Numerical simulations of supercritical coastal flows have been performed. The meso-γ-scale model which has been used in this study is non-linear, hydrostatic and has a higher-order turbulence closure. Previous studies of supercritical coastal flows with this model have given rise to some questions and hypotheses, e. g. is the gradual curvature of the main coastal mountains north of Cape Mendocino sufficient to excite an expansion fan? Is the local terrain of Cape Mendocino responsible for the collapse of the marine atmospheric layer (MABL) in Shelter Cove? This study was designed to answer these questions. The terrain used in the simulations was generated by a simple analytical function and fitted to the real terrain north of Cape Mendocino in a sense that it would reflect it as good as possible, neglecting ”small” changes in the orientation of the coast and height of the terrain. This made it possible to test hypotheses related to the coastline shape one by one. Simulations that were performed are: Piecewise linear coasts with constant terrain height where the change in coastline orientation, the height of the inversion and strength of the background wind speed was varied; Piecewise linear coasts where the height of the terrain was varying along the coast; Curved coastlines with different curvatures; Piecewise linear coasts with simplified capes perpendicular to the coast where the height of the cape was varied. It was found that the angle with which the coast turns away from the flow regulates the amount of acceleration in the following expansion fan. A decreasing height of the terrain along the coast lead to an increased acceleration of the flow, the largest acceleration was found when the slope of the terrain was confined to the change in coastline orientation. It was concluded that this is comparable to an increased change in coastline orientation. The simulations with curved coastlines confirmed the hypothesis that the gradual curvature of the main coastal mountains north of Cape Mendocino is sufficient to excite an expansion fan. In fact, a curved coastline leads to a stronger acceleration of the flow than a piecewise linear coastline. One of the most striking features in this study was that the acceleration of the flow started far upstream of the change in coastline orientation, even though the flows were supercritical. This phenomenon was mainly found in the cases with the highest wind speeds. It is suggested that the upstream acceleration of the flow is due to either high amplitude gravity waves propagating within the MABL or internal gravity waves propagating above the inversion. When a cape was inserted perpendicular to the main coastline, this showed that even with a cape as low as approximately half the depth of the MABL, the flow was significantly blocked. Indications of wave-breaking on the lee side of the cape was also found, which confirmed the hypothesis that the local terrain of Cape Mendocino is responsible for the collapse of the MABL in Shelter Cove.

Melting glaciers are the major contributor to sea level rise. Glaciers are sensitive indicators of climate change and current experience strong developments in a rapidly warming Arctic environment. Time-series of the mass balance of the glacier Nordenskiöldbreen are constructed by using height observations from the stake measurements on the glacier. The connection between the glacier mass balance and monthly averaged weather parameters observed at nearby meteorological stations will be analyzed. The total net balance on glacier Nordenskiöldbreen is found to be negative (-0.09 m w.e. per year) between 2005 and 2017. The mass balance during the summer season correlates strongest with maximum air temperature, while the winter balance is found to be mostly influenced by cloud cover and temperature, rather than precipitation. The results show that precipitation observed at nearby weather stations are not representative for precipitation amounts observed on the glacier. / Glaciärer som smälter är en av de största bidragen till den förhöjda havsnivån. Det är därför viktigt att studera Svalbards glaciärer för att kunna svara på hur den arktiska uppvärmningen påverkar issystemen. En tidsserie över massbalansen för glaciären Nordenskiöldbreen skapades genom höjdobservationer från stavmätningar befintliga på glaciären. I nästa steg analyserades kopplingen mellan glaciärmassbalansen och väderparametrarna som observerats vid närliggande meteorologiska stationer. Den totala netbalansen på glaciären Nordenskiöldbreen visade sig vara negativ (-0.09 m w.e. per år) mellan år 2005 och 2017. Massbalansen under sommarsäsongen korrelerade starkast med maximal lufttemperatur medan vinterbalansen var mest påverkad av molntäcke och temperatur, snarare än nederbörd. Resultaten visar att nederbörd observerad vid närliggande väderstationer inte är representativ för nederbördsmängder observerade på glaciären.

Previous studies, such as van der Veen (2012) and White et al. (2017), have demonstrated the potential of using measurement-based cloud data to improve Numerical Weather Prediction (NWP) based cloud forecasts. This can be done through cloud initialization; a process of injecting cloud data after the regular data assimilation in an NWP model. The purpose of this study was to use cloud data from the Mesoscale Analysis system MESAN to investigate cloud initialization in the HARMONIE-AROME model system for improving short-range cloud forecasts. The cloud initialization method that was used was similar to a method used by van der Veen (2012), where specific humidities, temperatures, and hydrometeor concentrations were altered using information on cloud fractions, cloud base heights and cloud top heights. MESAN input data analyses as well as cloud initialization investigations were carried out. MESAN input data analyses revealed significant differences in cloud fractions between MESAN and the background model field in MESAN. Overestimations of cloud fractions in MESAN over sea were caused by satellite data, particularly due to the inclusion of the fractional cloud category. Underestimations of cloud fractions over land were caused by limitations of the synoptic weather (SYNOP) stations in measuring clouds. Furthermore, larger differences between MESAN and SYNOP were found over Sweden and Finland compared to Norway, which may be tied to Norway having mostly manual SYNOP stations, and Sweden and Finland having mostly automatic stations. Shortcomings were found in the investigated cloud initialization method. Such shortcomings involved a limit check on the specific humidity change, the cloud initialization being repeated for an unnecessarily large amount of iterations, and the use of a sub-optimal profile of critical relative humidity. Using a one-dimensional vertical column version of HARMONIE-AROME, named MUSC, to integrate forward in time revealed a large sensitivity to the use of forcing profiles and forcing time scales in MUSC. Alterations made through cloud initialization were found to last over 12 h, with varying effects depending on the investigated height. A reasonably good agreement between MUSC results and results from the three-dimensional version of HARMONIE-AROME was found. Findings in this thesis point at potential to further enhance the HARMONIE-AROME cloud initialization technique. These enhancements concern a revised MESAN cloud product and taking care of some flaws in the cloud initialization method. / I en operationell vädermodell inkluderas olika mätdata, såsom temperatur och atmosfärstryck, i ett regelbundet intervall. Molnighet är inte vanligtvis en del av dessa cykler; istället bildas molnen av modellen utifrån balanser i de andra fysikaliska fälten. Detta projekt gick ut på att direkt införa molnmätningar från väderanalyssystemet MESAN i vädermodellsystemet HARMONIE-AROME genom en metod som kallas molninitialisering. Specifikt förbättringar för korttidsprognoser var av i ntresse. MESAN är ett system vars produkter är en sammanslagning av ett bakgrundsfält från en vädermodellkörning med olika mätdata. I MESAN kommer molndata från tre källor: bakgrundsfältet, satellitdata och synoptisk väderstationsdata (SYNOP-data). Undersökningar av indata till MESAN samt molninitialiseringsmetoden har utförts. Analyser av indata till MESAN visade på överskattningar av moln i satellitdata över hav och underskattningar av moln i SYNOP-data över land. För satellitdatat berodde detta på medtagande av moln på liten skala eller väldigt tunna moln, medan det för SYNOP berodde på begränsningar i mätmetoderna. Det fanns även en skillnad i kvalitet i SYNOP-data i Sverige och Finland gentemot Norge, vilket kan bero på att de flesta mätstationer i Norge är manuella medan de flesta i Sverige och Finland är automatiska. Molninitialiseringsmetoden bestod i att extrahera data om molnbashöjd och molntopphöjd från MESAN, och sedan modifiera fuktighet, temperatur och hydrometeorer (såsom molndroppar och iskristaller) i HARMONIE-AROME utifrån molnens position. Brister i metoden hittades. Initialiseringsprocessen upprepades ett suboptimalt antal gånger. En begränsning i hur mycket fuktigheten tillåts modifieras förändras under initialiseringsprocessen och fungerade inte som avsett. Dessutom, jämförese med radiosonddata pekar på att relativa fuktighetsgränserna för villket moln bildas inledningsvis inte ansattes korrekt. Effekterna av metoden kunde vara i över 12 timmar, men denna studie pekar på ytterligare troliga förbättringsmöjligheter i HARMONIE-AROME genom införande av reviderad version av metoden samt förbättrade satellitprodukter.

In this study, four and a half months of ceilometer data from Östergarnsholm are used to analyze cloud related to processes in the boundary layer. Measurements are divided into two categories, which are defined by wind direction: a continental and a marine sector. The results show that there are significant differences in the height of the lowest cloud bases detected for the two sectors, where cloud base heights are lower for the marine wind sector during unstable and neutral conditions. The ceilometer’s ability to detect several cloud base heights simultaneously is utilized to test whether a double layer structure (DLS) can be detected. The results of this particular analysis are inconclusive as to whether a DLS has been observed or not. Detected cloud base heights differ greatly from heights suggested by the lifting condensation level (LCL). A new empirical formula for lowest cloud base height is then derived using the measurements. The Ceilometer’s estimations of sky cover are assessed to be of reasonable quality. This is suggested by computed high correlation with incoming shortwave radiation at noon for three months.  However, histograms of cloud cover measurements suggest that the ceilometer tends to probably either overestimate or underestimate cloud cover.  Large differences in cloud cover were observed for the two wind sectors during unstable conditions. For the months of July and August, a diurnal cycle in cloud cover for the continental wind sector was observed which suggest the presence of Stratocumulus. Measurements performed during upwelling conditions closely resemble those of the marine wind sector performed during stable conditions.

The launch of large stratospheric balloons is highly dependant on the meteorological conditions at ground level, including wind speed. The balloon launch base Esrange Space Center in northern Sweden currently uses forecasts delivered through the Swedish Meteorological and Hydrological Institute to predict opportunities for balloon launches. However the staff at Esrange Space Center experience that the current forecasts are not accurate enough. For that reason the Weather Research and Forecasting model is used to improve the forecast. The model performs a Large Eddy Simulation over the area closest to Esrange Space Center to predict wind speed and turbulence. During twelve hypothetical launch days the improved forecast have an overall accuracy of 93% compared to the old forecast accuracy of 69%. With some improvements and the right computational power the system is thought to be operationally viable.

Dimma råder då sikten understiger 1 km och kan mätas av både markstationer och satelliter. RGB-produkterna Dimma och Nattdimma från det geostationära satellitinstrumentet SEVIRI bygger på dimmans emissivitetegenskaper vid våglängderna 8.7 μm respektive 3.9 μm jämfört med vid 10.8 μm. Kanalerna vid 8.7 μm och 3.9 μm är bland annat känsliga för molnens fas, och en kanaldifferens mellan respektive kanal och den rena IR-kanalen vid 10.8 μm framhäver därigenom låga moln och dimma. Produkten Dimma består av kanalerna vid 12.0 μm, 10.8 μm och 8.7 μm och fungerar dygnet runt. Produkten Nattdimma består av kanalerna vid 12.0 μm, 10.8 μm och 3.9 μm, och är endast gångbar under natten på grund av kontamination från solinstrålning. Kanalen vid 3.9 μm måste även korrigeras på grund av det överlappande CO2-absorptionsbandet. Denna fallstudie och utvärdering av satellitprodukterna, visade att dimma går att detektera med båda produkterna. På grund av Nattdimmas begränsade användningstid var dock Dimma att föredra. Produkterna är oanvändbara då högre moln döljer lägre moln och någon tydlig korrelation mellan sikten och strålningstemperatur fanns inte. Därför kan inte produkterna användas för att uppskatta sikten där markstationer inte finns. / Fog prevails if the visibility falls below 1 km and can be detected with ground stations and satellites. The RGB-products 24-hour Microphysics and Night Fog from the geostationary satellite instrument SEVIRI are based on the emissivity properties of fog at wavelengths 8.7 μm and 3.9 μm respectively compared to 10.8 μm. The channels at 8.7 μm and 3.9 μm are, among other things, sensitive to cloud phase, and the difference beteween each channel and the pure IR-channel at 10.8 μm highlights low clouds and fog. The product 24-hours Microphysics consists of the channels at 12.0 μm, 10.8 μm and 8.7 μm, and is operational around the clock. The product Night Fog consists of the channels at 12.0 μm, 10.8 μm and 3.9 μm and works only during night because of sunlight contamination of the 3.9 μm channel. The 3.9 μm channel also needs to be corrected for, due to overlap with the CO2 absorption band. This case study and evaluation of the satellite products showed that fog can be detected with both products. 24-hour Microphysics was preferred, because of Night Fog’s limited usage time. The products are unusable when higher clouds cover the lower clouds, and no clear correlation between visibility and brightness temperature was found. The products can therefor not be used to estimate visibility where ground stations do not exist.

One of the most interesting questions about Mars is if life ever existed on it. One of the main requirements for life to exist as we know it is the presence of liquid water. It has been suggested by Martín-Torres et al. (2015a) that a daily-transient liquid water cycle takes place on the surface of Mars through deliquescence and efforescence (binding and releasing of water vapour) of perchloratic salts in the Martian soil. Given the right conditions regarding water activity and temperature, certain planetary areas have been defined as Special Regions where there is a chance of life-form reproduction to occur (Kminek et al. 2017). Sub-surface cavities and caves are defined as such and are still a relatively unexplored and not yet studied feature of the Martian surface. This report is an assessment of the environmental conditions in Martian subsurface cavities such as caves and how it can be considered as a Special Region. Based on observations of lava tubes made by Cushing and Titus (2010) with atmospheric and thermal data from REMS on board the Curiosity rover by Martín-Torres et al. (2015b), simulation models were set up in ANSYS Fluent to examine the behaviour of the temperature and relative humidity within these caves. Different properties of the studied models included size, shape, inclination, materials of the ground composition and air flow behaviour. The results showed that a cave roof with a thickness greater than 1-2 m prevents the ground temperature variation during the day to have any considerable impact on the air temperature in the cave which implies that the thermal waves are the main driving factor of the thermal environment in larger models. The average temperature and relative humidities throughout the entire models resulted in unfavourable conditions (relative humidity under 20% RH) to allow for any perchloratic salts to hydrate or form brines. The most interesting results were found in smaller models where different phenomena with higher relative humidity near the floor and in corners occurred for several hours during the same day. This happened at certain times during the day (LMST 7 and 17) when the inlet temperature surpassed the average temperature in the cave and resulted in relative humidities of up to 90% RH which potentially could allow perchloratic salts to stay in brine form, or at least in a hydrated state throughout the day. While the low temperatures in today's Martian caves may be too harsh for life forms to exist, a previous warmer climate might have allowed for extremophiles to thrive in highly saline solutions. This could be an implication that Martian caves should be defined as Special Regions and that further studies should be done on the subject.

The potential for wind power development in Greenland is evaluated based on the analysis of 58 years of data (1957-2015) from RACMO 2.3 (Regional Atmospheric Climate Model). In order to create a wind power development tool, mesoscale maps based on RACMO 2.3 model were created containing the following characteristics: mean wind speeds (at 10 m), averaged maximum wind speed (with and without gusts at 10 m), temperature, humidity, geopotential, ice sheet mask and land sheet mask. A relevant aspect for this thesis is the mean wind speed. Over Greenland, the lower mean wind speeds range from 2-3 m/s on the tundra areas near the coast. This is influenced by high temperature inversion over the arctic tundra which disintegrates the predominant katabatic flow leading to lower wind speeds. On the other hand, the highest mean wind speeds range from 6 to 10 m/s and are observed in the northeastern region, due to cyclonic activity over the Greenland Sea. Maps of both the mean wind speed and averaged maximum wind speed are combined in order to achieve the highest mean wind speed value while at the same time avoiding maximum wind speeds higher than the cut-off value of the selected turbine model. This map combination is synchronized with pre-determined construction constraints, resulting in the suggestion of three different sites (sites 4, 5 and 6) as potential targets for wind power development. Multi-level data is sorted for different heights (10, 35, 70, 100 and 120 m) to perform a micro-scale analysis exercise for the three different site suggestions. A Vestas V90 3MW with an 80 meter hub height is selected as the standard turbine model to be deployed at the three recommended positions and for use in further simulations using WindSim. Annual Energy Production (AEP) for these three turbines in the recommended locations is calculated based on the interpolation from the climatology data at 70 m which is closest to the turbines’ hub heights. The AEP results are compared and show that site suggestion 4 presents the best potential for wind power development, surpassing by 79% and 23% the production results from sites 5 and 6, respectively. Based on the study developed, it is concluded that the in terms of wind resource assessment the potential for wind power development in Greenland exists. However the selection of possible deployment sites should be carefully done and real measurements must be performed.

Surface gravity waves play a vital role in the air-sea interaction. They can alter the turbulence ofthe bottom atmospheric layer as well as the upper-ocean layer. Accordingly, they can affect themomentum flux, heat fluxes, as well as the upper-ocean mixing. In most numerical models, waveinfluences are not considered or not fully considered. The wave influences on the atmosphereand the ocean are important for weather forecasts and climate studies. Here, different aspects ofwave impact on the atmosphere and the ocean are introduced into numerical models.In the first study, a wave-state-dependent sea spray generation function and Charnock co-efficient were applied to a wind stress parameterization under high wind speeds. The newlyproposed wind stress parameterization and a sea spray influenced heat flux parameterizationwere applied to an atmosphere-wave coupled model to study their influence on the simulationof mid-latitude storms. The new wind stress parameterization reduces wind speed simulationerror during high wind speed ranges and intensifies the storms. Adding the sea spray impacton heat fluxes improves the model performance concerning the air temperature. Adding the seaspray impact both on the wind stress and heat fluxes results in best model performance in allexperiments for wind speed, and air temperature.In the second study, the influence of surface waves on upper-ocean mixing was parameter-ized into a 1D k − ε ocean turbulence model though four processes (wave breaking, Stokes driftinteraction with the Coriolis force, Langmuir circulation, and stirring by non-breaking waves)based mainly on existing investigations. Considering all the effects of surface gravity waves,rather than just one effect, significantly improves model performance. The non-breaking-wave-induced mixing and Langmuir turbulence are the most important terms when considering theimpact of waves on upper-ocean mixing. Sensitivity experiments demonstrate that vertical pro-files of the Stokes drift calculated from 2D wave spectrum improve the model performancesignificantly compared with other methods of calculating the vertical profiles of the Stokes drift.Introducing the wave influences in modelling systems, the results verified against measure-ments. Concluding from these studies for the further model development, the wave influencesshould be taken into account to improve the model performance.

As wind farms continue to take up more land throughout Northern Europe, developers are looking to sparsely populated areas, particularly in northern Fennoscandia, which hosts strong winds but also mixed and patchy forests over complex terrain. The complexity makes wind resource assessments difficult, raising uncertainty and therefore cost. Computational fluid dynamics (CFD) has the potential to increase the accuracy and reliability of wind models, but the most common form of commercial CFD modeling, Reynolds averaged Navier-Stokes (RANS), makes limiting assumptions about the effect of the forest on the wind. The wind resource assessment and energy estimation tool WindSim® , developed by WindSim AS, utilizes a porous medium model of a homogeneous forest with the influence of the forest on the airflow as a drag force term in the momentum equations. This method has provided reliable wind speed results but has been less reliable in estimating turbulence characteristics. The measure we evaluate in this study is turbulence intensity (TI). In this investigation, we make two types of modifications to the model and evaluate their impact on the TI estimates by using a benchmark data set collected by Meroney [1]. The first method is a variable profile of leaf area index (LAI) to represent the physical shape of the forest more accurately, and the second is a series of modifications to the closure coefficients in the turbulence transport equations. These modifications focus on the work of Lopes et al. [2], who used a large eddy simulation (LES) model to show that the turbulence production terms originally proposed by Green [3], expanded upon by Sanz [4], and widely used in the industry are unnecessary. Our investigations found that the implementation of a variable LAI profile has a small but non-negligible effect and that the elimination of the production terms from the turbulence transport equations does lead to a significant reduction in TI immediately above the forest. Both methods have minor effects on wind speed estimates, but the modification of closure coefficients has a much more significant impact on the TI. The coefficients proposed by Lopes et al. [2] drastically reduce TI estimates, but the model is still unable to reflect the Meroney data throughout the forest. Continued modification to new closure coefficients in combination with a variable forest LAI and other modifications such as a limited length scale may lead to significant improvement in TI estimates in future models, but these modifications must be compared against real-world data to ensure their applicability.