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.

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

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.

The atmospheric spatial variability over Isfjorden, Svalbard, was investigated through statistical data analysis. The data used in the thesis was measured by mobile weather stations installed on three ships crossing the fjord, and two stationary weather stations close to the shoreline, during the autumn of 2021 and spring to autumn 2022. The spatial distributions of temperature, specific humidity, and wind speed were filtered into categories of season, ambient wind direction, and ambient wind speed, before they were studied. Gradients in temperature and humidity are re-occurring patterns along the Isfjorden axis during various seasons and wind directions. The temperature gradient was found to be partly generated by local drainage winds and further to be connected to the difference between air and sea surface temperature. The humidity gradient was consistent across all seasons and predominantly controlled by advection and differences in available water from surrounding land surfaces. A peak in wind speed around the mouth of Sassenfjorden indicated forced channeling effects, as the pattern dominated when the ambient wind aligned with the axis of the fjord. The results indicate local processes that can be expected from previous research.

I den här rapport har 4 stycken väderprognoser rankats och statistiskt utvärderats på vindstyrka och vindriktning utifrån hur väl de stämmer överens med verkligheten där verkligheten har varit 2 olika observationskällor. Ett av målen var att undersöka vilken av prognosleverantörerna som gav bäst prognos under kappseglingen ÅF offshore race 2015 samt analysera huruvida seglare kan använda den sortens information. Det visade sig att SMHI gav bäst resultat jämfört med observationer från deras egna väderstationer runt om Gotland. Prognoserna visade olika resultat jämfört mot den andra observationskällan som kom från en tävlandes båt. YR visade lägst medel absolut fel på väderparametrarna och en kommersiell prognosleverantör A gav bäst bias och högst träffsäkerhet på vindstyrkan på 91% med ett felintervall på +-2m/s. Som kappseglare har man användning av en rankning från föregående dygn som kan underlätta valet av prognos som används till underlag vid ruttplanering. En metod som bör testas under en längre tid är att undersöka felet mellan prognos och observationsvärden i föregående dygns prognos och därefter korrigera den aktuella prognosen efter felvärdena. I denna fallstudie visade många av fallen förbättra prognosen vid användning av denna metod. I dag finns många mjukvaror som används inom kappsegling där observationer inte används utan baseras på prognoser och polardiagram. Att ta hänsyn till observationer i mjukvarans optimeringsalgoritm kan hjälpa till att förbättra resultaten och är en utvecklingsmöjlighet för produkten. / 4 different weather models have statistically been evaluated in this case studie on the parameters wind speed and wind direction. They have been compared to 2 different observations sources. The goals with this project was to investigate which of the supplier of weather predictions that provided the best forecast during ÅF offshore race 2015 and analys wether or not offshore racers could use a statistically evaluating as a support while planning routes. It is shown that SMHI gave the best forecast compared to observation stations around Gotland. Compared to the second observation source which was a competing boat YR supplied the best mean absolute error on both wind speed and wind direction. A commercial supplier A gave the best bias values on both parameters and highest forecast index on 91% within an interval of +-2m/s. As an offshore racer you could use an evaluation of weather forecast from 24 hour before to facilitate the choice of forecast supplier to plan the route after. A method which should be tested during a longer time period is to correct the current forecast with previous bias values. In this case studie it was shown in many events the forecasts was improved by using this method. Many navigation softwares do not include weather observations in their algorithms and is entirely based on polardiagrams and weather predictions. Taking observations into the software by correct the current forecast by previous errors could help to improve the final results of the navigation system.

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.

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&lt;z/L&lt;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.