A LOFAR observation of ionospheric scintillation from two simultaneous travelling ionospheric disturbances

Richard Fallows, Biagio Forte, Ivan Astin, Tom Allbrook, Alex Arnold, Alan Wood, Gareth Dorrian, Maaijke Mevius, Hanna Rothkaehl, B Matyjasiak, A. Krankowski, J. M. Anderson, A Asgekar, I.M. Avruch, M.J. Bentum, M.M. Bisi, H.R. Butcher, B. Ciardi, B. Dabrowski, S. DamstraF. de Gasperin, S. Duscha, J. Eisloffel, T.M.O Franzen, M.A. Garrett, J.-M. Grießmeier, A.W. Gunst, M. Hoeft, J.R. Horandel, M. Iacolbelli, H.T. Intema, L.V.E. Koopmans, P. Maat, G. Mann, A. Nelles, H. Paas, V.N. Pandey, W. Reich, A. Rowlinson, M. Ruiter, D.J. Schwarz, M. Serylak, A. Shulevski, O.M. Smirnov, M. Soida, M. Steinmetz, S. Thoudam, M. C. Toribio, A. van Ardenne, I.M. van Bemmel, M.H.D. van der Wiel, M.P. van Haarlem, R. C. Vermeulen, C. Vocks, R.A.M.J. Wijers, O. Wucknitz, P. Zarka, P. Zucca

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Abstract

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 Cassiopeia 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 10-80 MHz. 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 ~20-40 ms-1 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 ~110 ms-1 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.

Original languageEnglish
Article number10
Pages (from-to)1-16
Number of pages16
JournalJournal of Space Weather and Space Climate
Volume10
Issue number10
Early online date20 Mar 2020
DOIs
Publication statusPublished - 31 Oct 2020

Bibliographical note

Funding Information:
Acknowledgements. This paper is based on data obtained with the International LOFAR Telescope (ILT) under project code “IPS”. LOFAR (van Haarlem et al., 2013) is the Low Frequency Array designed and constructed by ASTRON. It has observing, data processing, and data storage facilities in several countries, that are owned by various parties (each with their own funding sources), and that are collectively operated by the ILT foundation under a joint scientific policy. The ILT resources have benefitted from the following recent major funding sources: CNRS-INSU, Observatoire de Paris and Université d’Orléans, France; BMBF, MIWF-NRW, MPG, Germany; Science Foundation Ireland (SFI), Department of Business, Enterprise and Innovation (DBEI), Ireland; NWO, The Netherlands; The Science and Technology Facilities Council, UK; Ministry of Science and Higher Education, Poland. The work carried out at the University of Bath was supported by the Natural Environment Research Council (grant number NE/R009082/1) and by the European Space Agency/Thales Alenia Space Italy (H2020-MOM-TASI-016-00002). We thank Tromsø Geophysical Observatory, UiT the Arctic University of Norway, for providing the lyr, bjn, nor, tro, rvk, and kar magnetometer data. The Kp index and the Chilton ionosonde data were obtained from the U.K. Solar System Data Centre at the Rutherford Appleton Laboratory. Part of the research leading to these results has received funding from the European Community’s Horizon 2020 Programme H2020-INFRADEV-2017-1under grant agreement 777442. The editor thanks two anonymous reviewers for their assistance in evaluating this paper.

Funding Information:
Since this observation was taken, many more have been carried out under a number of projects, recording ionospheric scintillation data at times when the telescope would otherwise be idle. These demonstrate a wide range of scintillation conditions over LOFAR, some of which are seen only very occasionally and perhaps by only one or two of the international stations, illustrating the value to be had by monitoring the ionosphere at these frequencies. A design study, LOFAR4SpaceWeather (LOFAR4SW – funded from the European Community’s Horizon 2020 Programme H2020 INFRADEV-2017-1 under grant agreement 777442) currently underway will design a possible upgrade to LOFAR to enable, amongst other space weather observations, ionospheric monitoring in parallel with the regular radio astronomy observations. Such a design, if implemented, would enable a full statistical study of ionospheric scintillation at these frequencies, alongside the advances in scintillation modelling and our understanding of the ionospheric conditions causing it which can be gleaned in focussed studies such as that presented here.

Publisher Copyright:
© R.A Fallows et al., Published by EDP Sciences 2020.

Keywords

  • Instability mechanisms
  • Ionospheric scintillation
  • Travelling ionospheric disturbances

ASJC Scopus subject areas

  • Atmospheric Science
  • Space and Planetary Science

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