På grund av världens växande befolkning och urbaniseringen blir problem relaterade till fenomenet urbana värmeöar mer och mer påtagliga. Eftersom urbana parker kan minska påfrestningen skapad av urbana värmeöar kan de vara ett kraftfullt verktyg vid klimatdesign i städer. Temperaturen nära en yta bestäms av energiutbytet mellan ytan och luften ovanför och det är därför nödvändigt att man förstår energibalansen vid markytan för att kunna hantera parkernas mikroklimat. Syftet med det här arbetet var att studera skillnaderna mellan energibalansen för olika ytor i parken och i dess omgivning och att relatera skillnaderna i energibalanserna till temperaturskillnaderna. Mätningarna utfördes under tre klara sommardagar i parken Humlegården i centrala Stockholm. Mätutrustningen var monterad på en kärra som flyttades från mätplats till mätplats. Mätplatserna representerade olika typiska ytor i Humlegården och i dess omgivning: en skuggad och en öppen gräsmatta, en öppen och en skuggad grusyta och två asfaltytor, varav en löper i nord-sydlig riktning och en i öst-västlig riktning. Energiflödena beräknades med hjälp av data för luft- och yttemperatur, vindhastighet, luftfuktighet och nettostrålning. Resultaten visade att den tydligaste skillnaden mellan gräs- och grusytorna i parken var att gräsytorna hade ett större nedåtriktat latent värmeflöde under natten och ett mindre markvärmeflöde under hela dygnet. Den mest distinkta skillnaden mellan de skuggade och öppna ytorna i parken var att de skuggade ytorna hade mindre energiflöden under dagen och att de till skillnad från de andra ytorna hade ett nedåtriktat sensibelt värmeflöde under dagen. Den största skillnaden mellan ytorna i och utanför parken var att asfaltytorna hade ett större uppåtriktat sensibelt värmeflöde och markvärmeflöde under natten. Under natten var den svalaste mätplasten den öppna gräsmattan, vilken också var den enda mätplasten med ett nedåtriktat sensibelt värmeflöde under natten. Jämfört med de andra ickeskuggade mätplasterna hade den öppna gräsmattan ett mindre markvärmeflöde. Varmaste mätplasterna under natten var asfaltytorna som även hade ett större uppåtriktat sensibelt och markvärmeflöde än de andra ytorna. Under dagen var de skuggade ytorna i parken de svalaste platserna. De var de enda ytorna med ett nedåtriktat sensibelt värmeflöde och nettostrålningen vid ytan var mindre än för de flesta andra mätplatser. / The world’s growing population and the increasing urbanization has made problems related to the urban heat island phenomenon to become more pronounced and since urban parks reduce the stress produced by the urban heat island they can be powerful tools in urban climate design. The temperature near the surface in a park is determined by the energy exchanges between the surface and the air above and it is therefore necessary to understand the surface energy balance of parks to intelligently manage their thermal microclimate. The objectives of this work were to study how the energy balances differ between different surfaces inside parks and in their built-up surroundings and to relate the surface energy balances to temperature differences. Measurements were conducted during three clear summer days in the park Humlegården located in central Stockholm. The measuring instruments were mounted on a cart, which was transported from observation site to observation site. The observation sites represented typical surfaces found in an urban park and its surroundings: one shaded and one open grass surface, one open and one shaded gravel surface and two paved surfaces representing streets running in the north-south and east-west directions respectively. The energy fluxes were calculated using air and surface temperatures, wind speed, air humidity and net radiation data. The most pronounced differences between the shaded and open surfaces in the park was that the shaded surfaces in general had smaller energy fluxes during daytime and that they had a downward directed sensible heat flux while the open surfaces had an upward directed sensible heat flux during the day. The most significant difference between the grass and the gravel surfaces in the park was that the grass surfaces had a bigger downward directed latent heat flux during the night and a smaller ground heat flux during both day and night. The largest differences between the surfaces inside the park and those in its built-up vicinities were that the paved surfaces had a larger upward directed sensible and ground heat flux during the night than the other surfaces. During the day the north-south directed paved site had a downward directed ground heat flux that was much larger than the ground heat flux for the other sites. The coolest site during the night was the non-shaded grass surface, which was the only site with a downward directed sensible heat flux during the night. Compared to the other nonshaded sites the open grass surface had a much smaller ground heat flux. Warmest sites during the night were the paved surfaces, which had a larger upward directed sensible and ground heat flux than the other surfaces. At the built-up sites the walls also contributed with sensible heat flux, i.e. the total sensible heat flux in the built-up area was larger than what comes from the street surface only. During the day the shaded surfaces in the park were the coolest sites. The shaded surfaces had less net radiation compared to the other non-shaded surfaces and were the only sites that had a downward directed sensible heat flux.

Geomorphological evidence of glaciations exist for the Last Glacial Maximum (about 20 kyr ago). At this time, both North America and Eurasia were covered by extensive ice sheets which are both absent today. However, the temporal and spatial evolution of the ice sheets from the previous interglacial up to the fully-glaciated conditions at LGM is still unresolved and remains a vexing question in climate dynamics. The evolution of ice sheets is essentially controlled by the prevailing climate conditions. On glacial time-scales, the climate is shaped the by the orbital variations of the Earth, but also by internal feedbacks within the climate system. In particular, the ice sheets themselves have the potential to change the climate within they evolve. This thesis focuses on the interactions between ice sheets and the time-mean atmospheric circulation (stationary waves). It is studied how the stationary waves, which are forced by the ice-sheet topography, influence ice-sheet evolution through changing the near-surface air temperature. In this thesis, it is shown that the degree of linearity of the atmospheric response controls to what extent the stationary waves can reorganise the structure of ice sheet. Provided that the response is linear, the stationary waves constitute a leading-order feedback, which serves to increase the volume and deform the shape of ice sheets. If the stationary-wave response to ice-sheet topography is nonlinear in character, the impact on the ice-sheet evolution tends to be weak. However, it is further shown that the amplitude of the nonlinear topographical response, and hence its effect on the ice-sheet evolution, can be significantly enhanced if thermal cooling over the ice sheets is taken into account. / At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Submitted.

Clear Air Turbulence (CAT) is the turbulence experienced at high altitude on board an aircraft. The main mechanisms for its generation are often said to be Kelvin-Helmholtz instability and mountain waves. CAT is an issue to the aviation industry in the sense that it is hard to predict its magnitude and exact location. Mostly, it is just a nuisance for the crew and passengers, but occasionally it causes serious injuries and aircraft damage. It also prevents air-to-air refuelling to be conducted in a safe manner. The micro scale nature of CAT makes it necessary to describe it with turbulence indices. The first part of this study presents a verification of the two commonly used turbulence indices, TI1 and TI2, developed by Ellrod and Knapp in 1992. The verification is done with AMDAR (Aircraft Meteorological Data Relay) reports and computed indices from ERA-Interim data. The second part presents a 33-year climatology of the indices for describing CAT. Results show that the index TI1 is generally the better of the two indices based on hit rate, but TI2 performs better based on false alarm rate. The climatology suggests that CAT is more frequent at the northern east coast of the U.S., over the island of Newfoundland and east of Greenland. In the vertical, CAT seems to occur most frequently at the 225 hPa level but also occur frequently at the 300 hPa level at the aforementioned areas. Based on AMDAR reports from 2011, only 0.014% of the reports were positive turbulence observations. The low amount of reports suggests that CAT can be avoided effectively with current CAT predicting skills and flight planning. / Clear Air Turbulence (CAT) är den turbulens på hög höjd som upplevs ombord på flygplan och orsaken till denna turbulens sägs ofta vara Kelvin-Helmholtz-instabilitet och lävågor. På grund av svårigheten att förutsäga dess styrka och exakta position är CAT ett problem inom flygbranschen. Ofta är CAT bara ett irritationsmoment för besättning och passagerare, men kan ibland orsaka personskador och flygplansskador. Den mikroskaliga strukturen som CAT har gör det nödvändigt att beskriva den med turbulensindex. Den första delen av denna studie tar upp pålitligheten av två ofta använda turbulensindex, TI1 och TI2, utvecklade av Ellrod och Knapp år 1992. Verifikationen görs med hjälp av AMDAR-rapporter (Aircraft Meteorological Data Relay) och turbulensindex beräknade med data från ERA-Interim. Den andra delen består av en 33-års klimatologisk studie av CAT baserat på dessa index. Baserat på träffgrad presterar TI1 generellt bättre än TI2, men TI2 presterar bättre än TI1 vad gäller falsklarmsgrad. Den klimatologiska studien tyder på att CAT är mer frekvent över USAs norra ostkust, över Newfoundland och öster om Grönland. I vertikalled verkar CAT förekomma mest frekvent omkring 225 hPa-nivån, men även runt 300 hPa-nivån över de geografiska områden som nämnts ovan. AMDARrapporter från 2011 visar att endast 0.014% av rapporterna observerade turbulens. Den låga andelen antyder att man effektivt kan undvika CAT över nordatlanten med branschens nuvarande förmåga att förutse CAT och god färdplanering. / Research on a CRuiser Enabled Air Transport Environment, RECREATE