On the Source of the Anomalous ULF Waves Detected at Both Ground and Space‐Borne Data on 23 June 2020

Abstract

We have analyzed a highly monochromatic (f = 1.67 mHz) and large‐amplitude Ultra Low Frequency (ULF) wave event observed at satellites and ground observatories on 23 June 2020 during super solar quiet geomagnetic conditions. The train wave was detected between 6:22 and 7:55 UT across a wide longitudinal range of ground stations from low to high latitudes. Using Deep Space Climate Observatory and THEMIS‐B spacecraft, which were in the interplanetary medium, we have identified the possible driver of such global ULF wave activity in the impact of a small pressure pulse accompanied by a discontinuity in the magnetic field. The prolonged duration (90 min) of the ULF waves as well as their latitude‐independent frequency and the small azimuthal wave number (m ∼ 0−2) can be explained in terms of a global magnetospheric waveguide mode. The amplitude and cross‐phase analysis of the wave activity at ground, together with the polarization pattern, suggest the waveguide mode coupling with field line resonance. Nevertheless, during the same time interval, indirect evidence exists of a rapid reconfiguration of the magnetotail in the form of Pi2 waves in the night‐side region. The analysis of energetic particle flux at ionospheric height (500 km) shows a direct connection between the ULF wave activity and particle precipitation.

Solar-wind/magnetosphere coupling: Understand uncertainties in upstream conditions

“…In such conditions, the solar wind upstream conditions based on a single spacecraft might not be enough to correctly interpret the magnetosphere response missing the inherent variability of the solar wind, either due to en route processes or its formations at the Sun (Viall et al, 2021). For example, different physical processes can occur on different sides of the Earth's magnetosphere (Kessel et al, 1999;Nykyri et al, 2019) or observations from a single L1 monitor may not represent the actual upstream conditions [e.g., dusk-dawn aberrations of the solar wind plasma and magnetic structure approaching Earth (Borovsky, 2022c)], leading to misinterpretation of the magnetosphere response (Piersanti et al, 2022;Villante et al, 2022).…”

“…In fact, there are a variety of processes that can affect solar wind plasma upstream of the magnetopause interaction region. They include foreshock bubbles, hot flow anomalies, mirror mode waves, cavitons, and high-speed jets (Zhang et al, 2022). Even when an L1 monitor measures very steady solar wind values, the plasma that impacts the Earth's magnetosphere can be highly variable.…”

A Large‐Scale Magnetospheric Line Radiation Event in the Upper Ionosphere Recorded by the China‐Seismo‐Electromagnetic Satellite

“…In recent decades, with the successful operation of satellites in low earth orbit (LEO) space, many types of electromagnetic (EM) waves in the ULF/ELF/VLF (Ultra/Extreme/Very low frequency) range get well recorded in the ionosphere: for example, the most commonly observed ionospheric hiss waves (e.g., Chen et al., 2017; Xia et al., 2019; Zhima et al., 2017), the occasionally appearing chorus waves (e.g., Cao et al., 2005; Santolík et al., 2006; Zhima et al., 2013), the quasiperiodic waves (e.g., Němec, Bezděková, et al., 2016; Zhima et al., 2020), the low noise emissions (e.g., Němec, Parrot, & Santolík, 2016; Parrot et al., 2016), the magnetospheric line radiation (e.g., Němec, Parrot, & Santolík, 2012; Němec, Santolík, et al., 2012), the power line harmonic radiation (e.g., Parrot et al., 2007), or the geomagnetic pulsations (e.g., Piersanti et al., 2022; Zhima et al., 2020), etc.…”

Substorm Induced Nighttime Plasma Flow Pulsations Observed by ROCSAT‐1 at Topside Ionosphere

“…Ultralow frequency (ULF) geomagnetic pulsation phenomena in the Earth magnetosphere have been studied for decades theoretically, and observed experimentally with space‐borne instruments, ground magnetometers, and ground radars. The results have been reviewed in many reports published in the literature (see, e.g., Hynönen et al., 2020; Jacobs, 1970; Piersanti et al., 2022; Olson, 1999; Orr, 1973; Saito, 1969; Southwood & Hughes, 1983; Yumoto, 1986; Samson, 1991). The cause of ULF pulsations come from a disturbance on the dayside magnetopause or a Kelvin‐Helmholtz (KH) instability induced disturbance that propagates with a magneto‐hydrodynamic (MHD) fast wave speed across the magnetosphere radially toward the ionosphere (Engebretson et al., 1987, 1988; Greenstadt et al., 1983; Kim & Takahashi, 1999), or azimuthally along the flanks of the magnetosphere (Claudepierre et al., 2008; Liljeblad et al., 2016).…”

“…The C/NOFS (Communication/Navigation Outage Forecasting System) observations show the ULF fluctuations in the low‐latitude ionospheric electric field during the sudden commencement on 8 March 2012 (Zhang et al., 2022). The magnetometer onboard Swarm‐A satellite observed the ULF wave activity at low altitudes on 23 June 2020 (Piersanti et al., 2022).…”