Abstract
Discrete aurora at Mars, characterized by their small spatial scale and
tendency to form near strong crustal magnetic fields, are emissions
produced by particle precipitation into the Martian upper atmosphere.
Since 2014, Mars Atmosphere and Volatile EvolutioN’s (MAVEN’s) Imaging
Ultraviolet Spectrograph (IUVS) has obtained a large collection of
nightside UV discrete aurora observations. Initial analysis of these
observations has shown that, near the strong crustal field region (SCFR)
in the southern hemisphere, the aurora detection frequency is highly
sensitive to the interplanetary magnetic field (IMF) clock angle.
However, the role of other solar wind properties in controlling the
aurora detection frequency has not yet been determined. In this work, we
use IUVS discrete aurora observations, and MAVEN solar wind
observations, to determine how the discrete aurora detection frequency
varies with solar wind dynamic pressure, IMF strength, and IMF cone
angle. We find that, outside of the SCFR, the detection frequency is
relatively insensitive to the IMF orientation, but significantly
increases with solar wind dynamic pressure and moderately increases with
IMF strength. Interestingly, the auroral emission brightness outside the
SCFR is insensitive to the dynamic pressure. Inside the SCFR, the
detection frequency is moderately dependent on the dynamic pressure and
is much more sensitive to the IMF clock and cone angles. In the SCFR,
aurora are unlikely to occur when the IMF points near the radial or
anti-radial directions. Together, these results provide the first
comprehensive characterization of how upstream solar wind conditions
affect the formation of discrete aurora at Mars.