On the unexpected geomagnetic storm on june 8, 2019, and the heliospheric current sheet effect

Abstract

A period of minimum magnetic solar activity (such as June 2019) favors the observation of rare solar transient events, which would otherwise be lost in the magnetic vortex during a period of maximum solar activity. In this paper, we show that the most plausible explanation for the origin of an unexpected geomagnetic storm on June 8, 2019, is a small CME, ejected at low speed into a broad tube of an HCS on June 3, 2019, from an active region on the backside of the sun, and only detected by the STEREO Ahead Cor 2 probe. The magnetic entrapment of the flux-rope and the ejecta bulk, within the co-rotating HCS (already observed with other small slow CMEs), may be responsible for the large longitudinal deflection of this CME. Several remote observations, from the SECCHI and IMPACT instruments onboard STEREO-A, as well as the predictions of several heliospheric models, favor this scenario. We report the details of these observations.