Detection and Energy Dissipation of ULF Waves in the Polar Ionosphere: A Case Study Using the EISCAT Radar.

Ultra‐low frequency (ULF) waves transfer energy and momentum into the ionosphere‐thermosphere system. To quantify this energy, this paper first presents a new method to quantitatively detect ULF waves in Incoherent Scatter Radar (ISR) data based on 2D fast‐Fourier transforms and subsequent reconstruction of the wave. In parallel with other data sets, including optical, magnetometer, satellite, and models, we present the first full ionospheric energy dissipation rates for a ULF wave, split into electromagnetic (EM) and kinetic fluxes. The EM energy deposition is calculated from the use of the Poynting theorem, looking at Joule and frictional heating rates, where both rates show the same order of magnitude (1.24 × 1013 and 7.3 × 1012 J) respectively when integrated over the wave lifetime of 2 hr 15 min and an area of 4° magnetic latitude × 74° magnetic longitude. However, contrary to the common assumption that the EM flux is dominant, we determined the kinetic flux, to be almost equal in magnitude (8.7 × 1012 J). This indicates that previous papers might have underestimated the total energy dissipation by ULF waves. Compared to the substorm energy budget, we find that locally, the ULF wave event studied here makes up approximately 10% of a typical substorm cycle budget. Plain Language Summary: The Earth's magnetic field lines can move back and forth regularly, like waves on a guitar string. When this happens on the time scale of minutes, we call these ultra‐low frequency (ULF) waves. ULF waves play an important role in the transfer of energy from the Earth's magnetic field to the Earth's upper atmosphere. In this study, we developed a new method to detect ULF waves in radar data to obtain information about the wave. By combining several data sets, such as radar, optical, satellite, and magnetic field measurements, we were then able to determine how much energy is being transferred in one ULF wave event. Both electromagnetic and kinetic energy are important in this transfer of energy. Key Points: We present a new method to detect and reconstruct ULF waves in ISR data with a 2D fast‐Fourier transformWe estimate ionospheric energy dissipation rates due to EM and kinetic energy sources using the new methodWe find that kinetic and EM energy rates are of similar magnitude and should both be included in ionospheric energy deposition by ULF waves [ABSTRACT FROM AUTHOR]