Statistical correlation of low‐altitude ENA emissions with geomagnetic activity from IMAGE/MENA observations

Abstract

Plasma sheet particles transported Earthward during times of active magnetospheric convection can interact with exospheric/thermospheric neutrals through charge exchange. The resulting Energetic Neutral Atoms (ENAs) are free to leave the influence of the magnetosphere and can be remotely detected. ENAs associated with low‐altitude (300–800 km) ion precipitation in the high‐latitude atmosphere/ionosphere are termed low‐altitude emissions (LAEs). Remotely observed LAEs are highly nonisotropic in velocity space such that the pitch angle distribution at the time of charge exchange is near 90°. The Geomagnetic Emission Cone of LAEs can be mapped spatially, showing where proton energy is deposited during times of varying geomagnetic activity. In this study we present a statistical look at the correlation between LAE flux (intensity and location) and geomagnetic activity. The LAE data are from the MENA imager on the IMAGE satellite over the declining phase of solar cycle 23 (2000–2005). The SYM‐H, AE, and Kp indices are used to describe geomagnetic activity. The goal of the study is to evaluate properties of LAEs in ENA images and determine if those images can be used to infer properties of ion precipitation. Results indicate a general positive correlation to LAE flux for all three indices, with the SYM‐H showing the greatest sensitivity. The magnetic local time distribution of LAEs is centered about midnight and spreads with increasing activity. The invariant latitude for all indices has a slightly negative correlation. The combined results indicate LAE behavior similar to that of ion precipitation.

Terrestrial Energetic Neutral Atom Emissions and the Ground‐Based Geomagnetic Indices: Implications From IBEX Observations

“…Therefore, parent particles regularly undergo multiple charge exchanges and stripping collisions to create ENA emissions (Bazell et al, 2010;Roelof, 1997). LAEs are bright and perpendicular to the local magnetic field due to the gyro-tropic behavior of parent ions (Mackler et al, 2016;Pollock et al, 2009). Brandt et al (1997) analyzed 26-to 52-keV ENA images from Prelude in Planetary Particle Imaging, on the Swedish satellite Astrid (Barabash et al, 1997), and found that LAE flux enhancements occur during the main phase of geomagnetic storms.…”

“…Brandt et al (1997) analyzed 26-to 52-keV ENA images from Prelude in Planetary Particle Imaging, on the Swedish satellite Astrid (Barabash et al, 1997), and found that LAE flux enhancements occur during the main phase of geomagnetic storms. Mackler et al (2016) performed a statistical investigation using the Medium Energy Neutral Atom instrument on the IMAGE satellite (Pollock et al, 2000) and reported a generally positive correlation between LAE intensities and geomagnetic indices, such as the longitudinally symmetric disturbance index (Sym-H, a higher-cadence representative of the Dst index), the auroral electrojet index (AE), and the Kp index. They found that the LAE intensity had the strongest correlation with Sym-H, though the temporal profiles were not studied.…”

“…Therefore, parent particles regularly undergo multiple charge exchanges and stripping collisions to create ENA emissions (Bazell et al., ; Goldstein & McComas, ; Roelof, ). LAEs are bright and perpendicular to the local magnetic field due to the gyro‐tropic behavior of parent ions (Mackler et al., ; Pollock et al., ). Brandt et al.…”

“…Mackler et al. () performed a statistical investigation using the Medium Energy Neutral Atom instrument on the IMAGE satellite (Pollock et al., ) and reported a generally positive correlation between LAE intensities and geomagnetic indices, such as the longitudinally symmetric disturbance index ( Sym‐H , a higher‐cadence representative of the Dst index), the auroral electrojet index ( AE ), and the Kp index. They found that the LAE intensity had the strongest correlation with Sym‐H , though the temporal profiles were not studied.…”