(SHeI-Ra) Solar, Heliospheric and Ionospheric Radio
The Low-Frequency Array (LOFAR) is a new-generation radio telescope currently dedicated to scientific research. Its design as a “software telescope” allows tremendous flexibility beyond its primary remit as a radio imager for radio astronomy purposes, such as making high-resolution dynamic spectra of pulsars or the Sun, and simultaneous observations in time, frequency, and sky coverage.
LOFAR has 52 stations across Europe, with its core located in the Netherlands; it operates at frequencies between 10 and 240 MHz. LOFAR allows us to follow Space weather events from the Sun through the heliosphere into the ionosphere. LOFAR detects the emission from radio bursts at the Sun with exceptional sensitivity and high time and frequency resolution; heliospheric measurement through the distortion of the light of astronomical radio sources as their light passes through the solar wind, e.g., density measurement through the dispersion of polarized light from pulsars; ionospheric disturbances also distort the light from radio sources, observed as scintillation in dynamic spectra recorded at the individual LOFAR stations all over Europe. As such, LOFAR is sensitive to scintillation at mid latitudes at low frequencies.
In the previous activity, several products based on the utilization of LOFAR capabilities have been developed and presented. The main focus of the current activity is to demonstrate these products in a campaign simulation, and gather feedback from potential end users.
Figure 1: LOFAR core in Exloo (the Netherlands)
Demonstration of an extended set of dynamic spectra of the Sun, including an automatic detection catalogue with the list of radio bursts (type III) with duration and frequency drift.
An investigation of a method for automatic classification of detected radio bursts using machine learning techniques.
Demonstration of scintillation spectra of bright radio sources at different stations plus associated pierce-points through the ionosphere at a fixed altitude. Derived amplitude scintillation parameter at a range of frequencies between 30 and 80 MHz
An investigation of correlation of LOFAR scintillation parameters with those from higher Global Navigation Satellite System (GNSS) frequencies as well as of correlation with disrupting High Frequency (HF) events.
Figure 2: Example of a dynamic spectra. A series of solar type III radio bursts are displayed
Creation of time series of heliospheric column density of free electrons derived from pulsar observations.
Demonstration of the usefulness of such products for the validation of space-weather software such as EUHFORIA.
The study is being undertaken by a team of space weather scientists and radio astronomers with expertise in the Heliosphere, the Ionosphere, and the Sun. The project also includes feedback from expert end users, and the Expert Service Centers (ESCs) coordinators of the ESA Space Weather Service Network.
Figure 3: Example of a time series of electron column density obtained from observations of pulsar J0034-0534 carried out with 4 international LOFAR stations. The electron column density is parametrized with the 'dispersion measure' prox (from Tiburzi et al. 2019)