Blar i forfatter "Rietveld, Michael T"

Viser treff 1-20 av 24

    • The 3‐D Distribution of Artificial Aurora Induced by HF Radio Waves in the Ionosphere 

      Kvammen, Andreas; Gustavsson, Björn Johan; Sergienko, Tima; Brändström, Urban; Rietveld, Michael T; Rexer, Theresa; Vierinen, Juha (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-03-21)
      We present 3‐D excitation rate estimates of artificial aurora in the ionospheric F layer, induced by high‐frequency radio waves from the European Incoherent Scatter heating facility. Simultaneous imaging of the artificial aurora was done with four separate Auroral Large Imaging System stations, permitting tomography‐like 3‐D auroral reconstruction of the enhanced atomic oxygen emissions at 6,300, ...

    • Aspect angle sensitivity of pump-induced optical emissions at EISCAT 

      Kosch, Michael J.; Bryers, Carl; Rietveld, Michael T; Yeoman, Timothy K; Ogawa, Yasunobu (Journal article; Tidsskriftartikkel; Peer reviewed, 2014-12-04)
      We investigate the aspect angle sensitivity of the pump-induced artificial optical emissions in the ionosphere over the European Incoherent Scatter Scientific Association (EISCAT) high-frequency transmitter facility at Ramfjord, Norway, as a function of the pump beam launch angle relative to the magnetic field line direction. The highest intensity optical emissions occur when the pump beam pointing ...

    • Change of the high-latitude ionosphere during heating by a powerful short radio wave of the EISCAT/Heating complex according to signals of the GLONASS satellite and the incoherent scattering radar 

      Tereshchenko, E. D.; Milichenko, A. N.; Rietveld, Michael T; Chernyakov, S. M.; Shvets, M. V. (Journal article; Tidsskriftartikkel; Peer reviewed, 2018)
      Results of observations of variations of temperature, electron concentration and total electron content of the high-latitude region of the ionosphere during its modification by powerful short radio waves of the heating complex EISCAT/Heating (Tromsø, Norway) according to signals of the GLONASS satellites and the incoherent scattering UHF EISCAT radar (Tromsø, Norway) have been provided. The geometry ...

    • A comparison of overshoot modelling with observations of polar mesospheric summer echoes at radar frequencies of 56 and 224 MHz 

      Havnes, Ove; Pinedo Nava, Henry; La Hoz, Cesar; Senior, Andrew; Hartquist, Thomas W.; Rietveld, Michael T; Kosch, Michael J. (Journal article; Tidsskriftartikkel; Peer reviewed, 2015)
      We have compared radar observations of polar mesospheric summer echoes (PMSEs) modulated by artificial electron heating, at frequencies of 224 MHz (EISCAT VHF) and 56 MHz (MORRO). We have concentrated on 1 day of observation, lasting ~ 3.8 h. The MORRO radar, with its much wider beam, observes one or more PMSE layers all the time while the VHF radar observes PMSEs in 69% of the time. Statistically ...

    • Ducting of incoherent scatter radar waves by field-aligned irregularities 

      Rietveld, Michael T; Senior, Andrew (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-10-22)
      We provide an explanation for a mysterious phenomenon that has been recognized in recent years in European Incoherent Scatter (EISCAT) UHF incoherent scatter radar (ISR) measurements during many high-power high-frequency (HF) ionospheric pumping experiments. The phenomenon is an apparent increase in electron density observed above the HF reflection altitude, extending up to the observable limits ...

    • Dust charging and density conditions deduced from observations of PMWE modulated by artificial electron heating 

      Havnes, Ove; La Hoz, Cesar; Rietveld, Michael T; Kassa, Meseret; Baroni, Giovanni; Biebricher, Alexander (Journal article; Tidsskriftartikkel; Peer reviewed, 2011)
      We present an analysis of relatively strong Polar Mesospheric Winter Echoes (PMWE) under artificial electron heating that changes the PMWE intensity. A major purpose is to find reliable estimates of the relaxation time of the heater modified PMWE to their undisturbed state during the heater switch-off phase; the implications regarding charge/discharge mechanisms; and to exploit the diagnostic potential ...

    • Electron heating by HF pumping of high-latitude ionospheric F-region plasma near magnetic zenith 

      Leyser, Thomas B; Gustavsson, Björn Johan; Rexer, Theresa; Rietveld, Michael T (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-03-06)
      High-frequency electromagnetic pumping of ionospheric F-region plasma at high and mid latitudes gives the strongest plasma response in magnetic zenith, antiparallel to the geomagnetic field in the Northern Hemisphere. This has been observed in optical emissions from the pumped plasma turbulence, electron temperature enhancements, filamentary magnetic field-aligned plasma density irregularities, and ...

    • Electron Temperature Inversion by Stimulated Brillouin Scattering During Electron Gyroharmonic Heating at EISCAT 

      Fu, H. Y.; Jiang, M. L.; Wang, K. N.; Wu, J.; Li, Q.L.; Rietveld, Michael T; Varberg, E.; Häggström, I.; Jin, Y.-Q. (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-08-25)
      This work reports a holistic experimental investigation of stimulated Brillouin scattering (SBS) features and electron temperature inversion near the third electron gyroharmonic 3<i>f</i><sub>ce</sub> using the European Incoherent Scatter (EISCAT) heating facility. The evolution of SBS features including spectral offset, width, and power varies asymmetrically near 3<i>f</i><sub>ce</sub>. The asymmetries ...

    • Evidence of L-mode electromagnetic wave pumping of ionospheric plasma near geomagnetic zenith 

      Leyser, Thomas B; James, H Gordon; Gustavsson, Björn Johan; Rietveld, Michael T (Journal article; Peer reviewed, 2018-02-21)
      The response of ionospheric plasma to pumping by powerful HF (high frequency) electromagnetic waves transmitted from the ground into the ionosphere is the strongest in the direction of geomagnetic zenith. We present experimental results from transmitting a left-handed circularly polarized HF beam from the EISCAT (European Incoherent SCATter association) Heating facility in magnetic zenith. The ...

    • The Extending of Observing Altitudes of Plasma and Ion Lines During Ionospheric Heating 

      Wu, Jun; Wu, Jian; Rietveld, Michael T; Häggström, I.; Xu, Zhengwen; Zhao, Haisheng (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-26)
      The ultrahigh-frequency observation during an ionospheric heating experiment on 11 March 2014 at the European Incoherent Scatter Scientific Association Tromsø site illustrated a remarkable extension of observing altitudes of the enhanced plasma line and the ion line, implying that the enhanced ion acoustic wave and Langmuir wave should satisfy the Bragg condition within the extending altitude range. ...

    • 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)

    • 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 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 ...

    • Multi-frequency SuperDARN radar observations of the modulated ionosphere by high-power radio-waves at EISCAT 

      Mahmoudian, A.; Yeoman, T. K.; Senior, A.; Kosch, M.; Scales, W. A.; Shi, X.; Ruohoniemi, M.; Rietveld, Michael T (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-04-02)
      This paper presents the first joint observations of multi-frequency SuperDARN (Super Dual Auroral Radar Network) radar of the heated ionosphere by high-power high-frequency (HF) ground-based radio-waves along with the stimulated electromagnetic emissions (SEE) measurements. The unique heating experiment design at EISCAT (The European Incoherent Scatter Scientific Association) including fine frequency ...

    • New capabilities of the upgraded EISCAT high-power HF facility 

      Rietveld, Michael T; Senior, Andrew; Markkanen, Jussi; Westman, Assar (Journal article; Tidsskriftartikkel; Peer reviewed, 2016-09-22)
      The high-power HF (high-frequency) facility (commonly known as Heating) near Tromsø, Norway, which is an essential part of the European Incoherent Scatter Scientific Association, has been upgraded in certain key areas in recent years. It is one of only four similar facilities in the world operating at present. An updated description of the facility is given, together with scientific motivation and ...

    • A New Technique for Investigating Dust Charging in the PMSE Source Region 

      Mahmoudian, Alireza; Kosch, Michael J.; Vierinen, Juha; Rietveld, Michael T (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-09-21)
      A new technique for investigating dust charging in the PMSE (polar mesospheric summer echoes) source region is proposed and discussed in this paper. The first high-frequency (HF) modulation of the PMSE with varying pump power was employed during a recent experimental campaign at EISCAT (European Incoherent Scatter Scientific Association). Two experiment setups including HF pump power stepping as ...

    • Observations of HF-induced instability in the auroral E region 

      Schlatter, Nicola M.; Ivchenko, Nickolay; Gustavsson, Björn Johan; Leyser, Thomas; Rietveld, Michael T (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      Enhancements were observed in backscattered radar power during an ionospheric heating experiment from two distinct altitude regions in the auroral E region above Tromsø. For the experiment the EISCAT Tromsø heater was operated with O mode and X mode alternated at 4.04 MHz, close to the 3rd electron gyroharmonic. Ion-line data recorded with the EISCAT UHF radar reveal different temporal ...

    • Remote Oxygen Sensing by Ionospheric Excitation (ROSIE) 

      Kalogerakis, K. S.; Gustavsson, Björn Johan; Slanger, T. G.; Rietveld, Michael T; Kendall, E. A.; Pedersen, T. R.; Kosch, M. J. (Journal article; Tidsskriftartikkel; Peer reviewed, 2009)

    • Severe and localized GNSS scintillation at the poleward edge of the nightside auroral oval during intense substorm aurora 

      van der Meeren, Christer; Oksavik, Kjellmar; Lorentzen, Dag Arne; Rietveld, Michael T; Clausen, Lasse Boy Novock (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-12-01)
      In this paper we study how GPS, GLONASS, and Galileo navigation signals are compromised by strong irregularities causing severe phase scintillation (σϕ>1) in the nightside high-latitude ionosphere during a substorm on 3 November 2013. Substorm onset and a later intensification coincided with polar cap patches entering the auroral oval to become auroral blobs. Using Global Navigation Satellite Systems ...

    • Stimulated Brillouin scattering during electron gyro-harmonic heating at EISCAT 

      Fu, Haiyang; Scales, Wayne A.; Bernhardt, Paul A.; Briczinski, Stan J.; Kosch, Michael J.; Senior, Andrew; Rietveld, Michael T; Yeoman, Timothy Kenneth; Ruohoniemi, J. Michael (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-08-11)
      Observations of secondary radiation, stimulated electromagnetic emission (SEE), produced during ionospheric modification experiments using ground-based, high-power, high-frequency (HF) radio waves are considered. The High Frequency Active Auroral Research Program (HAARP) facility is capable of generating narrowband SEE in the form of stimulated Brillouin scatter (SBS) and stimulated ion Bernstein ...