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Abstract. We investigate the response of the mid-latitude thermospheric neutral winds to a sub-auroral polarization stream (SAPS) event. Using red line (F region) airglow data from two Fabry–Pérot interferometers (FPIs), and F-region ionospheric flow velocities from four Super Dual Auroral Radar Network (SuperDARN) radars, the drivers behind changes seen in the neutral winds are explored within the context of the larger SAPS structure. Different, although strong, neutral wind responses to the SAPS are seen at the two FPI sites, even though they are relatively close geographically. We attribute the wind differences to the varying balance of pressure gradient, ion drag, and Coriolis forces, which ultimately depend on proximity to the SAPS. At the FPI site equatorward of the SAPS, pressure gradient and Coriolis forces drive the winds equatorward and then westward. At the FPI site co-located with the SAPS, the ion drag is strong and results in the winds surging westward before turning eastward when becoming influenced by dawnside sunward plasma convection drifts. 

Abstract. We present the first observations from a new low-cost obliqueionosonde located in Antarctica. The transmitter is located at McMurdoStation, Ross Island, and the receiver at Amundsen–Scott Station, South Pole.The system was demonstrated successfully in March 2019, with the experimentyielding over 30 000 ionospheric echoes over a 2-week period. These dataindicate the presence of a stable E layer and a sporadic and variableF layer with dramatic spread F of sometimes more than 500 km (in units ofvirtual height). The most important ionospheric parameter, NmF2, validateswell against the Jang Bogo Vertical Incidence Pulsed Ionospheric (VIPIR) ionosonde (observing more than 1000 kmaway). GPS-derived TEC data from the Multi-Instrument Data Analysis Software(MIDAS) algorithm can be considerednecessary but insufficient to predict 7.2 MHz propagation between McMurdoand the South Pole, yielding a true positive in 40 % of cases and a truenegative in 73 % of cases. The success of this pilot experiment at a totalgrant cost of USD 116 000 and an equipment cost of ∼ USD 15 000 indicates that a large multi-static network could be built to provide unprecedented observational coverage of the Antarctic ionosphere. 

Dense, fast-moving regions of ionization called polar cap patches are known to occur in thehigh-latitudeFregion ionosphere. Patches are widely believed to be caused by convection of dense, sunlitplasma into a dark and therefore low-density polar cap ionosphere. This leads to the belief that patches are awinter phenomenon. Surprisingly, a long-term analysis of 3 years of ionospheric measurements from theSwarm satellites shows that large density enhancements occur far more frequently in local summer than localwinter in the Southern Hemisphere (SH). The reverse is true in the Northern Hemisphere (NH). Previouslyreported patch detections in the SH are reexamined. Detection algorithms using only a relative doubling testcount very small densityfluctuations in SH winter due to extremely low ambient densities found there,while much larger enhancements occurring in SH summer are missed due to especially high ambientdensities. The same problem does not afflict results in the NH, where ambient densities are more stableyear-round due to the ionospheric annual asymmetry. Given this new analysis, the definition of a patch as adoubling of the ambient density is not suitable for the SH. We propose a test for patches linked to long-termaveraged solarflux activity, characterized by the 81 day centered meanF10.7index. Importantly, thecurrent patch formation theory is at least incomplete in that it does not predict the observed lack of patchesin SH winter, or the many large enhancements seen in SH summer 

The polarFregion ionosphere frequently exhibits sporadic variability (e.g., Meek, 1949,https://doi.org/10.1029/JZ054i004p00339; Hill, 1963,https://doi.org/10.1175/1520‐0469(1963)020<0492:SEOLII>2.0.CO;2). Recent satellite data analysis (Noja et al., 2013,https://doi.org/10.1002/rds.20033; Chartier et al., 2018,https://doi.org/10.1002/2017JA024811) showed that the high‐latitudeFregion ionosphere exhibits sporadic enhancements more frequently in January than in July in both the northern and southern hemispheres. The same pattern has been seen in statistics of the degradation and total loss of GPS service onboard low‐Earth orbit satellites (Xiong et al. 2018,https://doi.org/10.5194/angeo‐36‐679‐2018). Here, we confirm the existence of this annual pattern using ground GPS‐based images of TEC from the MIDAS algorithm. Images covering January and July 2014 confirm that the high‐latitude (>70 MLAT)Fregion exhibits a substantially larger range of values in January than in July in both the northern and southern hemispheres. The range of TEC values observed in the polar caps is 38–57 TECU (north‐south) in January versus 25–37 TECU in July. First‐principle modeling using SAMI3 reproduces this pattern, and indicates that it is caused by an asymmetry in plasma levels (30% higher in January than in July across both polar caps), as well as 17% longer O⁺plasma lifetimes in northern hemisphere winter, compared to southern hemisphere winter.