A. Bonardi

Measurement of the circular polarization in radio emission from extensive air showers confirms emission mechanisms

We report here on a novel analysis of the complete set of four Stokes parameters that uniquely determine the linear and/or circular polarization of the radio signal for an extensive air shower. The observed dependency of the circular polarization on azimuth angle and distance to the shower axis is a clear signature of the interfering contributions from two different radiation mechanisms, a main contribution due to a geomagnetically-induced transverse current and a secondary component due to the build-up of excess charge at the shower front. The data, as measured at LOFAR, agree very well with a calculation from first principles. This opens the possibility to use circular polarization as an investigative tool in the analysis of air shower structure, such as for the determination of atmospheric electric fields.

Thunderstorm electric fields probed by extensive air showers through their polarized radio emission

We observe a large fraction of circular polarization in radio emission from extensive air showers recorded during thunderstorms, much higher than in the emission from air showers measured during fair-weather circumstances. We show that the circular polarization of the air showers measured during thunderstorms can be explained by the change in the direction of the transverse current as a function of altitude induced by atmospheric electric fields. Thus by using the full set of Stokes parameters for these events, we obtain a good characterization of the electric fields in thunderclouds. We also measure a large horizontal component of the electric fields in the two events that we have analyzed.

Characterisation of the radio frequency spectrum emitted by high energy air showers with LOFAR

The high number density of radio antennas at the LOFAR core in Northern Netherlands allows to detect radio signals emitted by extensive air showers in the energy range 10

LOFAR Lightning Imaging : Mapping Lightning With Nanosecond Precision

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Realtime processing of LOFAR data for the detection of nano-second pulses from the Moon

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Search for Cosmic Particles with the Moon and LOFAR

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Overview and Status of the Lunar Detection of Cosmic Particles with LOFAR

eV, and to characterise the geometry of the observed cascade in a detailed way. The radio signal emitted by extensive air showers along their propagation in the atmosphere has been studied in the 30 − 70 MHz frequency range. The study has been conducted on real data and simulated showers. Regarding real data, cosmic ray radio signals detected by LOFAR since 2011 have been analysed. For simulated showers, the CoREAS code, a plug-in of the CORSIKA particle simulation code, has been used. The results show a clear dependence of the frequency spectrum on the distance to the shower axis for both real data and simulations. In particular, the spectrum flatten at a distance around 100 m from the shower axis, where the coherence of the radio signal is maximum. This behaviour could also be used to reconstruct the position of the shower axis at ground. A correlation between the frequency spectrum and the geometrical distance to the depth of the shower maximum X

Cosmic ray mass composition with LOFAR

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Expansion of the LOFAR Radboud Air Shower Array

has also been investigated. The final aim of this study is to find a method to improve the inferred information of primary cosmic rays with radio antennas, in view of affirming the radio detection technique as reliable method for the study of extensive air showers.

The effect of the atmospheric refractive index on the radio signal of extensive air showers using Global Data Assimilation System (GDAS)

Abstract Lightning mapping technology has proven instrumental in understanding lightning. In this work we present a pipeline that can use lightning observed by the LOw‐Frequency ARray (LOFAR) radio telescope to construct a 3‐D map of the flash. We show that LOFAR has unparalleled precision, on the order of meters, even for lightning flashes that are over 20 km outside the area enclosed by LOFAR antennas (∼3,200 km2), and can potentially locate over 10,000 sources per lightning flash. We also show that LOFAR is the first lightning mapping system that is sensitive to the spatial structure of the electrical current during individual lightning leader steps.