Journal of Advances in Physics Vol 16 (2019) ISSN: 2347-3487 https://rajpub.com/index.php/jap 64 DOI: https://doi.org/10.24297/jap.v16i1.8229 Diurnal and Seasonal Variations of Equivalent Slab thickness over Low and Mid Latitude Regions Temitope Owolabi 1,2 , Emmanuel Ariyibi 2 , Olatunbosun Lilian 3 and Olabode A.O 2 . 1 African Regional Center for Space Science and Technology Education, Ile Ife, Nigeria 2 Department of Physics and Engineering Physics Obafemi Awolowo University Ile Ife, Nigeria 3 Department of Science Technology, Federal Polytechnic, Ado-Ekiti, Nigeria Abstract The equivalent slab-thickness () is very important in the study of the complex dynamics of the ionosphere as a result of its ability to determine the skewness of the ionospheric electron density profile. This study involves the day to day and monthly variations of . Ionosonde (FoF2) and Total electron content (TEC) data at the low latitude station of Sao Luis (Glat 2.60° S, Glong 315.80° E and Mlat 6.05° N and Mlong 28.40° E), Brazil and mid latitude station of Chilton (Glat 51.50° N, Glong 359.40° E and Mlat 53.35° N and Mlong 84.34° E), United Kingdom from January 2013 to December 2015 were used in the study of  . For Sao Luis station, the diurnal pattern for the different days are characterized by day time (08:00 – 16:00 UT) high values and nighttime (20:00 – 04:00 UT) low values; however, Chilton shows signatures, such as day time low values and nighttime high values. Also, the daytime values (~600 km) of  for the low latitude station (Sao Luis) is more than double the mid latitude station (Chilton) maximum value (~235 km) over the years considered. The monthly variation of  also indicate a seasonal variation with highest daytime values (400 km) during winter months and lowest (below 300 km) during summer months for the low latitude station (Sao Luis). However, the nighttime values are of the same order (about 200 km) for the low latitude station (Sao Luis). Also, highest daytime values (above 250 km) are observed during summer months and the nighttime values are below 200 km over the years for the mid latitude station (Chilton). Keyword: Ionosphere; Total electron content; Critical frequency (FoF2); equivalent slab thickness. 1. Introduction Ionospheric slab thickness () is an essential ionospheric parameter which provides information on both the top and bottom sides of the ionosphere. The study of this parameter provides information about the nature of the distribution of ionization in the study locations. Information about the neutral temperature and an assumed electron density profile has made the study of slab thickness significant. It can be related directly to the scale height of the ionizable constituents [1] .  is basically the ratio of the total electron content (TEC) to the F- region peak electron density (NmF2). This could also be calculated through various ionospheric models [1, 3, 6, 8]. Slab thickness is a vital parameter because it allows conversion between FoF2 and TEC. NmF2 is proportional to the square of the F2 – layer critical frequency (FoF2). The combination of NmF2 with TEC is useful for the estimation of equivalent ionospheric slab thickness [e.g. 2, 4, 5, 7, 9]; this is represented in equation (1) as follows:           (1) Where foF2 is in MHz     (2) The slab thickness  is in km.