A travelling ionospheric disturbance (TID) containing embedded plasma structures which generated Fresnel type asymmetric quasi-periodic scintillations (QPS: Maruyama, 1991) was tracked over a distance of >1200 km across Northern Europe using the LOw Frequency ARray (LOFAR: van Haarlem et al., 2013). Broadband ionospheric scintillation observations of these phenomena are rarely reported in the literature as is the ability to track asymmetric QPS generating plasma structures over such a distance. Asymmetric QPS are characterised by an initial broadband signal fade and enhancement which is then followed by ‘ringing pattern’ interference fringes. These results demonstrate that QPS generating plasma structures can retain their characteristics consistently for several hours, and over distances exceeding 1200 km. A propagation altitude of 110 km was estimated with observations of plasma density modulation in a sporadic-E region detected by the Juliusruh ionosonde, and direct measurements of a wavefront from the TID by co-located medium frequency radar, in which the front is clearly oriented NW-SE, and at an altitude of ~110 km. The TID propagated SW with a calculated velocity of 170 ms-1 and an azimuth of 255°. Periodicity analysis, using the calculated velocity, yielded a spacing between each QPS-generating plasma sub-structure of between 20-40 km. Co-temporal GNSS data were used to establish that these plasma density variations were very small, with a maximum amplitude of no more than +/- 0.05 TECu deviation from the background average.

A document by Gareth Dorrian. Click on the document to view its contents.

The high latitude ionospheric evolution of the May 10-11, 2024, geomagnetic storm is investigated in terms of Total Electron Content and contextualized with Incoherent Scatter Radar and ionosonde observations. Substantial plasma lifting is observed within the initial Storm Enhanced Density plume with ionospheric peak heights increasing by 150km to 300km, reaching levels of up to 630km. Scintillation is observed within the cusp during the initial expansion phase of the storm, spreading across the auroral oval thereafter. Patch transport into the polar cap produces broad regions of scintillation that are rapidly cleared from the region after a strong Interplanetary Magnetic Field reversal at 2230UT. Strong heating and composition changes result in the complete absence of the F2-layer on the 11th, suffocating high latitude convection from dense plasma necessary for Tongue of Ionization and patch formation, ultimately resulting in a suppression of polar cap scintillation on the 11th.

Radio interferometers used to make astronomical observations, such as the LOw Frequency ARray (LOFAR), experience distortions imposed upon the received signal due to the ionosphere as well as those from instrumental errors. Calibration using a well-characterised radio source can be used to mitigate these effects and produce more accurate images of astronomical sources, and the calibration process provides measurements of ionospheric conditions over a wide range of length scales. The basic ionospheric measurement this provides is differential Total Electron Content (TEC, the integral of electron density along the line of sight). Differential TEC measurements made using LOFAR have a precision of <1 mTECu and therefore enable investigation of ionospheric disturbances which may be undetectable to many other methods. We demonstrate an approach to identify ionospheric waves from these data using a wavelet transform and a simple plane wave model. The noise spectra are robustly characterised to provide uncertainty estimates for the fitted parameters. An example is shown in which this method identifies a wave with an amplitude an order of magnitude below those reported using GNSS TEC measurements. Artificially generated data are used to test the accuracy of the method and establish the range of wavelengths which can be detected using this method with LOFAR data. This technique will enable the use of a large and mostly unexplored dataset to study travelling ionospheric disturbances over Europe.

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). The observations were made under geomagnetically quiet conditions, between 0400-0800 UT on 7 January 2019, over the UK. In combination with ionograms and Global Navigation Satellite System (GNSS) Total Electron Content (TEC) anomaly data we estimate the TID velocity to ~65ms-1, in a NorthWesterly direction. Clearly defined substructures with oscillation periods of ~300 seconds were identified within the LOFAR observations of the TID, corresponding to scale sizes of ~ 20 km. At the geometries and observing wavelengths involved, the Fresnel scale is between 3-4 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 where the scale sizes of the plasma structure varied from ~500 m – 5 km.