Equatorial plasma bubbles and L-band scintillations in Africa during solar minimum
- 1Institute for Scientific Research, Boston College, Chestnut Hill, MA, USA
- 2Air Force Research Laboratory, Hanscom Field, MA, USA
- 3University of Ilorin, Ilorin, Nigeria
- 4University of Lagos, Lagos, Nigeria
- 5Bahir Dar University, Bahir Dar, Ethiopia
- 6Makerere University, Kampala, Uganda
- 7Jomo Kenyatta University, Nairobi, Kenya
- 8University of Nairobi, Nairobi, Kenya
- 9Université de Cocody à Abidjan, Abidjan, Cote d'Ivoire
- 10University of Nigeria, Nsukka, Nigeria
- 11Addis Ababa University, Addis Ababa, Ethiopia
- *now at: Institute for Scientific Research, Boston College, Chestnut Hill, MA, USA
Abstract. We report on the longitudinal, local time and seasonal occurrence of equatorial plasma bubbles (EPBs) and L band (GPS) scintillations over equatorial Africa. The measurements were made in 2010, as a first step toward establishing the climatology of ionospheric irregularities over Africa. The scintillation intensity is obtained by measuring the standard deviation of normalized GPS signal power. The EPBs are detected using an automated technique, where spectral analysis is used to extract and identify EPB events from the GPS TEC measurements.
Overall, the observed seasonal climatology of the EPBs as well as GPS scintillations in equatorial Africa is adequately explained by geometric arguments, i.e., by the alignment of the solar terminator and local geomagnetic field, or STBA hypothesis (Tsunoda, 1985, 2010a). While plasma bubbles and scintillations are primarily observed during equinoctial periods, there are longitudinal differences in their seasonal occurrence statistics. The Atlantic sector has the most intense, longest lasting, and highest scintillation occurrence rate in-season. There is also a pronounced increase in the EPB occurrence rate during the June solstice moving west to east. In Africa, the seasonal occurrence shifts towards boreal summer solstice, with fewer occurrences and shorter durations in equinox seasons. Our results also suggest that the occurrence of plasma bubbles and GPS scintillations over Africa are well correlated, with scintillation intensity depending on depletion depth. A question remains about the possible physical mechanisms responsible for the difference in the occurrence phenomenology of EPBs and GPS scintillations between different regions in equatorial Africa.