We will long remember the exceptional solar storm of May 10^th which generated intense northern lights even at mid-latitudes, painting Italian skies red. This phenomenon was not directly related to the entry of solar particles through the Earth’s magnetic poles (thus not a true aurora borealis at our latitudes) but rather linked to the intensification of the Van Allen currents around the equator. Only two months earlier, on March 24, 2024, another solar storm had reached the Earth, causing significant radio disturbances and generating gorgeous northern lights.

The amazing phenomenon was also observed by the EEE Project telescopes, that measure the flux of muons, generated by cosmic rays, that reach the Earth’s surface. Cosmic particles, mainly protons, are deflected by Earth’s magnetic field as they approach. Some of these particles manage to penetrate and interact with the upper atmosphere, creating showers of particles, including muons, which can reach the surface.

During a solar storm, the Sun emits large amounts of plasma from its corona: charged particles that interact with planetary magnetic fields and can reach Earth within a few days. One observable effect is the increase of the shielding effect, preventing cosmic rays from reaching the Earth’s atmosphere. The resulting descrease of muon flux measured at ground is known as the Forbush effect, named after Scott Forbush, the American physicist who studied cosmic rays in the mid-20th century.

The three EEE telescopes, named POLA-R and installed in 2019 at the Arctic research base of Ny Ålesund in Svalbard (79° North latitude), clearly observed both phenomena. The muon telescopes, also built by students, use different technology from school telescopes: they consist of two planes of scintillating material coupled with silicon photomultipliers (SiPM).

Just a few weeks ago, a group of EEE researchers visited Svalbard, hosted at the Dirigibile Italia base of the CNR Institute of Polar Sciences, to perform maintenance on the telescopes and ensure the detectors operations.

The data acquired are currently being analyzed by the researchers of the EEE Collaboration: measurements at these latitudes are very rare, and the length of the time series (five years) allows interesting studies on periodicities that can reveal the nature of cosmic ray sources.

cover image: The installation sites at Ny Ålesund