Quiet Time Structured Pc1 Waves Generated During Transient Foreshock

Abstract

We study two events of structured Pc1 waves (pearls) observed by CARISMA magnetometers during a period of quiet magnetic (Kp~1) and solar wind conditions on 1 August 2008. Bursts of proton precipitations and electromagnetic ion-cyclotron waves were simultaneously observed by NOAA/POES and GOES satellites at dayside. Apparent correspondence was found between ground pearl pulsations and magnetospheric compressions observed by GOES and THEMIS satellites. We have found the Pc1 wave splitting into very close subfrequencies (within 0.1 Hz) that can be explained by weak magnetospheric compressions. The compressions are caused by pressure pulses originated from transient foreshock and interplanetary magnetic field discontinuities observed upstream of the bow shock by the THEMIS-C probe. Thus, the observed pearls are compression-related Pc1 waves generated under transient foreshock conditions.

Interhemispheric Observations of ULF Waves Caused by Foreshock Transients Under Quiet Solar Wind Conditions

“…There have been several studies that discuss the possible relationship between foreshock transients and ground Pc1 activities (Engebretson et al, 2013;Posch et al, 2013;Suvorova et al, 2019). Our study reports unique and clear observational characteristics which are distinct from previous studies.…”

“…There have been several studies that discuss the possible relationship between foreshock transients and ground Pc1 activities (Engebretson et al., 2013; Posch et al., 2013; Suvorova et al., 2019). Our study reports unique and clear observational characteristics which are distinct from previous studies. We found that there were at least 3 events (events 1, 4, and 5 or 6) showing ∼8 min time delay between space FT observations and ground Pc1 wave observations. Waves were observed in both hemispheres in the high‐latitude region. During the entire event period, no inner magnetospheric EMIC waves were observed by spacecraft, such as Van Allen Probes, THEMIS, and GOES13 (Figure ). Wave observation times were slightly different between the hemispheres.…”