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The aim of the study is to obtain quantitative information on the conditions of ionospheric plasma and its variability at mid-latitudes. For this purpose, we use the S4 scintillation index parameter, which is widely used in other diagnostic techniques, such as Global Navigation Satel-lite System (GNSS). This paper presents a method for determination of ionospheric scintillation intensity with the use of single LOw-Frequency ARray for radio astronomy (LOFAR)station - PL610. We show the specificity of LOFAR measurements, related problems, and methods to obtain ionospheric scintillation index.

We take the frozen-in assumption of the scatter evolution and derive simple formulas for characteristics of the spatiotemporal correlation function of the observed diffraction pattern. Using Low-Frequency Array (LOFAR) Cassiopeia intensity observation, we can validate the assumptions qualitatively and compute diffraction pattern velocities for three different geophysical conditions. The results allow us to attribute estimated quantities to ionospheric irregularities.

Scintillation of beacon satellite signals or distant cosmic radio emissions can provide interesting information on the cosmic medium itself, its internal spatial structure and basic evolution characteristics. LOFAR network gives consistent scintillation data with good coverage both in time and space and for the frequency range that goes down close to the local plasma frequency (LBA) being thus sensible to ionospheric plasma irregularities. LOFAR Scintillation measurements in the LBA range exhibit very interesting morphologies. Based on scintillation simulations using the phase screen method, including multiple scattering and refraction, we try to untangle the information contained in the full range (time, space, frequency) of LOFAR data and verify a number of hypotheses about the local structure of the ionosphere and its evolution.

Perturbation of an electromagnetic signal due to its passing through the Earth’s ionosphere is one of the limiting factors in obtaining high quality astronomical observations at low frequencies. Since the establishment of the Low Frequency Array (LOFAR) radio interferometer, which is operating in the frequency range between 10 and 240 MHz, effort has been made in order to properly remove this effect during the calibration routine.In this study we use differential TEC solutions obtained from calibration of Epoch of Reionization project’s observations and investigate their sensitivity to weak geomagnetic disturbances with wavelet transform analysis. Comparison to the different geomagnetic indices allows us to study the possible origin of medium scale ionospheric structures that have been detected.

Due to their low intensity, ionospheric scintillations in the middle latitude region are difficult to observe. However, scintillations intensity increases at lower frequencies. Those below 90 MHz, covered by LOFAR, enable scintillation measurements in mid-latitude region. Long-term observations, with the use of PL610 station, allow the study of weak scintillation climatology, unavailable for measurement led with other methods. The developement of functional tool for the scintillation parameters analysis described in the paper enabled the study of scintillations in the mid-latitude region and future application to the data collected by LOFAR.LOFAR PL610 station in Borowiec (23E,50N) regularly observes ionospheric scintillation using signals from the 4 strongest radio sources, members of LOFAR A-team: Cas A, Cyg A, Vir A and Tau A. The measurements are taken by LBA antennas at frequencies in the range of 10-90 MHz. Since 2018 we have collected more than 8000 hours of observations. In this work research, we present the results of the automatic s4 calculation system based on our observations. The observations are led in 4-bit mode, for 4 independent sources, with sampling of 10 Hz at 244 subbands. Sources are selected automatically depending on their visibility. Due to the fact that natural radio sources are relatively weak and beamforming is not ideal, the data are noisy. In order to improve the quality of data, the measured amplitudes are filtered and S4 index is computed for each beamlet. All processed data are stored in a database and enable in-depth analysis of scintillation behavior in the mid-latitude region.We look at the intrinsic features of the observation: dependence on the geometry of the measurement, impact of RFI depending on the strength of the radiosource, the observation frequency then show the dependence of scintillation on the global conditions caused by space weather.

LOFAR single station observation mode is often used for ionospheric studies. Observations of A-Team (the brightest radio sources CasA, CygA, TauA) enables measure of ionospheric scintillation. Relatively low brightness of the radio sources compared to signals coming from the Earth and originating from man-made activity (in particular RFI) can make the analysis difficult. In order to fully utilize the data, it is necessary to apply methods that eliminate interference. Combination of broadband observations and careful selection of observation frequencies should also improve the results. Another problem is the frequency (very low compared to GPS) which requires very careful data analysis. We observe large structures in relatively quiet conditions and low velocity of ionospheric drift resulting in low frequency scintillations compared to GPS. Amplitude observations conducted as a standard observations suggest using the S4 index to monitor the state of the ionosphere. In this paper, we present methods for calculating the S4 index for LOFAR data that eliminates the obstacles mentioned above. We compare different methods that resolve the problem and present the results. Signal spectra were also examined in detail to explore the possibility of using them to eliminate interference effects. The analyzes were carried out on the basis of data collected during the last 3 years at the PL610 station in Borowiec.

The Low Frequency Array (LOFAR) interferometer is a radio telescope network that provides the radio astronomical observations with the highest up-to-date sensitivity in the frequency regime between 10 and 240 MHz. As these frequencies approach the ionospheric plasma frequency, ionospheric perturbation of propagating electromagnetic signal is the main environmental factor affecting the quality of observations. Removal of ionospheric influence is a part of routinely conducted data calibration, resulting in high sensitivity differential Total Electron Content (dTEC) values between LOFAR stations. In this study we present a method for medium scale ionospheric structures detection applied to interferometric data obtained from calibration solutions of one of the key LOFAR projects- the Epoch of Reionization. Each observation spans 110-250 MHz of frequency range and lasts 6-8 hours during winter nighttime. Due to operating frequency and sensitivity of interferometric data, studies conducted with LOFAR can complement GNSS research with medium scale structures.

The Earth’s ionosphere is a highly variable medium on a wide range of spatio-temporal scales. The responsiveness of plasma to the geomagnetic field and its changes gives rise to anisotropy, which may introduce wave-like characteristics while scanning the ionosphere with a line-of-sight towards a radio source. Previous studies of LOw Frequency ARray (LOFAR) calibration phase solutions report that the estimated beta parameter of a structure function calculated over 6–8 h of astronomical observation timespan has a range of values from 1.6 to 2.0, with an average of 1.89. Such difference between the observations could result from transient wave-like disturbances within the data. This study aims to present a method of signal processing of ionospheric calibration datasets that allows the extraction of a transient wave-like signal and discuss its possible origin. We use complex Morlet wavelet analysis applied to two 8 h observations corresponding to very quiet geomagnetic conditions. We find a wave-like signal in the interferometric Total Electron Content data even during periods of no geomagnetic activity. We suggest it results from the relative velocity changes between the LOFAR line-of-sight and a convection pattern in the ionospheric F layer. Establishing the relationship between quiet time ionosphere, geomagnetic field changes and LOFAR’s calibration solutions may prove beneficial to determination of the dominant signals in the more disturbed conditions, which we leave for future study.