An Auroral Boundary‐Oriented Model of Subauroral Polarization Streams (SAPS)

Abstract

An empirical model of subauroral polarization stream (SAPS) electric fields has been developed using measurements of ion drifts and particle precipitation made by the Defense Meteorological Satellite Program from 1987 to 2012 and Dynamics Explorer 2 as functions of magnetic local time (MLT), magnetic latitude, the auroral electrojet index (AE), hemisphere, and day of year. Over 500,000 subauroral passes are used. This model is oriented in degree magnetic latitude equatorward of the aurora and takes median values instead of the mean to avoid the contribution of low occurrence frequency subauroral ion drifts so that the model is representative of the much more common, latitudinally broad, low‐amplitude SAPS field. The SAPS model is in broad agreement with previous statistical efforts in the variation of the SAPS field with MLT and magnetic activity level, although the median field is weaker. Furthermore, we find that the median SAPS field is roughly conjugate in both hemispheres for all seasons, with a maximum in SAPS amplitude and width found for 1800–2000 MLT. The SAPS amplitude is found to vary seasonally only from about 1800–2000 MLT, maximizing in both hemispheres during equinox months. Because this feature exists despite controlling for the AE index, it is suggested that this is due to a seasonal variation in the flux tube averaged ionospheric conductance at MLT sectors where it is more likely that one flux tube footprint is in darkness while the other is in daylight.

Dynamics of Auroral Precipitation Boundaries Associated With STEVE and SAID

“…We sorted data by latitude relative to the equatorward boundary of the plasma sheet electrons, which is the sharpest flux gradient and typically at ~10 11 (eV/cm 2 s sr) total energy flux at 30 eV to 30 keV for DMSP and ~10 5 (/cm 2 s sr) total number flux at 1–10 keV for NOAA. The use of the latitudes relative to the boundary is consistent with the approach used in past studies (Landry & Anderson, 2018; Wang & Lühr, 2013). We note that the number of events is small, and we do not intend that this is a large statistical study.…”

Bifurcated Region 2 Field‐Aligned Currents Associated With Substorms

“…This polarization electric field leads to a strong E x B drift, which forms the fast westward drifting SAPS flow (Kunduri et al, 2017Landry & Anderson, 2018;Lejosne et al, 2018). During the growth phase, the R1/R2 currents progress equatorward as the polar cap expands.…”

Challenges to Understanding the Earth's Ionosphere and Thermosphere

“…Next generation advances in constructing models of precipitation, convection, and field-aligned currents should also take into account the dynamics of the boundaries (Landry & Anderson, 2018;Sotirelis & Newell, 2000) and use simultaneous observations of precipitation and convection to insure that the relative locations of systematic convection and precipitation features are preserved. Increasingly available are plasma drift measurements from ground-based radars (Bristow & Spaleta, 2013), ground-based magnetometer measurements (Waters et al, 2015) at high latitudes, and observations of magnetic field perturbations from satellite constellations (Coxon et al, 2016;He et al, 2012).…”