Monochromatic Pc5 Modulations of the Ionospheric Velocities and TEC and
GOES-16 Magnetic Field Associated with Repeated Solar Wind Dynamic
Pressure Enhancement
Abstract
This study presents ultra-low frequency (ULF) Pc5 discrete spectrum
simultaneously observed in the magnetosphere and high- to low-latitude
ionospheres near noon hours (~10-14 MLT) during the
recovery phase of geomagnetic storm on November 4, 2021. During the
recovery phase, magnetospheric toroidal mode oscillations (GOES-16 Bn)
appeared according to solar wind dynamic pressure enhancements after
GOES Bp and Be (poloidal mode) oscillations precede during high solar
wind speeds. When Bn oscillates, the ionospheric line-of-sight (LOS)
velocity and echo power oscillate at the same discrete frequencies of
1.7 and 2.2 mHz (9.7 and 7.5 min), observed by Super Dual Auroral Radar
Network (SuperDARN) at Saskatoon (eastward LOS). The period of negative
LOS velocity (away from the radar) for 7.5 min or 9.7 min corresponds to
echo power increase. This signifies that both the ionospheric density
and poleward convection velocity increase are driven by the periodic
forcing of the convection electric field and energetic electron
precipitation. The same frequency pulsations have also been observed in
the geomagnetic field (H-component) and Global Positioning System (GPS)
total electron content (TEC) from high- to low-latitude ionosphere. The
oscillation frequency of the H-component is consistently preserved at
1.7 mHz (9.7 min) down to low latitudes. The Pc5 oscillations at high to
low latitudes can be attributed to toroidal mode Alfven waves and the
compressional mode propagating across magnetic field lines as well as
the fast magnetosonic waveguide mode at work by the solar wind dynamic
pressure enhancements at high solar wind speeds.