Casper Rutjes

Probing atmospheric electric fields in thunderstorms through radio emission from cosmic-ray induced air showers

We present measurements of radio emission from cosmic ray air showers that took place during thunderstorms. The intensity and polarization patterns of these air showers are radically different from those measured during fair-weather conditions. With the use of a simple two-layer model for the atmospheric electric field, these patterns can be well reproduced by state-of-the-art simulation codes. This in turn provides a novel way to study atmospheric electric fields.

Influence of atmospheric electric fields on the radio emission from extensive air showers

The atmospheric electric fields in thunderclouds have been shown to significantly modify the intensity and polarization patterns of the radio footprint of cosmic-ray-induced extensive air showers. ...

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.

LOFAR Lightning Imaging : Mapping Lightning With Nanosecond Precision

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.

Adaptive selection of sampling points for uncertainty quantification

textabstractWe present a simple and robust strategy for the selection of sampling points in uncertainty quantification. The goal is to achieve the fastest possible convergence in the cumulative distribution function of a stochastic output of interest. We assume that the output of interest is the outcome of a computationally expensive nonlinear mapping of an input random variable, whose probability density function is known. We use a radial function basis to construct an accurate interpolant of the mapping. This strategy enables adding new sampling points one at a time, adaptively. This takes into full account the previous evaluations of the target nonlinear function. We present comparisons with a stochastic collocation method based on the Clenshaw-Curtis quadrature rule, and with an adaptive method based on hierarchical surplus, showing that the new method often results in a large computational saving.

Discharge inception near dielectric bodies: The Meek criterion revisited

Summary form only given. We study the inception of positive streamer discharges from a sharp dielectric body in a sub-breakdown electric field on the basis of the Meek criterion. The criterion is widely used in the high voltage technology where discharges are to be avoided. We take into account the high non-uniformity of the electric field around the tip of a dielectric particle, which makes it important where an electron avalanche starts and which electric field lines it follows. We also study the influence of the spatial distribution of the initial electrons that start the avalanches. This initial spread of electrons is possible when, for example, the electrons are instantaneously injected around the tip of the dielectric. This finds its application when lightning inception is studied from ice particles in thunderclouds and the initial electrons are produced by highly energetic cosmic particles bombarding our atmosphere. We consider a wide class of dielectric particles of various shapes, sizes, as well as dielectric permittivities and select those that are favorable for discharge inception. We found that the frequency dependence of the dielectric permittivity can significantly slow down discharge development. We complement our phenomenological findings with full timedependent simulations of discharge development in cylindrical geometry.