more stable, due them being more a function of the orbital mechanics of our planet than the prevailing weather. Varying surface conditions of the lake ice cover make the measurement of especially the surface temperature complicated. Snow and ice are under a continuous metamorphosis due to the weather. This makes surface emissivity difficult to estimate, causing significant errors in the measurement of the outgoing longwave radiation. This in turn causes problems in defining the surface temperature from it. Also, the precipitation heat flux is difficult to estimate due to the lack of knowledge on the surface temperature.

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.

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.

Ocean reanalysis products (ORAs) can provide information on the state of the ocean. Although the different data sources, model configurations, forcing choices and assimilation methods cause the ORAs to deviate from each other, the ensemble approach has been previously found to produce realistic mean states. This raises the question if ORAs could be used for studying temporal and spatial changes in the Arctic Ocean, where measurements are generally sparse. Such study has not been previously published. In this thesis, the changes in the hydrography of the Arctic Ocean are examined over the previous decades based on selected ORAs. Eleven ORAs, TOPAZ4, C-GLORS025v5, ECDA3, GECCO2, GLORYS2v4, GloSea5-GO5, MOVE-G2i, ORAP5, SODA3.3.1, UR025.4 and ORAS5, were chosen for this study due to their overlap over 1993–2010 and the multimodel ensemble (MMM) was formulated based on the products, excluding ECDA3. The data were divided into depth layers and layer-average salinities and temperatures were used to calculate basin-average anomaly time series and trends to study the observed temporal changes. Per-grid trends were also produced to study both spatial and temporal changes in more detail. To assess their reliability, trends from the MMM and individual ORAs were compared to an observational product, EN4.2.0.g10 and the variability in the products and the MMM was assessed using statistical measures. The Eurasian Basin was found to be warming across all layers (up to 0.3 ◦ C decade −1 ) accompanied by salinification, except for localised cooling in the top 100 meters in the western basin, near the Fram Strait (-0.2 ◦ C decade −1 ). This indicates additional heat uptake by the surface 0–100 meters and also increasing heat and salinity content of the AW inflow, while the transport of sea ice out of the AO has increased. The Amerasian Basin, on the other hand, showed a strong freshening trend culminating at the Beaufort Gyre. This is most likely due to the anticyclonic wind forcing and increasing freshwater inflow to the Beaufort Sea. The Amerasian Basin also showed a warming trend in the 300–700 m layers but a cooling trend in the 100–300 m layer north of the Chukchi Sea. The ensemble approach worked well in dampening the extremities of singular ORAs, but some trends observed in the literature were missed due to disagreements between ORAs, especially in the Fram Strait and Beaufort Sea, which suggest that further improvements in both models and measurements are needed in those areas. Furthermore, improvements in deep ocean observations, how models handle the deeper ocean and assimilation methods are needed in order to study trends in the deeper depths in the AO. All in all, as the improvements come, the ORA MMM shows great potential for studies in the AO.

Freshwater ecosystems are an important part of the carbon cycle. Boreal lakes are mostly supersaturated with CO2 and act as sources for atmospheric CO2. Dissolved CO2 exhibits considerable temporal variation in boreal lakes. Estimates for CO2 emissions from lakes are often based on surface water pCO2 and modelled gas transfer velocities (k). The aim of this study was to evaluate the use of a water column stratification parameter as proxy for surface water pCO2 in lake Kuivajärvi. Brunt-Väisälä frequency (N) was chosen as the measure of water column stratification due to simple calculation process and encouraging earlier results. The relationship between N and pCO2 was evaluated during 8 consecutive May–October periods between 2013 and 2020. Optimal depth interval for N calculation was obtained by analysing temperature data from 16 different measurement depths. The relationship between N and surface pCO2 was studied by regression analysis and effects of other environmental conditions were also considered. Best results for the full study period were obtained via linear fit and N calculation depth interval spanning from 0.5 m to 12 m. However, considering only June–October periods resulted in improved correlation and the relationship between the variables more closely resembling exponential decay. There was also strong inter-annual variation in the relationship. The proxy often underestimated pCO2 values during the spring peak, but provided better estimates in summer and autumn. Boundary layer method (BLM) was used with the proxy to estimate CO2 flux, and the result was compared to fluxes from both BLM with measured pCO2 and eddy covariance (EC) technique. Both BLM fluxes compared poorly with the EC flux, which was attributed to the parametrisation of k.

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.

The impacts of dust aerosols on human health and climate change are increasing as the particulate matter (PM) mass concentrations and frequency of Sand and Dust Storm (SDS) episodes have shown an increasing trend in recent studies, especially for the Middle East and North Africa (MENA). In this thesis, particulate matter (PM10 and PM2.5) concentrations were measured during May 2018–March 2019 in the urban atmosphere of Amman, Jordan. The PM sampling was 24-hours every 6 days. The overall mean PM10 mass concentration was 64±39 μg/m3 with the median (+interquartile range) value of 49.2+53.5 μg/m3, the PM2.5 mass concentration varied between 15 μg/m3 and 190 μg/m3 with an annual average 47±32 μg/m3 and with the median (+interquartile range) value of 35.8+26.3 μg/m3. The PM2.5 / PM10 ratio was 0.8±0.2. According to the Jordanian Air Quality standards, the annual mean PM10 needs to be below a limit value of 120 μg/m3, which was true in this work. However, the PM2.5 mass concentration was three times higher the corresponding limit value (65 μg/m3). However, both exceeded the World Health Organization (WHO) air quality annual guideline of 20 μg/m3 for PM10 and 10 μg/m3 for PM2.5. The results show that the observed PM10 mass concentrations in Jordan were lower than what was reported in other cities in the Middle East but were higher when compared to other Mediterranean cities. During the measurement period, Jordan was affected by Sand and Dust Storms (SDS), which were observed on 14 sampling days. The source origins of these SDS were traced back to North Africa, the Arabian Peninsula, and the Levant. The 24-hour PM10 concentrations during these SDS episodes ranged between 108.1 μg/m3 and 187.3 μg/m3. In the future, measurements with a higher time resolution (one sample per day) are recommended for a more precise seasonal trend interpretation.

This thesis analyses the alterations of vertically integrated atmospheric meridional energy transport due to polar amplification on an aqua planet. We analyse the energy transport of sensible heat, latent energy, potential energy and kinetic energy. We also cover the energy flux of the mean meridional circulation, transient eddies and stationary eddies. In addition, we also address the response of the zonal mean air temperature, zonal mean zonal wind, zonal mean meridional wind, zonal mean stream function and zonal mean specific humidity. Numerical model experiments were carried out with OpenIFS in its aqua planet configuration. A control (CTRL) and a polar amplification (PA) simulation was set up forced by different SST (sea surface temperature) patterns. We detected tropospheric warming and atmospheric specific humidity increase 15-90° N/S and reduction of the meridional temperature gradient throughout the troposphere. We also found reduced strength of the subtropical jet stream and slowdown of the mean meridional circulation. Important changes were identified in the Hadley cell: the rising branch shifted poleward and caused reduced lifting in equatorial areas. Regarding the total atmospheric vertically integrated meridional energy transport, we found reduction in case of the mean meridional circulation and transient eddies in all latitudes. The largest reduction was shown by the Hadley cell transport (-15%) and by midlatitude transient eddy flux (-23%). Unlike most studies, we did not observe that meridional latent energy transport increases by polar amplification. Therefore, it is stated that the increased moisture content of the atmosphere does not imply increased meridional latent energy transport, and hence there is no compensation for the decrease of meridional dry static energy transport. Lastly, we did not detect stationary eddies in our simulations which is caused by the simplified surface boundary (i.e. the water-covered Earth surface). The main finding of this thesis is that polar amplification causes decreasing poleward energy transport on an aqua planet.

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.