Viser treff 282-301 av 939

    • F-region electron heating by X-mode radiowaves in underdense conditions 

      Gustavsson, Björn Johan; Löfås, H.; Ivchenko, N.; Rietveld, Michael T; Leyser, T. B. (Journal article; Tidsskriftartikkel; Peer reviewed, 2009)
    • Faraday rotation fluctuations of MESSENGER radio signals through the equatorial lower corona near solar minimum 

      Wexler, D.B.; Jensen, E.A.; Hollweg, J.V.; Heiles, C.; Efimov, A.I.; Vierinen, J.; Coster, A.J. (Journal article; Peer reviewed; Tidsskriftsartikkel, 2016-12-26)
      Faraday rotation (FR) of transcoronal radio transmissions from spacecraft near superior conjunction enables study of the temporal variations in coronal plasma density, velocity, and magnetic field. The MESSENGER spacecraft 8.4 GHz radio, transmitting through the corona with closest line-of-sight approach 1.63–1.89 solar radii and near-equatorial heliolatitudes, was recorded soon after the deep ...
    • Faster decline and higher variability in the sea ice thickness of the marginal Arctic seas when accounting for dynamic snow cover 

      Mallett, Robbie; Stroeve, Julienne C.; Tsamados, Michel; Landy, Jack Christopher; Willatt, Rosemary; Nandan, Vishnu; Liston, Glen (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-06-04)
      Mean sea ice thickness is a sensitive indicator of Arctic climate change and is in long-term decline despite significant interannual variability. Current thickness estimations from satellite radar altimeters employ a snow climatology for converting range measurements to sea ice thickness, but this introduces unrealistically low interannual variability and trends. When the sea ice thickness in the ...
    • Faszination Nano-Staubteilchen im Kosmos - Astronomie als Puzzle 

      Mann, Ingrid (Conference object; Konferansebidrag, 2018)
    • The Fate of Nanodust near the Sun - Comparison of Sputtering and Sublimation lifetimes during CMEs 

      Baumann, Carsten; Myrvang, Margaretha; Stamm, Johann Immanuel; Mann, Ingrid (Conference object; Konferansebidrag, 2018)
      The dust environment in the inner Solar system has not been probed so far, but ESA’s Solar Orbiter (2020) and NASA’s Parker Solar Probe (2018) are about cross the inner solar system. From [1] we expect a layer of trapper Nanodust around the Sun. [2] investigated the interaction of grains with the Solar wind. But what is the dust’s fate when they are struck by a Coronal Mass Ejection (CME). Are they ...
    • Federated Partially Supervised Learning With Limited Decentralized Medical Images 

      Dong, Nanqing; Kampffmeyer, Michael; Voiculescu, Irina; Xing, Eric (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-12-20)
      Data government has played an instrumental role in securing the privacy-critical infrastructure in the medical domain and has led to an increased need of federated learning (FL). While decentralization can limit the effectiveness of standard supervised learning, the impact of decentralization on partially supervised learning remains unclear. Besides, due to data scarcity, each client may have access ...
    • Finite element simulation of transmission and reflection of acoustic waves in the ultrasonic transducer 

      Shukla, Kaushik; Ahmad, Azeem; Ahluwalia, Balpreet Singh; Melandsø, Frank; Habib, Anowarul (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-03-30)
      In scanning acoustic microscopy (SAM), the image quality depends on several factors such as noise level, resolution, and interaction of the waves with sample boundaries. The theoretical equations for the reflection coefficient and transmission coefficient are suitable for plane boundaries but fail for curved/rough boundaries. We presented a finite element method-based modeling for the loss ...
    • Finite element simulation of transmission and reflection of acoustic waves in the ultrasonic transducer 

      Shukla, Kaushik; Ahmad, Azeem; Habib, Anowarul; Singh Ahluwalia, Balpreet; Melandsø, Frank (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-03-30)
      In scanning acoustic microscopy (SAM), the image quality depends on several factors such as noise level, resolution, and interaction of the waves with sample boundaries. The theoretical equations for the reflection coefficient and transmission coefficient are suitable for plane boundaries but fail for curved/rough boundaries. We presented a finite element method-based modeling for the loss ...
    • First dust measurements with the Solar Orbiter Radio and plasma wave instrument 

      Zaslavsky, A.; Mann, I.; Soucek, J.; Czechowski, A.; Píša, D.; Vaverka, J.; Meyer-Vernet, N.; Maksimovic, M.; Lorfèvre, E.; Issautier, K.; Rackovic Babic, K.; Bale, S.D.; Morooka, M.; Vecchio, A.; Chust, T.; Khotyaintsev, Y.; Krasnoselskikh, V.; Kretzschmar, M.; Plettemeier, D.; Steller, M.; Štverák, Š; Trávnícek, P.; Vaivads, A. (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-12-14)
      Context - Impacts of dust grains on spacecraft are known to produce typical impulsive signals in the voltage waveform recorded at the terminals of electric antennas. Such signals (as may be expected) are routinely detected by the Time Domain Sampler (TDS) system of the Radio and Plasma Waves (RPW) instrument on board Solar Orbiter.<p> <p>Aims - We investigate the capabilities of RPW in terms of ...
    • First estimates of volume distribution of HF-pump enhanced emissions at 6300 and 5577 Å : a comparison between observations and theory 

      Gustavsson, Björn Johan; Kosch, Mike; Wong, Alfred; Pedersen, Todd; Heinselman, Craig; Mutiso, Charles; Bristow, Bill; Hughes, John; Wang, Weiyuan (Journal article; Tidsskriftartikkel; Peer reviewed, 2008)
      We present bi-static observations of radio-wave induced optical emissions at 6300 and 5577 Å from a night-time radio-induced optical emission ionospheric pumping experiment at the HIPAS (Fairbanks) facility in Alaska. The optical observations were made at HIPAS and from HAARP located 285 km south-east. From these observations the altitude distribution of the emissions is estimated with tomography-like ...
    • The First Magnetotelluric Image of the Lithospheric-Scale Geological Architecture in Central Svalbard, Arctic Norway 

      Beka, Thomas Ibsa; Smirnov, Maxim; Bergh, Steffen G; Birkelund, Yngve (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-12-17)
      Magnetotelluric data, collected from 30 stations on Spitsbergen as part of a reconnaissance geothermal resource assessment along a profile with 0.53-km spacing in 0.0031000-s period range, were used to develop a lithospheric-scale two-dimensional (2D) resistivity model, heretofore unavailable for the region. Inverting the determinant of the impedance tensor in 2D, we found the smoothest model ...
    • 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 ...
    • First observation of the anomalous electric field in the topside ionosphere by ionospheric modification over EISCAT 

      Kosch, Michael; Vickers, Hannah; Ogawa, Yasunobu; Senior, Andrew; Blagoveshchenskaya, Natalya (Journal article; Tidsskriftartikkel; Peer reviewed, 2014-10-24)
      We have developed an active ground-based technique to estimate the steady state field-aligned anomalous electric field (E*) in the topside ionosphere, up to ~600 km, using the European Incoherent Scatter (EISCAT) ionospheric modification facility and UHF incoherent scatter radar. When pumping the ionosphere with high-power high-frequency radio waves, the F region electron temperature is significantly ...
    • First Observations of Recurring HF-Enhanced Topside Ion Line Spectra Near the Fourth Gyroharmonic 

      Rexer, Theresa; Gustavsson, Björn Johan; Leyser, Thomas; Rietveld, Michael T; Yeoman, Tim; Grydeland, Tom (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-09-28)
      We present first incoherent scatter radar observations of systematically recurring, high‐frequency (HF)‐enhanced ion line spectra at the topside F‐region ionosphere, during magnetic field aligned HF pumping in an O‐mode polarization. The European Incoherent Scatter UHF radar was directed in magnetic zenith on 9–11 March 2016 while stepping the pump frequency across the double resonance of the fourth ...
    • First observations of the McMurdo-South Pole oblique ionospheric HF channel 

      Chartier, Alex T.; Vierinen, Juha; Jee, Geonhwa (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-06-09)
      We present the first observations from a new low-cost oblique ionosonde located in Antarctica. The transmitter is located at McMurdo Station, Ross Island, and the receiver at Amundsen–Scott Station, South Pole. The system was demonstrated successfully in March 2019, with the experiment yielding over 30 000 ionospheric echoes over a 2-week period. These data indicate the presence of a stable E layer ...
    • First results from the Njord device for space related plasma experiments 

      Fredriksen, Åshild; Tribulato, Giulio; Watts, Christopher (Conference object; Konferansebidrag, 2007-08-05)
      The Njord device at Aurolab, University of Tromsø, has been constructed to carry out experiments on instabilities and heating in plasma flows and beams, with relevance to near-Earth space plasmas. For plasma production, Njord combines a 13.56 MHz RF source with a Double Plasma chamber equipped with filaments along the walls. The source is equipped dwith two coils operated at 0-6A, providing magnetic ...
    • First simultaneous measurements of waves generated at the bow shock in the solar wind, the magnetosphere and on the ground 

      Clausen, L. B. N.; Behlke, Rico; Yeoman, T. K.; Fear, R. C.; Lucek, E. A.; Engebretson, M. J. (Journal article; Tidsskriftartikkel; Peer reviewed, 2009)
    • First Simultaneous Rocket and Radar Detections of Rare Low Summer Mesospheric Clouds 

      Havnes, O.; Latteck, R.; Hartquist, T.W.; Antonsen, T. (Journal article; Peer reviewed, 2018-06-10)
      On 30 June 2016 a layer of dust, possibly meteoric smoke particles (MSPs), was observed with a rocket borne probe at 69.29°N, 16.02°E and altitudes of ~74 km where patchy thin cloud layers, detected with the Middle Atmosphere Alomar Radar System, were present. The rocket traversed a layer with a net positive dust charge density of ~107 unit charges per cubic meters and a number density of neutral ...
    • First Studies of Mesosphere and Lower Thermosphere Dynamics Using a Multistatic Specular Meteor Radar Network Over Southern Patagonia 

      Conte, J. F.; Chau, Jorge L.; Urco, Juan M.; Latteck, Ralph; Vierinen, Juha; Salvador, Jacobo (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-01-18)
      This paper presents for the first time results on winds, tides, gradients of horizontal winds, and momentum fluxes at mesosphere and lower thermosphere altitudes over southern Patagonia, one of the most dynamically active regions in the world. For this purpose, measurements provided by SIMONe Argentina are investigated. SIMONe Argentina is a novel multistatic specular meteor radar system ...
    • First wind shear observation in PMSE with the tristatic EISCAT VHF radar 

      Mann, Ingrid; Häggström, I.; Tjulin, A; Rostami, S; Anyairo, CC; Dalin, P (Journal article; Tidsskriftartikkel; Peer reviewed, 2016-11-05)
      The Polar Summer Mesosphere has the lowest temperatures that occur in the entire Earth system. Water ice particles below the optically observable size range participate there in the formation of strong radar echoes (Polar Mesospheric Summer Echoes, PMSE). To study PMSE we carried out observations with the European Incoherent Scatter (EISCAT) VHF and EISCAT UHF radar simultaneously from a site near ...