• Observations of plasma density structures in association with the passage of traveling convection vortices and the occurrence of large plasma jets. 

      Valladares, C.E.; Van Eyken, A.P.; Alcaydé, D.; Rodriguez, J.V.; Ruohoniemi, J.M. (Journal article; Peer reviewed; Tidsskriftartikkel, 1999)
      We report important results of the first campaign specially designed to observe the formation and the initial convection of polar cap patches. The principal instrumentation used in the experiments comprised the EISCAT, the Sondrestrom, and the Super DARN network of radars. The experiment was conducted on February 18, 1996 and was complemented with additional sensors such as the Greenland chain of ...
    • ELF wave generation in the ionosphere using pulse modulated HF heating. Initial tests of a technique for increasing ELF wave generation efficiency. 

      Barr, R.; Rietveld, Michael T.; Stubbe, P. (Journal article; Peer reviewed; Tidsskriftartikkel, 1999)
      This paper describes the results of a preliminary study to determine the effective heating and cooling time constants of ionospheric currents in a simulated modulated HF heating, `beam painting' configuration. It has been found that even and odd harmonics of the fundamental ELF wave used to amplitude modulate the HF heater are sourced from different regions of the ionosphere which support significantly ...
    • Irregular structures of the F layer at high latitudes during ionospheric heating. 

      Tereshchenko, E.D.; Rietveld, Michael T.; Brekke, Asgeir; Kozlova, M.O.; Evstafiev, O.V.; Khudukon, B.Z.; Nygren, T. (Journal article; Peer reviewed; Tidsskriftartikkel, 2000)
      Results on heating the ionospheric F region above Tromsø, Norway are presented. The ionosphere was monitored by satellite tomography and amplitude scintillation methods as well as the EISCAT incoherent scatter radar. No effect of heating was observed in the daytime. In the evening and in the pre-midnight sector, noticeable tilts of the F region were observed during heating periods. The tilts overlapped ...
    • Comparison of the orientation of small-scale electron density irregularities and F region plasma flow direction. 

      Rietveld, Michael T.; Tereshchenko, E.D.; Brekke, Asgeir; Khudukon, B.Z.; Kozlova, M.O.; Evstafiev, O.V.; Nygren, T. (Journal article; Tidsskriftartikkel; Peer reviewed, 2000)
      Results are shown from an experimental campaign where satellite scintillation was observed at three sites at high latitudes and, simultaneously, the F region plasma flow was measured by the nearby EISCAT incoherent scatter radar. The anisotropy parameters of field-aligned irregularities are determined from amplitude scintillation using a method based on the variance of the relative logarithmic ...
    • Comparison of high latitude electron density profiles obtained with the GPS radio occultation technique and EISCAT measurements. 

      Stolle, C.; Rietveld, Michael T.; Jakowski, N.; Schlegel, K: (Journal article; Peer reviewed; Tidsskriftartikkel, 2004)
      To obtain a comprehensive view on high latitude processes by applying different observation techniques, the SIRCUS campaign was initiated in 2001/2002. This paper compares electron density profiles derived from CHAMP radio occultation data and those measured with the EISCAT facility. Since ionospheric profiling with the help of space-based received GPS is a relatively new technique, validations with ...
    • Multi-frequency HF radar measurements of artificial F-region field-aligned irregularities. 

      Rietveld, Michael T.; Senior, A.; Borisov, N.D.; Kosch, M.J.; Yeoman, T.K.; Honary, F. (Journal article; Tidsskriftartikkel; Peer reviewed, 2004-11-03)
      We present radar backscatter power measurements using the CUTLASS HF radar at Hankasalmi, Finland from F-region field-aligned irregularities induced by HF radio pumping with the EISCAT Heating facility. A novel radar operating mode is used in which the radar frequency is rapidly swept through a number of bands, making use of the varying ionospheric refraction to probe different heights within the ...
    • An interferometer experiment to explore the aspect angle dependence of stimulated electromagnetic emission spectra. 

      Rietveld, Michael T.; Isham, B.; Hagfors, T.; Belyey, Vasyl; La Hoz, Cesar; Khudukon, B.; Brekke, Asgeir; Yurik, R.Yu; Tereshchenko, E.D.; Grill, M.; Heinselman, C. (Journal article; Peer reviewed; Tidsskriftartikkel, 2005-01-31)
      When the Earth's ionosphere is irradiated by a radiofrequency (RF) electromagnetic wave of sufficiently high power density and tuned to match a natural E- or F-region plasma frequency, ionospheric magnetoionic wave modes may be excited and may generate RF electromagnetic sideband waves via nonlinear interactions. These secondary emissions, which may then escape from the ionosphere, have been termed ...
    • The electron energy distribution during HF pumping, a picture painted with all colors. 

      Gustavsson, B.; Rietveld, Michael T.; Sergienko, T.; Grydeland, Tom; La Hoz, Cesar; Kosch, M.J.; Brändström, B.U.E.; Leyser, T.B.; Isham, B.; Gallop, P.; Aso, T.; Ejiri, M.; Steen, A.; Kaila, K.; Jussila, J.; Holma, H. (Journal article; Tidsskriftartikkel; Peer reviewed, 2005-07-28)
      The shape of the electron energy distribution has long been a central question in the field of highfrequency radio-induced optical emission experiments. This report presents estimates of the electron energy distribution function, fe(E), from 0 to 60 eV, based on optical multiwavelength (6300, 5577, 8446, 4278 A° ) data and 930-MHz incoherent scatter radar measurements of ion temperature, electron ...
    • Infrasound - the cause of strong Polar Mesosphere Winter Echoes? 

      Rietveld, Michael T.; Kirkwood, S.; Chilson, P.; Belova, E.; Häggström, I.; Singer, W.; Dalin, P. (Journal article; Peer reviewed; Tidsskriftartikkel, 2006-03-23)
      The ESRAD 52-MHz and the EISCAT 224-MHz radars in northern Scandinavia observed thin layers of strongly enhanced radar echoes from the mesosphere (Polar Mesosphere Winter Echoes - PMWE) during a solar proton event in November 2004. Using the interferometric capabilities of ESRAD it was found that the scatterers responsible for PMWE show very high horizontal travel speeds, up to 500 ms-1 or more, and ...
    • Directional features of the downshifted peak observed in HF-induced stimulated electromagnetic emission spectra obtained using an interferometer. 

      Rietveld, Michael T.; Tereshchenko, E.D.; Belyey, Vasyl; Yurik, R.Yu; Brekke, Asgeir; Khudukon, B.Z.; Isham, B.; Hagfors, T.; Grill, M. (Journal article; Peer reviewed; Tidsskriftartikkel, 2006-08-09)
      A high frequency (HF) ionospheric modification experiment was carried out between 25 September and 8 October 2004, using the EISCAT HF transmitter located near Tromsø, Norway. During this experiment the spectra of the stimulated HF sideband waves (stimulated electromagnetic emission or SEE) induced by the HF pump were observed using an interferometer consisting of three spaced receiving antennas ...
    • Probing of medium-scale traveling ionospheric disturbances using HF-induced scatter targets 

      Blagoveshchenskaya, N. F.; Rietveld, Michael T.; Borisova, T. D.; Kornienko, V. A.; Moskvin, I. V.; Frolov, V. L.; Uryadov, V. P.; Kagan, L. M.; Yampolski, Yu. M.; Galushko, V. L.; Koloskov, A. V.; Kasheev, S. B.; Zalizovski, A. V.; Vertogradov, G. G.; Vertogradov, V. G.; Kelley, M. C. (Journal article; Tidsskriftartikkel; Peer reviewed, 2006-09-20)
      Experimental results from the Tromsø and Sura heating experiments at high and mid-latitudes are examined. It is shown that the combination of HF-induced target and bi-static HF Doppler radio scatter observations is a profitable method for probing medium-scale traveling ionospheric disturbances (TIDs) at high and mid-latitudes. HF ionospheric modification experiments provide a way of producing ...
    • The relationship between small-scale and large-scale ionospheric electron density irregularities generated by powerful HF electromagnetic waves at high latitudes 

      Rietveld, Michael T.; Tereshcenko, E.D.; Khudukon, B.Z.; Brekke, Asgeir; Isham, B.; Hagfors, T. (Journal article; Tidsskriftartikkel; Peer reviewed, 2006-11-21)
      Satellite radio beacons were used in June 2001 to probe the ionosphere modified by a radio beam produced by the EISCAT high-power, high-frequency (HF) transmitter located near Tromsø (Norway). Amplitude scintillations and variations of the phase of 150- and 400-MHz signals from Russian navigational satellites passing over the modified region were observed at three receiver sites. In several papers ...
    • Statistical signature of active D-region HF heating in IRIS riometer data from 1994–2004 

      Kero, A.; Rietveld, Michael T.; Enell, C.-F.; Ulich, Th.; Turunen, E.; Honary, F. H. (Journal article; Tidsskriftartikkel; Peer reviewed, 2007-03-08)
      In this paper we study the effect of artificial HF heating on cosmic radio noise absorption in the D-region ionosphere. The effect has earlier been studied theoretically in idealised cases and without experimental verification. Here we present a 3-dimensional modelling of the effect, taking into account the directivity patterns of the vertical beam of the EISCAT Heater at Tromsø, Norway, and ...
    • A case study of a sporadic sodium layer observed by the ALOMAR Weber Na lidar 

      Rietveld, Michael T.; Nesse, H.; Heinrich, D.; Williams, B.; Hoppe, Ulf-Peter; Stadsnes, J.; Singer, W.; Blum, U.; Sandanger, M. I.; Trondsen, E. (Journal article; Tidsskriftartikkel; Peer reviewed, 2008-05-28)
      Several possible mechanisms for the production of sporadic sodium layers have been discussed in the literature, but none of them seem to explain all the accumulated observations. The hypotheses range from direct meteoric input, to energetic electron bombardment on meteoric smoke particles, to ion neutralization, to temperature dependent chemistry. The varied instrumentation located on Andøya ...
    • 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 ...