M. Iacobelli, M. A. Garrett, I. Max Avruch, Bartosz Dabrowski, Hanna Rothkaehl, Richard Fallows, Michiel van Haarlem, Olaf Wucknitz, A. W. Gunst, Tom Allbrook, Jean Matthias Grießmeier, Harvey Butcher, Christian Vocks, Jörg R. Hörandel, Vishambhar Pandey, Léon V. E. Koopmans, Anna Nelles, Biagio Forte, Barbara Matyjasiak, P. Maat, Gareth Dorrian, Thomas M. O. Franzen, M. Ruiter, Ashish Asgekar, Oleg Smirnov, Ilse van Bemmel, Antonia Rowlinson, Matthijs H. D. van der Wiel, M. Serylak, Ivan Astin, Dominik J. Schwarz, Mark J. Bentum, Arnold van Ardenne, Matthias Hoeft, Gottfried Mann, S. Duscha, Alex Arnold, Huib Intema, H. Paas, S. Damstra, Francesco de Gasperin, James M. Anderson, Jochen Eislöffel, Maaijke Mevius, Benedetta Ciardi, Andrzej Krankowski, M. Carmen Toribio, Alan Wood, Satyendra Thoudam, Aleksander Shulevski, Mario M. Bisi, Ralph A. M. J. Wijers, Pietro Zucca, Philippe Zarka, Wolfgang Reich, Marian Soida, Rene C. Vermeulen, Matthias Steinmetz, Netherlands Institute for Radio Astronomy (ASTRON), Environmental Systems Science Centre [Reading] (ESSC), University of Reading (UOR), Space Research Centre of Polish Academy of Sciences (CBK), Polska Akademia Nauk = Polish Academy of Sciences (PAN), Department of Computer Science [Chapel Hill], University of North Carolina [Chapel Hill] (UNC), University of North Carolina System (UNC)-University of North Carolina System (UNC), Eindhoven Technical University, STFC Rutherford Appleton Laboratory (RAL), Science and Technology Facilities Council (STFC), Thüringer Landessternwarte Tautenburg (TLS), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud university [Nijmegen], Leiden Observatory [Leiden], Universiteit Leiden [Leiden], Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), SKA South Africa, Ska South Africa, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), and Astronomy
This paper presents the results from one of the first observations of ionospheric scintillation taken using the Low-Frequency Array (LOFAR). The observation was of the strong natural radio source Cas A, taken overnight on 18-19 August 2013, and exhibited moderately strong scattering effects in dynamic spectra of intensity received across an observing bandwidth of 10-80MHz. Delay-Doppler spectra (the 2-D FFT of the dynamic spectrum) from the first hour of observation showed two discrete parabolic arcs, one with a steep curvature and the other shallow, which can be used to provide estimates of the distance to, and velocity of, the scattering plasma. A cross-correlation analysis of data received by the dense array of stations in the LOFAR "core" reveals two different velocities in the scintillation pattern: a primary velocity of ~30m/s with a north-west to south-east direction, associated with the steep parabolic arc and a scattering altitude in the F-region or higher, and a secondary velocity of ~110m/s with a north-east to south-west direction, associated with the shallow arc and a scattering altitude in the D-region. Geomagnetic activity was low in the mid-latitudes at the time, but a weak sub-storm at high latitudes reached its peak at the start of the observation. An analysis of Global Navigation Satellite Systems (GNSS) and ionosonde data from the time reveals a larger-scale travelling ionospheric disturbance (TID), possibly the result of the high-latitude activity, travelling in the north-west to south-east direction, and, simultaneously, a smaller--scale TID travelling in a north-east to south-west direction, which could be associated with atmospheric gravity wave activity. The LOFAR observation shows scattering from both TIDs, at different altitudes and propagating in different directions. To the best of our knowledge this is the first time that such a phenomenon has been reported., Comment: 24 pages, 16 figures. Accepted for open-access publication in the Journal of Space Weather and Space Climate. For associated movie file, see https://www.swsc-journal.org/10.1051/swsc/2020010/olm