Unexpected major geomagnetic storm caused by faint eruption of a solar trans-equatorial flux rope
Weilin Teng, Yingna Su, Haisheng Ji, Qingmin Zhang
Abstract
Some geomagnetic storms’ solar origins are ambiguous, making them hard to predict. On March 23, 2023, a severe geomagnetic storm occurred, however, forecasts based on remote-sensing observations failed to predict it. Here, we show clear evidence that this storm originates from the eruption of a trans-equatorial, longitudinal and low-density magnetic flux rope (FR) with weaker coronal emission and no chromospheric signs. The FR’s gentle eruption results in a faint full-halo coronal mass ejection (CME), which is missed by forecasters and not included in CME catalogs. Combining magnetic field modeling and in-situ measurements, we reveal the FR’s southward axial magnetic field as the main cause of the geomagnetic storm. This CME is the stealthiest one reported causing a severe geomagnetic storm. Our study highlights that erupting trans-equatorial FRs can generate major geomagnetic storms in a stealthy way. Characteristic observational signatures of similar eruptions are proposed to help in future forecasts. Geomagnetic storms are common, and a strong one occurred on 23 March 2023. Here, the authors show that it was due to a stealthy solar coronal mass ejection originated from the faint eruption of a trans-equatorial magnetic flux rope.