Magnetic Local Time and Latitude Distribution of Ionospheric Large‐Spatial‐Scale EMIC Wave Events: Swarm Observations

Abstract

In the present work, the magnetic local time and latitude (MLT and MLat) distributions of ionospheric large‐spatial‐scale (>20° MLat) electromagnetic ion cyclotron waves were investigated using high‐resolution 50‐Hz geomagnetic field data from Swarm A and B satellites. Both parallel and transverse waves were studied in a comparative manner for different geomagnetic activities and seasons. Frequent occurrences of large‐spatial‐scale waves in the South Atlantic Anomaly and North America, where the parallel waves propagate over the longest distance, were observed. Waves appear mostly in the 02–10 MLT sector wherein the pre‐noon parallel waves propagate farthest in latitudinal range. With the enhancement of geomagnetic activity, both transverse and parallel waves increase in occurrence. The dayside occurrence rate is higher during weak geomagnetic activity, whereas the situation is reversed on the nightside and duskside. The dayside waves are located outside the mid‐latitude trough, and the nightside waves are located near (inside) the equatorward boundary of the mid‐latitude trough. Large‐spatial‐scale waves tend to occur at the equinoxes when the absolute value of the dipole tilt angle is less than 10°, while the long‐distance transmission in the waveguide occurs in the pre‐noon in summer. Parallel waves propagate in the region where the electron density is higher than that of the transverse waves. There is a close relationship between EMIC wave and electron density oscillation.

Distinguishing Electromagnetic Ion Cyclotron (EMIC) Waves From Other Pc1 Signatures in Satellite Recordings by Means of the Swarm Satellite Constellation

“…In a number of publications authors relate Pc1 oscillations, observed by LEO satellites, to EMIC waves (e.g., Kim et al., 2020, 2021; Wang, He, & Lühr 2022; Wang, Sun, et al., 2022; Wang et al., 2019, 2021). All of their results are based on single‐satellite recordings, which do not allow to resolve the spatial/temporal ambiguity.…”

“…We investigated further published EMIC events such as the one on 29 March 2015 from Wang, Sun, et al. (2022). From the spectrogram in Figure 12 wave activity around 1 Hz can be seen in the northern and southern hemispheres.…”

“…Common observability in the ionosphere and on the ground requires long wavelengths, of the order of 1,000 km. During subsequent years many more studies appeared (mainly based on Swarm B‐field data) that interpreted the LEO Pc1 recordings as ionospheric signatures of EMIC waves (e.g., Kim et al., 2020, 2021; Wang, He, & Lühr 2022; Wang, Sun, et al., 2022; Wang et al., 2019, 2021).…”

Transpolar Pc1 Wave Ducting: Swarm, DMSP, and Ground Observations

“…As ducted Pc1 waves can be attenuated, their sustainability (or travel distance) depends on the amplitude of the incident transverse wave and the structure of the ionospheric plasma which plays a major role in the transmission of Pc1 waves. Ducted Pc1 waves can transfer thousands of kilometers through the ionospheric waveguide, and they are observed by magnetometers on both ground and low Earth orbit satellites over a wide latitudinal range (Kawamura et al., 1981; Kim, Shiokawa, Park, Miyoshi, Miyashita, et al., 2021; Kim et al., 2010, 2011, 2018, 2020; Pisa et al., 2015; Wang et al., 2022).…”

“…Hence, it is worth studying whether ducting can expand from the auroral oval into the polar cap when the plasma density is sufficient. Also, (b) previous studies just addressed 1‐dimensional features of ionospheric ducting along the satellite track (e.g., Wang et al., 2022) or magnetic meridian on the ground (e.g., Kim et al., 2010). Although a theoretical study predicted that the ducting is most efficient in the magnetic meridian (Greifinger & Greifinger, 1973), this expectation has not yet been thoroughly tested observationally.…”