Small Scale Magnetic Structure in the Induced Martian Ionosphere and Lower Magnetic Pile-Up Region

摘要

Small-scale magnetic structures have been observed in the induced Martian ionosphere by magnetometers onboard the Mars Global Surveyor (MGS) and the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. The origin and evolution of these structures remain poorly understood and the goal of the current paper is to better characterize them and their distribution in the dayside ionosphere using Mars Atmosphere and Volatile EvolutioN (MAVEN) data. Mars Atmosphere and Volatile EvolutioN (MAVEN) Langmuir probe data is used to find thermal pressures in the ionosphere. The structures studied range in size from about 20 km up to a couple of hundred km. We constrain our investigation to the northern hemisphere, dayside Martian ionosphere in order to minimize crustal magnetic field interference. Magnetic pressure spikes (and/or field component variations), along with thermal pressure behavior can also sometimes characterize small-scale structures. In addition to pressures and field components, minimum variance analyses are carried out for each structure in order to help classify them (e.g., horizontal slabs, ionopause-like structures, flux tube and flux ropes). A “statistical” catalog of properties (pressure, field amplitude, ellipticity, width, etc.) is generated for about 1,000 structures. One conclusion we reached from this survey is that slab-like features are more likely to be found than rope-like features for altitudes above 250 km.