Ionospheric Flow Vortex Induced by the Sudden Decrease in the Solar Wind
Dynamic Pressure
Abstract
Abrupt changes in the solar wind dynamic pressure can greatly affect the
Earth’s magnetosphere‐ionosphere system. We present an ionospheric flow
vortex in the morning side during the sudden decrease in the solar wind
dynamic pressure. The flow vortex was clearly observed by both the
Hankasalmi radar and the azimuthal scan mode of the European Incoherent
Scatter (EISCAT) Svalbard Radar (ESR). The flow vortex was first seen in
the eastern field of view (FOV) of the Hankasalmi radar, and then
propagated poleward and westward into the FOV of the ESR. During the
passage of the flow vortex, a gradual decrease of electron density was
observed by the field-aligned ESR 42 m antenna. When the equatorward
directed ionospheric flow reached the ESR site, weak and visible
increases in the electron density and electron temperature were
observed. This impact was likely caused by soft electron precipitation
associated with the clockwise flow vortex and upward field-aligned
current. The azimuthal scan mode of the ESR 32 m radar at low elevation
angle (30°) allowed us to measure key ionospheric parameters over a
larger area (6° in latitude and 120° in azimuthal angle). The
latitudinal scan of the electron temperature was used to derive the
equatorward auroral boundary, which shows that the flow vortex was
located in the subauroral region. We further demonstrated that it is
possible to study the weak increase of electron density by using GPS
total electron content (TEC) data. A minor TEC increase was observed
near the center of the flow vortex.