Variability of NmF2 during solar minima at the Equatorial Ionization Anomaly crest region

Publication date: Available online 20 September 2019Source: Advances in Space ResearchAuthor(s): Madeeha Talha, Nabeel Ahmed, Muneeza M. Ali, Ghulam MurtazaAbstractThe variability of NmF2 during solar minima of solar cycle 21-22, 22-23 and 23-24 has been studied for two low latitude stations, Karachi (Pakistan) and Okinawa (Japan), as both stations are situated at the Equatorial Ionization Anomaly (EIA) crest region. Diurnal, seasonal and annual behaviour of variability has been investigated using relative standard deviation approach. At both the stations, a direct relation of variability (CV) with Smoothed Sunspot Numbers (SSN) is noted which is opposite to the results found by many authors who have worked on different solar activity periods. It is suggested that the E-layer is responsible for this direct relation as an increase in the E-layer ionization with decrease in SSN for solar minimum has also been noted for Karachi in our previous work (Talha et al., 2019). The interaction of tides and waves with the E-layer might be responsible for the increase in ionization of the E-layer and the decrease in variability in the F-layer. Also, the night-time variability is observed to be higher than the daytime variability during minima as expected due to the low mean NmF2 or large deviation during night-time. Very prominent post-midnight peaks and not very well shaped post-sunset peaks are also noticed at both stations. Besides the mentioned peaks, a small increase in variability d...
Source: Advances in Space Research - Category: Science Source Type: research