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Browsing Fakultet for naturvitenskap og teknologi by Title
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Ahluwalia, Balpreet Singh; Mccourt, peter anthony; Huser, Thomas Rolf; Hellesø, Olav Gaute (Journal article; Tidsskriftartikkel; Peer reviewed, 2010)[+][-]
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Nermo, Thomas (Master thesis; Mastergradsoppgave, 01-Jun-2007)[+][-]
Abstract: Målet med denne oppgaven er å karakterisere bølgeledere av silisium-rik nitrid, SiRN, med hensyn på koblingstap, propagasjonstap, tall på modi og feltfordeling. Det skal gjøres forsøk på å redusere tapet mest mulig ved å prøve ut forskjellige måter å koble inn lys og forbedre kuttingen av bølgelederene. Det skal også gjøres forsøk på å finne tykkelse og brytningsindeks på bølgelederene ved hjelp av prismekobler og hvittlys-målinger med spektrometer. Oppgaven er derfor mest basert på eksperimentelt arbeide. Comsol Multiphysics skal bli brukt for simuleringer av feltfordelingen for bølgelederen. Det skal ut fra de eksperimentelle resultatene og simuleringene foreslås forbedringer av bølgelederene. Det skal også gjøres forsøk for å måle hvor effektiv bølgelederene er til å fange og flytte mikropartikler ved å måle fart som funksjon av effekt på laseren for en eller flere typer partikler. Prinsippet med å bruke høyeffektslaser igjennom optiske bølgeledere for å flytte og posisjonere mikropartikler kan brukes i en såkalt Lab-on-a-chip som fungerer som et mikrolaboratorium på en databrikke, som kan brukes for å analysere mikropartikler og celler. URI: http://hdl.handle.net/10037/1206 File(s) in this item: 1
thesis.pdf (5.500Mb) -
Husabø, Bjarne Janson (Master thesis; Mastergradsoppgave, 15-Jun-2009)[+][-]
Abstract: I denne oppgaven har vi sett på effekten av lys som kobles fra en bølgeleder inn i optiske mikrokuler av høyindeksglass. Vi har studert Q-faktorer, og funnet at disse er lavere for kuler omgitt av vann enn tørre kuler, men at forskjellen er mindre enn mellom individuelle kuler. Vi har observert høyere ordens resonanser i kuler med større diameter. Vi har også forsøkt å utnytte resonans til å flytte mikrokuler, men har foreløpig ikke fått dette til. URI: http://hdl.handle.net/10037/2091 File(s) in this item: 1
thesis.pdf (4.627Mb) -
Zivkovic, Tatjana; Rypdal, Kristoffer (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)[+][-]
Abstract: The change in degree of organization of the magnetosphere during substorms is investigated by analyzing various geomagnetic indices, as well as interplanetary magnetic field z-component and solar wind velocity x-component. We conclude that the magnetosphere self-organizes globally during substorms, but neither the magnetosphere nor the solar wind become more predictable in the course of a substorm. This conclusion is based on analysis of substorms in the period from 2000 to 2002. A minimal dynamic-stochastic model of the driven magnetosphere that reproduces many statistical features of substorm indices is discussed. Description: This article is part of Tatjana Živkovics' doctoral thesis. Available in Munin at http://hdl.handle.net/10037/3231 URI: http://hdl.handle.net/10037/4644 File(s) in this item: 1
article.pdf (963.3Kb) -
Øiesvold, Marte Beate (Master thesis; Mastergradsoppgave, May-2007)[+][-]
Abstract: Formålet med oppgaven er å gjøre en systematisk petrografisk og petrologisk undersøkelse av en mafisk linse med omgivende granat-glimmerskifer/marmor innen Tromsødekket. Den mafiske linsa har opprinnelig sannsynlig vært en basaltisk gang/sill som har blitt metamorfosert under eklogittfacies. Lokaliteten er blottlagt i ei veiskjæring ved universitetet i Tromsø (UiT). Den valgte mafiske linsa har en tilnærmet udeformert kjerne, og graden av deformasjon og hydrering tiltar mot marginene mot de omgivende sterkt folierte skifere og marmorer. Den mafiske linsa har også en gjennomskjærende felsisk gang som er deformert. Lokaliteten er derfor godt egnet til å se på den gradvise endringen fra massiv og retrogradert eklogitt (høytrykksgranulitt) via ulike retrograderingsstadier til sterkt foliert og rekrystallisert amfibolitt. Datering av den gjennomskjærende felsiske gangen vil kunne gi informasjon om når retrograderingen skjedde. Tromsødekket utgjør den øverste delen av øverste allokton i de Skandinaviske kaledonidene. Under Tromsødekket ligger Skattøra migmatittkompleks, som tilhører Nakkedal dekkekompleks, disse er tektonisk separert av en stor skyveforkastning. Resultatene er basert på dateringer og metamorf utvikling. Proterozoiske aldre på henholdsvis 1105,0 ± 8,6 (Grenvillisk/Svekonorvegisk alder) og 1513,6 ± 3,1 Ma er antatt å representere provenansalder for metasedimentene, og de kan ha blitt termalt påvirket samtidig som intrusjon av den magmatiske gangen/sillen rundt 493 Ma. Avsetningsalderen på sedimentene må da være i tidsrommet 1000-500 Ma. Opptreden av rekrystalliserte symplektitter og stedvis høyt Si-innhold i phengitt tyder på at de mafiske bergartene sannsynligvis har vært eklogitter. De mafiske bergartene viser en overpreging av amfibolittfacies. Det antas at den felsiske gangen er dannet ved oppsmelting av de omliggende metapelittene. Gangen kan ha blitt inturdert under amfibolittfacies metamorfosen ved 447,7 ± 0,5 Ma eller muligens rundt 460 Ma. Granatene i de mafiske bergartene har en prograd vekstsonering og har vokst under økende trykk og temperatur. P-T estimatene viser at både amfibolittfacies metamorfosen og den partielle oppsmeltingen i den mafiske linsa er dannet under samme P-T forhold på 1,15 ± 0,11 GPa og 690 ± 40 °C. Metapelittene viser P-T estimat på 1,15 ± 0,15 GPa ved 710 ± 30 °C og ned til 610 ± 30 °C ved samme trykk (1,1 ± 0,15 GPa). Dette kan tolkes som at den kjemiske ekvilibreringen i noen prøver fortsatte ettersom temperaturen avtok etter at de kjemiske systemene hadde ”frosset” i de andre bergartene. URI: http://hdl.handle.net/10037/1140 File(s) in this item: 1
Thesis.pdf (6.694Mb) -
Godtliebsen, Fred; Holmström, L.; Miettinen, A.; Erästö, P.; Divine, Dmitry V; Koc, Nalan (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)[+][-]
Abstract: In this paper, we study how sea surface temperature variations in the North Atlantic and the Norwegian Sea are correlated with the climate in the Northern Hemisphere in late Holocene. The analysis is performed by testing statistical hypotheses through novel scale space methodologies. In late Holocene, the proposed techniques reveal that the climate development in the subpolar North Atlantic has been incoherent with the development in the Norwegian Sea and the Northern Hemisphere. A prominent discrepancy between the three analyzed series is identified for the periods associated with the Medieval Warm Period and the Little Ice Age. A divergence between the oceanic series and the global Northern Hemisphere temperature estimate detected in the twentieth century is in line with the inferred imprint of recent climate change which suggests accentuated warming, in particular over continental regions. Overall, the results obtained by scale space analysis underscore the significance of the northern North Atlantic in shaping the climate globally, mainly through changes in the strength and structure of the Atlantic meridional overturning circulation. URI: http://hdl.handle.net/10037/4569 File(s) in this item: 1
article.pdf (371.3Kb) -
Rüther, Denise Christina (Doctoral thesis; Doktorgradsavhandling, 01-Mar-2012)[+][-]
Abstract: The scope of this PhD thesis is twofold: Firstly, processes, patterns and timing of the last deglaciation in the Barents Sea are reconstructed and secondly, depositional conditions on the Barents shelf during Holocene are elucidated. This cumulative PhD thesis encompasses an introductory part and five papers - three as first-author and two as co-author. Three papers are focused on the most prominent geomorphological freature of the western Barents shelf, 850 km long cross-shelf trough Bjørnøyrenna (The Bear Island Trough). One detailed study examines processes and timing of the first step of glacial retreat in outer Bjørnøyrenna and establishes a minimum age of 17 cal ka for initial deglaciation. A second study focuses on a grounding line system in uppermost Bjørnøyrenna, witnessing a surge-type readvance towards the final collapse of the marine-based Barents Sea Ice Sheet. A third study focuses on contrasting ice stream flow regimes and processes observed from glacial maximum over initial deglaciation towards final deglaciation. Two additional studies are located in the relatively small formerly glaciated trough Kveithola, north-west of Bjørnøya (Bear Island). The first focuses on the most recent deglaciation history and establishes an indirect deglaciation age for Spitsbergenbanken 14.2-13.9 cal ka ago. The other reconstructs the complex glacial retreat through Kveithola and associated processes based on geophysical data. As a whole, this PhD thesis improves existing chronology during deglaciation and Holocene for the Barents Sea, advances existing depositional models of ice-marginal and deglacial processes as well as it adds to established conceptional models of glacial retreat. While presented Holocene data is less conclusive, it might create the awareness that the large Storegga tsunami at 8.2 cal ka may have had an erosional impact on shelf sediments and thereby motivate further research. Description: The papers of this thesis are not available in Munin:
1. Rüther, D. C., Mattingsdal, R., Andreassen, K., Forwick, M. and Husum, K.: 'Seismic architecture and sedimentology of a major grounding zone system deposited by the Bjørnøyrenna Ice Stream during Late Weichselian deglaciation', Quaternary Science Reviews (2011) vol.30:2776-2792. Available at http://dx.doi.org/10.1016/j.quascirev.2011.06.011
2. Rüther, D. C., Bjarnadóttir, L. R. Junttila, J., Husum, K., Rasmussen, T., Lucchi, R. G. and Andreassen, K.: 'Pattern and timing of the north-western Barents Sea Ice Sheet deglaciation and indications of episodic Holocene deposition' (accepted paper in Boreas).
3. Bjarnadóttir, L. R., Rüther, D. C., Winsborrow, M. C. M. and Andreassen, K.: 'Grounding line dynamics during the last deglaciation of Kveithola, W Barents Sea, as revealed by seabed geomorphology and shallow seismic stratigraphy' (submitted manuscript to Boreas).
4. Andreassen, K., Winsborrow, M. C. M., Bjarnadóttir, L. R. and Rüther, D. C.: 'Landform assemblage from the collapse of a marine-based ice stream' (submitted manuscript to Geology).
5. Rüther, D. C., Andreassen, K. and Winsborrow, M. C. M.: 'Changing ice stream flow regimes during the last deglaciation of Bjørnøyrenna, western Barents Sea' (manuscript)URI: http://hdl.handle.net/10037/3876 File(s) in this item: 1
thesis.pdf (786.4Kb) -
Lorentzen, Dag Arne; Lunde, June; Ogawa, Y; Gustavsson, B; Ogawa, Yasunobu; Løvhaug, U.P. (Journal article; Tidsskriftartikkel; Peer reviewed, 2007)[+][-]
Abstract: In this paper we present Naturally Enhanced Ion Acoustic Lines (NEIALs) observed with the EISCAT Svalbard Radar (ESR). For the first time, long sequences of NEIALs are recorded, with more than 50 events within an hour, ranging from 6.4 to 140 s in duration. The events took place from ~08:45 to 10:00 UT, 22 January 2004. We combine ESR data with observations of optical aurora by a meridian scanning photometer at wavelengths 557.7, 630.0, 427.8, and 844.6 nm, as well as records from a magnetometer and an imaging riometer. The large numbers of observed NEIALs together with these additional observations, enable us to characterise the particle precipitation during the NEIAL events. We find that the intensities in all optical lines studied must be above a certain level for the NEIALs to appear. We also find that the soft particle precipitation is associated with the down-shifted shoulder in the incoherent scatter spectrum, and that harder precipitation may play a role in the enhancement of the up-shifted shoulder. The minimum energy flux during NEIAL events found in this study was ~3.5 mW/m2 and minimum characteristic energy around 50 eV. URI: http://hdl.handle.net/10037/3126 File(s) in this item: 1
article.pdf (7.856Mb) -
Lunde, June; Løvhaug, Unni Pia; Gustavsson, Björn Johan (Journal article; Tidsskriftartikkel; Peer reviewed, 2009)[+][-]
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Lunde, June (Doctoral thesis; Doktorgradsavhandling, 26-Nov-2009)[+][-]
Abstract: The motivation behind this thesis has been to study particle precipitation from the Sun into the Earth’s upper atmosphere and its effects on selected ionospheric phenomena. Particles from the solar wind can enter the Earth's magnetosphere through magnetic merging, either at the sub-solar point, or at higher latitudes, depending on the configuration of the interplanetary magnetic field. This interaction can be studied from the ground at Svalbard, due to its fortuitous location beneath the magnetospheric cusp region on the dayside, and its location inside the polar cap during night-time. It has been studied how these precipitating particles act on the aurora and ion-acoustic waves in the ionized part of the atmosphere. The studies have been conducted using various methods, including extracting data from databases, running different experiments and building new instrumentation. The latter was a radiation detector for measuring Bremsstrahlung X-rays. The main instrument used for this study has been the EISCAT (European Incoherent SCATtering) radar located at Svalbard, together with an assortment of other ground based instruments such as photometers, riometers and magnetometers. In addition, particle instruments onboard satellites have been used as well as an X-ray instrument mounted on a balloon launched from Longyearbyen. Primarily, it is the effect of particle precipitation on large ion-acoustic waves that has been studied. These waves can be observed by advanced radar facilities, both from Svalbard and Tromsø (EISCAT) in the form of spectra known as natural enhanced ion acoustic lines (NEIALs). It has been found that the most energetic particle precipitation causes ion-acoustic waves which mainly propagate downward, while the less energetic part of the particle precipitation is related to ion-acoustic waves which propagate upward. In this project, large ion-acoustic waves have been discovered during night-time at very high latitudes where they were not expected to occur. Previously, these phenomena have only been observed during daytime at Svalbard. Furthermore, in this work, the infrared atomic oxygen emission line (844.6 nm) has been introduced as a new possible method to detect NEIALs in optical data. Particle precipitation sometimes cause flickering aurora, hence intensity variation and the apparent motion of flickering spots in the aurora have been studied. Finally, precipitating particles typically consists of electrons and ions, and in this study, an example is given on of how the merging of the Earth’s and Sun’s magnetic fields guide the precipitation. Description: Papers 2 and 4 are not available in Munin:
2. T. Grydeland, B. Gustavsson, L. Baddeley, J. Lunde, and E. M. Blixt: 'Conditional integration of Incoherent Scattering in relation to flickering aurora', Journal of Geophysical Research (2008), vol.113, A08305, 8pp. Available at http://dx.doi.org/doi:10.1029/2008JA013039
4. B. Gustavsson, J. Lunde, and E. M. Blixt: 'Optical observations of flickering aurora and its spatio-temporal characteristics', Journal of Geophysical Research (2008), vol.113, A12317, 8pp. Available at http://dx.doi.org/10.1029/2008JA013515URI: http://hdl.handle.net/10037/4221 File(s) in this item: 4
paper_1.pdf (2.832Mb)paper_3.pdf (14.41Mb)paper_5.pdf (7.665Mb)thesis.pdf (7.645Mb) -
Asplin, Jo; Johansen, Dag (Research report; Forskningsrapport, Jun-1995)[+][-]
Abstract: Volume rendering is a useful but cpu-intensive method for visualizing large scalar fields. The time to render a single image may be reduced by parallel processing. This paper reports on performance experiments with the StormView volume renderer, which is parallelized on a set of 57 MIPS / 17 MFLOPS workstations connected by a 10 Mbps Ethernet. For certain user patterns, we show that our parallelization exhibits substantial speedups. We compare the performance of a dynamic and a static load balancing algorithm. URI: http://hdl.handle.net/10037/384 File(s) in this item: 1
report.pdf (383.3Kb) -
Kvalnes, Aage; Renesse, Robbert van; Johansen, Dag (Research report; Forskningsrapport, 10-Jan-2003)[+][-]
Abstract: Vortex is a new multiprocessor operating system kernel intended for emerging Internet service applications. The architecture is based on SEDA's staged computational model. Vortex provides mechanisms for performance isolation and dynamic adaptation. Performance results validate that the resource control mechanisms of Vortex are effective, and that Vortex significantly outperforms Linux on single-threaded web servers. The paper concludes with a description of how we plan to support a highly scalable event stream filtering service. URI: http://hdl.handle.net/10037/399 File(s) in this item: 1
report.pdf (174.8Kb) -
Brodal, Eivind; Melandsø, Frank; Jacobsen, Svein Ketil (Journal article; Tidsskriftartikkel; Peer reviewed, 2011)[+][-]
Abstract: New designs of high-resolution ultrasonic imaging systems that operate in the 30–100MHz region, for example, those based on linear transducer systems, are currently being investigated for medical purposes. Acoustic waves with frequencies in this range can detect microscopic structures in human tissue but will typically only penetrate a few mm because of large attenuation. However, this is sufficient for a diagnostic ultrasound scan of human skin. The signal-to-noise ratio and the focusing properties of the scanner are critical factors in dermatology, which are determined by the transducer design. A linear pulsed PVDF transducer array with a center frequency around 45MHz is studied by applying numerical simulations, based on the finite element method (FEM), of this electromechanical system. Tx-beamforming properties of linear arrays with one, three, five, and seven active elements are investigated at different depths. The image quality obtained from synthetic Rx-beamforming, using responses from five electrodes, is estimated from reconstructed images of 25–100 μm thick objects. The axial and lateral resolutions of these images are found to be similar with the Tx-beamforming resolution parameters estimated from the time-derivative of the pressure beams. URI: http://hdl.handle.net/10037/3941 File(s) in this item: 1
article.pdf (4.220Mb) -
Nozawa, S.; Hall, Chris; Meek, C.E.; Manson, A.H.; Luo, Yi (Journal article; Peer reviewed, 2003)[+][-]
Abstract: It is possible for medium-frequency (MF) radar systems to estimate kinetic energy dissipation rates by measuring signal fading times. Here, we present approximately 5 years of such results from Tromsø (69° N, 19° E) and in particular, investigate the periodicities present at different altitudes in the regime 80 to 100 km. We detect the known annual variation in the mesosphere and the semiannual variation on the lower thermosphere. In addition, other features are observed including terannual and ~ 27-day components in the lower thermosphere. URI: http://hdl.handle.net/10037/577 File(s) in this item: 1
article.pdf (691.3Kb) -
Dillema, Feike W.; Stabell-Kulø, Tage (Research report; Forskningsrapport, May-2002)[+][-]
Abstract: Pesto aims at providing highly available and secure storage for longlived data to mobile users roaming into untrusted environments. Security in Pesto encompasses the following three aspects: availability, safety, and privacy. A mechanism supporting one aspect may adversely affect another. For example, replication may increase availability but complicates supporting confidentiality, and simply encrypting data for confidentiality may defeat the whole purpose of replication. We show that an integral approach to these aspects leads to considerable savings in overall system complexity, and thus to a more secure system. In Pesto, users may specify different levels of trust in different parts of the infrastructure. In particular, a user may trust a node to merely store (encrypted) data, and/or to distribute replicas to other nodes on his behalf, and/or he may trust a node to enforce access control on his behalf to his (plaintext) content. This report gives an overview of the main security mechanisms that makes this separation of concerns possible. We present its novel encryption framework and its trust management and discuss how it can be used to build distributed infrastructures with advanced security and safety properties. URI: http://hdl.handle.net/10037/364 File(s) in this item: 1
report.pdf (135.8Kb) -
Priyatkina, Nadezda (Master thesis; Mastergradsoppgave, 31-Jan-2013)[+][-]
Abstract: The studied mafic-ultramafic rock association occurs within Archean tonalitic gneisses and metasupracrustal suites of the Astridal belt belonging to the West Troms Basement Complex in the northwestern part of the Senja Island. The rock association appears in lens-shaped bodies, up to 200 m long, which are oriented conformal to the major metamorphic fabric of the host rock. The rock association is made up by interlayered units of green spinel-bearing olivine orthopyroxene-hornblendite, hornblende peridotite, olivine hornblendite, hornblendite and amphibolite (metagabbroic rock). Microscope studies and whole rock geochemical data indicate that the ultramafic rocks represent a single magmatic series of mafic and ultramafic olivine-amphibole cumulates, which have been significantly affected by metamorphism. Igneous mineral and whole rock trace element data indicate MORB affinity of the cumulates and suggest their emplacement in oceanic rift or rifted continental margin setting. The studied cumulates may represent a crustal remnant of the Paleoproterozic Svecofennian ocean. The rocks were metamorphosed together with the supracrustal suites of the Astridal belt during the major Svecofennian event about 1.74 Ga ago as indicated by a U-Pb age of metamorphic zircons from the metagabbroic rock belonging to the studied suite. URI: http://hdl.handle.net/10037/4843 File(s) in this item: 1
thesis.pdf (13.80Mb) -
Gjerløw, Eirik (Master thesis; Mastergradsoppgave, 15-Nov-2008)[+][-]
Abstract: Formålet med denne oppgaven er å gjøre petrologiske og petrografiske undersøkelser av en mafisk linse på Sandøya i vest-Troms for å rekonstruere metamorfe trykk og temperaturforhold, samt å gjøre dateringer for å utrede alderen på metamorfosen(e). Linsa ligge blottlagt ved havet ved Mjølvika på Sandøya. Kjernen er tilnærmet udeformert og består av en en massiv granatførende bergart med en grønn grunnmasse. Graden av deformasjon og hydrering tiltar mot marginene mot de båndede gneisene som omgir linsa. Den mafiske linsa er også kuttet av en liten felsisk gang, dateringer av denne gangen vil kunne gi minimumsalder på den mafiske linsa. Resultatene er basert på dateringer og metamorf utvikling Aldre på 1776,6 ± 1,1 Ma, 1774,4 ± 1,7, 1777 ± 12 Ma tolkes til å representere granulittfacies metamorfose og intrusjon av den kuttende felsiske gangen og det antaes at denne gangen er dannet ved partiell oppsmelting av omkringliggende bergarter. Ut fra strukturer og mineralkjemiske analyser tolkes det til at det er minst 5 forskjellige faser av metamorfose: Stadium 1 er høytrykks granulittfacies med trykk og temperaturforhold på 715-922 ºC og 1,1-1,43 Gpa. Stadium 2 er granulittfacies med trykk og temperaturverdier på 710-715 ºC og 0,51-0,92 GPa. Stadium 3 er grønnskiferfacies. Stadium 4 er amfibolittfacies med trykk og temperaturverdier på 595-660 ºC og 0,17-0,62 Gpa. Stadium 5 er grønnskiferfacies. URI: http://hdl.handle.net/10037/1657 File(s) in this item: 1
thesis.pdf (20.95Mb) -
Grydeland, Tom; Sullivan, J.M.; Ivchenko, N.; Blixt, Erik Mårten; Lockwood, M.; Lanchester, B.S. (Journal article; Peer reviewed, 20-Sep-2006)[+][-]
Abstract: The link between natural ion-line enhancements in radar spectra and auroral activity has been the subject of recent studies but conclusions have been limited by the spatial and temporal resolution previously available. The next challenge is to use shorter sub-second integration times in combination with interferometric programmes to resolve spatial structure within the main radar beam, and so relate enhanced filaments to individual auroral rays. This paper presents initial studies of a technique, using optical and spectral satellite signatures, to calibrate the received phase of a signal with the position of the scattering source along the interferometric baseline of the EISCAT Svalbard Radar. It is shown that a consistent relationship can be found only if the satellite passage through the phase fringes is adjusted from the passage predicted by optical tracking. This required adjustment is interpreted as being due to the vector between the theoretical focusing points of the two antennae, i.e. the true radar baseline, differing from the baseline obtained by survey between the antenna foot points. A method to obtain a measurement of the true interferometric baseline using multiple satellite passes is outlined. URI: http://hdl.handle.net/10037/549 File(s) in this item: 1
article.pdf (800.0Kb) -
Brekke, Asgeir; Blagoveshchenskaya, N. F.; Carlson, H. C.; Kornienko, V. A.; Borisova, T. D.; Rietveld, M. T.; Yeoman, T. K. (Journal article; Tidsskriftartikkel; Peer reviewed, 08-Jan-2009)[+][-]
Abstract: Multi-instrument observational data from an experiment on 13 October 2006 at the EISCAT/HEATING facility at Tromsø, Norway are analysed. The experiment was carried out in the evening hours when the electron density in the F-region dropped, and the HF pump frequency fH was near and then above the critical frequency of the F2 layer. The distinctive feature of this experiment is that the pump frequency was just below the third electron gyro harmonic frequency, while both the HF pump beam and UHF radar beam were directed towards the magnetic zenith (MZ). The HF pump-induced phenomena were diagnosed with several instruments: the bi-static HF radio scatter on the London- Tromsø-St. Petersburg path, the CUTLASS radar in Hankasalmi (Finland), the European Incoherent Scatter (EISCAT) UHF radar at Tromsø and the Tromsø ionosonde (dynasonde). The results show thermal electron excitation of the HF-induced striations seen simultaneously from HF bi-static scatter and CUTLASS radar observations, accompanied by increases of electron temperature when the heater frequency was near and then above the critical frequency of the F2 layer by up to 0.4 MHz. An increase of the electron density up to 25% accompanied by strong HF-induced electron heating was observed, only when the heater frequency was near the critical frequency and just below the third electron gyro harmonic frequency. It is concluded that the combined effect of upper hybrid resonance and gyro resonance at the same altitude gives rise to strong electron heating, the excitation ofstriations, HF ray trapping and extension of HF waves to altitudes where they can excite Langmuir turbulence and fluxes of electrons accelerated to energies that produce ionization. Description: This is the publisher’s version/PDF (published in Annales Geophysicae, an open access journal of the European Geosciences Union) URI: http://hdl.handle.net/10037/2384 File(s) in this item: 1
angeo-27-131-2009.pdf (1.432Mb)
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