Plasma Convection in the Terrestrial Magnetotail Lobes Measured Near the Moon's Orbit

Abstract

In order to study the plasma convection in the deep magnetotail lobes near lunar orbit, we investigated ions originating from the tenuous exosphere and surface of the Moon, which are measured by the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) spacecraft. Directly measuring the plasma convection in the tail lobes is difficult, due to the typically large positive spacecraft potential. In this work we show that in the terrestrial magnetotail near the Moon, the convection velocity can be estimated by measuring the velocity of lunar ions. Determining what factors control the lobe convection is important in understanding the linkage between the upstream conditions and the dynamics of the tail lobes. Based on systematic analysis of multiple ARTEMIS observations and OMNI data, we find that the interplanetary magnetic field (IMF) and magnetospheric activity plays an important role in controlling plasma convection in the near-Moon lobes. Plain Language Summary Studying the plasma convection is important for us to understand the magnetospheric dynamics. We used the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun spacecraft to investigate the convection pattern in the terrestrial magnetotail lobes near the Moon's orbit, by analyzing the motion of lunar ions. Combined with the solar wind data and the magnetospheric activity index, we found that the magnetospheric convection near the Moon's orbit may be influenced by the upstream solar wind. This technique provides a useful method to estimate the plasma motion in a tenuous space environment.

ARTEMIS Observations of Lunar Nightside Surface Potentials in the Magnetotail Lobes: Evidence for Micrometeoroid Impact Charging

“…Between the dusk terminator (  90 ) and midnight (  180 ), the distribution and median values lie only slightly below unity (median ratio  0.8), indicating that the surface charging theory describes the data generally well. The slight mismatch between the model and data here is likely due to a bias in either the secondary electron emission yield,  M , or the properties of the magnetotail lobe ion population, both of which are difficult to precisely constrain (e.g., Cao et al, 2020;Halekas et al, 2009a;Liuzzo et al, 2021). In contrast, between midnight and the dawn terminator (  270 ), the ratio of the observed-to-theoretical surface potentials falls well below unity, indicating that the lunar surface potential is smaller in magnitude (i.e., less negative) than theory predicts.…”

Machine Learning Solar Wind Driving Magnetospheric Convection in Tail Lobes

“…The measurements made in the deep tail lobes typically reveal a dominant positive or negative Bx component, which indicates the northern or southern lobes, respectively. As discussed in (Cao, Halekas, Chu, et al, 2020b), since the mass loading effect couples the lunar ions to the ambient plasma convection, the motion of lunar ions serves as an approximate tracer of the convection patterns in the tail lobes. More details about this method can be found in (Cao, Halekas, Poppe, et al, 2020;Cao, Halekas, Chu, et al, 2020b, 2020a.…”

“…(Ohma et al, 2019) revealed that the asymmetry of the convection flow could also be affected by magnetic reconnection in the tail, which relates to magnetospheric activity. (Cao, Halekas, Chu, et al, 2020b) used the two Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) lunar ion data to show that the dawn-dusk component of plasma convection velocity near the Moon's orbit ( 60 RE) has a high correlation with the corresponding component of the upstream Interplanetary Magnetic Field (IMF). The magnetosphere of the Earth responds to the solar wind flow and IMF, through the Dungey Cycle driven by dayside magnetic reconnection (J. W. Dungey, 1961).…”

“…Accordingly, the plasma convection in the deep magnetotail lobes can be estimated by measurement of lunar ion motion. This technique allows ARTEMIS to estimate the convection velocity by utilizing the heavy lunar ions (which have higher energy per charge for a given convection speed), despite the fact that it cannot typically directly detect the convection of ambient low-mass ions, given the large positive spacecraft potential in the tenuous lobe environment (Cao, Halekas, Chu, et al, 2020b, 2020a.…”

Electrostatic Waves and Electron Heating Observed Over Lunar Crustal Magnetic Anomalies

“…For example, the surface of the Moon, immersed in the solar wind plasma, charges to an electrostatic potential in order to balance the total incident currents (Halekas et al., 2002, 2011; Whipple, 1981). Moreover, solar wind sputtering from the lunar surface and ionization of the tenuous neutral exosphere can produce heavier lunar pickup ions, which can then be accelerated downstream from the Moon by the motional electric field (Cao, Halekas, Poppe, et al., 2020; Cao, Halekas, Chu, et al., 2020; Halekas, Poppe, Delory, Sarantos, et al., 2012; Yokota et al., 2009). Some other examples of lunar interaction include backscattering of solar wind ions and photoelectron emission from the lunar surface (Bhardwaj et al., 2015; Goldstein, 1974; Harada et al., 2017; Lue et al., 2014; Reasoner & Burke, 1972).…”