An Empirical Model of Vertical Plasma Drift Over the African Sector

Abstract

Daytime vertical E × B drift can be derived from difference of H‐component magnetic field measurements (ΔH) using a pair of low‐latitude and equatorial latitude magnetometer stations. Knowledge of E × B drift is of utmost importance in space weather‐related predictions since it can significantly affect ionospheric density structures and dynamics. For the first time, we developed a quantitative relationship between equatorial electrojet (ΔH) and vertical E × B drift over the African region using magnetometer data and E × B drift observations from the Communication and Navigation Outage Forecasting System (C/NOFS) satellite during local daytime (0700–1800 LT) from 2008 to 2013 when magnetometer data were available. Additionally, we have constructed vertical E × B drift models over the African sector based on C/NOFS vertical E × B drift data and relevant physical and geophysical inputs. Validating using data not included in model development, our model estimated C/NOFS vertical E × B drift with correlation coefficient values of 0.85 and 0.56 during quiet and disturbed conditions, respectively. The daily pattern of the E × B drift velocity is consistent between the developed model based on C/NOFS data and the climatological Scherliess‐Fejer model. However, the Scherliess‐Fejer model generally overestimated C/NOFS vertical E × B drift (in most cases) with a correlation coefficient of 0.54 during quiet conditions.

Longitudinal and Seasonal Variability of Equatorial Ionospheric Irregularities and Electrodynamics

“…Although much has been learned about equatorial density irregularities, such as the causative mechanism and the seasonal variability of its occurrence, several important questions remain, including the longitudinal and the day‐to‐day variability of irregularity occurrence and the seeding mechanisms favorable to the bottomside ionospheric instability, usually referred as Rayleigh‐Taylor instability (RTI). Several mechanisms have been suggested as the possible triggering mechanisms for the day‐to‐day and longitudinal variability of irregularities, including seeding mechanisms from the lower atmosphere, such as gravity wave (e.g., Kelley et al, ), neutral wind‐driven gradient drift instability (e.g., Kudeki et al, ), and postsunset vertical drift enhancements (e.g., Dubazane & Habarulema, ; Eccles, ; Hysell et al, ; Thampi et al, ; Tsunoda et al, ).…”

Counter‐Electrojet Occurrence as Observed From C/NOFS Satellite and Ground‐Based Magnetometer Data Over the African and American Sectors

“…Due to the unusual extended solar minimum at the end of solar cycle 23 during 2008–2010 (e.g., Chen et al, ; Ezquer et al, ) when vertical E × B drift did not show expected direct relationship with solar activity (e.g., Dubazane & Habarulema, ; Habarulema et al, ), the presentation of results is categorized into two periods of 2008–2010 and 2011–2014, respectively, for both the American and African sectors. This was however done only for the 69°W (American) and 38°E (African) longitude sectors where 2008–2014 data were available; otherwise, 2011–2014 data sets were analyzed for the 56°W (American) and 9°E (African) longitude sectors.…”

“…The derived Δ H data from PUER‐LETI pair of magnetometer stations is mostly available from 2009 and further contains significant data gaps especially in 2010–2011, explaining the difference in data points displayed in scatter plots of Figure for PUER and AAE. The correlation values are comparable to earlier results which reported values of 0.57 and 0.51 over Jicamarca (Habarulema et al, ) and AAE (Dubazane & Habarulema, ), respectively, between C/NOFS vertical E × B drift and Δ H . The low correlation values are attributed to the altitude differences at which C/NOFS vertical E × B drift and Δ H are computed.…”

“…Due to the intention of directly comparing with magnetometer‐derived EEJ, it was necessary to limit the latitudinal coverage of satellite's data around the geomagnetic equator by constraining the latitude of observations to remain within the EEJ band. For this purpose, the latitude range used was ±4° around the geomagnetic equator and within a longitude range of ±8° centered around the meridian of the pair of magnetometer stations (e.g., Dubazane & Habarulema, ; Habarulema et al, ) for both African and American sectors. In an effort to minimize potential outliers associated with C/NOFS vertical ion plasma drift data within 400–550 km, we employed the median and scaled median absolute deviation (e.g., Huber, ; Huber & Ronchetti, ) for each satellite track during the entire period (2008–2014) of analysis.…”

“…In an effort to minimize potential outliers associated with C/NOFS vertical ion plasma drift data within 400-550 km, we employed the median and scaled median absolute deviation (e.g., Huber, 1981;Huber & Ronchetti, 2009) for each satellite track during the entire period (2008-2014) of analysis. This filtering method has been previously used in related analyses (e.g., Habarulema et al, 2018;Lomidze et al, 2017) and is demonstrated in Dubazane and Habarulema (2018) for C/NOFS satellite data treatment. After removing outliers, the C/NOFS data are averaged in 3-min intervals.…”