The characterization and validation of ROTI over the African Sector
Abstract
The Rate of Change of TEC Index (ROTI) is one of the ionospheric scintillation indices required by the International Civil Aviation Organization (ICAO) to be included in air navigation advisories on space weather conditions that may indicate the degradation of GNSS-based navigation and surveillance. The ROTI index can be derived from data from the GNSS receivers of the International GNSS Service (IGS) of which there are more than 40 deployed in Africa and the Trignet network of more than 60 receivers in South Africa. Due to the paucity of other instruments for measuring ionospheric scintillation in Africa the ROTI may serve as a useful proxy for ionospheric scintillation. Ionospheric scintillation regularly occurs post sunset at equatorial latitudes mainly due to ExB instability which can be excited when there is a strong eastward electric field. The mid-latitudes are commonly regarded as low scintillation regions. However, in December 2014, during the peak of solar cycle 24, there were periods of significant irregularities in the mid-latitude ionosphere over Southern Africa, which prompted a several studies of the dynamics of the mid-latitude ionosphere to observe and model the development of plasma instabilities. This paper characterizes ROTI over the African sector by examining GNSS data from the African GNSS receiver network during the peak of solar cycle 24. ROTI is validated by comparison with other indices of ionospheric perturbation including S4, spread F (derived from Ionosonde data) and Rate of Change of Density Index (RODI) derived from Swarm satellite data. For the low-latitude region of Africa, we demonstrate the longitudinal variation of irregularities which may give rise to ionospheric scintillation. There are times when the irregularities are limited to West Africa, with no activity in East Africa on the same day, and other times when there are significant irregularities in the East African region, with little or no activity in the West African Region. The trends in the occurence of ionospheric irregularities are statistically represented in terms of counts of nighttime ROTI values above a threshold of 0.4 TECU/min. We further investigate the possible mechanisms responsible for mid- latitude ionospheric irregularities. Our results highlights the need to further study of the mechanisms responsible for the formation of ionospheric irregularities in the mid-latitudes and to validate whether these irregularities cause ionospheric scintillation that gives rise to errors in navigation.
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E2377C