| Knowledge of solar sector polarity effects on the ionosphere may provide some clues in
understanding of the ionospheric day-to-day variability. A solar-terrestrial connection ranging
from solar sector boundary (SB) crossings, geomagnetic disturbance and ionospheric
perturbations has been demonstrated. The increases in interplanetary solar wind speed within
three days are seen after SB crossings, while the decreases in solar wind dynamic pressure
and magnetic field intensity immediately after SB crossings are confirmed by the
superposed epoch analysis results. Furthermore, the interplanetary magnetic field
(IMF) Bz component turns from northward to southward in March equinox and
June solstice as the Earth passes from a solar sector of outward to inward directed
magnetic fields, whereas the reverse situation occurs for the transition from toward to
away sectors. The F2 region critical frequency (foF2) covering about four solar
cycles and total electron content (TEC) during 1998–2011 are utilized to extract
the related information, revealing that they are not modified significantly and vary
within the range of 15% on average. The responses of the ionospheric TEC to SB
crossings exhibit complex temporal and spatial variations and have strong dependencies
on season, latitude, and solar cycle. This effect is more appreciable in equinoctial
months than in solstitial months, which is mainly caused by larger southward Bz
components in equinox. In September equinox, latitudinal profile of relative variations
of foF2 at noon is featured by depressions at high latitudes and enhancements in
low-equatorial latitudes during IMF away sectors. The negative phase of foF2 is
delayed at solar minimum relative to it during other parts of solar cycle, which
might be associated with the difference in longevity of major interplanetary solar
wind drivers perturbing the Earth’s environment in different phases of solar cycle. |