Variations of Crest-to-Trough TEC Ratio of the East African Equatorial Anomaly Region
International Journal of Astrophysics and Space Science
Volume 4, Issue 1, February 2016, Pages: 12-20
Received: Dec. 21, 2015; Accepted: Dec. 29, 2015; Published: Mar. 2, 2016
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Bosco Oryema, Department of Physics, Busitema University, Tororo, Uganda
Edward Jurua, Department of Physics, Mbarara University of Science and Technology, Mbarara, Uganda
Nicolausi Ssebiyonga, Department of Physics, Makerere University, Kampala, Uganda
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In this paper, Vertical Total Electron Content (VTEC) data derived from dual-frequency GPS measurements obtained at two ground stations were used to study the variability of the equatorial ionization anomaly (EIA). The present study only focuses on analysis of the crest-to-trough TEC ratio (TEC-CTR) in the southern crest region. Data used in this study was obtained for the high solar activity year 2012. MAL2 station (Geomag Lat. -12.4°S, Geomag Long. 111.9°E) was considered for the southern crest region whereas ADIS station (Geomag Lat. 0.2°N, Geomag Long. 110.5°E) was considered for the trough region. Diurnal and seasonal variations as well as the dependency of TEC-CTR on solar activity levels were investigated in the present study. The results showed that the diurnal variation pattern of TEC-CTR is characterized by two remarkable peak values, one occurring in the post‐midnight hours around 02: 00-03: 00 UT (05: 00-06: 00 LT) and the second (highest) peak occurred in the post-sunset hours around 18: 00-20: 00 UT (21: 00-23: 00 LT). Seasonal TEC-CTR variations showed a semi-annual variation pattern, with maximum peak values occurring in the equinoctial months. TEC-CTR also revealed an existence of winter anomaly in this region, with higher values of TEC-CTR in the winter solstice than summer solstice. TEC-CTR in the daytime post-noon hours; between 01: 00-04: 00 UT (04: 00-07: 00 LT) does not vary much with the solar activity; however, TEC-CTR in the post-sunset hours; between 16: 00-20: 00 UT (19: 00-23: 00 LT) shows a clear dependence on the solar activity, with its values increasing with solar activity.
Total Electron Content (TEC), Equatorial Ionization Anomaly (EIA), GPS Measurements, Solar Activity
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Bosco Oryema, Edward Jurua, Nicolausi Ssebiyonga, Variations of Crest-to-Trough TEC Ratio of the East African Equatorial Anomaly Region, International Journal of Astrophysics and Space Science. Vol. 4, No. 1, 2016, pp. 12-20. doi: 10.11648/j.ijass.20160401.12
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Abdullah, M.; Bahari S. A. & Yatim, B. (2008). TEC determination over single GPS receiver station using PPP technique, International Symposium on GPS/GNSS 2008, November 11-14, 2008 Tokyo.
Adewale A. O.; Oyeyemi E. O.; Adeloye, A. B.; Ngwira C. M.; Athieno R. (2011). Responses of equatorial F region to different geomagnetic storms observed by GPS in the African sector, J. Geophys. Res. VOL. 116, A12319, doi: 10.1029/2011JA016998
Alex, S., Koparkar, P. V., Rastogi, R. G. (1989). Spread-F and ionization anomaly belt. J. Atmos. Terr. Phys. 51, 371–379.
Balan, N., Otsuka, Y., Bailey, G. J., and Fukao, S.: Equinoctial asymmertries in the ionosphere and thermosphere observed by the MU radar, J. Geophys. Res., 103, 9481–9495, 1998.
Breed, A. M. (1996). Investigation of the ionosphere over Australia using satellite transmissions, PhD thesis, School of Applied Physics, University of South Australia.
Chakraborty, S. K and Hajra, R. (2009). Electrojet control of ambient ionization near the crest of the equatorial anomaly in the Indian zone. Ann. Geophys, 27, 93-105.
Chakraborty, S. K., Hajra, R., 2007. Solar control of ambient ionization of the ionosphere near the crest of the equatorial anomaly in the Indian zone. Bull. Astron. Soc. India 35, 599–605.
D’ujanga, F. M; Mubiru, J.; Twinamasiko, B. F.; Basalirwa, C and Ssenyonga, T. J. (2012). Total electron content variations in equatorial anomaly region. Advances in Space Research. 50(4), 441-449. DOI: 10.1016/j.asr.2012.05.005
Essex, E. A.: Equinoctial variations in the total electron content of the ionosphere at northern and southern hemisphere stations, J. Atmos. Terr. Phys., 39, 645–650, 1977.
Farley, D. T., Bonelli, E., Fejer, B. G., Larsen, M. F. (1986). The prereversal enhancement of the zonal electric field in the equatorial ionosphere. J. Geophys. Res. 91, 13723–13728.
Fayose, R. S., Babatunde, R., Oladosu, O., Groves, K., (2012). Variation of total electron content and their effect on GNSS over Akure, Nigeria. Appl. Phys. Res. 4 (2). http: //
Feichter, E., Leitinger, R., 1997. A 22-year cycle in the F layer ionization of the ionosphere. Ann. Geophys. 15, 1015-1027. Bailey et al., 2000;
Fejer, B. G., L. Scherliess, and E. R. de Paula (1999), Effects of the vertical plasma drift velocity on the generation and evolution of equatorial spread F, J. Geophys. Res., 104(A9), 19, 859–19, 869.
Fejer, B. G., de Paula, E. R., Heelis, R. A., Hanson, W. B. (1995). Global equatorial ionospheric vertical plasma drifts measured by the AE-E satellite. J. Geophys. Res. 100 (4), 5769–5776.
Fejer, B. G.; Scherliess, L. (2001). On the variability of equatorial F-region vertical plasma drifts. J. Atmos. Terr. Phys. 63 (9), 893–897.
Goodman, J. M. (2005). Space Weather and Telecomm-unications. Radio Propagation Services, Inc., USA. (RPSI). Alexandria VA 22308-1943. ISBN 0-387-23670-8
Hansen, A.; Blanch, J. & Walter, T. et al. (2000). Ionospheric correction analysis for WAAS quiet and stormy. ION GPS, Salt Lake City, Utah, September 19-22, 2000, pp 634-642, America.
Henderson, S. B., Swenson, C. M., Christensen, A. B., Paxton, L. J. (2005). Morphology of the equatorial anomaly and equatorial plasma bubbles using image subspace analysis of Global Ultraviolet Imager data. J. Geophys. Res. 110, A11306, doi: 10.1029/2005JA011080.
Horvath, I & Essex, E. A. (2000). Using observations from the GPS and TOPEX satellites to investigate night-time TEC enhancement at mid-latitudes in the southern hemisphere during a low sunspot number period, Journal of Atmospheric and solar Terissterial-Physics, Vol. 62, No. 5, pp. 371-391.
Jakowski, N., Sardon, E., Engler, E., Jungstand, A., and Klhn, D. (1996). Relationships between GPS-signal propagation errors and EISCAT observations, Ann. Geophys., 14, 1429–1436, http: //
Jayachandran, P. T., Sri R. P., Somayajulu, Y. V., Rama Rao, P. V. S. (1997). Effect of equatorial ionization anomaly on the occurrence of spread-F. Ann. Geophys. 15, 255–262.
Kelley, M. C. (1989), The Earth’s Ionosphere, Academic Press, London.
Kherani, A., De-Paula, E., Olusegun, J., 2013. Observations and simulations of equinoctial asymmetry during low and high solar activities. In: Presentation at a Proceeding of the Thirteenth International Congress of the Brazilian Geophysical Society, held in Rio de Janeiro, Brazil, August 26–29.
Klobuchar, J. A. (1991). Ionospheric effects on GPS, GPS World, 48–51.
Klobuchar, J. A. (1996) Ionospheric effects on GPS, in: Global Positioning System: Theory and application Vol. 1, edited by: Parkinson, B. W. and Spilker, J. J., American Institute of Aeronautics and Astronautics INC.
Lanyi, G. E. and Rolh, T. (1988). A comparison of mapped and measured total ionospheric electron content using global positioning system and beacon satellite observations, Radio Sci., 23, 483–492.
Liu, L., He, M., Yue, X., Ning, B., Wan, W., (2010). Ionosphere around equinoxes during low solar activity. J. Geophys. Res. 115, A09307. http: // 2010JA015318.
Memarzadeh, Y. (2009). Ionospheric Modeling for Precise GNSS Applications. Master’s Thesis. ISBN-13 978-90-6132-314-3
Mukherjee, S.; Sarkar, S.; Purohit, P. K.; Gwal, A. K. (2010). Seasonal variation of total electron content at crest of equatorial anomaly station during low solar activity conditions. Adv. Space Res. 46 (3), 291–295.
Ngwira C. M., Klenzing J., Olwendo J., D’ujanga F. M., Stoneback R. and Baki P., (2013b). A study of intense ionospheric scintillation observed during a quiet day in the East African low latitude region. Radio Science, 48, 1-9, doi: 10.1002/rds.20045.
Ngwira, C. M., G. K. Seemala, and J. B. Habarulema (2013a), Simultaneous observations of ionospheric irregularities in the African low-latitude region, J. Atmos. Sol.-Terr. Phys., 97, 50–57, doi: 10.1016/j.jastp.2013.02.014.
Okonkwo, P and Ugwuanyi, J. (2012). IRI and GPS TEC Variations over Ilorin, Nigeria. Journal of Space Science & Technology. 1(3), 1-11.
Olwendo, O. J., Baki, P., Cilliers, P. J., Mito, C., Doherty, P., (2012). Comparison of GPS TEC measurements with IRI-2007 TEC prediction over the Kenyan region during the descending phase of solar cycle 23. Adv. Space Res. 49, 914–921.
Oron, S.; D’ujanga, F. M and Ssenyonga, T. J. (2013). Ionospheric TEC variations during the ascending solar activity phase at an equatorial station, Uganda. Indian Journal of Radio and Space Physics. 42, 7-17.
Oryema, B., Jurua, E., D’ujanga, F. M., and Ssebiyonga, N. (2015). Investigation of TEC variations over the magnetic equatorial and equatorial anomaly regions of the African sector. Adv. Space Res. (2015), http: //
Ouattara, F and Fleury, R. (2011). Variability of CODG TEC and IRI 2001 total electron content (TEC) during IHY campaign period (21 March to 16 April 2008) at Niamey under different geomagnetic activity conditions. Scientific Research and Essays, 6 (17), 3609-3622.
Pavlov, A. V.; Pavlova, N. M. (2005a). Causes of the mid-latitude NmF2 winter anomaly at solar maximum. J. Atmos. Terr. Phys. 67, 862–877.
Paznukhov, V. V., et al. (2012), Equatorial plasma bubbles and L-band scintillations in Africa during solar minimum, Ann. Geophys., 30, 675–682.
Richards, P. G.: Seasonal and solar cycle variations of the ionospheric peak electron density: comparison of measurement and models, J. Geophys. Res., 106 (A12), 12 803–12 819, 2001.
Rishbeth, H.; Muller-Wodarg, I. C. F.; Zou, L.; Fuller-Rowell, T. J.; Millward, G. H.; Moffett, R. J.; Idenden, D. W.; Aylward, A. D. (2000). Annual and semiannual variations in the ionospheric F2-layer: II. Physical discussion. Ann. Geophys. 18, 945–956.
Sardon, E., Rius, A., and Zarraoa, N. (1994). Estimation of the receiver differential biases and the ionospheric total electron content from Global Positioning System observations, Radio Sci., 29, 577–586.
Schaer, S.; Markus, R.; Gerhard, B. & Timon, A. S. (1996). Daily Global Ionosphere Maps based on GPS Carrier Phase Data Routinely produced by the CODE Analysis Center, Proceeding of the IGS Analysis Center Workshop, Silver Spring, Maryland, pp. 181-192, USA.
Schunk, R. W and Nagy, A. F. (2000). Ionospheres. Cambridge University Press, New York.
Seemala, G. K., and C. E. Valladares (2011), Statistics of total electron content depletions observed over the South American continent for the year 2008, Radio Sci., 46, RS5019, doi: 10.1029/2011RS004722.
Titheridge, J. E. (1972). The total electron content of the southern mid-latitude ionosphere, 1965–1971, J. Atmos. Terr. Phys., 35, 981–1001.
Titheridge, J. E.: The electron content of the southern mid-latitude ionosphere, 1965–1971, J. Atmos. Terr. Phys., 981–1001, 1973.
Titheridge, J. E., Buonsanto, M. J., 1983. Annual variations in the electron content and height of the F layer in the Northern and Southern Hemispheres, related to neutral composition. J. Atmos. Terr. Phys. 45, 683-696.
Tsai, H. F., Liu, J. Y., Tsai, W. H., Liu, C. H., Tseng, C. L., Wu, C.-C. Seasonal variations of the ionospheric total electron content in Asian equatorial anomaly regions. J. Geophys. Res. 106 (A12), 30363–30370, 2001.
Tsai, H. F; Liu, J. Y; Tsai, W. H and Liu, C. H. (2001). Seasonal variations of the ionospheric total electron content in Asian equatorial anomaly regions. Journal of Geophysical research. 106 (A12), 30, 363–30, 369.
Valladares, C. E., Basu, S., Groves, K., Hagan, M. P., Hysell, D., Mazzella Jr., A. J., Sheehan, R. E. (2001). Measurements of the latitudinal distributions of total electron content during equatorial spread F events. J. Geophys. Res. 106 (A12), 29133–29152.
Valladares, C. E., Villalobos, J., Sheehan, R., Hagan, M. P. (2004). Latitudinal extension of low-latitude scintillations measured with a network of GPS receivers. Ann. Geophys. 22, 3155–3175.
Whalen, J. A. (2004). Linear dependence of the post-sunset equatorial anomaly electron density on solar flux and its relation to the maximum pre-reversal ExB drift velocity through its dependence on solar flux. J. Geophys. Res. 109, A07309, doi: 10.1029/2004JA010528.
Wu, C. C., Liou, K., Shan, S.-J., Tseng, C.-L. Variation of ionospheric total electron content in Taiwan region of the equatorial anomaly from 1994 to 2003. Adv. Space Res. 41 (2008), 611–616, doi: 10.1016/j.asr.2007.06.013, 2008.
Yeh, K. C., Franke, S. J., Andreeva1, E. S., Kunitsyn, V. E. An investigation of motions of the equatorial anomaly crest. Geophys. Res. Lett. 28 (24), 4517–4520, 2001.
Yue, X; Schreiner, W. S; Kuo, Y. H; Lei, J. (2015). Ionosphere equatorial ionization anomaly observed by GPS radio occultations during 2006-2014, JASTP, 30-40.
Zhang, M. L.; Wan, W.; Liu, L.; Ning, B. (2009). Variability study of the crest-to-trough TEC ratio of the equatorial ionization anomaly around 120°E longitude. Advances in Space Research. 43, 1762–1769.
Zhao, B; Wan, W; Liu, L and Ren, Z. (2009). Characteristics of the ionospheric total electron content of the equatorial ionization anomaly in the Asian-Australian region during 1996–2004. Ann. Geophys., 27, 3861–3873.
Zhao, B; Wan, W; Liu, L; Mao, T; Ren, Z; Wang, M and Christensen, A. B. (2007). Features of annual and semiannual variations derived from the global ionospheric maps of total electron content, Ann. Geophys., 25, 2513–2527.
Zoundi, C.; Ouattara, F.; Fleury, R.; Amory-Mazaudier, C and Duchesne, L. P. (2012). Seasonal TEC Variability in West Africa Equatorial Anomaly Region. European Journal of Scientific Research. ISSN 1450-216X. 77 (3), 303-313.
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