Details

Autor(en) / Beteiligte

• Goldstein, J.
• LLera, K.
• McComas, D. J.
• Redfern, J.
• Valek, P. W.

Titel

Empirical Characterization of Low‐Altitude Ion Flux Derived from TWINS

Ist Teil von

• Journal of geophysical research. Space physics, 2018-05, Vol.123 (5), p.3672-3691

Ort / Verlag

Washington: Blackwell Publishing Ltd

Erscheinungsjahr

2018

Link zum Volltext

Quelle

Wiley Online Journals

Beschreibungen/Notizen

• In this study we analyze ion differential flux from 10 events between 2008 and 2015. The ion fluxes are derived from low‐altitude emissions (LAEs) in energetic neutral atom (ENA) images obtained by Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS). The data set comprises 119.44 hr of observations, including 4,284 per energy images with 128,277 values of differential ENA flux from pixels near Earth's limb. Limb pixel data are extracted and mapped to a common polar ionospheric grid and associated with values of the Dst index. Statistical analysis is restricted to pixels within 10% of the LAE emissivity peak. For weak Dst conditions we find a premidnight peak in the average ion precipitation, whose flux and location are relatively insensitive to energy. For moderate Dst, elevated flux levels appear over a wider magnetic local time (MLT) range, with a separation of peak locations by energy. Strong disturbances bring a dramatic flux increase across the entire nightside at all energies but strongest for low energies in the postmidnight sector. The arrival of low‐energy ions can lower the average energy for strong Dst, even as it raises the total integral number flux. TWINS‐derived ion fluxes provide a macroscale measurement of the average precipitating ion distribution and confirm that convection, either quasi‐steady or bursty, is an important process controlling the spatial and spectral properties of precipitating ions. The premidnight peak (weak Dst), MLT widening and energy‐versus‐MLT dependence (moderate Dst), and postmidnight low‐energy ion enhancement (strong Dst) are consistent with observations and models of steady or bursty convective transport. Plain Language Summary This paper performs a statistical analysis of data measured by NASA's Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS) mission. The data consist of measurements of energetic neutral atoms that are emitted from the near Earth region, several hundred kilometers in altitude. We find that there is a profound change in the distributions in space and in energy that occurs for large space storms. Key Points As Dst increases from weak to strong, average precipitating flux increases and covers wider magnetic local time extent For stronger disturbances, at lowest energies, average ion precipitation peak shifts from premidnight to postmidnight Strong Dst: average flux increases across nightside at all energies but most intensely at low energies in postmidnight sector