Characteristics of Equatorial and Low‐Latitude Plasma Irregularities as Investigated Using a Meridional Chain of Radio Experiments Over India. Issue 5 (28th May 2018)

• Record Type: Journal Article
• Authors: Sripathi, S.; Sreekumar, Sreeba; Banola, S.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 5(2018)
• Page Start: 4364
• Page End: 4380
• Publication Date: 2018-05-28
• Subjects: equatorial ionosphere -- equatorial spread F -- ionospheric plasma irregularities -- radio wave propagation -- midlatitude spread F -- traveling ionospheric disturbances (TIDs); Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2017JA024980
• Languages: English
• ISSNs: 2169-9380

Abstract

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. 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 integration of these two observations to bring morphological differences between these two scales and their general characteristics during different seasons over Indian equatorial and low‐latitude stations using chain of ionosondes and GPS receivers. Interestingly, the postmidnight spread F during summer is found to be stronger and earlier at low latitudes followed by their occurrence at the equator. 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. Key Points: Characteristics of premidnight and postmidnight plasma irregularities are studied over India Results suggest that while postsunset ESF is linked mostly to the equatorial process, a few of the postmidnight ESFs could be linked to the nonequatorial process Persistence of equinoctial asymmetry in the plasma irregularities for several years