Daytime twin-peak structures observed at southern African and European middle latitudes on 8–13 April 2012

Abstract

Abstract. Daytime twin-peak structures, also known as biteout or diurnal double-maxima structures, are ionospheric phenomena in which the diurnal ionospheric trend shows two peaks (instead of the normal one) during the daytime. This study reports on first simultaneous observations of these structures in the Global Positioning System and ionosonde measurements from the southern African and European middle-latitude stations during a mostly quiet geomagnetic condition period of 8-13 April 2012, which indicates that their occurrence and therefore driving mechanism(s) may not be localised. It is found that the daytime twin-peak structures generally appear later in the Northern Hemisphere with a 1-3 h latency although they propagate mostly equatorward in both hemispheres. Proxies of meridional neutral winds were calculated from available manually scaled ionosonde measurements and used to explore their potential as drivers of the structures. Bite-out events were linked to downward drifts of the vertical component of equivalent neutral winds causing plasma depletions. In addition, evidence of sporadic E layers at the same time as enhancements of daytime twin-peak structures suggests that the tides had influence via the meridional wind shear in generating these structures through the dynamo electric field which resulted in upward E × B drifts.

Ionospheric Diurnal Double‐Maxima Patterns Observed by the TEC From Beidou Geostationary Satellites in the Asian‐Australian Sector During 2016–2018

“…Additionally, the ionospheric DDM with different occurrence times at middle latitudes could be attributed to different generation mechanisms. Previous studies suggested that the poleward neutral winds play a dominant role in the generation of ionospheric DDM at middle latitudes (Katamzi et al, 2016;Zhang et al, 2000). Abur-Robb (1969) suggested that the poleward neutral winds during 4:30-16:30 LT could cause the ionospheric depletion around noontime.…”

“…The ionospheric DDM occurs generally at low latitudes and in the equatorial region, which is suggested to be associated with the effect of upward E×B drift that produces the equatorial ionization anomaly (EIA; Abur-Robb, 1969;Adebesin et al, 2018;Baxter & Kendall, 1968;Rajaram, 1977;Rastogi, 1966). It can also be observed at middle latitudes, as a result of dynamic processes in terms of poleward neutral winds and thermal expansion (Abur-Robb, 1969;Katamzi et al, 2016;Khan et al, 1985;Kohl & King, 1967;Saryo et al, 1989;Zhang et al, 2000). In addition, the ionospheric DDM can be connected with substorms and storms (Pi et al, 1993;Sojka et al, 2001).…”

Daytime Ionospheric Large‐Scale Plasma Density Depletion Structures Detected at Low Latitudes Under Relatively Quiet Geomagnetic Conditions

“…Another possible candidate responsible for the decrease of plasma density associated with a downward plasma transport is the poleward meridional neutral wind. Based on the ionosonde measurements at specific locations, plasma density depletions were observed and suggested to be associated with downward ion drift driven by poleward neutral winds (e.g., Katamzi et al, 2016;Saryo et al, 1989). Mikhailov et al (2007) demonstrated that the quiet time negative ionospheric disturbances always corresponded to strong poleward neutral winds according to the Millstone Hill ISR observations.…”

Response of Ionospheric Profile Parameters to Equatorial Electrojet Over Peruvian Station

“…The daytime noon bite-out is caused by the motion of plasma blown away from the dip equator into the hemispheres. The vertical plasma drift is the combined result of the zonal electric field and the thermospheric winds owing to the geomagnetic field-aligned motion of ions (Katamzi et al, 2016). Subsequently, the buildup in the electron density continues and the second peak in NmF2 forms at about 1500-1700 hr (postnoon peak) with values of 8.8 × 10 11 m −3 during equinoxes, 9.5 × 10 11 m −3 in summer, and 5.7 × 10 11 m −3 in winter.…”