Abstract:
The characteristics of equatorial and low-latitude plasma irregularities are studied using a
meridional chain of ionosondes located at Tirunelveli, Hyderabad, and Allahabad and Global Positioning
System (GPS) receivers located at Tirunelveli, Mumbai, and Nagpur during the year 2015. The observations
suggest that while stronger and longer duration of equatorial spread F irregularities occur in the postsunset
sector during equinoxes and winter, they occur mostly in the postmidnight sector during summer, while
being weaker in strength and shorter in duration. Further, the postsunset spread F occurs first at the equator
followed by their occurrence at low latitudes during equinoxes and winter, while the postmidnight spread F
during summer are found to be stronger and earlier at low latitudes followed by their occurrence at the
equator. While plasma irregularities are observed by both the ionosondes and GPS receivers during both
equinoxes and winter, it is observed mostly by the ionosondes during summer. The results further strengthen
the view that while postsunset spread F in equinoxes and winter are generated by the equatorial processes,
postmidnight spread F in the summer may be linked to the nonequatorial processes. The results also
reemphasize the asymmetric distribution of plasma irregularities or scintillations during equinoxes wherein
vernal (autumn) equinox shows more intense plasma irregularities than autumn (vernal) equinox during
certain years. Also, using a larger data set of simultaneous GPS and ionosonde observations, the relationship
of prereversal enhancement and strength of L-band scintillations with solar flux, Kp index, and equatorial
electrojet strength are examined.
