Nesse estudo foram mapeadas e mensuradas as variações de área, elevação mínima e orientação das geleiras da Colômbia e da Venezuela (trópicos internos), entre os anos 1985-2015. Para o mapeamento das áreas das geleiras foram utilizadas como base imagens Landsat, sensores TM, ETM+ e OLI. Às imagens selecionadas foi aplicado o Normalized Difference Snow Index (NDSI), no qual são utilizadas duas bandas em que o alvo apresenta comportamento espectral oposto ou com características bem distintas: bandas 2 e 5 dos sensores TM e ETM+ e bandas 3 e 6 do sensor OLI. Os dados de elevação e orientação das massas de gelo foram obtidos a partir do Modelo Digital de Elevação SRTM (Shuttle Radar Topography Mission – v03). Em 1985, a soma das áreas das sete geleiras estudadas correspondia a 92,84 km², enquanto no último ano estudado (2015/2016) esse valor passou para 36,97 km². A redução de área ocorreu em todas as geleiras analisadas, com taxas de retração anual variando entre 2,49% a.a. e 8,46% a.a. Houve retração das áreas de gelo localizadas em todos os pontos cardeais considerados, bem como, elevação da altitude nas frentes de geleiras. Além da perda de área ocorrida nas menores altitudes, onde a taxa de ablação é mais elevada, também se observou retração em alguns topos, evidenciado pela ocorrência de altitudes menores nos anos finais do estudo, em comparação com os anos iniciais. Como parte das geleiras colombianas está localizada sobre vulcões ativos, essas áreas sofrem influência tanto de fatores externos, quanto de fatores internos, podendo ocorrer perdas de massa acentuadas causadas por erupção e/ou terremoto. / In this study, glaciers located in Colombia and Venezuela (inner tropics) were mapped between 1985-2015. The area of these glaciers was measured and the variations that occurred in each glacier were compared to identify whether the glacier was growing or shrinking. The minimum elevation of the glaciers fronts and the aspect of the glaciers were analyzed. The glaciers areas ware obtained by the use of Landsat images, TM, ETM+ and OLI sensors. The Normalized Difference Snow Index (NDSI) was applied to the selected images, in which two bands were used, where the ice mass has opposite (or very different) spectral behavior: bands 2 and 5 from sensors TM and ETM+, and bands 3 and 6 from sensors OLI. The elevation and the aspect data of the glaciers were obtained from SRTM (Shuttle Radar Topography Mission – v03) Digital Elevation Model. In 1985/1986, the sum of the areas of the seven studied glaciers corresponded to 92.84 km², while in the last year analyzed (2015/2016), this value shrank to 36.97 km². The area shrinkage occurred in all the glaciers that were mapped, with annual decline rates ranging from 2.49%/year to 8.46%/year. It is also possible to observe a decrease of the ice covered in all aspects considered, as well as an elevation in all glaciers fronts. In addition to the area loss occurred at lower altitudes, where the ablation rate is higher than in higher altitudes, shrinkage in some mountain tops was also present, which is evidenced by the occurrence of lower maximum elevations in the final years of the study, when compared with the initial years. Considering that part of the Colombian’s glaciers are located on active volcanoes, these areas are influenced by external and internal factors, and the occurrence of volcanic eruption and/or earthquake can cause sharp mass losses.

Interception av snö eller regn på trädkronor är en viktig del av det hydrologiska kretsloppet. Upp till en tredjedel av all snö som faller över skogsområden når aldrig marken på grund av stora avdunstningsförluster av interceptionsförrådet, vilket minskar vårflöden i älvar. Goda prognoser av dessa flöden är viktiga för vattenkraftsindustrin. För att kunna förbättra modeller, i vilka interceptions-avdunstningsprocessen ingår, krävs lämpliga mätmetoder för interceptionförrådet av snö. Syftet med detta arbete var att undersöka om impulsradarutrustning kan användas för att mäta interceptionsförrådet av snö på barrträd. Metoden bygger på att mäta hastigheten och utsläckningen hos en elektromagnetisk impulsvåg, vilken skickas från en sändarantenn genom ett avsnitt skog till en mottagarantenn. Både utsläckningen och hastigheten påverkas av snö och vatten på trädens kronor, och kan med så kallade blandningsformler relateras till mängd vatten. Blandningsformler beskriver de elektromagnetiska egenskaperna hos heterogena material. Laboratorietester visade att interception av flytande vatten på små trädkronor gav upphov till förändringar av impulsvågens hastighet och utsläckning mätbara med radarutrustningen. Uppskattningar av mängden intercepterat vatten från radarmätningarna gav en överskattning jämfört med oberoende referensmätningar, däremot stämde relativa variationer väl överens mellan mätningarna. Tydliga samband mellan impulsvågens utsläckning och mängden intercepterat vatten kunde inte bestämmas från experimenten. Utsläckningsresultaten var svårtolkade och lämpliga blandningsformler hittades inte i litteraturen. Metoden testades även en vecka i fält i norra Sverige. Trots att installationen inte var den bästa visade resultaten ändå god överensstämmelse mellan uppskattade förändringar av interceptionsförrådet från radarmätningarna, och observerade väderförändringar samt oberoende referensmätningar med en trädvågsanordning. Resultaten tyder på att metoden kan ge goda uppskattningar av interceptionsförrådet, då en väl fungerande installation av utrustningen används och efter att vidare kalibreringsförsök genomförts. / Interception of rain or snow in forest canopies is an important component of the hydrological cycle. Up to one third of the total winter precipitation never reaches the ground in forest areas due to evaporation losses of intercepted snow, which reduces spring-time water flow in rivers. Accurate spring flow predictions are important for the hydro-power industry. Appropriate measurement methods of intercepted snow are needed in order to improve models involving the interception evaporation process. The aim of this study was to explore the possibilities of an impulse radar system to measure the snow interception storage on coniferous trees. The method is based on measurements of the velocity and attenuation of an electromagnetic impulse wave, generated in a transmitting antenna and sent through a forest section and detected by a receiving antenna. The attenuation and velocity is affected by ice and water in the canopy air space, and can be related to amounts of water using so-called mixing formulas that describe the average electromagnetic properties of heterogeneous materials. Controlled laboratory measurements on small canopies showed that interception of liquid water was well above the detectable limits of the radar system, with respect to both attenuation and velocity changes. Estimations of the mass of intercepted water based on velocity changes overestimated the reference measurements, but relative variations were well captured. No clear relation could be found between amount of water on canopies and impulse wave attenuation from the experiments. The attenuation results were difficult to interpret, and appropriate mixing formulas were not found in the literature. The method was further tested for one week under field conditions in northern Sweden. In spite of a non-optimal equipment installation results of estimated changes of the interception storage showed a good agreement with observed weather variations and reference measurements using a tree weighing device. The method can have good conditions to give correct estimations of the snow interception storage, using appropriate installation and further calibration measurements.

We present a method for stable buildup of snow on surfaces of arbitrary topology and geometric complexity. This is achieved by tracing quantities of snow, so-called snow packages, through a dynamic wind field. Dual compact level sets are used to represent geometry as well as accumulated snow. The level sets have also proven to be well suited for the internal boundaries for our Navier-Stokes solver, which produces a wind field that changes according to snow buildup. Our method is different from previous work in that all the addition of snow is done by local operations, avoiding computationally expensive global refinement procedures. The main contribution of this work is a dual level set method for particle interaction with level sets.

The Deepwater Horizon (DWH) oil spill in the Gulf of Mexico (GoM) in the spring of 2010 introduced 4.4 million of barrels of oil to the ecosystem. Some biodegradation of the oil occurs when microorganisms, particularly bacteria, metabolize the oil as a carbon source. During this process, the microbes also require nutrients for energy. An introduction of oil at this magnitude has the ability to induce large blooms of microbes, which in turn can affect nutrient concentrations. Microbial petroleum degradation decreases nutrient concentrations, whereas the microbial assimilation and decay of organic matter increase nutrient concentrations. This study assessed whether any changes in nitrate, ammonium, and/or phosphate concentrations from historical levels could be attributed to the oil spill as a result of biodegradation, and how those changes can impact the GoM ecosystem. Nutrient samples were collected at discrete depths throughout the water column, in a cross-shelf transect inland from the spill site outside the DeSoto Canyon, in August 2010, February 2011, and May 2011 (four months to one year after the spill). In August 2010, a subsurface oil plume was found at depths of 1000 m to 1200 m. At the same depth of ~1000 m, a significant decrease in nitrate was observed, indicating the biodegradation of oil by heterotrophic bacteria of the aphotic zone, compared to earlier data during August 2000, when no known oils were present. Overall temporal increases in ammonium and dissolved organic nitrogen (DON) were observed both in near-surface waters and at an intermediate depth of ~400 m next to the walls of the DeSoto Canyon, suggesting an incremental die-off of both plankton and benthic organisms during accelerated recycling of nutrients. Continued decreases of phosphate were observed into February 2011, supporting ongoing biodegradation then as well. By May 2011, however, there were more increases in near-surface ammonium concentrations, compared to April 2000, with the implication that continued interseasonal recycled nitrogen accumulations may have been due to a decadal ecological regime shift, after a combination of top-down overfishing, petroleum perturbations, and/or increases of toxic harmful algal blooms (HABs).

Accurate simulation of energy, water, and carbon fluxes exchanging between the land surface and the atmosphere is beneficial for improving terrestrial ecohydrological and climate predictions. We systematically assessed the Noah land surface model (LSM) with mutiparameterization options (Noah-MP) in simulating these fluxes and associated variations in terrestrial water storage (TWS) and snow cover fraction (SCF) against various reference products over 18 United States Geological Survey two-digital hydrological unit code regions of the continental United States (CONUS). In general, Noah-MP captures better the observed seasonal and interregional variability of net radiation, SCF, and runoff than other variables. With a dynamic vegetation model, it overestimates gross primary productivity by 40% and evapotranspiration (ET) by 22% over the whole CONUS domain; however, with a prescribed climatology of leaf area index, it greatly improves ET simulation with relative bias dropping to 4%. It accurately simulates regional TWS dynamics in most regions except those with large lakes or severely affected by irrigation and/or impoundments. Incorporating the lake water storage variations into the modeled TWS variations largely reduces the TWS simulation bias more obviously over the Great Lakes with model efficiency increasing from 0.18 to 0.76. Noah-MP simulates runoff well in most regions except an obvious overestimation (underestimation) in the Rio Grande and Lower Colorado (New England). Compared with North American Land Data Assimilation System Phase 2 (NLDAS-2) LSMs, Noah-MP shows a better ability to simulate runoff and a comparable skill in simulating R-n but a worse skill in simulating ET over most regions. This study suggests that future model developments should focus on improving the representations of vegetation dynamics, lake water storage dynamics, and human activities including irrigation and impoundments.

Plants have an important role in the tundra carbon (C) cycle by storing C in primary production and thus potentially counteract the C released from thawing permafrost. Tundra vegetation is limited by nitrogen (N), which is predicted to increase with rising temperatures and increased snow depth. In permafrost systems, rooting depth will determine whether plants can access N in the deep soil which, with increasing snow depth, has the potential to turn into a significant N source. Increased plant-available N is thus expected to affect both plant productivity and vegetation composition. This study aims to investigate vegetation responses to increased temperature and snow depth in a permafrost system of moist tussock tundra by combining open-top chambers with a realistic snow manipulation (snowfences). The shallow-rooted shrubs, Betula nana and Rhododendron tomentosum, and the deep-rooted sedge Eriophorum vaginatum were analyzed for responses in growth and reproduction effort. Also, vegetation responses in terms of normalized difference vegetation index (NDVI) were investigated. Winter warming increased flower density of E. vaginatum while B. nana showed an increased shoot growth in response to winter warming, but only during mid-growing season. Although winter warming increased winter soil temperature and generated a trend of increased thaw depth, there were no responses in NDVI or further species-specific responses in reproduction effort, leaf and shoot growth, leaf production or leaf dry weight to warming treatments. These results indicate that E. vaginatum respond in reproduction effort while B. nana respond in (mid-season) growth to winter warming. In total, the warming treatments generated a weak response in tundra plants which indicate that tussock tundra might not be very responsive to short-term warming. These results suggest that tundra plants have a low ability to counteract increased releases of soil C in response to short-term warming.

South Africa is located in the sub tropics with an elevated plateau which is located approximately 1500 m above mean sea level (a.m.s.l). Every year, snow occurs on the mountains of Lesotho, but on occasions this snow descends to lower elevations which impacts on the livelihood of people. Severe weather originating from extra-tropical weather systems has been well documented in South Africa and yet very little research has been done to predict significant snowfall from these weather systems. The main aim of this research is to identify those weather systems responsible for snow and to understand the processes causing snow to form when these systems occur. A comprehensive database of significant snowfall events is supplied from 1981 to 2011. The database is subjectively classified into characteristic synoptic patterns. The snow cases are then objectively classified using self-organising maps (SOMs) to obtain synoptic configurations most typically associated with significant snowfall over South Africa. Case studies which aim to explain the synoptic conditions, formation mechanisms as well as critical surface temperature and relative humidity during snowfall events are described. This is done by analysing each case study with respect to synoptic circulations, surface observations, atmospheric soundings, satellite imagery as well as atmospheric thickness. Conclusions are drawn and critical threshold values of atmospheric thickness, surface temperature and humidity are identified when snowfall occurs. A methodical snow forecasting decision tree is devised. It takes the synoptic classification of circulation patterns during significant snowfall, atmospheric thickness, height of the freezing level, surface temperature, and relative humidity into account. This process is explained by case studies. It is recommended that results from this dissertation are made available to weather forecasters in South Africa and that the results are implemented in the operational forecasting environment. Further case study investigations are suggested, taking the mesoscale processes effects into account. / Dissertation (MSc)--University of Pretoria, 2013. / am2013 / Geography, Geoinformatics and Meteorology / MSc / Unrestricted

This thesis describes the comparison of time-lapse field observations of suncups on alpine snow with numerical simulations. The simulations consist of solutions to a nonlinear partial differential equation which exhibits spontaneous pattern formation from a low amplitude, random initial surface. Both the field observations and the numerical solutions are found to saturate at a characteristic height and fluctuate chaotically with time. The timescale of these fluctuations is found to be instrumental in determining the full set of parameters for the numerical model such that it mimics the nonlinear dynamics of suncups. These parameters in turn are related to the change in albedo of the snow surface caused by the presence of suncups. This suggests the more general importance of dynamical behaviour in gaining an understanding of pattern formation phenomena. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The Gulf of Mexico (GoMx) is among the most productive regions for offshore oil and natural gas recovery. In 2010, the Deepwater Horizon (DWH) drilling rig exploded, burned for three days, sank, and released over 4 million barrels of oil in the subsequent 84 days before it was capped. Some oil was buoyant enough to float to the ocean surface, where some was removed via a myriad techniques. Importantly, a plume of oil remained suspended in the water column at approximately 1,100 m water depth, where it drove a marine snow event, and deposited large quantities of oil on the seafloor. The northern GoMx seafloor is complex and dynamic. Submarine canyons, mounds, channels, and salt domes dominate the seafloor along the continental slope surrounding the DWH well. Using high-resolution bathymetric data, variables derived to characterize the seafloor (water depth, distance, slope, and aspect), and spatial relationships between seafloor stations and the DWH well, relationships between concentrations, fluxes and inventories of polycyclic aromatic hydrocarbons, and other seafloor variables were hypothesized to be statistically significantly related. The most significant seafloor characteristic to predict distributions was water depth, followed by distance, relative aspect, and slope.

Syftet med denna studie är att undersöka hur den klimataktivistiska organisationen Extinction Rebellion Sverige gestaltar klimatfrågan och på vilka sätt denna gestaltning ligger till grund för skapandet av en kollektiv identitet. Det har jag gjort genom att fokusera på organisationens pressmeddelanden som de publicerat på sin hemsida. Det blir relevant att studera pressmeddelanden då dessa kan ses som en slags intern och extern kommunikationskanal där Extinction Rebellion Sverige kan förmedla sina värderingar och åsikter. Jag analyserar mitt material utifrån gestaltningsteorin och teorier om nya sociala rörelser och kollektiv identitet. De huvudsakliga resultaten visar på en väldigt alarmistisk syn på klimatfrågan där stort ansvar läggs på svenska politiker. Samtidigt finner de stor tilltro till deras aktioner av civil olydnad. Den kollektiva identitet som ges uttryck för i pressmeddelandena grundar sig mycket i att ifrågasätta systemet och att medlemmar skriver under på den verklighetsbild som presenteras. / The study aims to examine how the climate activism-organization Extinction Rebellion Sweden frames climate change and how the framing plays a part of their collective identity. This is done by studying press releases published on their website. I find press releases relevant for this study since it is a way of both internal and external communication where Extinction Rebellion Sweden can mediate their values and opinions. The theory being used is framing theory as well and theories of new social movements and collective identity. The results show that they tend to frame climate change in an alarmistic way where a lot of the responsibility is put on Swedish politicians. At the same time, they express great faith in civil disobedience as action. The collective identity being expressed in the press releases is based in questioning the system and the fact that their members agrees on the reality being presented.