<p>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. </p><p>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. </p><p>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. </p>

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.

<p>Data assimilation in Numerical Weather Prediction (NWP) optimally blends observations with atmospheric model data in order to obtain the best possible initial state for an atmospheric model prediction. Specification of error characteristics is an important part of data assimilation. This thesis is concerned with representation of background error standard deviations, with handling of observations, and with observation error characteristics. The research includes both the study of basic assimilation problems within the framework of an idealised quasi-geostrophic model and the development of assimilation algorithms for a full scale limited area high resolution forecasting system.</p><p>It is shown in this thesis that an accurate representation of background error standard deviations is important for the quality of NWP forecasts. In particular the effect of introducing a time-dependency is investigated and a novel approach to relate the flow-dependency of background error standard deviations to an Eady baroclinic instability measure is developed. The Eady based flow-dependent background error representation is demonstrated to have a positive impact on NWP, as compared to horizontally and temporally independent background error statistics. An alternative method, based on on-line error estimation and maximum likelihood theory, is proven to be able to represent the flow-dependency of background error standard deviations and encouraging results are obtained within the quasi-geostrophic model framework. Furthermore, it is shown that a proper observation handling is an important part of data assimilation. The treatment of error characteristics is specifically shown to be of major importance when exploiting the potential benefit of radar radial wind observations within data assimilation.</p>

Data assimilation in Numerical Weather Prediction (NWP) optimally blends observations with atmospheric model data in order to obtain the best possible initial state for an atmospheric model prediction. Specification of error characteristics is an important part of data assimilation. This thesis is concerned with representation of background error standard deviations, with handling of observations, and with observation error characteristics. The research includes both the study of basic assimilation problems within the framework of an idealised quasi-geostrophic model and the development of assimilation algorithms for a full scale limited area high resolution forecasting system. It is shown in this thesis that an accurate representation of background error standard deviations is important for the quality of NWP forecasts. In particular the effect of introducing a time-dependency is investigated and a novel approach to relate the flow-dependency of background error standard deviations to an Eady baroclinic instability measure is developed. The Eady based flow-dependent background error representation is demonstrated to have a positive impact on NWP, as compared to horizontally and temporally independent background error statistics. An alternative method, based on on-line error estimation and maximum likelihood theory, is proven to be able to represent the flow-dependency of background error standard deviations and encouraging results are obtained within the quasi-geostrophic model framework. Furthermore, it is shown that a proper observation handling is an important part of data assimilation. The treatment of error characteristics is specifically shown to be of major importance when exploiting the potential benefit of radar radial wind observations within data assimilation.

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.

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.

Diss. (sammanfattning) Umeå : Univ., 2002. / Härtill 5 uppsatser.

<p>Aerosol particles are likely important contributors to our future climate. Further, during recent years, effects on human health arising from emissions of particulate material have gained increasing attention. In order to quantify the effect of aerosols on both climate and human health we need to better quantify the interplay between sources and sinks of aerosol particle number and mass on large spatial scales. So far long-term, regional observations of aerosol properties have been scarce, but argued necessary in order to bring the knowledge of regional and global distribution of aerosols further. In this context, regional studies of aerosol properties and aerosol dynamics are truly important areas of investigation.</p><p>This thesis is devoted to investigations of aerosol number size distribution observations performed through the course of one year encompassing observational data from five stations covering an area from southern parts of Sweden up to northern parts of Finland. This thesis tries to give a description of aerosol size distribution dynamics from both a quantitative and qualitative point of view. The thesis focuses on properties and changes in aerosol size distribution as a function of location, season, source area, transport pathways and links to various meteorological conditions.</p><p>The investigations performed in this thesis show that although the basic behaviour of the aerosol number size distribution in terms of seasonal and diurnal characteristics is similar at all stations in the measurement network, the aerosol over the Nordic countries is characterised by a typically sharp gradient in aerosol number and mass. This gradient is argued to derive from geographical locations of the stations in relation to the dominant sources and transport pathways. It is clear that the source area significantly determine the aerosol size distribution properties, but it is obvious that transport condition in terms of frequency of precipitation and cloudiness in some cases even more strongly control the evolution of the number size distribution. Aerosol dynamic processes under clear sky transport are however likewise argued to be highly important.</p><p>Southerly transport of marine air and northerly transport of air from continental sources is studied in detail under clear sky conditions by performing a pseudo-Lagrangian box model evaluation of the two type cases. Results from both modelling and observations suggest that nucleation events contribute to integral number increase during southerly transport of comparably clean marine air, while number depletion dominates the evolution of the size distribution during northerly transport. This difference is largely explained by different concentration of pre-existing aerosol surface associated with the two type cases. Mass is found to be accumulated in many of the individual transport cases studied. This mass increase was argued to be controlled by emission of organic compounds from the boreal forest. This puts the boreal forest in a central position for estimates of aerosol forcing on a regional scale.</p>

<p>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.</p><p>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</p><p>S=(1+Am)(I0*(1-N*Aso))/(1-Am*Asu*N)</p><p>där N är molnmängden, Aso molnöversidans albedo, Asu molnundersidans albedo, Am markens albedo och I0 den inkommande strålningen ovan eventuella moln.</p><p>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.</p><p>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.</p>

Aerosol particles are likely important contributors to our future climate. Further, during recent years, effects on human health arising from emissions of particulate material have gained increasing attention. In order to quantify the effect of aerosols on both climate and human health we need to better quantify the interplay between sources and sinks of aerosol particle number and mass on large spatial scales. So far long-term, regional observations of aerosol properties have been scarce, but argued necessary in order to bring the knowledge of regional and global distribution of aerosols further. In this context, regional studies of aerosol properties and aerosol dynamics are truly important areas of investigation. This thesis is devoted to investigations of aerosol number size distribution observations performed through the course of one year encompassing observational data from five stations covering an area from southern parts of Sweden up to northern parts of Finland. This thesis tries to give a description of aerosol size distribution dynamics from both a quantitative and qualitative point of view. The thesis focuses on properties and changes in aerosol size distribution as a function of location, season, source area, transport pathways and links to various meteorological conditions. The investigations performed in this thesis show that although the basic behaviour of the aerosol number size distribution in terms of seasonal and diurnal characteristics is similar at all stations in the measurement network, the aerosol over the Nordic countries is characterised by a typically sharp gradient in aerosol number and mass. This gradient is argued to derive from geographical locations of the stations in relation to the dominant sources and transport pathways. It is clear that the source area significantly determine the aerosol size distribution properties, but it is obvious that transport condition in terms of frequency of precipitation and cloudiness in some cases even more strongly control the evolution of the number size distribution. Aerosol dynamic processes under clear sky transport are however likewise argued to be highly important. Southerly transport of marine air and northerly transport of air from continental sources is studied in detail under clear sky conditions by performing a pseudo-Lagrangian box model evaluation of the two type cases. Results from both modelling and observations suggest that nucleation events contribute to integral number increase during southerly transport of comparably clean marine air, while number depletion dominates the evolution of the size distribution during northerly transport. This difference is largely explained by different concentration of pre-existing aerosol surface associated with the two type cases. Mass is found to be accumulated in many of the individual transport cases studied. This mass increase was argued to be controlled by emission of organic compounds from the boreal forest. This puts the boreal forest in a central position for estimates of aerosol forcing on a regional scale.