Characteristics of a Gradual Filament Eruption and Subsequent CME Propagation in Relation to a Strong Geomagnetic Storm

Abstract

An unexpected strong geomagnetic storm occurred on 2018 August 26, which was caused by a slow coronal mass ejection (CME) from a gradual eruption of a large quiet-region filament. We investigate the eruption and propagation characteristics of this CME in relation to the strong geomagnetic storm with remote sensing and in situ observations. Coronal magnetic fields around the filament are extrapolated and compared with EUV observations. We determine the propagation direction and tilt angle of the CME flux rope near the Sun using a graduated cylindrical shell (GCS) model and the Sun-to-Earth kinematics of the CME with wide-angle imaging observations from STEREO A. We reconstruct the flux-rope structure using a Grad-Shafranov technique based on the in situ measurements at the Earth and compare it with those from solar observations and the GCS results. Our conclusions are as follows: (1) the eruption of the filament was unusually slow and occurred in the regions with relatively low critical heights of the coronal field decay index; (2) the axis of the CME flux rope rotated in

A Peculiar ICME Event in August 2018 Observed With the Global Muon Detector Network

“…The pink vertical line indicates the timing of IP‐shock identified by the shock of IMF at 03:00 UT on 25 August, while a pair of blue vertical lines delimit the MFR period reported by Chen et al. (2019). The blue shaded area indicates 6 h between 03:00 UT and 09:00 UT on 26 August when an increase is observed in the cosmic‐ray density (see Figure 2a and Section 4).…”

“…Since Chen et al. (2019) reported that the MFR in Figure 1 is left‐handed and its mean magnetic field directs southward, the theory predicts cosmic rays to enter the MFR at the southern leg and exit at the northern leg, resulting in a negative (north directing flow) at Earth's orbit. However, the observed in Figure 2b (red curve) is positive (south directing flow) during the blue shaded period, in contradiction to the prediction.…”

“…10.1029/2020SW002531 3 of 14 Chen et al (2019). The blue shaded area indicates 6 h between 03:00 UT and 09:00 UT on 26 August when an increase is observed in the cosmic-ray density (see Figure 2a and Section 4).…”

“…From top to bottom, each panel shows 1-min solar wind parameters; (a) magnitude of solar wind velocity (black curve) and "flow angle" of solar wind (ϕ SW = tan −1 (V y /|V x |) (blue curve), (b) proton density (black) and temperature (blue), (c) IMF magnitude (black) and its fluctuation (blue), (d) GSE-longitude (black) and latitude (blue) of IMF orientation, (e) GSM-z component of IMF (blue) and hourly value of the D ST index (black). The pink vertical line indicates the timing of IP-shock identified by the shock of IMF at 03:00 UT on 25 August, while a pair of blue vertical lines delimit the MFR period reported byChen et al (2019). The blue shaded area indicates 6 h between 03:00 UT and 09:00 UT on 26 August when an increase is observed in the cosmic-ray density (see Figure2aand Section 4).…”

First Observation of Ionospheric Convection From the Jiamusi HF Radar During a Strong Geomagnetic Storm

“…The NOAA Space Weather Prediction Center classified this storm as a strong G3 geomagnetic storm. Caused by a weak coronal mass ejection during solar minimum, the unexpected strong geomagnetic storm was attributed to the enhanced magnetic field with a persistent southward IMF (Chen et al, ).…”