Dissertationen zum Thema „Meteorology“

The theory used in today’s weather- and climate models to describe processes near the earth’s surface, i.e. transport of heat, moisture and momentum between the ground and the atmosphere, is based on the idea that only local factors are important, such as temperature and wind speed near the ground. However, from measurements made at two sites, one agricultural and one marine, it has been found that large eddies, which are related to the convective boundary layer height, influence the turbulence structure near the ground during unstable conditions more than previously realized. Especially the momentum transport is affected. The large eddies have similar size over land and over the sea, typically 1000 m. The important difference being that over land diurnal variation plays a fundamental role; over the sea such variations are typically absent.

From the marine site it has also been found that the turbulence structure of the temperature field over the Baltic Sea is very different from over land. Instead of having a height dependence as expected from theory, the temperature structure seems to be constant with height within the surface layer.

Typically, the heat flux over the sea is smaller than over land during convective conditions. This gives rise to a turbulence transport regime which is fundamentally different from that observed during daytime convective conditions over land.

Climate is a tremendously complex topic, affecting many aspects of human activity and constantly changing. Defining some structures and rules for how it works is thereof of the utmost importance even though it might only cover a small part of the complexity. Cluster analysis is a tool developed in data analysis that is able to categorize data into groups of similar type. In this paper data from the Swedish Meteorological and Hydrological Institute (SMHI) is clustered to find a partitioning. The cluster analysis used is called Spectral clustering which is a family of methods making use of the spectral properties of graphs. Concrete results over different groupings of climate over Sweden were found.

In the atmosphere vertical extended layers that are in the state of super saturation with respect to ice can appear; these layers have been termed ice-supersaturated layers (ISSL). If an aircraft passes through an ISSL, persistent condensation trails can form. These contrails absorb the long wave radiation from the earth and reflect the incoming short wave radiation from space. The absorbing effect of the long wave radiation is although greater than the reflecting effect of the short wave radiation and therefore these contrails increase the greenhouse effect.This study contain statistics of when ice-supersaturated layers occur in the Swedish airspace, based on data from balloon soundings that take place each day at four locations in Sweden. The soundings that are used in this report were carried out from January 2006 to December of 2010. The results show that ISSL are more common in the Swedish airspace than expected. The layers are by average 42 hPa thick, located at the height of 339 hPa and are present in 44 % of the soundings.
I atmosfären kan det uppkomma vertikalt utsträckta skikt som är övermättade med avseende på is; dessa lager har blivit benämnda som ice-supersaturated layers (ISSL). Om ett flygplan flyger igenom dessa ISSL luftmassor kan permanenta kondensationsstrimmor bildas.Dessa kondensationsstrimmor absorberar den långvågiga strålningen från jorden och reflekterar den inkommande kortvågiga strålningen från rymden. Den absorberande effekten är större än den reflekterande effekten, vilket bidrar till en förstärkning av växthuseffekten. Den här studien innehåller statistik för när dessa ISSL uppkommer i det Svenska luftrummet, baserat på data från ballongsonderingar som var utförda från Januari 2006 till December 2010. Resultatet från denna statistik visar att ISSL är mer vanliga i det Svenska luftrummet än förväntat. Lagren är i medeltal 42 hPa tjocka, placerade på 339 hPa höjd och förekommer i 44 % av sonderingarna.

The urban heat island is an area restricted to a city center where the temperatureis higher than its surrounding environment. The greatest temperature difference isfound at night when the weather is calm and the sky is clear of clouds. There are twomajor causes behind this phenomena and the first one is the use of energy forheating of houses. The heat leaks through the walls of the buildings and warms upthe surrounding mass of air. The second one is the use of building material whichstore the suns radiation on daytime and releases the heat during night. The heatisland leads to larger costs for cooling buildings. It also has an effect on humanhealth, since increased temperatures lead to heat stress which may be fatal. Thisreport aims to investigate if there is an urban heat island located over Uppsala cityand how it can affect daily life for the citizens. To find out how big the urban heatisland effect is in Uppsala city, a number of temperature measurements whereconducted. The results show that there is a visible temperature difference betweenurban and rural areas.

The overall purpose of this thesis work has been to further our understanding of the growth and removal of inclusions in gas- and induction-stirred ladles. The primary focus has been on alumina inclusions.

Growth mechanisms were studied using data from fundamental mathematical models of gas- and induction-stirred ladles. The results showed the turbulence mechanism to be the most dominant in alumina inclusion growth. The dynamic growth and removal of inclusions in a gas-stirred ladle was studied using mathematical modelling. The model results showed concentration gradients of inclusions. The effect was most obvious in the steel flow past the removal sites: top slag, ladle refractory, and gas plume (bubble flotation). A new removal model was developed for large spherical caps bubbles.

In order to verify the predicted concentration gradients for the size population of inclusions, three experiments were carried out in production. The sampling equipment enabled sampling at five different positions and different locations at the same time. The results showed that concentration gradients of inclusions do exist both in induction-stirred and gas-stirred ladles. A theoretical analysis showed that the drag force on the inclusions to be the dominating force and that therefore inclusions follow the fluid flow.

The cluster behaviour of alumina inclusions were examined on steel samples taken in an industrial-scale deoxidation experiment in a ladle. The samples were examined by microscope and the results used to study cluster growth. It was found that there was rapid cluster growth due to collision during stirring and that at the end of the deoxidation experiment a majority of the small inclusions were bound in clusters. The cluster growth data determined using the microscopic results were compared with predicted cluster-growth data. A method was developed for converting the experimental data observed per unit area into data given per unit volume and vice versa. An expression for the collision diameter of the cluster was also developed. The results showed that the predicted cluster growth agreed well with the microscopic observations for the assumptions made in the growth model.

An important factor in forecast models today is cirrus clouds, but not much are known about their dynamics which makes them hard to parameterize. In this study a new theory was derived to enable a more correct way to describe the interplay between radiative heating and dynamical motions in these clouds. This hypothesis was tested by performing three dimensional simulations of cirrus clouds, using the University of Utah Large Eddy Simulator (UULES). Eleven clouds of varying initial radius and ice water mixing ratio were examined, with the aim of finding a pattern in their dynamical features. The model was set up without short wave radiation from the sun, and without any precipitation affecting the clouds, leaving only terrestrial heating and atmospheric cooling to create motions in the clouds. Two categories of initial dynamics could be seen:

• Isentropic adjustment: The isentropes within the cloud are adjusting to the environment due to rising of the cloud. Causes horizontal spreading through continuity.

• Density current: A dominating initial feature is spreading in small mixed layers at the cloud top and bottom. Caused by the density difference between the cloud and its environment.

An interesting phenomenon showing up in the simulations was mammatus clouds, which were visible in two of the cases. The only instability available to create these clouds was the radiative heating difference, which does not agree with present theories for how they form.

Two dimensionless numbers S and C were derived to describe the nature of the spreading motions and convection in the cloud. Both these numbers agreed with results.

Cirrusmoln har en viktig roll i dagens prognosmodeller, men är svåra att parametrisera på ett bra sätt eftersom man inte har tillräcklig kunskap om deras dynamik och utveckling. I denna studie togs en ny teori fram för att göra det möjligt att på ett mer korrekt sätt beskriva samspelet mellan strålningsuppvärmning och dynamiska rörelser i dessa moln. Hypotesen testades sedan genom att utföra tredimensionella simuleringar av cirrus moln med hjälp av University of Utah Large Eddy Simulator (UULES). Elva moln med varierande initiella radier och isvatteninnehåll undersöktes, med målet att finna ett mönster i dynamik och utveckling. UULES ställdes in så att miljön där molnen simulerades varken innehöll kortvågsstrålning från solen eller nederbörd. Således fanns det bara en resterande faktor för att skapa rörelser i molnen; skillnaden i den infraröda strålningsuppvärmningen mellan molntopp och molnbas. Två kategorier av initiella rörelser uppstod i molnen:

• Justering av isotroper: Molnen stiger i höjd vilket gör att isotroperna inuti dem justeras till omgivningen. Detta orsakar horisontell spridning genom kontinuitet.

• Densitets ström: Horisontell spridning av molnen koncentrerad till mixade skikt i de övre och undre delarna. Orsakas av skillnad i densitet mellan moln och omgivning.

Ett intressant fenomen som visade sig i två av simuleringarna var mammatusmoln. Den enda instabiliteten tillgänglig för att skapa dessa moln var skillnaden i strålningsuppvärmning mellan molntopp och -bas. Detta stämmer inte överrens med nuvarande teorier för hur dessa moln skapas.

Två dimensionslösa tal, S och C togs fram för att indikera vilken av de initiella rörelserna som dominerar i molnet, samt vilken typ av konvektion som dominerar. Båda dessa tal stämde väl överrens med resultat.

This thesis examines the relationship between synoptic meteorology and particulate matter (PM10). PM10 is a pollutant of high interest to UK health policy (DEFRA, 2016) and this study evaluates the importance of Rossby wave breaking (RWB) on UK PM10 concentration ([PM10]). RWB can result in atmospheric blocking, which is one extreme of mid-latitude synoptic meteorological variability that favours the accumulation of PM10. This study finds significant increases (p < 0.01) in UK Midlands [PM10] resulting from winter-time northeast Atlantic/ European RWB. Furthermore, this study shows that northeast Atlantic/ European RWB increases the probability of exceeding a hazardous [PM10] threshold. We have identified the Omega block as the most hazardous RWB subset, with a probability of exceeding a hazardous [PM10] threshold (0.383) over three times that for days without RWB (0.129). We have implemented a tracer framework within a Hadley centre Met-Office climate model (HADGEM3-GA4) to identify flow regimes influencing the UK throughout northeast Atlantic/European RWB events. A present-day HADGEM3-GA4 simulation, nudged to ERA-Interim reanalysis data, is used to verify the tracer framework and to identify the flow regimes influencing Omega block events. This study finds that the advection of European tracer and the accumulation of locally sourced tracer contribute to hazardous [PM10] throughout Omega block events. This study’s principal aim is to determine climatic shifts in both the frequency of synoptic meteorological conditions conducive to UK PM10 accumulation and in the corresponding flow regimes. Using a further two HADGEM3-GA4 simulations, we find a north-eastward climate shift in northeast Atlantic/European RWB, with an overall reduction in events. Additionally, we find that uture RWB events result in significantly (p<0.01) increased European and reduced stagnant air masses within the UK. This result indicates a reduced frequency of UK [PM10] exceedances, however a tendency for increased transport of toxic particles from Europe.

Inom Försvarsmaktens vädertjänst används ett PC-program för att beräkna illuminansen från måne och stjärnor under loppet av en vald natt. Korrektion för moln görs därefter genom ett schematiskt förfarande. I detta arbete ges förslag till två förändringar av ljusprognosmodellen.

1. Parametern ”markytans tillstånd” införlivas i modellen, samtidigt som hänsyn tas till mängden (och typen av) moln. Det sammanlagt tillgängliga ljuset under eventuella moln, S, kan beräknas genom sambandet

S=(1+Am)(I0*(1-N*Aso))/(1-Am*Asu*N)

där N är molnmängden, Aso molnöversidans albedo, Asu molnundersidans albedo, Am markens albedo och I0 den inkommande strålningen ovan eventuella moln.

2. Det artificiella ljuset och dess spridning under molnfria förhållanden införlivas i modellen. Detta sker lämpligtvis genom användande av satellitbilder som visar det artificiella ljusets spridning under molnfria nätter, vid genomsnittliga absorptions- och spridningsförhållanden.

Ett ytterligare förslag är att illuminansen för artificiellt ljus vid icke molnfria förhållanden införlivas i modellen i ett senare skede. Detta görs förslagsvis genom att man utgår ifrån satellitbilder som visar artificiellt ljus, men som inte är justerade med avseende på ljusets spridning vid molnfria förhållanden. Denna information kombineras med en enklare modell som beskriver ett samband mellan molnbas, sikt, ljusspridning och avståndet till artificiella ljuskällor. Samtidigt sker förbättringar i den grafiska presentationen.

Dimma är ett komplext småskaligt väderfenomen som gäckat meteorologerna ända sedan väderprognosernas start och varit en bidragande orsak till att många mist livet inte minst inom flyget. Än idag är prognostisering av dimma mycket svårt i synnerhet strålningsdimma. Studier (COST, 2007) har visat att för att en modell ska kunna fånga formation av dimma krävs det i vissa fall att den skall kunna lösa upp inversionsskikt på 10m.Därtill uppgår osäkerheten i många fall för numeriska modeller vid fastställande av sikten i dimma till 50 %. Då kan en statistisk kartläggning specifikt för varje dimtyp utgöra ett bra komplement till modellerna för att få en uppfattning om exempelvis sikten i dimman. I den här studien användes observationer gjorda med en halvtimmes mellanrum från Arlanda under perioden 1993-07-01 – 2009-11-03.I denna kartläggning identifierades de fyra dimtyperna: strålningsdimma, nederbördsdimma, advektionsdimma samt dimma orsakad av en sänkning av molnbasen till marknivå (molndimma). Här framkom att strålningsdimman var den vanligaste dimtypen (43,6%) och mest frekvent under sommaren och hösten, till skillnad från nederbördsdimma och advektionsdimma som var vanligast under vinterhalvåret. För strålningsdimman fann man också de sämsta siktvärdena följt av molndimma. Det framkom också att frekvensen av de fall där strålningsdimman täcker hela flygplatsen avsevärt minskat sedan början på 2000-talet, detta samtidigt som utbyggnaden av flygplatsen stod klar.Vid studierna av isdimma och vattendimma visade det sig att den lägsta sikten för vattendimmor uppkom då temperaturen och den specifika fuktigheten var som högst. Medan för isdimma fann man de lägsta siktvärdena vid temperaturer runt -20 °C
Since the beginning of weather forecasting fog has caused many meteorologists severe problems, and in aviation it has been one of the main reasons for several crashes. Even today with the latest numerical models, predicting fog is a difficult task. New studies have shown that to predict fog the model must be able to resolve inversion layers down to 10 m. Even then the precision in determination of the visibility inside the fog is down to 50 % (Gultepe, 2007). In those cases a statistical mapping of fog at a certain place could be a good complement to the numerical models in determining time of formation and visibility. In this study I have used METAR observations made at Arlanda airport from 1993-07-01 to 2009-11-03, which are made every half an hour. In the mapping Radiation fog, Advection fog, Precipitation fog and fog caused by lowering of clouds (cbl. fog) was sorted out. I also looked into the behavior of ice fog vs. water fog.The results showed that radiation fog was the most common fog type (43,6 %) and had the lowest rate of visibility followed by cbl. fog. Radiation fog also had its highest frequency on summer and autumn, while advection fog and precipitation fog was concentrated into wintertime. Additionally the study showed that the frequency of the times when radiation fog covers the whole airport started to decrease at the beginning of the 21st century. Coinciding with when the expansion of the airport was finished including a new runway. In the comparison between water fog and ice fog it was clear that the distribution of visibility was similar. The lowest visibilities in water fog was found at the highest temperatures and highest specific liquid water content while in ice fog the lowest visibilities where found for temperatures in the neighborhood of - 20 °C. For temperatures below - 20 °C there were no observations of fog.

A new large eddy simulation (LES) code is developed and used to investigate non-local features of turbulent planetary boundary layers (PBLs). The LES code is based on filtered Navier-Stokes equations, which describe motions of incompressible, Boussinesq fluid at high Reynolds numbers. The code computes directly large-scale, non-universal turbulence in the PBL whereas small-scale, universal turbulence is parameterized by a dynamic mixed subgrid closure. The LES code is thoroughly tested against high quality laboratory and field data.

This study addresses non-local properties of turbulence which emphasis on the stable stratification. Its basic results are as follows. The flow stability in PBLs is generally caused by two mechanisms: the negative buoyancy force (in the stable density stratification) and the Coriolis force (in the rotating system). The latter stabilizes the flow if the earth’s vorticity and the turbulent vorticity are anti-parallel. The Coriolis force stability suppresses large-scale turbulence and makes large eddies asymmetric. The density stratification suppresses vertical scales of turbulence. Joint actions of the Coriolis and the buoyancy forces result in a more complex behavior of turbulence. Particularly, the layers of vigorous turbulence may appear in the course of development of low-level jets in baroclinic atmosphere.

Non-local effects determine integral measures of PBLs, first of all the PBL depth. This study clearly demonstrates its pronounced dependences on the Coriolis parameter, the Kazanski-Monin internal stability parameter, and newly introduced imposed-stability and baroclinicity parameters. An LES database is created and used to validate an advanced PBL-depth formulation. LES support the idea that PBLs interact with the stably stratified free flow through the radiation of gravity waves, excited by large turbulent eddies at the interface.

This thesis considers the development and implementation of a moving mesh strategy which is suitable for the numerical solution of partial differential equations (PDEs) that arise in problems relevant to meteorology. We concentrate primarliy on developing the Parabolic Monge-Ampère (PMA) moving mesh method. This is an r-adaptive method which is based on ideas from optimal transportation combined with the equidistribution principle applied to a (time varying) scalar monitor function (used successfully in moving mesh methods in one-dimension). The mesh is obtained by taking the gradient of a (scalar) mesh potential function which satisfies an appropriate nonlinear parabolic partial differential equation. This method is straightforward to program and implement, requiring the solution of only one simple scalar time-dependent equation in arbitrary dimension. Furthermore it produces meshes of provable regularity and smoothness. The mesh equation is augmented with suitable Neumann or periodic boundary conditions, with adaptivity along the boundaries handled automatically. Examples are presented of periodic and non-periodic meshes generated for a prescribed monitor function. The PMA mesh equation is then successfully coupled to a number of convection dominated PDEs in 1D and 2D and the relative merits of solving the resultant systems, using a simultaneous or an alternate solution procedure, are explored. The main test problem considered is the two-dimensional Eady problem, a meteorological problem which models the development of cyclones at mid-latitudes. Numerical solutions obtained on an adaptive grid using PMA are presented. The results show improved resolution of the front when compared to uniform grid solutions with an equivalent number of mesh points and computed with the same time step. A pressure-correction method is implemented on a semi-staggered adaptive grid that also conserves important physical properties of the solution. All numerical solutions presented involve discretising the underlying equations in the computational domain, which is fixed and uniform, using a finite difference scheme. An alternating strategy is implemented whereby the Eady equations are integrated first and then the mesh is updated. A conservative interpolation scheme is used to interpolate the updated solution from the old grid onto the new grid.

Many millions of people watch television weather forecasts everyday, but a detailed analysis of the information such forecasts convey and how and why viewers watch them has not previously been undertaken. New technology is presenting television stations with both challenges and opportunities. Viewers no longer have to rely on watching a forecast at a time dictated by the television station, they can now choose when, where and how to watch forecasts. This thesis reviews the visual presentation of weather forecasts from paintings of the 14th Century to the latest on-demand technology. Viewers are surveyed to assess their recall of weather forecasts and their preferences for how information should be presented, displayed and broadcast in order to maximise audience figures and the financial attractiveness of the television weather forecast to potential sponsors or licence fee payers. Using the results of the research, a proposal is made for the creation of an internet based television weather channel.

El propósito de esta investigación es maximizar el impacto de la asimilación de datos radar sobre el pronóstico de precipitación a muy corto plazo usando el modelo Weather Research and Forecasting (WRF), de tal manera que pueda ser implementado de modo operativo en los Servicios Meteorológicos Nacionales. En una primera fase se utiliza un episodio de precipitación extrema que tuvo lugar en Cataluña (NE de España) para probar varias configuraciones de predicción inmediata, basadas en el modelo WRF con la asimilación de datos radar, y en una segunda fase, se profundizan los resultados a través de una serie de experimentos basados en diez eventos de precipitación extrema ocurridos en Cataluña en el periodo 2015 - 2017. Las configuraciones consideradas se generan modificando: 1) el ciclo de inicialización del WRF, 2) los procedimientos de preprocesamiento de datos radar utilizados por el Centro Nacional de Investigación Atmosférica (NCAR) y por el Servicio Meteorológico de Cataluña (SMC), 3) datos convencionales y de radar asimilados dentro del sistema variacional tridimensional (3DVAR), y 4), otros parámetros tales como la escala de longitud de las observaciones, el número de bucles externos y la parametrización de la convección húmeda. El efecto de los anteriores parámetros se evalúa mediante la habilidad de una serie de experimentos para simular la cantidad y localización de la precipitación usando técnicas estadísticas convencionales, índices categóricos y el Receiver Operating Characteristic (ROC). Sin embargo, en este estudio la construcción de las tablas de contingencia está condicionada al desplazamiento del patrón de precipitación y la cercanía entre los valores observados y pronosticados, sin considerar los umbrales de precipitación. El método de control de calidad desarrollado por el SMC es confiable y en el caso particular del 12 de octubre de 2016, produjo mejores resultados que el método de NCAR. La predicción inmediata de precipitación logra mejores resultados cuando el modelo WRF es ejecutado con dos ciclos de asimilación, uno en frío y otro en caliente con un length scale de 0.75 y 0.50 respectivamente, asimilando en cada ciclo datos radar y datos convencionales en un mismo momento y con el error del background CV7. Los largos ciclos de inicialización, las actuales parametrizaciones usadas en el SMC y el uso de tres bucles externos no mejoran los resultados del pronóstico.
The purpose of this research is to maximize the radar data assimilation impact on precipitation nowcasting using the Weather Research and Forecasting (WRF), in such a way that it can be implemented operationally in the National Meteorological Services. In a first phase is used an episode of extreme precipitation that took place in Catalonia (NE Spain) to test several nowcasting system configurations, which are based on the Weather Research and Forecasting (WRF) model with radar data assimilation, and in a second phase, the results are deepened through a series of experiments based on ten extreme precipitation events that occurred in Catalonia in the period 2015 - 2017. The configurations considered are generated by modifying the following elements: 1) the WRF initialization cycle, 2) the radar data preprocessing procedures used by the National Center for Atmospheric Research (NCAR) and by the Meteorological Service of Catalonia (SMC), 3) conventional and radar data assimilated within the three dimensional variational system (3DVAR), and 4), other parameters such as the observations length scale, number of outer loops and the cumulus parameterization. The effect of the previous parameters is evaluated through the skill of the different experiments to simulate both the amount and location of precipitation using conventional statistical techniques, categorical indices and the Receiver Operating Characteristic (ROC). However, in this study the construction of the contingency tables has been conditioned to the precipitation pattern displacement and the closeness between the observed and forecast values without considering precipitation thresholds. The quality control method developed by the SMC is trustworthy and in the particular case occurred on October 12, 2016, it produced better results than the NCAR method. The precipitation nowcasting achieves better results when the WRF model is executed with two assimilation cycles, one in cold and another in warm with a length scale of 0.75 and 0.50 respectively, assimilating in each of these cycles radar data and conventional data (METAR and SYNOP) at the same time and with the background error CV7. The long initialization cycles, the current parameterizations used in the SMC and the use of three external loops do not improve the forecast results.

If an estuarine system is to be investigated using an oceanographic modeling approach, a decision must be made whether to use a simple and robust framework based on e.g. mass-balance considerations, or if a more advanced process-resolving three-dimensional (3-D) numerical model are necessary. Although the former are straightforward to apply, certain fundamental constraints must be fulfilled. 3-D modeling, even though requiring significant efforts to implement, generates an abundance of highly resolved data in time and space, which may lead to problems when attempting to specify the "representative state" of the system, a common goal in estuarine studies.

In this thesis, different types of models suitable for investigating estuarine systems have been utilized in various settings. A mass-balance model was applied to investigate potential changes of water fluxes and salinities due to the restoration of a mangrove estuary in northern Colombia. Seiches, i.e. standing waves, in the Baltic Sea were simulated using a 2-D shallow-water model which showed that the dominating harmonic oscillation originates from a fjord seiche in the Gulf of Finland rather than being global. Another study pertaining to the Gulf of Finland used velocity-fields from a 3-D numerical model together with Lagrangian-trajectory analyses to investigate the mixing dynamics. The results showed that water from the Baltic proper is mixed with that from the river Neva over a limited zone in the inner parts of the Gulf. Lagrangian-trajectory analysis was finally also used as a tool to compare mass-balance and 3-D model results from the Gulf of Riga and the Bay of Gdansk, highlighting when and where each method is applicable.

From the present thesis it can be concluded that the above described estuarine-modeling approaches not only require different levels of effort for their implementation, but also yield results of varying quality. If oceanographic aspects are to be taken into account within Integrated Coastal Zone Managment, which most likely should be the case, it is therefore important to decide as early as possible in the planning process which model to use, since this choice ultimately determines how much information about the physical processes characterizing the system the model can be expected to provide.

The increasing levels of the greenhouse gas carbon dioxide (CO2) in the Earths atmosphere, caused by human release of CO2, has made it desirable to understand the factors determining the CO2-variation because of CO2’s warming effect on the Earths temperature which will change the premises of all life on earth.

The purpose of this investigation is to understand the effects of the largest factors of influence on the CO2-concentration - like sea, vegetation and anthropogenic outlets - in the Baltic Sea region, and possible surprises from the results. To be able to do this only from CO2-measurements some assumptions have to be done as starting point. Such are that, besides from the yearly trend of the CO2-concentration and the variation of oceanic influence, monthly variation only is caused by vegetation and that the yearly offset in CO2-levels only is affected by anthropogenic outlets. These factors are together called the local season and will be used for evaluation of the CO2-values for each site. This analysis is done for eight sites surrounding the Baltic Sea region and is compared with results from the site of Östergarnsholm, an island in the Baltic Sea east of Gotland.

The results show that stations with high vegetational influence has high amplitudes for the local season compared to sites more influenced by sea. This also makes the amplitude to be connected with latitude since sites with longer growing season is surrounded by higher density of vegetation. The minimum for the local season is also dependent on the growing season, since it occurs when the vegetational consumption is largest. Peaks in the local season can be seen in connection with the maximum decay of the natural vegetation in the early winter months, and with the planting and harvest season for agricultural land. Considering the effect from anthropogenic influence a clear connection in the offset of the local season can be seen, with higher offsets for sites of higher anthropogenic influence and vice versa. Anthropogenic influence also seems to give raised values in summer for the local season, indicating that the variation of the local season cannot be simply connected to only vegetational influence. For variability, higher values in the summer months are seen for the anthropogenic sites, while in winter the variability is more similar for all sites. This might be connected with a higher degree of local influence during summers, which for anthropogenic stations leads to high variability due to inhomogenous surroundings.

For Östergarnsholm we get higher amplitude for the local season than expected, this is partly due to unrepresentatively high amplitudes for the seasons used, but also probably to some degree of underestimation of the vegetational influence. Due to correction of the offset it was not possible to draw any conclusions from this factor, but rather give suggestions of what the correction should be. When analysing the local season for different source areas by WD-classification we see the surprising property that the sector that should be most influenced by land, due to higher values in summer, has a lower amplitude than the sector most influenced by sea. Since it was suggested that anthropogenic influence gives raised values in summer this was suggested as an explanation.

During the Arctic summer when the anthropogenic influence is limited, the natural marine source of sulfur in the form of gas-phase dimethyl sulfide viz. DMS(g), is of great importance for cloud formation. The harsh environment of the Arctic makes it difficult to perform in situ measurements of DMS(g) and hence regional model simulations can serve as a complement to increase our understanding of DMS related processes in the Arctic. In this thesis a regional scale meteorological forecast model, extended with DMS(g) calculations, is used to provide a consistent three-dimensional time evolving picture of DMS(g) over the pack-ice region. The analysis focus on meteorological aspects on the horizontal and vertical distribution of DMS(g). Our results show that the amount of DMS(g) over an oceanic source region alone does not determine concentration found over the pack-ice, the prevailing wind also exerts a large influence on the horizontal DMS(g) distribution. The modeled DMS(g) concentrations are advected in plumes in over the pack-ice, which, in combination with the photo-chemical decay, explain the large observed temporal variability of DMS(g) over the pack-ice. The modeled vertical structure show episodes with DMS(g) maxima well above the local boundary layer. Also shown is that DMS(g) maxima can be formed adjacent to frontal zones. In the presence of turbulence DMS(g) can be mixed downwards into the local boundary layer and aid growth to local particles and hence contribute to cloud formation in the boundary layer.
At the time of the doctoral defense the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2: Manuscript. Paper 4: Manuscript.

Natural disasters of hydro-meteorological origin are the biggest risk worldwide. In Catalonia (NE of the Iberian Peninsula), severe weather and flash floods occur each year, resulting in major damage to property, losses in agriculture, and also of human lives. To reduce its impact, we need to improve the early warning systems and storm short-term forecasting. There’s a need to gain in-depth knowledge of severe thunderstorm dynamics, since the current accused conditions of global warming can impact in factors triggering these storms. The main objective of the present thesis is to enhance the knowledge of severe storms dynamics and to improve their identification and monitoring in real time, in order to help prevent their surface effects on the citizens. The project addresses the unresolved problem of storm anomalous motion, as it becomes a great challenge to predict their evolution and impact in the next few hours. For this purpose, the area of Catalonia has been chosen as the study region of this project, due to the proximity to the sea and complex topography, which are often key factors in varying the weather at a local scale. There is also the advantage of having good radar coverage, which will be the essential tool for characterizing storms. We first propose a methodology that identifies potentially convective days from daily cumulative rainfall fields, selects them to search for storms, and determines if their motion is anomalous. We have found that the area with the highest convective activity between 2008-2015 in Catalonia was located in the eastern Pre-Pyrenees, due to the possible creation of a convergence line. It has also been identified that there are more convective structures with possible anomalous propagation in summer and spring, with the main patterns being related to splitting, merging, stationarity and elongated storms. Once the study sample is defined, we have developed an algorithm to improve the identification and tracking of these thunderstorms, especially those with anomalous propagations. The keys of improvement have been based on proposing new techniques in the three main modules; 2D, 3D identification and tracking. In addition, it incorporates alerts before possible cell splitting or merging. These changes have shown that the algorithm is able to faithfully reproduce storm life cycle, correctly identify in advanced anomalous motion, and correctly distinguish storms in highly dense convective situations. The algorithm has been verified first over 30 severe cases, proving that it can identify anomalous movements with a mean 30-min lead-time, being the splitting, the easiest one to do. It has also been demonstrated a good ability at not only identifying these movements but also separating cases with and without anomalous motion. On the other hand, the algorithm has demonstrated a good performance in cases of heavy rainfall on a Catalan flood-prone coastal area of touristic interest. It is identified that storms are usually organized in convergence lines, and that topography and the sea play a very important role, whether affecting the movement, the time of exposure, or the amount of precipitable water causing flash floods. Finally, the dual-Doppler technique is applied in Catalonia for the first time. This allows getting complete information of the internal dynamics of a thunderstorm, without the need of running idealized models, and then, getting to know the local topographic influence on the evolution and organization. It is demonstrated that the complex local topography changes and/or amplifies the wind flow inside and near thunderstorms, modifying completely their life cycle and their possible interactions with their neighbor cells. It is also shown that this qualitative improvement into storm-scale dynamic knowledge can improve the nowcasting techniques and the early warning systems in the future.
Els desastres naturals d’origen hidro-meteorològic constitueixen el major risc a nivell mundial. A Catalunya, cada any es succeeixen diferents episodis de temps advers i inundacions, provocant també danys importants en béns materials, pèrdues en l’agricultura, o pèrdua de vides humanes. Aquestes dades poden augmentar en les condicions cada cop més acusades d’escalfament global. Per reduir l’impacte d’aquest fenòmens és necessari millorar els sistemes d’alerta primerenca a molt curt termini, així com la monitorització dels sistemes meteorològics causants d’aquests fenòmens. En aquest context l’objectiu principal d’aquesta tesi doctoral es millorar el coneixement profund de la dinàmica de les tempestes severes, la seva identificació, predicció a molt curt termini, i monitoratge a temps real. Assolir aquest objectiu implica millorar la prevenció dels seus efectes en superfície. La tesis aborda una problemàtica encara no resolta sobre el moviment anòmal d’aquestes tempestes, que esdevé un gran repte a l’hora de pronosticar-ne la seva evolució en les properes hores, i per tant, el seu impacte. A més, es centra a Catalunya, degut a la seva proximitat al Mar Mediterrani i la complexa topografia, factors claus resultants en una meteorologia variada quasi a nivell de municipi, on hi ha l’avantatge de disposar d’una bona cobertura radar, eina essencial per la caracterització de les tempestes. Primer, es proposa una metodologia que permet identificar les situacions potencialment convectives a partir de camps de precipitació acumulada diària, seleccionant aquestes per cercar les tempestes i determinar si el seu moviment és anòmal (del Moral et al., 2017). Definida la mostra d’estudi, es desenvolupa un algoritme que permet millorar la identificació i seguiment d’aquestes tempestes, sobretot quan es tracta d’aquelles amb moviment anòmal (del Moral et al., 2018a). El funcionament de l’algorisme es verifica en dos règims de convecció diferent: casos severs d’interior (del Moral et al., 2018b), i pluges intenses a la costa (del Moral et al., 2020a). Finalment, s’introdueix per primer cop en un país sud-Europeu la tècnica dual-Doppler: obtenció de variables dinàmiques dins de les pròpies tempestes a partir d’observacions radar, per a l’estudi de les interaccions de més petita escala (del Moral et al., 2020b).

Extreme-temperature events are known to favor large wildland fires and have consequences for human health and mortality, forest disturbance patterns, agricultural productivity, and the economic repercussions of these consequences combined. To gain insight into whether extreme-temperature events are changing in light of global climate dynamics, the annual numbers of high-temperature days (those with temperatures higher than 20, 22.5, and 25 ºC at 850 hPa) were analyzed across southern Europe from the years 1978 to 2012. A significant increase in the frequency of these days was found in many areas over the time period analyzed, and patterns in the spatial distribution of these changes were identified. Additionally, this work analyzes the effects of high temperature days on medium and large fires from 1978 to 2010 in Spain and other areas (Sardinia, Italy). A high temperature day was defined as being when air temperature at 850 hPa was higher than the 95th percentile of air temperature at that elevation from June to September across the study period. Temperature at 850 hPa was chosen because it properly characterizes the state of the lower troposphere. The effects of high temperature on forest fires were remarkable and significant in terms of fire number (15 % of total large fires occurred under high temperature days), burned area (25 % of the total burned area occurred under high temperature days). Fire size was also significantly higher under 95th percentile air temperature at 850 hPa and a large part of the largest fires in the past 20 years were under these extreme conditions. Additionally, both burned area and fire number only decreased under non-high temperature days in the study period and not under high temperature conditions. The worst consequence of wildland fires is the loss of human lives, a regular phenomenon over the last few decades worldwide. This work analyzes all recorded wildland fires in Spain with victims between 1980 and 2010. We classified causality causes during wildland fires to study the most frequent causes of fatalities and how they were related to regions, fire size, and extreme weather conditions (i.e., high temperature days). Trends in number of both injured and killed individuals were analyzed. We observed that the annual number of victims did not decrease in the study period. Entrapment is the most frequent cause of death within the fire suppression employees. Fire size is a key factor in the occurrence of victims because 95% of fatalities in wildland fires (not counting aerial casualties) happened in fires larger than 100 ha. High temperature days also were important because 60% of entrapments were produced in this kind of days.
Los eventos con temperaturas extremas favorecen la ocurrencia de grandes incendios forestales y tienen consecuencias en la salud y mortalidad humana, los patrones de perturbación forestal, la productividad agrícola y las repercusiones económicas de estas consecuencias combinadas. Para conocer si los eventos de temperaturas extremas están cambiando bajo la dinámica de cambio global, se analizaron las cifras anuales de días de alta temperatura (aquellos con temperaturas superiores a los 20, 22,5 y 25 ºC a 850 hPa) en el sur de Europa en el periodo 1978-2012. Un aumento significativo en la frecuencia de este tipo de días se encontró en muchas áreas durante el período de tiempo analizado, y se identificaron patrones en la distribución espacial de estos cambios. Además, este trabajo analiza los efectos de días de alta temperatura en incendios forestales medianos y grandes en España desde 1978, así como en otras áreas (Cerdeña, Italia). Un día de alta temperatura se define cuando la temperatura del aire a 850 hPa es mayor que el percentil 95 de la temperatura del aire a 850 hPa de junio a septiembre en todo el período de estudio. Elegí la temperatura a 850 hPa porque caracteriza adecuadamente el estado de la baja troposfera. Los efectos de las altas temperaturas sobre los incendios forestales fueron notables y significativos en términos de número de incendios (el 15% del total de los grandes incendios ocurrieron bajo días de alta temperatura) y área quemada (25% del total de área quemada se produjo bajo días de alta temperatura). El tamaño de los incendios también fue significativamente mayor en condiciones de alta temperatura y gran parte de los incendios más grandes en los últimos 20 años fueron en este tipo de condiciones extremas. Además, tanto el número de incendios como el área quemada solamente disminuyeron bajo días de no alta temperatura en el período de estudio. La peor consecuencia de los incendios forestales es la pérdida de vidas humanas, un fenómeno que se ha producido con regularidad durante las últimas décadas en todo el mundo. Este trabajo analiza todos los incendios forestales en España con víctimas registradas entre 1980 y 2010. Los incendios se clasificaron por la causa que provocó la muerte de las víctimas durante los incendios forestales con el objetivo de estudiar las causas más frecuentes en accidentes mortales y cómo se relaciona con distintas regiones geográficas, el tamaño de los incendios, y las condiciones climáticas extremas (es decir, días de alta temperatura). Se analizaron tendencias temporales en el número de individuos heridos y muertos en el periodo de estudio. Se observa que el número anual de víctimas no disminuyó en el período de estudio. El atrapamiento es la causa más frecuente de muerte dentro de los empleados de extinción de incendios. El tamaño de los incendios es un factor clave en la aparición de las víctimas ya que el 95% de las muertes en incendios forestales (sin contar las bajas aéreas) ocurrió en incendios mayores de 100 ha. Los días de alta temperatura también fueron claves debido a que el 60% de atrapamientos se produjo en este tipo de días.
Els esdeveniments amb temperatures extremes afavoreixen l’aparició de grans incendis forestals amb conseqüències en la salut i mortalitat humana, els patrons de pertorbació forestal, la productivitat agrícola i les repercussions econòmiques d’aquestes conseqüències combinades. Per conèixer si els esdeveniments de temperatures extremes estan canviant amb la dinàmica de canvi global, es van analitzar les xifres anuals de dies amb altes temperatures (aquells dies amb temperatures superiors als 20, 22.5 i 25ºC a 850hPa) al sud d’Europa en el període 1978-2012. Un augment significatiu en la freqüència d’aquest tipus de dies es va trobar en moltes àrees durant el període de temps analitzat, i es van identificar patrons en la distribució espacial d’aquests canvis. A més, aquest treball analitza els efectes de dies d’alta temperatura en incendis forestals mitjans i grans a Espanya des de 1978, així com en altres àrees (Cerdenya, Itàlia). Es defineix un dia d’alta temperatura quan la temperatura de l’aire a 850hPa és més gran que el percentil 95 de la temperatura de l’aire a 850hPa de juny a setembre en tot el període d’estudi. Vaig triar la temperatura a 850hPa perquè caracteritza adequadament l’estat de la baixa troposfera. Els efectes de les altes temperatures sobre els incendis forestals van ser notables i significatius en termes de nombre d’incendis (el 15% del total dels grans incendis es van produir en dies d’alta temperatura) i àrea cremada (el 25% del total d’àrea cremada es va produir en dies d’alta temperatura). Les dimensions dels incendis també van ser significativament més grans en condicions de temperatura i gran part dels incendis més grans en els últims 20 anys van ser en aquest tipus de condicions extremes. A més, tant el nombre d’incendis com l’àrea cremada només van disminuir en dies de no alta temperatura en el període d’estudi. La pitjor conseqüència dels incendis forestals és la pèrdua d’éssers humans, un fenomen que s’ha produït amb regularitat durant les últimes dècades a tot el món. Aquest treball analitza tots els incendis forestals d’Espanya amb víctimes registrades entre els anys 1980 i 2010. Els incendis es van classificar per la causa que va provocar la mort de les víctimes durant els incendis forestals amb l’objectiu d’estudiar les causes més freqüents en accidents mortals i la seva relació amb les diferents regions geogràfiques, les dimensions dels incendis, i les condicions climàtiques extremes (és a dir, dies d’alta temperatura). Es van analitzar tendències temporals en el nombre d’individus ferits i morts en el període d’estudi. L’atrapament és la causa més freqüent de mort dins dels empleats d’extinció d’incendis. Les dimensions dels incendis són un factor clau en l’aparició de les víctimes, ja que el 95% de les morts en incendis forestals (sense tenir en compte les baixes aèries) es van produir en incendis que afectaven més de 100 ha. Els dies d’alta temperatura també van ser claus pel fet que el 60% d’atrapaments es van produir en aquest tipus de dies.

Catalunya, i en concret el Pla de Lleida, són zones sovint afectades per les pedregades. En general, els episodis més severs i freqüents es produeixen des de finals de la primavera fins a principis de la tardor. Aquest període coincideix amb el moment en què determinats cultius de la zona són altament vulnerables, degut al seu cicle vegetatiu. La importància a nivell econòmic i social que tenen les pedregades al territori català, com també la complexitat del fenomen, ha comportat que nombrosos científics hagin estudiat el tema des de diferents punts de vista. En aquesta tesi s'ha aprofundit en temes de diagnosi i predicció, amb una fase preliminar d'anàlisi per conèixer la distribució espacial i estacional de les pedregades a la zona. En temes de diagnosi, i amb l'objectiu de conèixer el diàmetre de la pedra obtinguda en indrets sense possibilitat d'observació directa, s'ha aplicat un mètode d'estimació de la mida de la pedra. Els resultats més òptims s'han aconseguit a partir del mètode cokriging universal, combinant poques dades puntuals, les observacions en superfície, amb una variable contínua secundària, que en aquest cas es tracta d'informació radar. Els valors estimats més propers a la realitat s'han aconseguit utilitzant el producte vertically integrated liquid (VIL) de la imatge no corregida del radar de la Panadella (CDV). Pel que fa al camp de la predicció, s'ha aplicat l'algorisme lightning jump (LJ), amb importants modificacions respecte a la metodologia original i adaptant-lo a les necessitats operatives del Servei Meteorològic de Catalunya (SMC), amb l'objectiu de pronosticar temps sever a curt termini al nostre país. El percentatge d'encert d'aquesta eina davant aquests fenòmens és molt elevat. A més, un altre fet important és que el percentatge d'error és molt baix. La distància de temps en què s'alerta de possible temps sever, coneguda com a lead time, inicialment, s'ha mogut entre 15 i 45 minuts amb un pic als 20 minuts. Posteriorment, a partir de la incorporació del paràmetre de la multiplicitat en l'algorisme, aquesta distància temporal s'ha incrementat fins a 120 minuts. L'anàlisi de la predicció segons la severitat de la tempesta o, altrament dit, segons el diàmetre de la pedra ha estat costosa i se n'han extret poques conclusions discriminatòries, a partir dels casos estudiats. En conjunt, l'activitat elèctrica i el comportament d'alguns paràmetres radar no han mostrat diferències significatives per arribar a determinar si una tempesta va acompanyada de pedra grossa o petita, en el moment que salta una alerta de LJ. Només el perfil de reflectivitat seria considerat una característica determinant que pot facilitar aquest tipus de pronòstic. Durant les campanyes més recents, l'eina de LJ ha estat aplicada en l'operativa de l'Equip de Predicció i Vigilància (EPV) de l’SMC. Inicialment, es va posar en mode de prova, i va passar, vistos els bons resultats, a l'operativa en temps real. Aquest seguiment ha permès portar un control diari de l'eina i trobar millores en l'algorisme. Per tant, es demostra l'aplicabilitat de la present tesi en tasques del dia a dia. La multiplicitat, esmentada prèviament, ha estat una característica afegida recentment, la qual ha permès pronosticar pedregades de mida inferior als 2 cm, precipitacions intenses, com també millora la predicció de temps sever. Finalment, per cobrir la manca d'observacions en determinades situacions de severitat, s'ha dut a terme la campanya de ciència ciutadana Plega/Caça la pedra. S'han obtingut uns resultats satisfactoris triplicant quasi el nombre d'observacions respecte d'anys anteriors. Aquesta quantitat d'observacions ha permès fer un millor control i validació de l'eina de LJ.
The hail is a common severe weather phenomenon in Catalonia, producing important damages in different society environments. Nowadays, there are a lot of doubts about its forecast and, although, on respect the diagnosis of size hail. Both uncertainties are due to the high variability of hailstorms. This PhD is based on the analysis of thunderstorms associated to severe weather (large hail, tornados or waterspout, downburst and strong wind gust). The PhD has been focus on answering some of the existent doubts. On one hand, a diagnosis forecast tool has been applied to obtain information about hail diameter recorded after that one thunderstorm had affected an area without any direct measure instrument. On the other hand, a severe forecast tool named “Lightning jump” has been studied, adapted and put in operational. This algorithm permits to do a nowcasting forecast about severe weather phenomena in one hour in advance. It is an innovation PhD considering the incorporation of diagnosis and forecast new tools. Moreover, some of them are used currently in the Servei de Meteorològic de Catalunya for severe weather forecasting purposes.

Els episodis de precipitació intensa en zones de muntanya sovint es veuen afavorits pels efectes orogràfics que actuen com a mecanismes que modifiquen la precipitació. Aquest treball vol contribuir a millorar el coneixement dels processos fonamentals que afecten la precipitació quan aquesta té lloc en una zona d'orografia complexa com és el cas de la zona oriental dels Pirineus, situada a la Mediterrània nord-occidental. En aquest treball de tesi, a partir de modelitzacions numèriques d'alta resolució realitzades amb els models WRF i MESO-NH de nou casos d'estudi diferents, s'investiguen les condicions sinòptiques i mesoescalars que afavoreixen el desenvolupament dels sistemes de precipitació als Pirineus Orientals. Entre d'altres, s'ha analitzat l'episodi del 7 novembre de 1982, que es troba entre els més intensos a Europa durant el període 1950-2005, en concret a Andorra, aquest ha estat l'episodi de risc que ha causat més morts al país. Els resultats obtinguts de les simulacions amb passos de malla horitzontal a 2,5 i 2 km reprodueixen estructures de precipitació amb una distribució i intensitat en concordança amb les observacions. Tot i això, també s'ha examinat la incertesa associada a la sensibilitat que mostra la modelització a variacions en les condicions inicials i a la microfísica. L'anàlisi mesoescalar s'ha dut a terme tant per a episodis caracteritzats per fluxos estables com condicionalment inestables. A la primera part del treball s'ha examinat l'efecte de l'orografia en la localització i intensitat dels sistemes de precipitació. L'anàlisi s'ha fet a partir de l'aplicació dels resultats extrets tant de simulacions numèriques idealitzades com de casos d'estudi en altres regions muntanyoses. Pels episodis condicionalment inestables amb condicions atmosfèriques que evolucionen molt ràpidament com és el cas de les ciclogènesis mediterrànies, l'anàlisi de dos dels paràmetres adimensionals (activació de la convecció i el nombre de Froude humit) reflecteix la complexitat d'aplicar aquests resultats teòrics. En canvi, pels episodis hivernals de nord sota condicions estables, el camp de precipitació mostra una dependència segons el nombre de Froude representatiu del flux incident. Els comportaments identificats s'han resumit en forma de model conceptual. A la segona part, l'anàlisi mesoescalar centrat en la descripció de la interacció entre el flux i la complexa orografia dels Pirineus ha permès identificar diferents factors tant dinàmics com microfísics que contribueixen a reforçar la precipitació orogràfica. Les retrotrajectòries basades en els traçadors eulerians passius, indiquen que l'ascens orogràfic directe és el principal mecanisme que desencadena la formació dels sistemes de precipitació als Pirineus. Mentre que, sota condicions atmosfèriques estables, les simulacions detecten la formació d'un màxim de vent al vessant nord paral•lel a la serralada a causa del marcat efecte de bloqueig exercit pels Pirineus. En canvi, per certes situacions mesoescalars, a l'extrem est de la serralada es forma una zona de confluència molt marcada que al mateix temps afavoreix la formació d'un corrent de densitat molt ben organitzat. La influència dels processos microfísics implicats en el reforç de la precipitació s'ha estudiat per mitjà de l'anàlisi de la distribució vertical dels hidrometeors. Les estructures verticals descrites són coherents amb els models conceptuals proposats a partir de les campanyes observacionals realitzades en altres regions muntanyoses com poden ser els Alps. Un dels mecanismes suggerits com a dominants en el procés d'intensificació de la precipitació està relacionat amb la formació del calabruix. S'ha realitzat l'anàlisi lagrangiana del flux d'alimentació dels sistemes de precipitació en episodis condicionalment inestables. Els resultats de les simulacions indiquen una important dependència de la intensitat de la precipitació als Pirineus amb dos factors: el component del vent perpendicular a la serralada i el transport d'humitat cap als Pirineus a la baixa troposfera. S'han suggerit diferents rangs de valors per tal de discriminar els episodis segons la intensitat de la precipitació orogràfica. En conjunt, i d'acord amb els resultats obtinguts a partir de simulacions idealitzades, es pot dir que com més fort sigui el camp de vent incidint perpendicular a la serralada i més elevada l'advecció d'humitat, més intensa serà la precipitació als Pirineus. Per l'episodi hivernal estudiat més intens, la detecció d'un corrent atmosfèric en forma de banda estreta i allargada amb un transport molt elevat d'humitat provinent de latituds equatorials (550 kg/m•s; atmospheric river en anglès) va contribuir clarament en la forta nevada. Una situació similar però molt més perillosa, va succeir el 1982 quan gràcies a la presència d'un màxim de vent de 30 m/s a 1500 m, la part càlida i molt humida situada davant una pertorbació Atlàntica va incidir directament sobre els Pirineus Orientals i va persistir durant més de 10 h. Per aquest darrer episodi, també s'ha comprovat la contribució limitada del Mediterrani com a font local d'humitat (2-3 g/kg), en contraposició a l'elevada quantitat d'humitat (7-9 g/kg) provinent de les fonts remotes (latituds subtropicals Atlàntiques i nord d'Àfrica).
Heavy precipitation events over complex terrain are often favoured by enhancement mechanisms of precipitation. The windward slopes of the Eastern Pyrenees, as other mountainous Mediterranean regions, are regularly affected by heavy precipitation events (HPE). This present work benefits from high resolution numerical simulations of several case studies to investigate the synoptic and mesoscale environment favourable to precipitating systems development over the Eastern Pyrenees. The mesoscale models WRF and MESO-NH run at horizontal grid-lengths of 2.5-2 km have reproduced realistic precipitation structures over the Pyrenees but the uncertainty associated to sensitivities to initial conditions and microphysics has also been highlighted. The analysis has been done for both stable and conditionally unstable conditions. The former part of the analysis has explored the application of the results from purely idealized simulations or previous studies in other mountainous regions to the case study simulations. For conditionally unstable events with dynamic evolving conditions (Mediterranean cyclogenesis), the analysis of a triggering term and the moist Froude number reflects the complexity of applying theoretical results. On the other hand, for winter northerly stable flows the precipitation field reveals a dependency on the upstream Froude number. These patterns are synthesised in a conceptual model. Backward trajectories based on Eulerian on-line passive tracers indicate that the direct orographic lifting is the main forcing mechanism which triggers precipitating systems over the Pyrenees. For stable conditions, the simulations capture the formation of an along barrier flow in the north slope due to the blocking effect exerted by the Pyrenees. Under specific mesoscale configurations, a distinct confluence zone is also formed in the easternmost part of the massif, which in turn favours the generation of a well developed density current. The understanding of the microphysical processes involved in precipitation enhancement has been examined by means of the hydrometeor vertical distribution. The dominant mechanisms for intense precipitation are associated with graupel. From the lagrangian analysis of the feeding flow in the conditionally unstable episodes, the simulations indicate a marked dependence of the precipitation intensity over the Pyrenees on two factors: the cross-barrier wind intensity and the moisture advection towards the Pyrenees in the lower atmosphere. Different ranges have been suggested to discriminate the orographic precipitation intensity over the Pyrenees. In general, the stronger the cross-barrier component wind and the water vapour flux the more intense the orographic precipitation will be. During the most intense winter event, the detection of a narrow corridor of strong water vapour transport (atmospheric river; 550 kg/m•s) contributed to the generation of persistent precipitation. A similar situation occurred during the 1982 HPE when the Atlantic moist and warm conveyor belt combined with a LLJ (30 m/s) impinged over the Eastern Pyrenees more than 10 h. For this last episode, it has been also proved the limited role of the Mediterranean as local moisture source (2-3 g/kg) as the moisture coming from remote source regions (subtropical Atlantic and Africa) is larger (7-9 g/kg).

The Arctic region attracts considerable scientific interest in these years. Some of the Earth's most pronounced signs of the recent climate change are found here. The summer sea-ice cover is shrinking at an alarming rate. At the same time the region warms faster than the rest of the globe.

The sea-ice reduction implies an increase of solar-radiation absorption at the surface leading to warming which is expected to be larger at higher than at lower latitudes. It is therefore often assumed that the sea-ice reduction is a major cause of the observed Arctic temperature amplification. However, results presented in this thesis suggest that the snow and ice-albedo feedbacks are a contributing but not dominating mechanism behind the Arctic amplification. A coupled climate-model experiment with a doubling of the atmospheric CO2 concentration reveals a considerable Arctic surface-air-temperature amplification in a world without surface-albedo feedback. The amplification is only 8 % larger when this feedback is included. Instead the greenhouse effect associated with an increase of humidity and cloud cover over the Arctic seems to play a major role for the amplification.

Reanalysis data, which are partly based on observations, show Arctic temperature amplification well above the surface in the troposphere. In the summer season, the amplification has its maximum at ~ 2 km height. These trends cannot be explained by the snow- and ice-albedo feedbacks which are expected to induce the largest amplification near the surface. Instead, a considerable part of the trends aloft can be linked to an increase of the atmospheric energy transport into the Arctic.

A major topic of this thesis is the linkage between the mid-latitude circulation and the Arctic warming. It is suggested that the atmospheric meridional energy transport is an efficient indicator of this linkage.

Wind is used as an energy source all over the world. To be able to use this effectively, there is a need for as good forecasts and forecast models as possible. One of these models is Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®) that is used to calculate short time forecasts. This model is used here to calculate wind speeds at two different areas in Västra Götaland, Bengtsfors and Vänersborg. There are also wind measurements with SODAR stations for these areas. The first part of this work is to investigate the difference between two model resolutions, 36 and 12 km, for the model results compared with the measurements. The comparison is done by calculating some different statistical values. The results of these parameters show that the difference between the two resolutions is fairly small and that the lower resolution gives a slightly better result.

The second and major part of this work is to use two different regression models to adjust the result of the forecast models to the result of the measurements. These regression models will then be possible to use even when there are no measurements to compare with. The idea of these regression models is to find a way to describe the difference between the result of the forecast model and the SODAR measurements. This difference is then subtracted from the result of the forecast model so that you get an adjustment and more accurate result. The first regression model calculates the difference according to time of the day, the other model calculates the difference according to the wind speed.

Furthermore, the measurements used are taken from 75 meters height above the ground. These are then compared to some different results from the forecast model, for example different model heights and different resolutions, and also the model results adjusted with the regression models. The comparison is done by calculating the same statistic values as before, both with and without an adjustment with the regression models, and also to look at histograms that show the distribution of the difference. It is shown that with the regression adjustment, there is a clear improvement of the statistical values compared to the original results of the forecasts. For example the value of the absolute mean difference is reduced with approximately 0.4-0.7 m/s with an adjustment of the regression model. The histograms clearly show that a more even distribution occurs after the adjustment with the regression models. From having a major part of the differences at 1-2 m/s to now having the major part at around 0 m/s and furthermore there is also generally a lower difference between the measurements and the results from the forecast model.

I kvällstidningen Aftonbladet har det under flera år publicerats artiklar med långtidsprognoser för sommaren. För prognoserna står en tysk man vid namn Wolfgang Röder, som tidigare arbetat på meteorologiska institutionen vid Freie Universität i Berlin. Röders metod att ställa långtidsprognoser är hemlig, men han har avslöjat för Aftonbladet att han bl.a. studerar vädret under våren och jämför med statistik från tidigare år. Han gör dessutom en rad påståenden om aprilvädrets påverkan på sommarvädret, framförallt juli månad. Syftet med undersökningen var att ta reda på hur pass bra Röders lång- tidsprognoser är med det verkliga utfallet och utifall hans påståenden om april- vädrets påverkan på sommarvädret stämmer. I denna undersökning granskades Röders prognoser för Östra Svealand, med Stockholm-Bromma som represente- rande mätstation. För att bedömma Röders prognoser antogs månadsmedeltemperaturerna föl- ja en normalfördelning under en 30-årsperiod. I och med normalfördelningsan- tagandet kunde en standardavvikelse ifrån temperaturmedelvärdet för en viss månad beräknas. Med hjälp av sannolikhetstabeller för standardiserad normal- fördelning beräknades sedan avvikelseintervall från månadsmedelvärdet, vilka delades in i fem klasser: “Mycket kallt”, “kallt”, “normalt”, “varmt” och “myc- ket varmt”. Denna indelning skulle göra det enkelt att avgöra om Röder haft rätt eller fel. Vidare undersöktes också korrelation mellan aprils månadsme- deltemperatur och julis månadsmedeltemperatur samt julinederbörd under en 49-årsperiod. Det gjordes även detaljstudier av somrar som följt av varma re- spektive kalla aprilmånader. Detta för att eventuellt kunna urskilja ett mönster beroende på vädret i april. Resultatet blev inte särskilt tillfredställande. Med gällande klassindelning fick Röder endast rätt vid 10 tillfällen av 33, vilket ger en tillförlitlighet på cirka 30%. Hans påståenden om aprilvädrets påverkan på sommarvädret kunde inte heller styrkas. Korrelationskoefficienterna mellan aprils månadsmedeltem- peratur och julis månadsmedeltemperatur samt julinederbörd hamnade på 0.11 respektive 0.015, vilket är mycket lågt. Ur detaljstudien av ett antal somrar som följt av kall respektive varm april, kunde heller inga tydliga mönster urskiljas. Sammansfattningsvis visade undersökningen att det praktiskt taget är omöjligt för Röder att ställa en långtidsprognos för sommaren. Det går lika bra att singla slant!

Wind atlases are interactive databases used extensively for preliminary wind resource assessment aimed at optimal wind power development. The selection and processing of wind atlas data are important and will determine the quality of the subsequent WRA (Wind Resource Assessment) phases. This study aims to compare, process, and interpret different wind atlases in determining effective wind resource analysis for 14 different sites in Sweden. The wind atlas data is accessed, parsed, and compared using multiple methodologies to ensure a fair comparison. Several variables like wind speed, wind direction, temperature, production values, etc. are analysed and compared amongst the wind atlas data. The corrected versions of the data are drawn out to conclude and determine how well those databases represent the realistic conditions in a forested site. The data is also compared and validated with measurement data. The results indicate several layers of insights into the wind resource regime. The preliminary results from 14 sites show that New European Wind Atlas (NEWA) and Global Wind Atlas (GWA) agreed sufficiently on the subject of the wind conditions for most of the sites. Methodologies like downscaling and long-term correction introduced to the wind atlas data provided more insights and proved that the database could expand and include more complex wind conditions in the coming years. Furthermore, the comparison and analysis of wind atlas data along with measurement data revealed that NEWA aligned the most to the actual wind conditions for a site. Several uncertainties are considered but more validation and thorough insights in the future could determine and give more affirmations to the idea put forward. Further studies could be conducted along with the inclusion of additional layers, variables, and databases to the wind atlases.

Conclusions In this work we have used a multiple linear regression model, to see how different predictors are correlated to each other, and how they are correlated to temperature and precipitation in the southern part of Sweden. The correlation between the large and small indices vary over the year, but both cases show an increase in correlation during the winter. The MoVa index and the ViGö index are much better correlated than what the NAO and the KaUp indices are. One possible explanation for this can be the much shorter distace between the lines MoVa and ViGö in the latitudinal direction, compared to the distance in the longitudinal direction between NAO and KaUp. The correlation between the predictors and the predictands, temperature and precipitation, vary between different stations. The south-north predictors, NAO and KaUp, show different signs concerning the temperature in the summer. This is remarkable, but one should have in mind, that the correlation coefficient between the two is very low during the summer months. To recieve a good approximation concerning the precipitation amount by using this multiple regression model, it’s almost enough to use the mean pressure predictor, because the other predictors are very low or not even significant, except for some stations. The NAO predictor is only significant for a few months concerning precipitation. It should also be mentioned, that the model shows a lower amount of precipitation than what is observed when we are talking about great amounts of precipitation.  Finally, this regression model is based on pressure differences or just the mean pressure. This means, that the model doesn’t take into account such phenomena as convective clouds, local rain or thunder storms, subsidence inversions, sea breeze effects, etc.

The turbulence structure in a stable boundary layer over ice has been studied. Data from the Bothnian Bay, measured during the BASIS field campaign in February/March 1998, have been used. Turbulence as well as wind- and temperature profiles were measured at three sites. The sites were Umeå at the Swedish East Coast, Kokkola at the Finnish West Coast and the ship R/V Aranda outside the Finnish coast.  Turbulence parameters are studied in terms of their stability dependence. At stronger stability σu/u*, σv/u* and σw/u* all increase with stability. At near neutral stratification σw/u* increases with height. A linear dependence of the pressure gradient scale ln(zf/u*) is seen for σw/u* in the interval 0<z/L<0.1. σw/σu  first increases and then decreases with stability in agreement with earlier results. From the results it is concluded that the turbulence structure in the stable boundary layer over ice follows the Monin-Obukhov similarity theory. In some of the studied parameters the results from the Umeå site deviate from the other two. Since Umeå has a larger measuring height (10 m) than the other two (2 and 3.5 m) the conclusion is drawn that the surface layer height is lower than 10 m.  Data from the Umeå site has been used to study atmospheric phenomena that develop over the marginal ice zone. During two days two phenomena were observed that were triggered by the temperature difference between ice and water - a stable internal boundary layer and an ’ice breeze’ similar to the land breeze. The development of the internal boundary layer has been studied by using an expression for internal boundary layer height. A criterion earlier used to forecast the sea breeze has been shown to be suitable also for the ’ice breeze’.

Two days with bora has been numerically analysed, using a three dimensional hydrostatic mesoscale model developed at the Department of Meteorology, Uppsala University. The two simulated days, 22 March and 15 April 1982, have been compared to aircraft measurements done during the ALPEX-SOP in 1982. The model area was the northeastern shore of the Adriatic Sea. The bora on 15 April was easier to simulate than the one on 22 March, mostly due to the fact that this bora was shallower than the one on 22 March, and since the used model is developed for mesoscale studies, it works better with smaller scales (on the mesoscale). The simulations show that the bora character is a function of both time and space, for example changes in turbulence intensity. Three dimensional effects play an important role, for example channeling effects, which was also confirmed by the simulations. Compared to measurements, the model simulates the two days well, especially 15 April. All the significant features of the bora wind were well simulated, the wind speed maximum at the ridge crest, the descent of isotherms and isolines of specific humidity downstream the crest, channeling effects etc. The turbulence was not always present just above the ridge crest, but at some times and some places it was well simulated. The most difficult variables to simulate was the specific humidity and the potential temperature.

Detta examensarbete har utförts för att bestämma fördelningen av blixtnedslag i Sverige. En databas med blixtdata för åren 1987-1994 har använts. Antalet blixtar per 100 km2 och månad har beräknats, de högsta medelvärdena är 10 blixtnedslag och dessa erhålles under juli månad. Andelen positiva blixtar har även undersökts och funnits variera beroende av latitud och temperatur. Under vintermånaderna är andelen positiva blixtnedslag större än under sommarmånaderna.

Syftet med studien är att finna korrelation mellan olika meteorologiska parametrar. För att göra detta har data insamlade av avdelningen Försök och Prov, vid flygvapnets väderskola, använts. Mätningarna som använts här är gjorda på Kostabasen i Småland från den 13 oktober 1993 till den 25 april 1994. Insamling har skett med den så kallade Bas90-vagnen. Studien är begränsad till atmosfärens gränsskikt. Gränsskiktet kan delas in i två delar, ett ytskikt närmast marken samt ett övergångsskikt ovanför detta. Då luft flödar över en ny typ av yta bildas ett internt gränsskikt. Utgående ifrån mätningarna har grafer ritats och analyserats. Med hjälp av minsta kvadrat metoden har enkla uttryck för korrelationen tagits fram och jämförts med mätdata. Korrelationer mellan följande parametrar har undersökts: • molnbas - vindhastighet och vindriktning • molnbas - stabilitet • molnbas - fuktighet, med och utan nederbörd • molnbas - sikt Bäst korrelation erhölls mellan molnbas och relativ fuktighet där ett tydligt samband erhölls. Korrelationen mellan molnbas och de övriga parametrarna var mycket sämre. Mellan molnbas och stabilitet erhölls ingen korrelation.

I den här studien analyseras gränsskiktshöjdens betydelse för hastighetsfältet i ytskiktet, med hjälp av Monin-Obukhovs (MO) similaritetsteori. Studien genomfördes för att verifiera tidigare resultat från en Large-Eddy simulering av Khanna och Brasseur (1995) som tyder på att hastighetsfältet inte bara beror på z/L utan även har ett starkt beroende av gränsskiktshöjden. Genom att använda mastmätningar och sonderingar från Marsta studeras hastighetsfältet och speciellt den dimensionslösa vindgradienten (Φm) och de normaliserade hastighetsvarianserna i horisontalled och vertikalled. Det visar sig att båda parametrarna är beroende av gränsskiktshöjden. Resultatet från studien är att MOs similaritetsteori inte gäller för hastighetsfältet vid instabil skiktning vilket är samma resultat som antyddes i Khanna och Brasseurs (1995) studie. Detta tyder på att de storskaliga rörelserna i gränsskiktet påverkar ytskiktet mer än vad som tidigare varit känt.

En sammanställning av en databas av inversionsdata från sonderingarna från Bromma under 1990 har utförts. I denna databas lagrades datum, tid, marktemperatur, marktryck samt tryck och temperatur för basen och toppen av upp till tre inversioner. Därur kunde sedan höjder till tryckytorna och temperaturdifferenser mellan topp och botten beräknas. En statistisk undersökning av materialet utfördes med avseende på höjden till inversionsbasen och temperaturökningen i inversionsskiktet. Även temperaturgradienten för inversionsskiktet studerades. Resultaten sammankopplades med den aktuella synoptiska situationen för att kunna förklara inversionernas fördelning i tid och rum. För att få en uppfattning om signifikansen av undersökningen gjordes en jämförelse med tillämpliga delar av en tysk undersökning gjord av Gutsche 1983. Resultaten visade en skillnad mellan sommar- och vinterhalvåret vad gäller fördelningen av inversioner över dygnet. Under sommaren förekom inversioner mycket oftare på natten än på dagen medan den skillnaden under vintern var betydligt mindre. Dessutom framkom att de flesta inversioner finns i de marknära skikten och i allmänhet har en liten temperaturökning från bas till topp. Vädersituationen under 1990 samt luckor i materialet gör dock att man ej bör dra alltför långtgående slutsatser av resultaten.

Examensarbete F1 om 7 p (10,5 hp)

I detta arbete har vindförhållandena på Utlängan, Ungskär och Ölands södra grund studerats. För att göra detta har synop-data från SMHI:s stationer på Ungskär och Ölands södra grund för tidsperioden 900801-911130 använts. Dessutom har data från en mast som stod uppställd på Utlängans södra udde under delar av -90 och -91 samt ett 50-tal enkelviseringar, utförda på Utlängans östra sida under perioden 910324-910614, använts. En vindmodell har använts för att räkna upp vinden till höjder högre än mätningarna (upp till 125 m). Denna modell användes också för att på data från masten beräkna vinden på viseringsplatsen. Genom att jämföra de modellberäknade vindarna med viseringsprofilerna kunde pilotballongernas stighastighet korrigeras och därmed erhölls en riktigare vindprofil från viseringarna. Modellen hade även möjlighet att korrigera för den ändring av vinden som en skrovlighetsförändring ger. Indata måste då vara — förutom vinden på en nivå, temperaturen på två nivåer, mäthöjder och z0 (vilka är de huvudsakliga inparametrarna till denna modell) — avståndet till skrovlighetsförändringen och dess art. Detta utnyttjades vid beräkningen av vinden för viseringsplatsen. För Ungskär och Ölands södra grund fanns bara en temperatur, varför två olika varianter av vindmodellen fick användas. På Ölands södra grund utnyttjades vattentemperaturen och för Ungskär bestämdes stabilitetsparametern 1/L genom att använda Turnerklassificering, vilken utnyttjar solhöjd, molnmängd och molnhöjd. Med hjälp av viseringsprofilerna har low-level jets studerats. Av de 52 viseringarna kunde ett — mer eller mindre utpräglat — vindmaximum ses i 27 av fallen. Drygt hälften av dessa hade ett tydligt maximum. Jämförelser mellan viseringsprofiler och modellberäknade vindar — för de övriga platserna — visade på att modellen gav för låga vindhastigheter runt 100 m:s höjd. Detta kan, åtminstone delvis, förklaras av att modellen ej tar hänsyn till low-level jets. En jämförelse mellan Ungskär och Ölands södra grund, för tidsperioden 900801-911130, gav högre vindhastigheter på Ölands södra grund (10,2 m/s mot 9,3 m/s på 125 m:s höjd) medan vindriktningsfördelningen var ungefär densamma. Även en jämförelse mellan Ungskär och masten på Utlängan, med uppmätta värden för de tidsperioder då samtidiga data fanns, gjordes. Resultaten från den gav lägre vindhastigheter på Utlängan än Ungskär (6,8 m/s mot 7,2 m/s på ca 14 m:s höjd) och en något annorlunda vindriktningsfördelning, vilket antyder lokal påverkan på vindhastighet och riktning.

Examensarbete F1 om 7 p (10,5 hp)

Efter stora påtryckningar från skandinaviskt håll genomfördes i början av 1970-talet ett sameuropeiskt mätprojekt för att klargöra huruvida svavelutsläpp i exempelvis Storbritannien påverkade försurningen av sjöar i Skandinavien. Elva västeuropeiska länder deltog i projektet – kallat LRTAP – vars mätningar pågick under åren 1972–1975. Dessa mätningar bekräftade de teorier som drivit fram projektet – att luftföroreningar (i detta fall svavelföreningar) kan transporteras långa vägar i atmosfären för att sedan deponeras i ett område långtifrån källan. Därigenom kom de fram till att ett land inte kan påverka depositionen inom landet till 100% genom egna restriktioner. Ett följdprojekt startades därför för att förse de olika ländernas regeringar med information om svavelutsläpp och svaveldeposition i de olika länderna. Ett mål uppsattes angående utsläppen – att 1993 inte släppa ut mer än 70% av 1980-års nivå – vilket tycks vara uppnåeligt. I Sverige har svavelutsläppen minskat från drygt 400 kton S/år i början av 1970-talet till 102 kton 1990, en reducering på ca 75%. Depositionen har dock inte minskat lika mycket, eftersom mängden svavel från Mellaneuropa fortfarande är stor. I Sverige är därför svaveldepositionen starkast koncentrerad i de sydvästra delarna och avtar sedan mot nordväst.

Examensarbete F1 på 7 p (10,5 hp)

Two days in May 1997 has been studied. During one of the days a sea breeze circulation occured, and the two days were compared in search for effects from the sea breeze on the fluxes in the marine boundary layer. Measurements were made on a tower at the small island Östergarnsholm east of the island Gotland, and by an instrumented aircraft over the sea east and west of Gotland. The direction of the geostrophic wind were about northwest during the time period, but 17 m/s during May 3 and 7 m/s during May 4. The stratification was stable over the main part of the Baltic sea because of the large temperature differences between land and sea surfaces. But as the sea breeze developed and the wind direction turned to the southeast, the stratification at Östergarnsholm changed to near neutral. Both the wind speed and the fluxes decreased with distance from the Swedish mainland and the west coast of Gotland, and the fluxes were over all very small. The momentum flux showed no big difference between the days. Because of the decrease with the distance from the coast and the wind speed it was concluded that the stratification was of greater importance than the sea breeze circulation for the momentum fluxe. But the heat flux was affected by the sea breeze. Because of the sea breeze the stratification became neutral, and thus the heat flux very small. The presence of swell in the baltic sea was also studied. The correlation coefficient gave unexpected result during May 3, with no difference for swell and no swell conditions. The angle between the swell and the wind wave was about 90° during both days, and could not be the reason for the difference. During the May 3 the stratification was mostly stable, while it on May 4 was unstable. It is suggested that this could be a reason for the behaviour of ruw.

The wind climate in a valley has been studied. Long time data from towers along the valley have been used, together with data from two field campaigns. The campaigns took place during two weeks in May 1999 and two weeks in September 2000. During the field campaigns wind speed and direction were measured, both with small masts and with pilot balloon tracking. A comparison of single and double theodolite tracking is performed. It is found that single theodolite tracking is good enough to use. The ascent rate of the balloon is seen to be slightly higher than the earlier assumed 4 m/s. An investigation of the wind field along and across the valley have been done. The result show that high mean wind speed are found at the sites were the valley is rather narrow. The wind direction was then either upstream or downstream the valley. The mean wind speed at Suorva is 6.6 m/s. Channelling effects, forced- and pressure-driven channelling, seem to dominate the winds in the valley giving high speeds. No correlation is found between the magnitude of the geostrophic wind and the wind in the valley. High winds in the valley is obtained both with high and low geostrophic winds. A peak in the southwesterly direction for the distribution of geostrophic wind is seen. This is due to the common synoptic situation with a low pressure area outside the coast of Norway. Data from sites across the valley show that the highest wind speeds are found at the northeastern side and the lowest at the southwestern side. The stratification is found to have strong effect of the air flow around a hill and the local terrain. When the stratification was stable the air was blowing around Jiertasuoloj, an island of about 50 m height. When the air is unstable the air is instead blowing over Jiertasuoloj.

The vertical structure in the coastal marine atmosphere has been investigated using data from aircraft measurements performed along the Blekinge coast. The present data are from the third of October 1990. The main feature is fairly homogeneous horizontal conditions and a subceeing boundary layer which lowers from 600 meters down to about 50 meters during the day. The turbulence were found to be in a decreasing state. The turbulence parameters were normalized using normal stationary scaling, in order to compare with other results.

l rapportens första del studeras ljudutbredningen i fjällterräng. Mätningar har gjorts på ett vindkraftverk som är placerat i en dal, i svenska fjällen. Vindkraftverkets källstyrka varierar. Medelljudtrycksnivån är 51 dBA ±3 och ljudnivåns variation för de olika frekvenserna pendlar mellan 0-8 dBA, detta diskuteras i kapitel 1.6. Ljudmätningarna uppfyller ej strikt de fastslagna normer och standarder som finns angivna i rapporten: Measurement of noise immission from wind turbines at noise receptor locations, 1997. I kapitel 1.7 beräknas ljudstrålarnas krökningstal. Talet beskriver hur de meteorologiska faktorerna böjer ljudvågorna, värdena ligger mellan –2 och 2. Utifrån topografin, kring vindkraftverket, bestäms den krökningsradie som borde ge upphov till höga ljudnivåer vid de olika mätstationerna. För station Ljudgrenen bestämdes radien till –0,4, se kapitel 1.8. I kapitel 1.10 beräknas den teoretiska ökningen av ljudnivån, då det placeras 100 vindkraftverk på den plats det för nuvarande står ett enda. Ökningen blir 20 dBA men avståndet till ljudkällan påverkar resultatet. Flera antaganden görs för att det skall vara möjligt att uppskatta förändringen i ljudnivån. Ljudutbredningen har studerats för fall då meteorologiska faktorer kan ge en ökning av ljudnivån. Vid tillfällen då det bildas ett inversions skikt i dalen kan ljudstrålarna stängas in i ett grundt skikt nära marken och ge förhöjda ljudnivåer, även på långa avstånd från ljudkällan. Se kapitel 1.7 och  1.11. I del 2 studeras ljudutbredningen över slättland, ljudkällan är den militära flygplatsen F16. Ljudnivån och relevanta meteorologiska parametrar uppvisar en dygns- och årsvariation, se kapitel 2.3. Under dagtid på sommaren minskar ljudnivåerna och samtidigt når krökningstalet sitt lägsta, negativa värde. Det låga värdet på krökningtalet böjer ljudvågorna uppåt och det är anledningen till att ljudnivån försvagas, se kapitel 2.4. Det omvända sker under vinterhalvåret och på nätterna. Krökningstalet får höga värden och ljudstrålarna böjer nedåt, vid dessa tillfällen ökar ljudnivån.

En enkel metod att genom beräkning av tryckgradienter i väst-ostlig och nord-sydlig riktning beräkna den geostrofiska vinden, används på tre områden i Sverige. Tryckdata fås från SMHI-bulletinen 1970-78. Resultaten analyseras statistiskt med avseende på hastighet, riktning, årstid och temperatur så att det sedan kan avgöras om metoden ger rimliga resultat. Det visar sig att på grund av, framför allt, systematiska fel i den ursprungliga tryckdatan blev resultaten av denna analys inte att betrakta som användbara. Det finns dock stort utrymme för förbättringar av metoden.

Comparisons between wind measurement with doppler weather radar and wind measurement with rawinds in different weather situations is done. The study is made in a statistical way with some comparable parameters as outcome. The importance of the weather and different weather situation’s effect on the results are discussed, both in form of the winds accuracy and the probability of getting any wind at all as outcome. The study shows that wind measurement with doppler radar at lower elevations not has so good accuracy, but it becomes better the higher up we measure. At the same time will we lose a lot of the measurements at higher levels by the reason that the reflected power is weakened very fast with the distance the transmitted ray travel.  The doppler effect is explained and the by SMHI used routine for wind measurement with radar is described. At the end of the work are some problems and disadvantages with the radar measurements and the used method discussed.