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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.

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 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.

Magnetospheric cusps are regions which are characterized by highly turbulent plasma. We have used Polar magnetic field data to study the structure of turbulence in the cusp region. The wavelet transform modulus maxima method (WTMM) has been applied to estimate the scaling exponent of the partition function and singularity spectra. Their features are similar to those found in the nonlinear multifractal systems. We have found that the scaling exponent does not allow one to conclude which intermittency model fits the experiment better. However, the singularity spectra reveal that different models can be ascribed to turbulence observed under various IMF conditions. For northward IMF conditions the turbulence is consistent with the multifractal p-model of fully developed fluid turbulence. For southward IMF experimental data agree with the model of non-fully developed Kolmogorov-like fluid turbulence.

We discuss mechanisms of the generation of ultralow frequency (ULF) upstream waves in the terrestrial foreshock that are essential for the acceleration of ions in space plasmas. The analysis is based on global hybrid kinetic simulations of the magnetosphere that provide realistic environment for the growth of the ULF waves in a quasi-radial configuration of the interplanetary magnetic field. We focus on a long-debated problem of the generation mechanism of oblique and parallel ULF waves and provide quantitative arguments in favor of the ion/ion cyclotron resonant instability. We also show that parallel propagating waves are predominantly generated in this configuration, but geometrical effects related to the phase space density in wave vector space lead to apparent predominance of obliquely propagating waves. Correspondence between the results outlined above and previously published experimental claims is thoroughly discussed and our results are shown to be consistent with spacecraft measurements.

We present a case study of ionospheric wave activity during solar terminator crossing using GPS TEC measurements. As a basic tool, the spatial gradient of total electron content (TEC) has been used. We tested with positive result the hypothesis on anisotropic response to assumed one-dimensional solar terminator forcing. The approximate drift velocity of irregularities has been computed. The wavelet analysis gave an interesting insight into variable frequency content of TEC gradient time series. We also proposed a filtering with respect to spatial scale allowing for resolving the spatio-temporal ambiguity.

We present a dispersion analysis of the phase of GPS signals received at high latitude. Basic theoretical aspects for spectral analysis of two-point measurement are given. To account for nonstationarity and statistical robustness a power distribution of the windowed Fourier transform cross-spectra as a function of frequency and phase is analysed using the Radon transform.

Sharp increase of the Alfven speed above the ionosphere is expected to create a resonant cavity for the Alfven waves traveling along the geomagnetic field lines (so-called Ionospheric Alfven Resonator). The wavelet transform has been used to analyze magnetic and electric fields recorded on Freja satellite. Cross-phase spectra between field components in the frequency range 0.5–10 Hz reveal a pattern similar to that predicted theoretically for the resonator. The Fourier cross-phase spectra fail to show any characteristic features. We conclude that this is due to the spatial structure of the resonator which can be examined only with local analysis techniques.