Equatorial Spread F (ESF), a manifestation of nighttime irregularities in the equatorial ionosphere has been linked to Atmospheric Gravity Waves (AGW) by different authors. However, there have not been much study to ascertain the extent of the relationship between the occurrence of AGW and the generation and occurrence of ESF. This study investigates the correlation between AGW and ESF occurrences during the year 2016, using data obtained with the aid of satellite borne Atmospheric Infrared Sounder (AIRS) and ionogram obtained with the aid of Digisonde Portable Sounder (DPS-4) located at Jicamarca, (geog. Lat. 11.95, Long. 76.87 and geomagnetic Lat. 9.28, Long.-7.92), an equatorial station in the Peruvian sector. During this period, 72.9% of AGW occurrence was observed between 18:00UT and 00:00UT (post-sunset period) while the remaining 27.1% occurrence was observed between 00:00 and 04:00UT (post-midnight period) coinciding with the period of occurrence of ESF. Results from the study reveal that the occurrences of ESF and AGW are independent of each other. An insignificant correlation (0.39) was found between the days of occurrence of the two phenomena. While ESF occurrence is a regular daily occurrence with local time dependence, AGW propagation is not dependent on local time. For Jicamarca, we found that ESF occurrence is greater during the solstice months than equinox. The probability of AGW reaching the bottomside F-layer depends on the properties of the wave. In this study, AGW was able to penetrate ionospheric heights on only six occasions. The results also show that AGW occurrence can only influence the conditions that trigger ESF rather than triggering ESF altogether. The occurrence of AGW tends to influence the occurrence of MSF type of ESF which is predominantly a post sunset phenomenon in preference to the other two types. Coefficient of correlation between AGW and MSF ranged between

At the equatorial latitude of a West African station (8.50N, 4.68E), we have examined the slab-thickness (τ) relative to peak electron density height (hmF2) at F2 layer, employing Digisonde Portable Sounder τ (DPS-τ) and Global Positioning System τ (GPS-τ) during the low solar activity year 2010. Our observation revealed maximum and minimum τ during the daytime and nighttime respectively, which may indicate maximum and minimum scale height in τ through daytime and nighttime, respectively. The discrepancies between the together reversed signatures of DPS-τ and GPS-τ around 0100 - 0600 LT in June could indicate the failure to incorporate a reflection of the composition changes in the topside-DPS model. We have reported the pre-sunrise and post-noon peaks in GPS-τ and hmF2, which are contributions of plasmaspheric TEC and pre-reversal enhancement (PRE) velocity, respectively. Around 1100 - 1700 LT, the stability in hmF2 show that the interaction of neutral wind and eastward electric field could be employed to predict the τ. We also reported that the pre-sunrise increase in GPS-τ is not an indication of PRE velocity as observed during the nighttime. The relationship between τ and hmF2 gives a high correlation coefficient (CC), but CC during the daytime is higher than the nighttime values which suggest the constant diffusion state of plasmasphere during the daytime whereas the nighttime is a function of the plasmaspheric flow of electron content and PRE velocity. We compared the experimental hmF2 with IRI-2016 and found that the IRI-2016 model is incapable of capturing the post-sunset and pre-sunrise increases.