Local time and longitudinal differences in the occurrence frequency of ionospheric EMIC waves during magnetic storm periods

Abstract

<div><span>The spatial and temporal distributions of ionospheric electromagnetic ion cyclotron (EMIC) waves during magnetic storms from 2014 to 2018 were studied using Swarm observations. Ionospheric EMIC waves preferably occurred during storms and their recovery phases at subauroral regions within an average magnetic latitude of 40°-55°. There were more wave events during more intense and longer period storms. However, the correlation between event number and storm duration was not good. This might be due to the effect of heavy oxygen ions on EMIC wave generation and the loss of ring current high-energy ions by the EMIC waves. There are obvious magnetic local time (MLT) differences in the peak occurrence frequency of EMIC waves during storm phases. The enhanced solar wind dynamic pressure was favorable for duskside EMIC waves. With an increased substorm activity the wave occurrence rate peak shifted from the morning side to the dusk-premidnight sector. During the recovery phase of a storm, EMIC waves in the 12-24 MLT sector appeare preferably in the earlier part than those in the 00-12 MLT sector. This shift in local time is related to the eastward rotation of the plasmaspheric plume towards morning during the late storm recovery phase and its overlap with the ring current.  Highest occurrence frequency of the storm time EMIC waves could be found in the South Atlantic Anomaly region, which might be related to the drift shell splitting </span></div><div><span>and the wave propagation effect </span><span>in the weak magnetic field region</span></div><div><span>.</span></div>

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

“…The rate is higher at the equinoxes, which might be related to the higher magnetic activity during these seasons. The occurrence rate of magnetospheric EMIC waves increases during higher magnetic activities (Erlandson & Ukhorskiy, 2001; Kim, Shiokawa, Park, Miyoshi, Stolle et al., 2021; Wang et al., 2021). To further validate this result, Figure 9 shows the distribution of large‐spatial‐scale transverse waves and parallel waves with magnetic local time and magnetic latitude under two different dipole tilt (DPT) angle conditions (|DPT| < 10° and |DPT| ≥ 10°).…”

“…Wang et al. (2021) studied the spatio‐temporal distribution characteristics of EMIC waves during magnetic storms using observational data from the Swarm satellites over the years 2014–2018. They showed that the peak occurrence rate of the storm‐time EMIC waves was approximately 4%.…”

“…If the number of wave signals exceed half the number of signals in the frequency range, we remove the signal at the corresponding time. Finally, the following event selection criteria are used (Kim, Hwang, Park, Bortnik, & Lee, 2018; Wang et al., 2021): the EMIC propagation range is larger than 20° MLat, the frequency band width is >0.15 Hz, and the peak wave power density is larger than 10 −7 nT 2 /Hz.…”

“…With the enhancement of geomagnetic activity, the peak occurrence rate of EMIC waves moves from pre‐noon to post‐noon (Saikin et al., 2016; D. Wang, Yuan et al., 2015; H. Wang, Ridley, & Zhu, 2015), and the peak occurrence rates of different wave bands appear at different local times (Saikin et al., 2015). Using the electromagnetic field observations from low Earth orbit satellites, previous studies investigated the local time distribution of ionospheric EMIC waves and disclosed that the incident waves mainly occurred in the morning sector during quiet periods and they were concentrated on the duskside and nightside during geomagnetic disturbance periods (Kim, Hwang, Park, Bortnik, & Lee, 2018; Park et al., 2013; D. Wang, Yuan et al., 2015; H. Wang, Ridley, & Zhu, 2015; H. Wang et al., 2021).…”

“…EMIC waves occur frequently during geomagnetic disturbance periods (Erlandson & Ukhorskiy, 2001; Wang et al., 2021). Whether EMIC waves occur frequently in the main phase or recovery phase of geomagnetic storms remains controversial (Halford et al., 2010; Kim, Hwang, Park, Bortnik, & Lee, 2018; Saikin et al., 2016; Wang et al., 2016, 2019).…”