A LOFAR observation of ionospheric scintillation from two simultaneous travelling ionospheric disturbances
Journal of Space Weather and Space Climate EDP Sciences 10 (2020) 10-10
Authors:
Richard A Fallows, Biagio Forte, Ivan Astin, Tom Allbrook, Alex Arnold, Alan Wood, Gareth Dorrian, Maaijke Mevius, Hanna Rothkaehl, Barbara Matyjasiak, Andrzej Krankowski, James M Anderson, Ashish Asgekar, I Max Avruch, Mark Bentum, Mario M Bisi, Harvey R Butcher, Benedetta Ciardi, Bartosz Dabrowski, Sieds Damstra, Francesco de Gasperin, Sven Duscha, Jochen Eislöffel, Thomas MO Franzen, Michael A Garrett, Jean-Matthias Grießmeier, André W Gunst, Matthias Hoeft, Jörg R Hörandel, Marco Iacobelli, Huib T Intema, Leon VE Koopmans, Peter Maat, Gottfried Mann, Anna Nelles, Harm Paas, Vishambhar N Pandey, Wolfgang Reich, Antonia Rowlinson, Mark Ruiter, Dominik J Schwarz, Maciej Serylak, Aleksander Shulevski, Oleg M Smirnov, Marian Soida, Matthias Steinmetz, Satyendra Thoudam, M Carmen Toribio, Arnold van Ardenne, Ilse M van Bemmel, Matthijs HD van der Wiel, Michiel P van Haarlem, René C Vermeulen, Christian Vocks, Ralph AMJ Wijers, Olaf Wucknitz, Philippe Zarka, Pietro Zucca
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.
