A statistical study of the subauroral polarization stream over North
American sector using the Millstone Hill incoherent scatter radar
1979--2019 measurements
Abstract
This work conducts a statistical study of the subauroral polarization
stream (SAPS) feature in the North American sector using Millstone Hill
incoherent scatter radar measurements from 1979 to 2019, which provides
a comprehensive SAPS climatology using a significantly larger database
of radar observations than was used in seminal earlier works. Key
features of SAPS and associated Ne/Ti/Te are investigated using a
superposed epoch analysis method. The characteristics of these
parameters are investigated with respect to magnetic local time, season,
geomagnetic activity, solar activity, and interplanetary magnetic field
orientation, respectively. The main results are as follows: (1)
Conditions for SAPS are more favorable for dusk than near midnight, for
winter compared to summer, for active geomagnetic periods compared to
quiet time, for solar minimum compared to solar maximum, and for IMF
conditions with negative By and negative Bz. (2) SAPS is usually
associated with a midlatitude trough of 15–20\%
depletion in the background density. The SAPS-related trough is more
pronounced in the postmidnight sector and near the equinoxes. (3)
Subauroral ion and electron temperatures exhibit a
3–8\% (50–120 K) enhancement in SAPS regions, which
tend to have higher percentage enhancement during geomagnetically active
periods and at midnight. Ion temperature enhancements are more favored
during low solar activity periods, while the electron temperature
enhancement remains almost constant as a function of the solar cycle.
(4) The electron thermal content, Te \times Ne, in the
SAPS associated region is strongly dependent on 1/Ne, with Te exhibiting
a negative correlation with respect to $Ne$.