Natural Orthogonal Component Analysis of Daily Magnetic Variations at the Martian Surface: InSight Observations

Abstract

AbstractDistinguishing different sources of magnetic field variations at InSight is important to understand dynamic processes in the Martian ionosphere as well as the coupling between the solar wind and the Martian induced magnetosphere. Recent studies based on magnetic field measurements from InSight have suggested that the daily and seasonal variations in the magnetic field at the Martian surface are at least partially the result of neutral wind‐driven ionospheric dynamo currents and their seasonal variations. However, the sources of the daily variations with different time scales need be further investigated. In this paper, magnetic field variations in a sol as well as during nearly a whole Martian year from InSight observations were decomposed into their natural orthogonal components. We found that the first eigenmode shows the previously identified early to midmorning peak, and varies with season. This corresponds to the solar quiet variations. The second and higher eigenmodes manifest the quasi‐Carrington and sub‐Carrington rotation periodicity represent disturbed components that may be stimulated by variations in the draped interplanetary magnetic field and/or the Martian ionospheric electron density. Different from their counterparts at the Earth, the amplitude of the first eigenmode is comparable with the sum of second to fifth ones, showing that the quiet and disturbed diurnal variations contribute similarly to the total diurnal variation. Decomposition of Martian surface magnetic field variations could provide monitoring of the Martian ionospheric current system as well as the solar wind conditions in the near‐Mars space, which will be greatly enhanced when combined with Zhurong Martian surface field measurements in the future.