Atmospheric escape of cold ions from the current and early Earth under different magnetospheric conditions

Escape to space of thermal ions which originate in the Earth's ionosphere is still poorly understood. The dominant loss process from the modern Earth is a non-thermal escape mechanism called the polar wind, which is currently dominated by ionized oxygen. The oxygen ions are accelerated by various physical processes, such as electric fields and wave-particle interactions, and escape to space from the polar regions. I present the new test-particle code KISEL (KInetic Simulator of Escaping Light ions), which can reproduce the main features of the cold polar outflow from the Earth and can be applied to other planets. We can reproduce the typical observed range of O⁺ loss rate from the Earth of 10²⁴-10²⁶ s^-1 depending on solar activity. We model the escape during the Gannon storm and obtain a range of escape rates typical for high kp-index conditions. We show that the ambipolar electric field plays a decisive role in uplifting the cold ions and allowing them to escape, and confirm previous findings that only a minor fraction of cold ions produced in the whole ionosphere escape to space (approximately 2\% of oxygen ions for typical quiet conditions). To study the parallels between the present-day Earth and the early Earth, we also simulate the ion escape from the Earth at the age of approximately 300 million years. We show that, first of all, the dominant escape ion is C⁺ and not O⁺ like today, and second, that a much higher fraction of initially cold ions (approximately 20%) can escape to space.