Statistical Study of Oxygen Ions Abundance and Spatial Distribution in the Dayside Magnetopause Boundary Layer: MMS Observations

Abstract

Using energetic ion composition data at the dayside magnetopause measured by Magnetospheric Multiscale (MMS) satellites, we study the responses of H+, O+ density (1–40 keV), and their ratio to geomagnetic activity and solar wind conditions; their spatial distributions in the XYGSM plane for different ranges of the above parameters are presented as well. The dependencies of the H+ and O+ fluxes spatial distributions on different energy ranges are also investigated. Statistical results show that the dependencies of the H+ density on SYM‐H index, IMF By, and IMF Bz are weak, while the O+ density and its abundance (O+/H+) vary with SYM‐H index and solar wind dynamic pressure exponentially. The IMF directions not only affect the O+ density and its abundance but also play a major role in their spatial distributions. The O+ density shows duskside asymmetry under southward IMF with positive IMF By and shows dawnside asymmetry under northward IMF with negative IMF By. The influence of the dawn‐dusk IMF direction on dawn‐dusk asymmetry is significant. The positive and negative IMF By can strengthen the O+ duskside asymmetry and dawnside asymmetry when the IMF is southward and northward, respectively. Otherwise, as particle energy enhances from ~10 to ~35 keV, the H+ fluxes concentrate more on the duskside magnetopause boundary layer while the O+ fluxes dawn‐dusk asymmetry shows minor difference. This suggests that the H+ and O+ at energies below 40 keV experience different processes when they are transported to the dayside magnetopause boundary layer.

Structure of Pc 5 Compressional Waves Observed in the Duskside Outer Magnetosphere: MMS Observations

“…To describe the variation trend of $${L}_{azm}$$ with R , the scale sizes are binned into 4 categories by different R values, and the mean value in each bin is overplotted with a gray curve with error bars. Confidence interval (CI) error bars are used in Figure 4d: $$\text{CI}=\text{SE}\cdot {t}_{n-1}$$, where $${t}_{n-1}$$ is the t‐distribution with $$n$$ degree of freedom, $$\text{SE}=\frac{1.4826\cdot \text{MAD}}{\sqrt{n}}$$ is the standard error, MAD is mean absolute deviation (See more details in Zeng et al., 2020). The azimuthal scale size increases gradually from 0.8 RE at R = 8.5 RE to approximately 1.7 RE at R = 11.5 RE, which is consistent with the general positive values of $$\hspace*{.5em}{\varphi }_{N1}^{\ast }$$.…”

Magnetospheric Multiscale observations of energetic oxygen ions at the duskside magnetopause during intense substorms

“…Due to not enough events that occurred under northward IMF being observed, the influence of IMF B z on the O + abundance (1-40 keV) during intense substorms is not clear, while Luo et al (2017) found that the O + intensity (>∼ 274 keV) was significantly higher under southward IMF than that under northward IMF, especially at the duskside magnetopause. Zeng et al (2020) also showed that the duskside asymmetry of O + density (1-40 keV) in the dayside magnetopause under northward IMF was less obvious than under southward IMF when the IMF B y was the same. Under the southward IMF, the interactions between the solar wind and the magnetosphere become active.…”

“…The density of energetic O + is in range from 0.007 to 0.599 cm −3 at the duskside magnetopause boundary layer during intense substorms. In a companion paper from Zeng et al (2020), they study the O + abundance variations on the solar wind conditions at the dayside magnetopause boundary layer and not specific to the events that occurred during intense substorms. The mean value of the O + density at the duskside magnetopause boundary layer is 0.038 cm −3 in that paper, while during the intense substorm, the O + density increases to 0.075 cm −3 in this study.…”

On the relationship between energy input to the ionosphere and the ion outflow flux under different solar zenith angles

“…Some of the O + ions that have reached the magnetosphere are transported to the boundary regions or the distant tail by their drift motion and eventually lost to the interplanetary space. Past studies reported that they can escape through the boundary layer (Zong et al 2004;Bouhram et al 2005;Cohen et al 2016;Zeng et al 2020), plasma mantle (Slapak et al 2017;Schillings et al 2019Schillings et al , 2020, and/or distant tail (Seki et al 1998;Kistler et al 2010). Additionally, some O + ions are lost as energetic neutral atoms due to the charge exchange process (Keika et al 2006;Valek et al 2018).…”