Escape of ions from Earth under various magnetospheric conditions

Atmospheric loss processes together with sources and sinks at the surface govern the evolution of the atmospheric composition. At present-day Earth, the main dominant escape process is polar wind, which predominantly removes ionized oxygen atoms from the polar regions of the Earth. Although a multitude of observations that cover atmospheric escape for different activity conditions of the Sun exist, theoretical and numerical aspects of the polar outflow are still not entirely understood.

 

In this work, we investigate the role different magnetospheric conditions play in governing the polar wind escape rates from the Earth. We use the Space Weather Modeling Framework and the BATS-R-US code to determine the magnetospheric structure in the polar areas of the Earth for quiet and storm conditions. The code output includes the configuration of the magnetic field in the vicinity of an exoplanet (using the Solar Corona and Inner Heliosphere modules) for a given stellar magnetic field and plasma parameters in the vicinity of the planet. The code offers significant flexibility and allows to study a wide range of quiet and storm conditions.

 

Using the magnetic and electric fields distributions calculated with the SWMF, we apply the test particle approach to track individual ions along the magnetic field lines and collect static on atmospheric ions that are lost. Depending on their energy, cold ions can end up in different regions of the magnetosphere, such as the magnetopause, the distant tail, and the ring currents, or fall down to the atmosphere. The idea of the test particle approach is to numerically calculate the trajectory of independent and non-interacting charged/uncharged particles, where external forces are well known. Particularly, for applications of the test particle approach for planetary magnetospheres it is common to use the magnetic and electric fields from global models such as the SWMF. To obtain a general picture of the percentage of particles that escape, we will study multiple test particles with different parameters such as initial energies, locations, and pitch angles (that can be inferred from the DSMC model) to accumulate statistics. As a result, we will obtain the distribution of locations, speeds and final destinations of ions in magnetospheres and/or ionospheres of planets. One of the main advantages of the test particle approach is that it avoids very expensive calculations (in terms of computational time and computer resources) and at the same time can reproduce the main features of the studied phenomena.

 

We show that magnetospheric parameters together with the current solar conditions play an important role for atmospheric escape. We discuss the influence of atmospheric loss processes on the Earth’s atmosphere over it’s history, and discuss the importance of preexisting modeling for stellar missions such as the SMILE satellite (Solar wind Magnetosphere Ionosphere Link Explorer).