[01] Ayokunnu Olalekan David, Physics Department, The Polytechnic, Ibadan Ibadan, Nigeria. [02] Adeniyi Jacob Olusegun, Physics Department, Landmark University, Omu-Aran, Nigeria. [03] Ogunsola Oluseyi Enitan, Physics Department, University of Ibadan, Ibadan, Nigeria. [04] Dare Oluseye David, Physics Department, Dominion University Ibadan, Ibadan, Nigeria.

The latitudinal effect on the morphology of the F2 layer of the equatorial region during the quiet period at low solar activity was studied. Digisonde data for year 2010, a year of low solar activity from three equatorial stations in the African and Southern American sectors namely; Ilorin, Nigeria (8.5°N, 4.5°E, -2.96 dip) Fortaleza, Brazil (3°S, 38°W, -7.03dip) and Jicamarca, Peru (12°S, 76.8°W, 0.74 dip) were used for the study. It was observed that the variation of the electron density covers the height range from 100 km up to the F2 peak. The result obtained showed that the h_mF2 rises sharply within the time interval of 0600-1000 LT. It has a smaller range of variation between 1100-1400 LT and after 1400 LT, it begins to decrease and usually get to a minimum around 1700-1900 LT. The maximum day time peak varies from 300-319 km and that of the post-noon is about 312-417 km. The h_mF2 at Fortaleza was observed to show no prominent pre-noon peak, during the September equinox. Generally, the N_mF2 diurnal variations are similar to those of h_mF2 and the general departure of the F2-layer from the simple Chapman layer from the height of 190-230 km were observed from the three stations studied. It was observed that the results from Ilorin and Jicamarca are similar and that of Fortaleza are different from those of other two stations. The peculiarity at Fortaleza is attributed to its closeness to the crest of the equatorial anomaly than the other two stations; these variations observed may be due to effect of the latitudinal differences.

Latitude, Morphology, F2 Layer and Quiet Ionosphere

[01] Mambia, S. and Maeda, K. (1939). Radio propagation, Tokyo, Corona. [02] Appleton, E. V. (1946). Two anomalies in the ionosphere. Nature, 157(3995), 691. https://doi.org/10.1038/157691aO. [03] Kenneth, J. W. L, Robert, S. G and Andrew, H. (2014). The spatial and temporal structure of twin peaks and midday bite out in foF2 (with associated height changes) in the Australian andSouth pacific low mid latitude ionosphere. Journal of Geophysical Res.: Space Physics. 10294-10304. 10.1002/2014JA020617. [04] Radicella, S. M. and Adeniyi, J. O. (1999). Equatorial ionospheric electron density below F2 layer. Radio Science, 34(5), 1153-1163. [05] Adeniyi, J. O. (1997). Experimental equatorial ionospheric profiles and IRI model profile. Journal of Atmospheric and Solar-Terrestrial Physics 59(10), 1205-1208. [06] Adeniyi, J. O, Oladipo, O. A and Radicella, S. M (2007). Variability of f_oF2 for an equatorial station and comparison with foF2 maps in IRI model. J. Atmos. Sol. Terr. Phys. 69721-733 [07] Fejer, B. G. (1997). The electrodynamics of the low latitude ionosphere recent results and future challenges. J. Atmos. Sol. Terr. Phys. 59 1465-1482 [08] Rishbeth, H. and Mendillo M. (2001). Patterns of F2-layer Variability. J. Atmos. Sol. Terr. Phys. 63 (15) 1661-1680. [09] Batista, I S and Abdu, M. A. (2004). Ionospheric variability at Brazilian low and equatorial latitudes: Comparison between the observations and IRI model. Advanced Space Res. 34 1894-1900. [10] Aderson, D., Anghel, A. Yumoto, K. Bhattacharyya, A and Alex, S. (2006). Daytime, low latitude, vertical ExB drift velocities, infrared from ground-based magnetometer observations in Peruvian, Philippine and Indian longitude sectors under quiet and disturbed conditions. ILWS workshop, GOA, feb. 19-24, 2006 pp. 1-6. [11] Oladipo, O. A., Adeniyi, J. O, Radicella, S. M. and Adimula, I. A. (2001). Variability of the ionospheric electron density at fixed height and validation ofIRI-2007 profile’s prediction at Ilorin. Advances in space Research, 47(2011)496-505. [12] Dabas, R. S, Singh, L, Lakshimi, D. R, Subramanyam, P. Chopra, P and Garg, S. C. (2003). Evolution and dynamics of equatorial plasma bubbles: Relationship to ExB drift, post-sunset TEC enhancement and EEJ strength. Radio Sci. 38 1075. dio:10.1029/2001IRS002586. [13] Liu, L. Yang, J., Le, H. Chen, Y, Wan, W and Lee C. C (2012). Comparative study of equatorial ionosphere over Jicamarca during recent two solar minima. J. Geophys. Res. 117 A01315. dio: 10.1029/2011JA017215. [14] Danilov, A. D (1986). Meteorological control of D region. Ionosphere. Res.(in Russian), 39, 33. [15] Danilov, A. D, Kazimirovsky, E. S, Vergasova, G. V and Khachikjan, G. Ya (1987). The meteorological effects in the ionosphere (in Russian) 40, 270. [16] Forbes, J. M and X. Zhang (1997). Quasi 2-day Oscillation of the ionosphere: A statistical study. J. Atmos. Sol. Terr. Phys. 59, 1025. [17] Forbes, J. M, S. E. Palo and X. Zhang (2000). Variability of the ionosphere. J. Atmos. Sol. Terr. Phys. (in Russian), 62, 685. [18] Mikhailov, A. V and Forster (1999). Some F2-layer effects during 06-11, 1997, CEDAR storm period asobserved with the Millstone hill incoherent scatter facility. Jour. Atm. Sol. Terr. 61, 249. [19] Farelo, A. F, M. Herraiz and Mikhailov, A. V (2002). Global Morphology of night-time NmF2 enhancements, Ann. Geophys. 20, 1795. [20] Adebesin, B. O, B. J Adekoya, S. O Ikubani, S. J Adebiyi, O. A Adebesin, B. W Joshua and K. O Olonade (2014). Ionospheric foF2 morphology and response of F2 layer height over Jicamarca during different solar epochs and comparison with IRI-2012 model. J. Earth System Sci. 123 (4), pp 751-765. [21] A. V Mikhailor, A. Kh. Depueva and T. Yu. Leschimaya (2004). Morphology of quiet time F2-layerdisturbance: High to low latitudes. Int. Journal of Geomagnetism and Aeronomy. 5, 1-14dio:10.1029/2003GI000058. [22] Huang, X. and Reinisch, B. W. (1996a). Vertical Electron density profiles from digisonde network, Adv. Space Res. 18(6), 121-129. [23] Huang, X. and Reinisch, B. W. (1996b). Vertical Electron density profiles from digisonde ionogram: The average representative profile, Ann. Geophys. 39(4). 751-756. [24] Adeniyi, J. O and Ayokunnu, O. D (2012). Characteristics of the equatorial F2 ionospheric layer at low solar activity period. In: Proceedings, AGU-Chapman Conference on longitude and hemispheric dependence of space weather (pp. 12) Addis Ababa, Ethiopia. [25] Egedai, J. (1947). The magnetic diurnal variation of the horizontal force near the magnetic equator. Terr. Magn. Atmos. Electr. 52(4), 449-451. https://doi.org/10.1029/TE052i004p00449 [26] Hanson, W. B and Moffett, R. J (1966). Ionization transport effects in the equatorial F region. J. Geophys. Res. 71(23), 5559-5572. https://doi.org/10.1029/JZ071i023p05559. [27] Oyama, K. I, Abdu, M. A, Balan, N. Bailey, G. J, Watanabe, S. Takahashi, T, de Paul, E. R, Batista, I. S, Isoda, F and Oya, H. (1997). High electron temperatureassociated with the pre-reversal enhancement in the equatorial ionosphere. J. Geophys. Res. 102(A1), 417-424. https://doi.org/10.1029/96JA02705 [28] Raghavarao, R. Wharton, L. E, Spencer, N. W, Mayr, H. G and Brace, L. H. (1991). An equatorial temperature and wind anomaly (ETWA). Geophys. Res. Letts. 18(7), 1193-1196. https://doi.org/10.1029/91GL01561 [29] Bailey, G. J and Balan, N. (1996). Alow latitude ionosphere-plasmasphere model. In: R. W, Schunk (Ed.), STEPH and book on ionospheric models (pp. 173). Logan: Utah State University. [30] Martyn, D. F (1955). Theory of height and ionization density changes at the maximum of a Chapman-like region, taking account of ion production, decay, diffusion and total drift. In:Proceedings, Cambridge Conference(pp. 254). London, Physical Society. [31] Balan, N. Li Bo Liu and Hui Jun Le (2018). A brief review of equatorial ionization anomaly and ionospheric irregularities. Earth and Planetary Physics. 2: 1-19. doi:10.26464/epp2018025