Characteristics of Equatorial and Low‐Latitude Plasma Irregularities as Investigated Using a Meridional Chain of Radio Experiments Over India

• Published in: Journal of geophysical research. Space physics 2018-05, Vol.123 (5), p.4364-4380
• Main Authors: Sripathi, S., Sreekumar, Sreeba, Banola, S.
• Format: Article
• Language: English
• Subjects: Autumn; Chains; Electrojets; Electron density; Equator; Equatorial electrojet; Equatorial ionosphere; equatorial spread F; Equinoxes; Global positioning systems; GPS; Ionosondes; Ionosphere; Ionospheric layers; ionospheric plasma irregularities; Irregularities; KP index; Latitude; midlatitude spread F; radio wave propagation; Radio waves; Receivers; Receivers & amplifiers; Satellite navigation systems; Skewed distributions; Solar flux; Space weather; Spread F; Summer; traveling ionospheric disturbances (TIDs); Weather; Weather conditions; Winter
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2017JA024980

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. Plain Language Summary It is known that nighttime equatorial ionosphere affects the radio wave communication due to presence of electron density fluctuations often known as plasma irregularities. These irregularities are observed by variety of ground‐ and space‐based instruments. These plasma irregularities have large variability due to forcing from the above and below. Due to advent of Global Positioning System (GPS) receivers, ionospheric scintillations caused by these plasma irregularities are used extensively to monitor them under varied space weather conditions. While GPS receivers monitor the scintillations, which are integrated quantity, ionosondes provide information about the altitude variation of ionospheric layers. Accordingly, uniqueness of this work lies in the int