Research Article

Global occurrences of whistlers detected in the Extremely Low Frequencies during Absolute Scalar Magnetometer burst mode acquisition campaigns of the Swarm mission

Université Paris Cité, Institut de physique du globe de Paris, CNRS, 75005 Paris, France

^* Corresponding author: coisson@ipgp.fr

Received: 15 May 2025
Accepted: 14 October 2025

Abstract

The Absolute Scalar Magnetometer (ASM) of the Swarm satellites acquired data at 250 Hz during monthly one-week campaigns that started in 2019. We process these data to detect and characterise whistler signals in the Extremely Low Frequencies (ELF). Whistler data are now distributed as a Level 2 scientific product of the mission. The corresponding files include whistlers’ characteristics: Their dispersion, their intensity, and the estimated time when these signals entered the ionosphere. This data set contains more than 100,000 whistler events. Global statistics of whistler occurrences between 2019 and 2024 reveal their geographical, local time, seasonal, and solar activity dependencies. Whistlers in ELF occur predominantly during the night at low latitudes, with a depletion close to the magnetic equator. During the rising phase of the solar cycle, an increasing number of whistlers is observed at night, whereas no influence of the solar cycle is observed during the daytime.