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Author: Boyde, Ben × Has files: Yes ×

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    Lensing from small-scale travelling ionospheric disturbances observed using LOFAR
    (Les Ulis : EDP Sciences, 2022) Boyde, Ben; Wood, Alan; Dorrian, Gareth; Fallows, Richard A.; Themens, David; Mielich, Jens; Elvidge, Sean; Mevius, Maaijke; Zucca, Pietro; Dabrowski, Bartosz; Krankowski, Andrzej; Vocks, Christian; Bisi, Mario
    Observations made using the LOw-Frequency ARray (LOFAR) between 10:15 and 11:48 UT on the 15th of September 2018 over a bandwidth of approximately 25-65 MHz contain discrete pseudo-periodic features of ionospheric origin. These features occur within a period of approximately 10 min and collectively last roughly an hour. They are strongly frequency dependent, broadening significantly in time towards the lower frequencies, and show an overlaid pattern of diffraction fringes. By modelling the ionosphere as a thin phase screen containing a wave-like disturbance, we are able to replicate the observations, suggesting that they are associated with small-scale travelling ionospheric disturbances (TIDs). This modelling indicates that the features observed here require a compact radio source at a low elevation and that the TID or TIDs in question have a wavelength <~30 km. Several features suggest the presence of deviations from an idealised sinusoidal wave form. These results demonstrate LOFAR-s capability to identify and characterise small-scale ionospheric structures.
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    LOFAR Observations of Substructure Within a Traveling Ionospheric Disturbance at Mid-Latitude
    ([New York] : Wiley, 2023) Dorrian, Gareth; Fallows, Richard; Wood, Alan; Themens, David R.; Boyde, Ben; Krankowski, Andrzej; Bisi, Mario; Dąbrowski, Bartosz; Vocks, Christian
    The large scale morphology and finer sub-structure within a slowly propagating traveling ionospheric disturbance (TID) are studied using wide band trans-ionospheric radio observations with the LOw Frequency ARray (LOFAR; van Haarlem et al., 2013, https://doi.org/10.1051/0004-6361/201220873). The observations were made under geomagnetically quiet conditions, between 0400 and 0800 on 7 January 2019, over the UK. In combination with ionograms and Global Navigation Satellite System Total Electron Content anomaly data we estimate the TID velocity to ∼60 ms−1, in a North-westerly direction. Clearly defined substructures with oscillation periods of ∼300 s were identified within the TID, corresponding to scale sizes of 20 km. At the geometries and observing wavelengths involved, the Fresnel scale is between 3 and 4 km, hence these substructures contribute significant refractive scattering to the received LOFAR signal. The refractive scattering is strongly coherent across the LOFAR bandwidth used here (25–64 MHz). The size of these structures distinguishes them from previously identified ionospheric scintillation with LOFAR in Fallows et al. (2020), https://doi.org/10.1051/swsc/2020010, where the scale sizes of the plasma structure varied from ∼500 m to 5 km.