Now showing items 461-480 of 1409

    • First modulation of high-frequency polar mesospheric summer echoes by radio heating of the ionosphere 

      Senior, Andrew; Mahmoudian, Alireza; Pinedo Nava, Henry; La Hoz, Cesar; Rietveld, Michael T; Scales, Wayne A.; Kosch, M.J. (Journal article; Tidsskriftartikkel; Peer reviewed, 2014-07-23)
      The first high-frequency (HF, 8 MHz) observations of the modulation of polar mesospheric summer echoes (PMSE) by artificial radio heating of the ionosphere are presented and compared to observations at 224 MHz and model predictions. The experiments were performed at the European Incoherent Scatter facility in northern Norway. It is shown that model results are in qualitative and partial quantitative ...
    • Increasing Multiyear Sea Ice Loss in the Beaufort Sea: A New Export Pathway for the Diminishing Multiyear Ice Cover of the Arctic Ocean 

      Babb, David G; Galley, Ryan; Howell, Stephen; Landy, Jack Christopher; Barber, David G. (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-05-16)
      Historically, multiyear sea ice (MYI) covered a majority of the Arctic and circulated through the Beaufort Gyre for years. However, increased ice melt in the Beaufort Sea during the early 2000s was proposed to have severed this circulation. Constructing a regional MYI budget from 1997 to 2021 reveals that MYI import into the Beaufort Sea has increased year-round, yet less MYI now survives through ...
    • Segmentation of PMSE data using random forests 

      Jozwicki, Dorota; Sharma, Puneet; Mann, Ingrid; Hoppe, Ulf-Peter Jürgen (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-06-22)
      EISCAT VHF radar data are used for observing, monitoring, and understanding Earth’s upper atmosphere. This paper presents an approach to segment Polar Mesospheric Summer Echoes (PMSE) from datasets obtained from EISCAT VHF radar data. The data consist of 30 observations days, corresponding to 56,250 data samples. We manually labeled the data into three different categories: PMSE, Ionospheric ...
    • Trans-polar drift-pathways of riverine European microplastic 

      Huserbråten, Mats Brockstedt Olsen; Hattermann, Tore; Broms, Cecilie; Albretsen, Jon (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-03-17)
      High concentrations of microplastic particles are reported across the Arctic Ocean–yet no meaningful point sources, suspension timelines, or accumulation areas have been identified. Here we use Lagrangian particle advection simulations to model the transport of buoyant microplastic from northern European rivers to the high Arctic, and compare model results to the flux of sampled synthetic particles ...
    • Stochastic Modelling and Numerical Simulations of Radial Filament Motion and Average Profiles at the Boundary of Fusion Plasmas 

      Paikina, Olga (Master thesis; Mastergradsoppgave, 2022-05-15)
      <p>The boundary region of magnetically confined plasmas is well known to have inherently fluctuating parameters. Advances in experimental measurements and numerical computations have revealed that the fluctuation-driven transport of particles and heat across the magnetic field lines is mainly dominated by the radial motion of blob-like filament structures. These structures, which are localized in ...
    • Numerical Simulations of Turbulence at the Boundary of Fusion Plasma 

      Jäntti, Henrik (Mastergradsoppgave; Master thesis, 2022-05-15)
      Numerical simulations of reduced fluid models describing magnetized plasmas have previously been used to study the boundary of fusion plasmas extensively. A common approximation applied to these models is the so-called Boussinesq approximation. One of the requirements for the Boussinesq approximation to be applicable is that the background particle density is significantly higher than the fluctuations ...
    • Quantitative assessment of two oil-in-ice surface drift algorithms 

      Martins de Aguiar, Victor Cesar; Dagestad, Knut-Frode; Hole, Lars Robert; Barthel, Knut Sven (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-02-04)
      The ongoing reduction in extent and thickness of sea ice in the Arctic might result in an increase of oil spill risk due to the expansion of shipping activity and oil exploration shift towards higher latitudes. This work assessed the response of two oil-in-ice surface drift models implemented in an open-source Lagrangian framework. By considering two numerical modeling experiments, our main finding ...
    • Climatic variations and sediment provenance during the last 16 000 years in the North Hinlopen Trough, Svalbard 

      Samuelsen, Kristine Reppen (Master thesis; Mastergradsoppgave, 2019-06-02)
      Gravity core HH18-1500GC retrieved from the Hinlopen Trough, Arctic Ocean, has been investigated in order to reconstruct the climatic evolution and ocean circulation over the last 16 000 years. The core was taken at the edge of the trough on the northern Svalbard shelf in order to be certain to reach into till, with the intent of dating the retreat of the ice sheet. The Fram Strait is located between ...
    • Impacts of a sudden stratospheric warming on the mesospheric metal layers 

      Feng, Wuhu; Kaifler, Bernd; Marsh, Daniel R.; Höffner, Josef; Hoppe, Ulf-Peter; Williams, Bifford P.; Plane, John M.C. (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-02-11)
      We report measurements of atomic sodium, iron and temperature in the mesosphere and lower thermosphere (MLT) made by ground-based lidars at the ALOMAR observatory (69°N, 16°E) during a major sudden stratospheric warming (SSW) event that occurred in January 2009. The high resolution temporal observations allow the responses of the Na and Fe layers to the SSW at high northern latitudes to be ...
    • A nested high-resolution unstructured grid 3-D ocean-sea ice-ice shelf setup for numerical investigations of the Petermann ice shelf and fjord 

      Prakash, Abhay; Zhou, Qin; Hattermann, Tore; Bao, Weiyang; Graversen, Rune Grand; Kirchner, Nina (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-03-18)
      Three-dimensional numerical simulation of circulation in fjords hosting marine-terminating ice shelves is challenging because of the complexity of processes involved in such environments. This often requires a comprehensive model setup. The following elements are needed: bathymetry (usually unknown beneath the glacier tongue), ice shelf draft (impacting water column thickness), oceanographic state ...
    • Multiplexed Mach-Zehnder interferometer assisted ring resonator sensor 

      Yadav, Mukesh; Aksnes, Astrid (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-01-04)
      A Mach-Zehnder interferometer assisted ring resonator configuration (MARC)-based multiplexed photonic sensor with a large measurement range is experimentally demonstrated. The presented MARC sensor consists of a balanced Mach-Zehnder interferometer and a ring resonator acting as a sensing component. It produces transmission responses with unique spectral signatures, which depend on the physical ...
    • A Study of Polarimetric Parameters Used for Sea Ice Classification 

      Kinderås, Ida G. (Master thesis; Mastergradsoppgave, 2021-12-15)
      The Arctic region of the Earth are largely covered by sea ice, which is important for the marine ecosystems locally in the region, but it also has an impact on the climate systems. Recent climate changes means that the sea ice is melting and the coverage is shrinking which can have a global impact. Monitoring these sea ice changes are important to get an understanding of this impact. There are ...
    • Application of quantitative phase microscopy in microbiology for label-free imaging of bacteria 

      Abrar, Attiqa (Master thesis; Mastergradsoppgave, 2022-03-15)
      Bacteria are the planet’s oldest and the most common life forms. Bacteria have developed alongside humans and are good and harmful to our health. Our bodies contain nearly ten times the number of bacteria as human cells, and this natural microbiota is critical for appropriate development, nutrition, and disease resistance. Unfortunately, we live in an environment rich with bacteria that may cause ...
    • Automatic snow layer detection in drone-borne radar data using edge detection and morphology 

      Blengsli, Martin Markus Løthman (Master thesis; Mastergradsoppgave, 2022-01-14)
      The thesis aims to detect the primary interfaces in ground-penetrating radar (GPR) data collected from a snow-pack. An airborne drone was used to collect the data, where a 2D image of the substructures was gattered, including GPS and laser altimeter data. Al these were used under the thesis to develop the method or presentation of the results. The method focused on simpler image processing techniques ...
    • Uncovering Contributing Factors to Interruptions in the Power Grid: An Arctic Case 

      Chiesa, Matteo; Bianchi, Filippo Maria; Eikeland, Odin Foldvik; Holmstrand, Inga Setså; Bakkejord, Sigurd; Santos, Sergio (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-01-03)
      Electric failures are a problem for customers and grid operators. Identifying causes and localizing the source of failures in the grid is critical. Here, we focus on a specific power grid in the Arctic region of Northern Norway. First, we collected data pertaining to the grid topology, the topography of the area, the historical meteorological data, and the historical energy consumption/production data. ...
    • The long sunspot cycle 23 predicts a significant temperature decrease in cycle 24 

      Solheim, Jan Erik; Stordahl, Kjell; Humlum, Ole (Journal article; Tidsskriftartikkel; Peer reviewed, 2012-02-16)
      Relations between the length of a sunspot cycle and the average temperature in the same and the next cycle are calculated for a number of meteorological stations in Norway and in the North Atlantic region. No significant trend is found between the length of a cycle and the average temperature in the same cycle, but a significant negative trend is found between the length of a cycle and the ...
    • Validating Uncertainty-Aware Virtual Sensors For Industry 4.0 

      Mohammad, Gutama Ibrahim (Mastergradsoppgave; Master thesis, 2022-01-26)
      In industry 4.0 manufacturing, sensors provide information about the state, behavior, and performance of processes. Therefore, one of the main goals of Industry 4.0 is to collect high-quality data to realize its business goal, namely zero-defect manufacturing, and high-quality products. However, hardware sensors cannot always gather quality data due to several factors. First, industrial 4.0 deploys ...
    • The influence of mass loss on the dynamics of dust near the Sun 

      Klepper, Kassi (Mastergradsoppgave; Master thesis, 2021-12-28)
      The Parker Solar Probe (PSP) mission by NASA and the Solar Orbiter (SolO) mission by ESA are two recently launched missions that measure dust in the inner solar system. The dust is produced by fragmentation of meteoroids, which are large fragments of the asteroids and comets. The dust particles are small enough that their motion is affected by the radiation pressure force from the Sun. Dust fragments ...
    • ConvMixerSeg: Weakly Supervised Semantic Segmentation for CT Liver Images 

      Joakimsen, Harald Lykke (Mastergradsoppgave; Master thesis, 2021-12-17)
      The predictive power of modern deep learning approaches is posed to revolutionize the medical imaging field, however, their usefulness and applicability are severely limited by the lack of well annotated data. Liver segmentation in CT images is an application that could benefit particularly well from less data hungry methods and potentially lead to better liver volume estimation and tumor detection. ...
    • Understanding Cassini RPWS Antenna Signals Triggered by Dust Impacts 

      Ye, Sheng - Yi; Vaverka, Jakub; Nouzak, Libor; Sternovsky, Zoltan; Zaslavsky, Arnaud; Pavlu, Jirka; Mann, Ingrid; Hsu, Sean; Averkamp, Terrance, F.; Sulaiman, Ali H.; Pisa, D.; Hospodarsky, George; Kurth, William, S.; Horanyi, Mihaly (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-09-04)
      Electric field antennas are capable of detecting dust impacts in different space environment. We analyze the dust impact signals detected by the Cassini Radio and Plasma Wave Science instrument at different locations around Saturn and compare them with dust impact signals simulated in laboratory conditions and numerically. The spacecraft potential, the size, and capacitance of the impacted element ...