Properties of Stream Interactions and Their Associated Shocks near 1.52 au: MAVEN Observations

Abstract

The measurements from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft are analyzed for the basic properties of solar wind stream interaction regions (SIRs) and their associated shocks at 1.52 au, as well as the evolution of SIRs from 1 to 1.52 au. A total of 149 SIRs are identified during the period from 2014 October to 2018 November, and 126 SIRs with high-quality data are selected for this study. The average occurrence rate of SIRs at 1.52 au is 36.3 yr−1, which is comparable to but slightly higher than that (32.4 yr−1) at 1 au, meaning that most SIRs are well formed at 1 au. The average duration of SIRs at 1.52 au is about 37.0 hr, comparable to that at 1 au (36.73 hr), indicating that SIRs have not yet expanded more rapidly as they are convected to 1.52 au. The maximum magnetic field strength and pressure of SIRs decrease significantly from 1 to 1.52 au. The shock association rates of SIRs increase from 20.3% to 33.3% or higher as SIRs evolve from 1 to 1.52 au. The forward shocks tend to occur twice more frequently than the reverse shocks. About 75% of shocks at 1.52 au are quasi-perpendicular shocks. The strength of the shocks becomes weaker and the average shock speed remains almost unchanged from 1 to 1.52 au. These results will help us understand the solar wind conditions at Mars and their potential impact on the Martian space environment.

Properties of stream interaction regions at Earth and Mars during the declining phase of SC 24

“…The catalogs given by Grandin et al (2019) and Huang et al (2019) are used for identification of time ranges covering SIRs and/or CIRs at Earth and Mars, respectively. The time intervals of the events are extracted from these catalogs and applied to the respective spacecraft data to determine the corresponding SW parameter profiles.…”

“…The fast SW propagates freely with its characteristic high speed in the rarefaction region following the SIR. CIRs and SIRs may develop forward or reverse shocks (or both) as they expand through the heliosphere (e.g., Jian et al 2006;Huang et al 2019).…”

“…To select the data measured during the solar wind intervals, Halekas et al (2017) developed an algorithm based on the SWIA aboard moments data and MAG measurements to extract solar wind quantities over the upstream segment of each MAVEN orbit. Lee et al (2017) and Huang et al (2019) studied SW events (i.e., SIRs/CIRs and coronal mass ejections) at Mars using MAVEN data, also comparing individual events to those measured at Earth. However, the statistical comparison of a larger sample of events measured both at Earth and Mars is still missing.…”

Radiation environment for future human exploration on the surface of Mars: the current understanding based on MSL/RAD dose measurements

“…SIR properties at Mars Recently, Huang et al (2019) have used the MAVEN measurements during the period from October 2014 to November 2018 and identified 149 SIRs and their associated shocks at Mars. Geyer et al (2021) further analyzed these events comparing in-situ solar wind data at Earth and Mars using as well the remote sensing image of the Solar coronal holes.…”

“…Furthermore, the radial evolution of the CIR needs to be taken into account. For instance, the occurrence of shocks has been evaluated to be more frequent at 1.5 au while the shock strength becomes weaker at Mars (Huang et al 2019;Geyer et al 2021), and the SIR structure tends to expand at larger heliospheric distances (e.g., Gosling and Pizzo 1999). The radial evolution of the SIR and how this affects the corresponding GCR depression is still an open question.…”