An Unusually Disappearing Solar Wind Condition Observed On Both Earth and Mars: Source Region and Its Impact

Abstract

On a few occasions, when the solar wind density near L1 drops by two orders of magnitude for a period exceeding 24 hours, the phenomenon is known as a disappearing solar wind (DSW) event. On 23 December 2022, Solar Orbiter (SolO) and STEREO-A (STA), positioned near 1 AU, detected such a DSW condition with an unusually low solar wind density (Np < 1 cm−3). Two days later, on 25 December 2022, Earth and Mars also encountered the similar DSW condition (Np ∼0.1-0.4 cm−3). In the present study, we investigate the cause of the DSW condition observed by Wind, SolO and STA spacecrafts, respectively. In-situ measurements from the Wind spacecraft revealed that a high-speed solar wind stream was preceded by a trailing rarefaction region, during which the unusually low solar wind density was observed on both Earth and Mars. In contrast, a detailed analysis of Solar Orbiter and STEREO-A data indicates that the low-density condition was caused by the passage of an interplanetary coronal mass ejection (ICME) at 1 AU. Using a velocity trace back method combined with a potential magnetic field computation, we tracked the source region of the DSW event of 25 December 22 on the Earth to the vicinity of an active region (AR 13169), adjacent to a coronal hole (CH) complex. Further, using Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) data from the Solar Dynamics Observatory (SDO) and the dynamic radio spec-trograph observations, the dynamical evolution of the AR-CH complex was investigated, which revealed the emergence of new photospheric magnetic structures, a plasma jet eruption in the corona hole with the subsequent reduction in the coronal hole area. Based on the results, we proposed a plausible explanation for the DSW condition observed both on Earth and Mars. As a result of the DSW condition, there was a significant expansion of the magnetopause and bow shock stand-off distances at both Earth and Mars. The study elucidate the distinct solar and interplanetary origins of the DSW condition and its significant impact on Earth and Mars.