Statistical Properties of Hot Flow Anomalies around Mars

Hot flow anomalies (HFAs) are not only a terrestrial, but also a solar-system-wide phenomenon that could cause strong perturbations of the planetary magnetosphere and ionosphere. Based on the observations of Mars Atmosphere and Volatile EvolutioN (MAVEN) upstream of the Martian bow shock from 2014 to 2020, we have investigated the statistical properties of HFAs around Mars in this study. Our observation results show that HFAs can distribute in a wide region from the dayside to the terminator region of Mars. On average, these HFAs can last 63 seconds and have a thickness of 28 local proton gyroradii. They are more prevalent when the ambient solar wind is denser and faster. HFAs occur most preferentially for IMF magnitude from 1-4 nT. Most of HFAs around Mars are formed during the interaction between tangential discontinues and the bow shock. Heavy ions originating from Mars do not appear to affect the formation of HFAs. Martian HFAs can lead to tens of times variations of solar wind dynamic pressure only in tens of seconds, which could strongly influence the heights of Martian ionopause and induced magnetosphere boundary.