Characteristics of Ultra Low Frequency Plasma Waves Near the Moon

Abstract:

Lacking a global magnetic field and atmosphere to protect it from the solar wind, the Moon instead has smaller magnetic fields that are embedded in the lunar surface. These crustal magnetic fields reflect a portion of the incoming solar wind ions. The ions that are reflected can then interact with the plasma around the Moon and drive plasma waves. In particular, these reflected ions are thought to generate plasma waves with a frequency around 0.01 Hz. Due to the solar wind, observations of waves with these low frequencies can be heavily Doppler shifted making it difficult to determine their intrinsic properties. In addition, solar wind and magnetic field conditions can influence the generation of these waves. To gain a better understanding of the intrinsic properties of these ultra low frequency waves, we combine in situ observations of the waves with ion tracing simulations. Results support that these waves are intrinsically right hand polarized. We also use a combination of observations and simulations to examine the influence of the solar wind and interplanetary magnetic field (IMF) on these waves. Our results indicate that these ultra low frequency waves are more likely to be observed during certain solar wind and IMF conditions.