Viser treff 61-80 av 1262

    • Investigating Spatial and Temporal Structuring of E-Region Coherent Scattering Regions Over Northern Norway 

      Huyghebaert, Devin Ray; Chau, Jorge L.; Spicher, Andres; Ivarsen, Magnus Fagernes; Clahsen, Matthias; Latteck, Ralph; Vierinen, Juha-Pekka (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-09-26)
      Recently, it has been shown that the Spread Spectrum Interferometric Multistatic meteor radar Observing Network radar system located in northern Norway is capable of measuring ionospheric E-region coherent scatter with spatial and temporal resolutions on the order of 1.5 km and 2 s, respectively. Four different events from June and July of 2022 are examined in the present study, where the coherent ...
    • Effects of subglacial meltwater runoff on the ocean circulation beneath the Filchner Ice Shelf 

      Hus, Johanne Jahnsen (Mastergradsoppgave; Master thesis, 2023-06-15)
      Antarctic ice shelves, by restraining ice streams and affecting the discharge of grounded ice, play a critical role in the mass balance of the Antarctic ice sheet. In this study, sub-ice shelf CTD measurements and time series data from an ice shelf cavity mooring were used to detect subglacial runoff beneath the Filchner Ice Shelf. CTD measurements from four boreholes across the southern Filchner ...
    • On the Linkage Between Rossby Waves and Heatwaves 

      Petříček, Jakub (Mastergradsoppgave; Master thesis, 2023-05-14)
      This thesis examines the relationship between upper-level atmospheric circulation and heatwaves. We studied the role of planetary Rossby waves in the observed increase in intensity, frequency, and duration of extreme temperature events in the mid-latitudes. Focusing on the summer season, we tested the proposed hypothesis that links recent changes in the Rossby wave amplitudes and propagation speed ...
    • Science goals for a high-frequency radar and radio imaging array 

      Isham, Brett Cameron; Bullett, Terence; Gustavsson, Björn Johan; Polisensky, Emil; Brum, Christiano; Fallen, Christopher; Belyey, Vasyl; Parra-Rojas, Francisco; Norouzi, Leila; Stramkals, Arturs; Ökten, Mehmet Baran (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-08-01)
      A medium and high-frequency antenna array for radar and radio imaging of the ionosphere is planned for installation in Aguadilla, Puerto Rico. Science goals include the study of space weather, radio propagation, meteors, lightning, and plasma physics. Radio imaging is ideal for the study of stimulated ionospheric radio emissions, such as those induced by the Arecibo Observatory high-power HF radio ...
    • The Stepwise Reduction of Multiyear Sea Ice Area in the Arctic Ocean Since 1980 

      Babb, D.G.; Galley, R.J.; Kirillov, S.; Landy, Jack Christopher; Howell, S.E.L.; Stroeve, J.C.; Meier, W.; Ehn, J.K.; Barber, D.G. (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-09-28)
      The loss of multiyear sea ice (MYI) in the Arctic Ocean is a significant change that affects all facets of the Arctic environment. Using a Lagrangian ice age product, we examine MYI loss and quantify the annual MYI area budget from 1980 to 2021 as the balance of export, melt, and replenishment. Overall, MYI area declined at 72,500 km<sup>2</sup> /yr; however, a majority of the loss occurred ...
    • Retrieval of Snow Depth on Arctic Sea Ice From Surface-Based, Polarimetric, Dual-Frequency Radar Altimetry 

      Willatt, Rosemary; Stroeve, Julienne; Nandan, Vishnu; Newman, Thomas; Mallett, Robbie; Hendricks, Stefan; Ricker, Robert; Mead, James; Itkin, Polona; Tonboe, Rasmus; Wagner, David N.; Spreen, Gunnar; Liston, Glen; Schneebeli, Martin; Krampe, Daniela; Tsamados, Michel; Demir, Oguz; Wilkinson, Jeremy; Jaggi, Matthias; Zhou, Lu; Huntemann, Marcus; Raphael, Ian A.; Jutila, Arttu; Oggier, Marc (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-10-18)
      Snow depth on sea ice is an Essential Climate Variable and a major source of uncertainty in satellite altimetry-derived sea ice thickness. During winter of the MOSAiC Expedition, the “KuKa” dual-frequency, fully polarized Ku- and Ka-band radar was deployed in “stare” nadir-looking mode to investigate the possibility of combining these two frequencies to retrieve snow depth. Three approaches ...
    • A long-term proxy for sea ice thickness in the Canadian Arctic: 1996-2020 

      Glissenaar, Isolde A.; Landy, Jack Christopher; Babb, David G.; Dawson, Geoffrey J.; Howell, Stephen E. L. (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-08-15)
      . This study presents a long-term winter sea ice thickness proxy product for the Canadian Arctic based on a random forest regression model – applied to ice charts and scatterometer data, trained on CryoSat-2 observations, and applying an ice type–sea ice thickness correction using the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) – that provides 25 years of sea ice thickness ...
    • Comparing elevation and backscatter retrievals from CryoSat-2 and ICESat-2 over Arctic summer sea ice 

      Dawson, Geoffrey J.; Landy, Jack Christopher (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-09-27)
      The CryoSat-2 radar altimeter and ICESat-2 laser altimeter can provide complementary measurements of the freeboard and thickness of Arctic sea ice. However, both sensors face significant challenges for accurately measuring the ice freeboard when the sea ice is melting in summer months. Here, we used crossover points between CryoSat2 and ICESat-2 to compare elevation retrievals over summer sea ...
    • The weakening AMOC under extreme climate change 

      Madan, Gaurav; Gjermundsen, Ada; Iversen, Silje Christine; Lacasce, Joseph Henry (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-10-06)
      Changes in the Atlantic Meridional Overturning Circulation (AMOC) in the quadrupled CO<sub>2</sub> experiments conducted under the sixth Coupled Model Intercomparison Project (CMIP6) are examined. Increased CO<sub>2</sub> triggers extensive Arctic warming, causing widespread melting of sea ice. The resulting freshwater spreads southward, frst from the Labrador Sea and then the Nordic Seas, and ...
    • The Detection and Attribution of Northern Hemisphere Land Surface Warming (1850–2018) in Terms of Human and Natural Factors: Challenges of Inadequate Data 

      Soon, Willie; Connolly, Ronan; Connolly, Michael; Akasofu, Syun-Ichi; Baliunas, Sallie; Berglund, Johan; Bianchini, Antonio; Briggs, William M.; Butler, C.J.; Cionco, Rodolfo Gustavo; Crok, Marcel; Elias, Ana G.; Fedorov, Valery M.; Gervais, François; Harde, Hermann; Henry, Gregory W.; Hoyt, Douglas V.; Humlum, Ole; Legates, David R.; Lupo, Anthony R.; Maruyama, Shigenori; Moore, Patrick; Ogurtsov, Maxim; ÓhAiseadha, Coilín; Oliveira, Marcos J.; Park, Seok-Soon; Qiu, Shican; Quinn, Gerré; Scafetta, Nicola; Solheim, Jan Erik; Steele, Jim; Szarka, László; Tanaka, Hiroshi L.; Taylor, Mitchell K.; Vahrenholt, Fritz; Velasco Herrera, Víctor M.; Zhang, Weijia (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-08-28)
      A statistical analysis was applied to Northern Hemisphere land surface temperatures (1850–2018) to try to identify the main drivers of the observed warming since the mid-19th century. Two different temperature estimates were considered—a rural and urban blend (that matches almost exactly with most current estimates) and a rural-only estimate. The rural and urban blend indicates a long-term warming ...
    • Demonstrating low Raman background in UV-written SiO2 waveguides 

      Jensen, Mathias Novik; Gates, James C.; Flint, Alex I.; Hellesø, Olav Gaute (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-09-06)
      Raman spectroscopy can give a chemical ’fingerprint’ from both inorganic and organic samples, and has become a viable method of measuring the chemical composition of single biological particles. In parallel, integration of waveguides and microfluidics allows for the creation of miniaturized optical sensors in lab-on-a-chip devices. The prospect of combining integrated optics and Raman spectroscopy ...
    • Barents-2.5km v2.0: an operational data-assimilative coupled ocean and sea ice ensemble prediction model for the Barents Sea and Svalbard 

      Röhrs, Johannes; Gusdal, Yvonne; Rikardsen, Edel S. U.; Durán Moro, Marina; Brændshøi, Jostein; Kristensen, Nils Melsom; Fritzner, Sindre Markus; Wang, Keguang; Sperrevik, Ann Kristin; Idzanovic, Martina; Lavergne, Thomas; Debernard, Jens Boldingh; Christensen, Kai Håkon (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-09-22)
      An operational ocean and sea ice forecast model, Barents-2.5, is implemented for short-term forecasting at the coast off northern Norway, the Barents Sea, and the waters around Svalbard. Primary forecast parameters are sea ice concentration (SIC), sea surface temperature (SST), and ocean currents. The model also provides input data for drift modeling of pollutants, icebergs, and search-and-rescue ...
    • Change in Climate Sensitivity and Its Dependence on the Lapse-Rate Feedback in 4 x CO2 Climate Model Experiments 

      Eiselt, Kai-Uwe; Graversen, Rune Grand (Journal article; Tidsskriftartikkel, 2022-04-19)
      Robust estimates of climate sensitivity are important for decision-making on mitigation of climate change. However, climate sensitivity and its governing processes are still subject to large uncertainty. Recently it has been established that climate sensitivity changes over time in numerical climate model experiments with abrupt quadrupling of the CO<sub>2</sub> concentration. Here we conduct an ...
    • Selective Imputation for Multivariate Time Series Datasets with Missing Values 

      Blazquez-Garcia, Ane; Wickstrøm, Kristoffer Knutsen; Yu, Shujian; Mikalsen, Karl Øyvind; Boubekki, Ahcene; Conde, Angel; Mori, Usue; Jenssen, Robert; Lozano, Jose A. (Journal article; Tidsskriftartikkel, 2023-01-31)
      Multivariate time series often contain missing values for reasons such as failures in data collection mechanisms. Since these missing values can complicate the analysis of time series data, imputation techniques are typically used to deal with this issue. However, the quality of the imputation directly affects the performance of downstream tasks. In this paper, we propose a selective imputation ...
    • Assimilation of high-resolution ice charts in a coupled ocean-sea-ice model 

      Fritzner, Sindre Markus; Christensen, Kai Håkon; Graversen, Rune; Wang, Keguang (Journal article; Tidsskriftartikkel, 2019)
      In this study, we show assimilation results from a coupled ocean sea-ice model. The model has a horizontal resolution of 2.5 km. In the assimilation system, we assimilate high-resolution ice charts, structured on a 1 km grid. We compare the assimilation of passive microwave observations with the assimilation of ice charts. It is shown that the ice charts have a larger impact on the assimilation ...
    • Image analysis and segmentation of polar mesospheric summer echoes 

      Jozwicki, Dorota (Conference object; Konferansebidrag, 2022-07)
    • Structured Illumination Microscopy of Biological Structures 

      Wolfson, Deanna; Villegas, Luis; Opstad, Ida Sundvor; Birgisdottir, Åsa birna; Øie, Cristina Ionica; Ahluwalia, Balpreet Singh (Conference object; Konferansebidrag, 2018)
      <p>Resolution in optical microscopy has long been limited to the Abbe diffraction limit, i.e. about 250 nm laterally for visible wavelengths on a very good microscope. In the last two decades several techniques have been devised to circumvent this limit: an achievement which was recognized with the 2014 Nobel Prize in Chemistry. Structured Illumination Microscopy (SIM) was the first of these techniques ...
    • Observing Oil Releases from Platforms Using Synthetic Aperture Radar 

      Skrunes, Stine; Johansson, Malin; Brekke, Camilla (Conference object; Konferansebidrag, 2018)
      Synthetic aperture radar (SAR) is used for operational surveillance of ocean areas and oil spill detection. Oil spills are frequently detected around oil platforms due to the releases of so-called produced water (PW), which is water containing low concentrations of oil that can form surface slicks similar to other oil spills. PW releases are legal within given limits. Understanding the signatures ...
    • Selecting principal attributes in multimodal remote sensing for sea ice characterization 

      Khachatrian, Eduard; Chlaily, Saloua; Eltoft, Torbjørn; Marinoni, Andrea (Chapter; Bokkapittel, 2021)
      Automatic ice charting cannot be achieved using only SAR modalities. It is fundamental to combine information from other remote sensors with different characteristics for more reliable sea ice characterization. In this paper, we employ principal feature analysis (PFA) to select significant information from multimodal remote sensing data. PFA is a simple yet very effective approach that can be applied ...
    • Detecting the linear and non-linear causal links for disturbances in the power grid 

      Foldvik Eikeland, Odin; Bianchi, Filippo Maria; Holmstrand, Inga Setsa; Bakkejord, Sigurd; Chiesa, Matteo (Chapter; Bokkapittel, 2021)
      Unscheduled power disturbances cause severe consequences for customers and grid operators. To avoid suchevents, it is important to identify the causes and localize the sources of the disturbances in the power distribution network. In this work, we focus on a specific power grid in the Arctic region of Northern Norway that experiences an increased frequency of failures of unspecified origin.