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

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 su...

major modifications have been made by adding another GPS station

“…Statistical and case 55 studies were successful in describing the occurrence features of the irregularity with local time, seasonal variations, solar cycle and its geographical dependence. They confirm already existing observational characteristics of the irregularity and give new insights into its global distribution scenarios (Otsuka et al, 2006, Nishoka et al, 2008Sripathi et al, 2018). Nevertheless, systematic research of the ionospheric irregularity with ROTI is lacking at specific area for varying solar 60 activity.…”

“…equatorial spread F mostly occurred in equinoxes and winter. Further the postmidnight spread F during summer is found to be stronger and earlier at low latitudes followed by their occurrence at the equator (Sripathi et al, 2018). 280 Figure 4 shows the variation of the irregularity's strength generally complies with its LOR in Taoyuan, although a one-to-one correspondence does not exist coming to those of latitude belt.…”

L-Band Amplitude Scintillations During Solar Maximum at a Low Latitude Station

“…The TEC itself depends on the activity of the sunspot, seasonal, diurnal and spatial variations and the line of sight that includes knowledge of the satellite's elevation and azimuth [26]. The TEC may be calculated as [18], [22], [27]: The rate of change of the total electron content (ROT), calculated from the differential carrier phase, may provide information on large scale electron density irregularities. While the ROT can be deterred as the equation below [22]:…”

A Statistical Study on The Local Time Dependence of Equatorial Spread F (ESF) Irregularities and Their Relation to Low‐Latitude Es Layers Under Geomagnetic Storms

“…In this study, a total of 73 moderate to intense geomagnetic storm events are identified and classified them into three categories according to Aarons (1991) criteria, which is commonly accepted criteria to explore the occurrence of ionospheric irregularities. It is believed that low-latitude Es layers may be modified due to modified winds/electric fields during the geomagnetic storms, and hence, examining their role in the generation of ESF irregularities is very important (e.g., Li et al, 2006;Sripathi et al, 2018). (2) Category II: if the maximum negative of Dst occurs during the midnight-down (at 00:00-06:00 LT), the height of the ionospheric F layer first rises and then falls, which generated the ionospheric irregularities.…”

“…As the E region at Hyderabad is connected to the base of the F region at 250 km at magnetic equator, any changes in the E ‐region density can have significant impact on the ESF irregularities as field‐integrated conductivity plays important role in deciding the growth of the plasma irregularities. It is believed that low‐latitude Es layers may be modified due to modified winds/electric fields during the geomagnetic storms, and hence, examining their role in the generation of ESF irregularities is very important (e.g., Li et al, ; Sripathi et al, ). The study also investigates the seasonal response of early morning height rise and their relation to occurrence of ionospheric irregularities during the disturbed conditions.…”