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LOFAR low band interferometric images of type III solar radio bursts during an M class flare on 7 September 2017 show distinct sources with variations in their positions and intermittent dual source structures. We identify these as fundamental and harmonic emission, with the one or other being dominant at times. The data show that transport effects due to refraction and scattering play a significant role, both in source separation and drift of their apparent positions. We present a method of automatically separating fundamental and harmonic contributions that allows for obtaining separate lightcurves. Comparing the lightcurves of fundamental and harmonic pairs, e.g. 35 MHz and 70 MHz, enables studies of radio wave propagation in the solar corona. Harmonic sources at the lowest observable frequencies are relevant for the transition into the solar wind, and for joint observing campaigns with Parker Solar Probe and Solar Orbiter that are currently investigating the inner heliosphere.

The Earth's ionosphere is a coupled system affected by interactions with precipitating energetic particles and electrical currents from the Earth's magnetosphere, and in addition by upward propagating disturbances from lower atmospheric layers. Geomagnetic disturbances triggered by solar activity influence the ionosphere, its fine and global structures. The energy injection into the magnetosphere during geomagnetic storms and substorms directly affects the auroral and sub-auroral region of the Earth’s ionosphere, where auroral oval expansion and variations of plasma density and field-aligned currents intensity can be observed. Main ionospheric trough (MIT) and field-aligned currents (FACs) are very sensitive to geomagnetic conditions. This work analyses both phenomenon response to the elevated geomagnetic conditions during October 2015 and September 2017 geomagnetic storms. The analysis is based on the data from the Swarm and DMSP missions.

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.

Space Weather (SW) research is a very important topic from the scientific, operational and civic society point of view. Knowledge of interactions in the Sun-Earth system, the physics behind observed SW phenomena, and its direct impact on modern technologies were and will be key areas of interest. The LOFAR for Space Weather (LOFAR4SW) project aim is to prepare a novel tool which can bring new capabilities into this domain. The project is realised in the frame of a Horizon 2020 INFRADEV call. The base for the project is the Low Frequency Array (LOFAR) - the worlds largest low frequency radio telescope, with a dense core near Exloo in The Netherlands and many stations distributed both in the Netherlands and Europe wide with baselines up to 2000 km. The final design of LOFAR4SW will provide a full conceptual and technical description of the LOFAR upgrade, to enable simultaneous operation as a radio telescope for astronomical research as well as an infrastructure working for Space Weather studies. In this work we present the current status of the project, including examples of the capabilities of LOFAR4SW and the project timeline as we plan for the Critical Design Review later in 2021.

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.

Formation the feature, in a form of deep trough, in frequency dependence of the wave field strength for single-hop paths with distances near classical limiting distance 3000 km at low level of solar activity was considered. Model calculations within the framework of the extended global ionospheric IRI model show high probability for appearing such situation in the local daytime with a developed regular E-layer of the ionosphere. Some experimental results in multifrequency radio sounding of the ionosphere with a registration of the deep trough in frequency dependence of signal-to-noise ratio (SNR) were analyzed. It is shown that the IRI model, in principle, makes it possible to reproduce this peculiarity in the wave field energy parameters, but in some cases of experimental data, to a large extent, is able to provide only a qualitative description of this effect. Possible reasons for the quantitative discrepancy between experimental and model results are discussed.

Mid-latitude trough (MIT) is the distinct structure observed in Earth’s ionosphere at high latitudes especially at the nighttimes. The phenomenon is observed at both hemispheres. As it resides at the topside ionosphere in the sub-auroral region, its behaviour and properties are highly sensitive to the solar and geomagnetic activity. Generally as the geomagnetic activity is more pronounced the MIT is observed at lower latitudes, it also deepens and becomes much more distinct in comparison to the low magnetic activity periods. MIT responds as well to the rapid changes in geomagnetic conditions, as are the geomagnetic storms, mainly caused by the CMEs. Based on the observations gathered by DEMETER data between 2005 and 2010 years we present a set of geomagnetic storm cases and how the MIT properties has been changing as the storm evolves. We also discuss how it corresponds to the current solar activity and their evolutionary history described by a set of different parameters.

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.

We hereby present the interferometric LOFAR observations made before and after the total solar eclipse on 21 August 2017, during which the type III radio bursts have been detected.The LOw-Frequency ARray (LOFAR) is a large radio interferometer operating in the frequency range of 10–240 MHz, designed and constructed by ASTRON (the Netherlands Institute for Radio Astronomy). The LOFAR telescope is an array of stations distributed throughout the Netherlands and other parts of Europe. Currently the system consist of 52 LOFAR stations located in Europe. Apart from the high time and frequency resolution of the dynamic spectra, LOFAR allows also a 2D imaging of the radio sources and tracking of their positions through the solar corona.In this work we present a preliminary analysis of the dynamic spectra of type III radio bursts with radio images.

The sub-auroral region of the main ionospheric trough is a very unique area strongly affected by different type of instabilities coming from both the bottom (Earth's atmosphere) and the top (Earth's magnetosphere) neighbouring regions. The main ionospheric trough’s general characteristics as well as the detailed features change accordingly to the time of day, season, solar cycle and many others. The location of MIT in the latitude-longitude coordinate system throughout the year reflects seasonal changes. Annual variations are observed also in the shape and intensity of the structure. Despite the representation of the structure in the geomagnetic coordinate system, northern and southern trough are not symmetric in the same local season. However some similarities have also been observed. In particular for both hemispheres the structure appears the deepest and well developed during local winter, whereas during local summer the structure becomes hardly visible. Observations show that the MIT tends to shift equatorward for some longitudes in both hemispheres. MIT properties for this study have been derived from DEMETER and COSMIC/FORMOSAT-3 observations.

The Earth’s auroral region and its close neighbourhood is the origin of strong radio emissions caused by complex physical plasma processes. Among them we can list auroral hiss, auroral roar, auroral medium frequency (MF) burst, and auroral kilometric radiation (AKR). Analysis of such emissions can provide information about magnetospheric structure and dynamics. In this work we present selected cases of Earth’s AKR-like radio emissions observed by RELEC and mission at the top side ionosphere leyers. The emissions are seen at frequencies of the order of hundreds of kHz in the ionosphere, just below the auroral oval and can be observed not only in disturbed geomagnetic conditions, but also during quiet periods. The maximum occurrence is at ∼ 75 ◦ invariant latitude and can have extent up to ∼ 11 ◦ in invariant latitude.

The Low Frequency Array (LOFAR) is an advanced phased-array radio-telescope system based across Europe. It is capable of observing over a wide radio bandwidth of ~10-250 MHz at both high spatial and temporal resolutions. LOFAR has capabilities that enable studies of many aspects of what we class as space weather (from the Sun to the Earth and afar) to be progressed beyond today’s state-of-the-art. However, with the present setup and organisation behind the operations of the telescope, it can only be used for space-weather campaign studies with limited triggering availability. This severely limits our ability to effectively use LOFAR to contribute to space-weather monitoring/forecast beyond its core strength of enabling world-leading scientific research. LOFAR itself is made up of a dense core of 24 stations near Exloo in The Netherlands with an additional 14 stations spread across the northeast Netherlands. In addition to those, there are a further 13 stations based internationally across Europe. These international stations are, currently, six in Germany, three in northern Poland, and one each in France, Ireland, Latvia, Sweden, and the UK. Further sites are under preparations (for example, in Italy). We are undertaking a Horizon 2020 (H2020) INFRADEV design study to undertake investigations into upgrading LOFAR to allow for regular space-weather science/monitoring observations in parallel with normal radio-astronomy/scientific operations. This project is called the LOFAR For Space Weather (LOFAR4SW) project (see: http://lofar4sw.eu/). Our work involves all aspects of scientific and engineering work along with end-user and political engagements with various stakeholders. This is with the full recognition that space weather is a worldwide threat with varying local, regional, continent-wide impacts, and also global impacts – and hence is a global concern. Here, we summarise the most-recent key aspects of the LOFAR4SW progress including outputs/progress following the Detailed Design Review (DDR) that took place at ASTRON, The Netherlands, in March 2020, as well as the implementation of recommendations from the earlier Preliminary Design Review (PDR) with an outlook to the LOFAR4SW User Workshop the week following EGU 2020. We also aim to briefly summarise a key set of the longer-term goals envisaged for LOFAR to become one of Europe’s most-comprehensive space-weather observing systems capable of shedding new light on several aspects of the space-weather system, from the Sun to the solar wind to Jupiter and Earth’s ionosphere.

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 Cas 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 10-80MHz. 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 ~30m/s 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 ~110m/s 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., Comment: 24 pages, 16 figures. Accepted for open-access publication in the Journal of Space Weather and Space Climate. For associated movie file, see https://www.swsc-journal.org/10.1051/swsc/2020010/olm

LOFAR is valuable tool not only for astronomical observation. I Poland was located 3 stations. Polish LOFAR stations makes possible carry out research programs on whole network but also realization of their own research programs by station owners. Space Research Centre of Polish Academy of Science is owner of PL610 station located in Borowiec near Poznan. We show uses of our station to ionospheric and space weather researches.

One of the most important effects occurring during the propagation of the pulsar-emitted radio waves through the interstellar medium (ISM) is the temporal pulse broadening caused by the scattering of the signal. Our latest studies of this phenomenon, which were performed for the largest sample of pulsars used for this purpose, have shown that the amount of the observed scattering strongly depends on the observing frequency. However, the slope of the dependence is different from the theoretical predictions based on simple scattering models of the turbulent ISM. Low frequency observations are crucial for the study of the scattering phenomenon, since it is at frequencies below a few hundred megahertz where the effects of scattering are the strongest. Currently for pulsar observations we are using all three POLFAR (POlish Low Frequency ARray) stations, which are a part of the International Low Frequency Array (ILT) telescope. The wide bandwidth of the telescope's receivers allows us to study the frequency evolution of interstellar scattering with a single observation. We will present the first results of this project.

The main ionospheric trough (MIT) is large structure observed in mid-latitude area of Earth's ionosphere. It is depleted region of ionospheric plasma typical for the topside ionosphere, especially F layer, where electron density level can significantly decrease as compared to densities measured for adjoining sub-auroral and equatorial regions. The MIT itself and its variability strongly affect the propagation of different natural and artificial signals thus its characteristic is important for radio communication and for communication and space industry in general. We compared data from in-situ measurements collected onboard DEMETER satellite and electron density profiles obtained from radio occultation method used by FORMOSAT-3/COSMIC mission to study the nature of MIT and its behavior during different seasons and magnetic conditions. This paper presents the results obtained in both geographic and magnetic system at fixed local time.

To give a more detailed and complete understanding of physical plasma processes that govern the solar-terrestrial space, and to develop qualitative and quantitative models of the magnetosphere-ionosphere-thermosphere coupling, it is necessary to design and build the next generation of instruments for space diagnostics and monitoring. Novel ground based wide area sensor networks, such as the LOFAR (Low Frequency Array) radar facility, comprising wide band, and vector sensing radio receivers and multi-spacecraft plasma diagnostics should help to solve outstanding problems of Space Physics and describe long-term environmental changes. The Low Frequency Array LOFAR is a new fully digital radio telescope designed for frequencies between 30 MHz and 240 MHz located in Europe. The three new LOFAR stations will be installed until summer 2015 in Poland. The LOFAR facilities in Poland will be distributed among three sites: Lazy (East of Krakow), Borowiec near Poznan and Baldy near Olsztyn. All they will be connected via PIONIER dedicated links to Poznan. Each site will host one LOFAR station (96 high band 96 low band antennas). They will be mostly working as a part of European network, however, when less occupied, they can operate as a national network. The new digital Radio Frequency Analyzer (RFA) on board the low orbiting RELEC satellite was designed to monitor and investigate the ionospheric plasma properties. This two-point ground-based and topside ionosphere located space plasma diagnostic can be a useful new tool for monitoring and diagnosing turbulent plasma properties. The RFA on board the RELEC satellite is the first in a series of experiments which was launched in July 2014 in order to study near-Earth environment. In order to improve and validate the large and small scales ionospheric structures we will used the GPS observations collected at IGS/EPN network employed to reconstruct diurnal variations of TEC using all satellite passes over individual GPS stations and the data retrieved from FORMOSAT-3/COSMIC radio occultation measurements. The main purpose of this presentation is to describe new advanced diagnostic techniques of the near-Earth space plasma and point out the scientific challenges of the radio frequency analyzer located on-board low orbiting satellites and LOFAR facilities.

The mid-latitude ionospheric trough is a depleted region of ionospheric plasma observed in the topside ionosphere. Its behavior can provide useful information about the magnetospheric dynamics, since its existence is sensitive to magnetospherically induced motions. Midlatitude trough is mainly a night-time phenomenon. Both, its general features and detailed characteristics strongly depend on the level of geomagnetic disturbances, time of the day, season, and the solar cycle, among others. Although many studies provide basic information about general characteristics of the main ionospheric trough structure, an accurate prediction of the trough behavior in specific events is still understood poorly. The paper presents the mid-latitude trough characteristics with regard to the geomagnetic longitude and season during a solar activity minimum, as based on the DEMETER in situ satellite measurements and the data retrieved from FORMOSAT-3/COSMIC radio occultation measurements.