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In the summer of 2008 (June 2nd September 19th) detailed measurements of meteorological conditions and glacier surface properties were conducted in the Belcher Glacier catchment (718 km2), Devon Island Ice Cap, Nunavut, Canada. These measurements were used to force and validate a distributed surface energy balance and sub-surface snow model capable of calculating surface ablation rates and meltwater runoff. This study represents a contribution to the International Polar Year (IPY) Glaciodyn project, whose overall aim is to examine the role of hydrology and ice dynamics in the response of marine-terminating glaciers in the Arctic to climate change. Spatially-averaged total water equivalent (w.e.) ablation was 677 mm w.e., and total predicted runoff during the 2008 summer was 3.9 x 108 m3. Net radiation (87%) was the main source of energy over the study period, followed by the sensible heat flux (13%). Net longwave radiation and the latent heat flux represented an overall energy loss from the surface. Modelled melt season duration lasted from June 17th August 15th, and the majority of ablation occurred in two main periods, from June 26th July 18th, and from July 27th to August 14th. Snowfall and lower air temperatures limited ablation between these dates and after August 15th. Ice exposure at elevations below 1000 m occurred by July 1st. Periods of high ablation rates were associated with positive air temperatures and high net shortwave radiation receipts, and with near surface air temperature gradients that were shallow or inverted (i.e. higher air temperatures at higher elevations). Periods of minimum ablation rates occurred when net shortwave radiation receipts were reduced (e.g. following summer snowfall) and when air temperatures were negative. The largest changes in both the net surface energy balance and ablation rates were linked to changes in surface albedo associated with (i) snowpack removal and ice exposure, and (ii) summer snowfall events. Modelled time series of runoff from individual sub-catchments within the Belcher catchment will be used to force a coupled hydrology and ice flow dynamics model of the Belcher Glacier that will be used to investigate the dynamic response of tidewater-terminating glaciers to surface hydrological forcing.

In the Kebnekaise Massif, Northern Sweden, the west facing glacier, Rabots glaciär, is loosing volume at a significantly higher rate than east facing, Storglaciären. By analyzing data from automatic weather stations situated on the ablation area on the glaciers we investigated the effect of meteorological differences on ablation. There was a difference in micro-climate between Rabots glaciär and Storglaciären. Generally Storglaciären had slightly warmer and drier air, had less or a thinner cloud layer but more precipitation. On both glaciers a glacier wind is dominant but high wind velocities were common especially on Storglaciären indicating a larger influence from the synoptic system. There was a good correlation for temperature and vapor pressure between the glaciers that indicate that both glaciers are strongly affected by the synoptic system. The meteorological parameters have similar effect on the ablation on the glaciers. Temperature, vapor pressure and the turbulent heat fluxes are the only meteorological parameters that suggest a linear affect on ablation. Net shortwave radiation contribute with the greatest amount of energy for ablation but decreased in relative importance as the temperature increased. Shortwave radiation, sensible and latent heat contributed with a total 184Wm-2 on Rabots glaciär and 222Wm-2 on Storglaciären. Rabots glaciär seem to have a significantly greater relative importance of the turbulent heat fluxes than Storglaciären. Although the differences in micro-climate were not great, using the ablation for Storglaciären to estimate ablation on Rabots glaciär would over estimate the ablation with 0.5m w.e..

Throughout the late 20th and early 21st century, the global temperature has been on the rise, a process that has been accelerated in the Arctic. The Arctic surface temperatures have risen at a factor of 3 greater rate than the global average, leading to the term Arctic Amplification of climate change. In this study, the enhanced warming of the Arctic, and the enhancement at the Arctic surface in comparison to the warming of the atmosphere aloft, is investigated through a reconstruction of the past surface energy balance by a model driven by downwelling irradiance reconstructed using radiosonde profiles and the radiative transfer code SBDART. The downwelling irradiance is shown to be increasing over the time-period of 1994-2009, and the sources of this increase are diagnosed. The time-evolution of the surface flux terms are discussed, and the sensitivity of the surface temperature to changes in atmospheric temperature is investigated.

<p>With the use of a process-orientated ecosystem model andmeasurements conducted at different Swedish coniferous forestsites, abiotic and biotic interactions between tree and soilwere identified and related to governing factors. Two differentmodelling approaches to describe soil temperatures at two sitesincluding hydrological transects were tested (I). The approachin which both canopy and soil were considered proved to be amore flexible tool to describe soil temperatures, especiallyduring snow-free winter periods. Five sites along a climatetransect covering Sweden were used to describe soil carbon poolchanges during an 80-year period simulation (II). The dynamicmodelling approach, with a feedback between abiotic and bioticsub-models, was successful in describing simplified patterns offorest stand dynamics and furthermore in differentiatingbetween climate and nitrogen availability factors. The largereffect of nitrogen availability compared to climate on soilcarbon pool changes was clearly shown.</p><p><b>Keywords:</b>SPAC; soil surface energy balance; Norwayspruce; canopy; LAI; climate; nitrogen; CoupModel</p>

<p>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.</p><p>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.</p><p>Energiflödena beräknades med hjälp av data för luft- och yttemperatur, vindhastighet, luftfuktighet och nettostrålning.</p><p>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.</p><p>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.</p> / <p>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.</p><p>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.</p><p>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.</p><p>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.</p>

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.

With the use of a process-orientated ecosystem model andmeasurements conducted at different Swedish coniferous forestsites, abiotic and biotic interactions between tree and soilwere identified and related to governing factors. Two differentmodelling approaches to describe soil temperatures at two sitesincluding hydrological transects were tested (I). The approachin which both canopy and soil were considered proved to be amore flexible tool to describe soil temperatures, especiallyduring snow-free winter periods. Five sites along a climatetransect covering Sweden were used to describe soil carbon poolchanges during an 80-year period simulation (II). The dynamicmodelling approach, with a feedback between abiotic and bioticsub-models, was successful in describing simplified patterns offorest stand dynamics and furthermore in differentiatingbetween climate and nitrogen availability factors. The largereffect of nitrogen availability compared to climate on soilcarbon pool changes was clearly shown. Keywords:SPAC; soil surface energy balance; Norwayspruce; canopy; LAI; climate; nitrogen; CoupModel

abstract: The role of environmental factors that influence atmospheric propagation of sound originating from freeway noise sources is studied with a combination of field experiments and numerical simulations. Acoustic propagation models are developed and adapted for refractive index depending upon meteorological conditions. A high-resolution multi-nested environmental forecasting model forced by coarse global analysis is applied to predict real meteorological profiles at fine scales. These profiles are then used as input for the acoustic models. Numerical methods for producing higher resolution acoustic refractive index fields are proposed. These include spatial and temporal nested meteorological simulations with vertical grid refinement. It is shown that vertical nesting can improve the prediction of finer structures in near-ground temperature and velocity profiles, such as morning temperature inversions and low level jet-like features. Accurate representation of these features is shown to be important for modeling sound refraction phenomena and for enabling accurate noise assessment. Comparisons are made using the acoustic model for predictions with profiles derived from meteorological simulations and from field experiment observations in Phoenix, Arizona. The challenges faced in simulating accurate meteorological profiles at high resolution for sound propagation applications are highlighted and areas for possible improvement are discussed. A detailed evaluation of the environmental forecast is conducted by investigating the Surface Energy Balance (SEB) obtained from observations made with an eddy-covariance flux tower compared with SEB from simulations using several physical parameterizations of urban effects and planetary boundary layer schemes. Diurnal variation in SEB constituent fluxes are examined in relation to surface layer stability and modeled diagnostic variables. Improvement is found when adapting parameterizations for Phoenix with reduced errors in the SEB components. Finer model resolution (to 333 m) is seen to have insignificant ($<1\sigma$) influence on mean absolute percent difference of 30-minute diurnal mean SEB terms. A new method of representing inhomogeneous urban development density derived from observations of impervious surfaces with sub-grid scale resolution is then proposed for mesoscale applications. This method was implemented and evaluated within the environmental modeling framework. Finally, a new semi-implicit scheme based on Leapfrog and a fourth-order implicit time-filter is developed. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2014

High latitude and altitude ecosystems are currently undergoing rapid and unprecedented warming in response to anthropogenically induced climate change. Subarctic, alpine regions are particularly vulnerable to increases in air temperature and changing precipitation regimes, which have caused cascading hydrological and ecological impacts. In addition to changing flow regimes, thawing permafrost, and declining glaciers, widespread changes in vegetation composition, density and distribution have been observed across northern regions. Specifically, treeline is advancing with increasing latitude and altitude and shrubs are increasing in height, extent, and density. Despite widespread documentation of this northern greening, few field-based studies have evaluated the hydrological implications of these changes. Quantification of total evapotranspiration (ET) across a range of vegetation gradients is essential for predicting water yield, yet challenging in cold alpine catchments due to heterogeneous land cover. Direct field-level measurements of transpiration (T) and evaporative partitioning across subarctic, alpine ecosystems and species are rare, yet essential to assess sensitivities and hydrological response to changing climate drivers. This thesis presents six years of surface energy balance components and ET dynamics and two years of sap flux measurements and critical zone stable water isotope sampling at three sites along an elevational gradient in a subarctic, alpine catchment near Whitehorse, Yukon Territory, Canada. These sites span a gradient of thermal and vegetation regimes, providing a space-for-time comparison for future ecosystem shifts: 1) a low-elevation boreal white spruce forest (~12-20 m), 2) a mid-elevation subalpine taiga comprised of tall, dense willow (Salix) and birch (Betula) shrubs (~1-3 m) and 3) a high-elevation subalpine taiga with short, sparse shrub cover (< 0.75 m) and moss, lichen, and bare rock. We utilize both mass flux measurements and stable water isotopes to evaluate the timing, magnitude, sensitivities, and sources of plant water uptake across these vegetation covers. Total ET decreased and interannual variability increased with elevation, with mean May to September ET totals of 349 (±3) mm at the forest, 249 (±10) mm at the tall, dense shrub site, and 240 (± 26) mm at the short, sparse shrub site. The shrub sites exhibited similar ET losses over 6 years despite differences in shrub height and abundance, although daily rates were higher at the tall shrub site in the peak growing season. From May to September, ET:R ratios were the highest and most variable at the forest (2.19 ± 0.37) and similar at the tall, dense shrub (1.22 ± 0.09) and short, sparse shrub (1.14 ± 0.05) sites. In the mid-growing season, mean T rates were greater at the dense shrub site (2.0 ± 0.75 mm d-1) than the forest (1.47 ± 0.52 mm d-1). During this time, T:ET was lower at the forest (0.48) than at the tall, dense shrub site (0.80). During the growing season between the two years, 2020 was considerably wetter and cooler than 2019. At the tall shrub site, during the mid-growing season (July 1-Aug 15), T dropped considerably in 2020 (-26%), as T was suppressed during the short, wet growing season. In contrast, T at the forest was only moderately suppressed (-3%) between years in this same period. Evapotranspiration was more strongly controlled by air temperature during the early and late season at the forest, while ET at the shrub site was more sensitive to warmer temperatures in the mid-growing season. At the shrub sites, ET was energy limited with no observed soil moisture limitation on T. While 2H and 18O of volume weighted precipitation became more depleted with elevation, the opposite was true in xylem water, where 2H and 18O became more enriched with elevation. Plant water uptake was more reflective of snow water at the forest site than both shrub sites, particularly early in the year and during dry periods. Near-surface bulk soil water had more negative lc-excess at the forest throughout the season and with depth, highlighting increased contributions from soil evaporation. This study combined direct measurements of sap flux, ET, and critical zone isotopes to provide new details on multi-year plant-soil-water dynamics, critical zone water cycling, and species-specific plant water uptake patterns in seasonally frozen soils, which have not previously been reported in cold regions. Our results suggest that advances in treeline will increase overall ET and lower interannual variability; however, the large growing season water deficit and stable water isotope signature at the forest indicates strong reliance on soil moisture from late fall and snowmelt recharge and the potential for plant water stress. Differences between the shrub species were apparent in the sap flux and stable isotope measurements, highlighting the need to further evaluate species specific responses and feedbacks when predicting hydrological fluxes across subarctic ecosystems. Overall, our results suggest that predicted changes in vegetation type and structure in northern regions will have a considerable impact on water partitioning and will vary in a complex way in response to changing precipitation timing, phase and magnitude. / Thesis / Candidate in Philosophy