Three-dimensional ionospheric electron density structure of the Weddell Sea Anomaly

This paper provides the first three‐dimensional description of the ionospheric density structure of the Weddell Sea Anomaly (WSA). The WSA is characterized by a nighttime ionospheric density greater than that in daytime in the Weddell Sea region around the Antarctic Peninsula during the southern hemisphere summer. It was first observed by ground‐based ionosondes located in the Antarctica back in the 1950s and was further investigated by two‐dimensional maps over the oceans using TEC measurements collected by the TOPEX/Poseidon recently. Although these TEC maps have provided two‐dimensional views for tracking the time‐evolution and spatial coverage of the WSA, the vertical distribution of this peculiar feature is still unavailable. With the vertical ionospheric density profiles observed by the FORMOSAT‐3/COSMIC, three‐dimensional density structure of the WSA is presented here for the first time. Meanwhile, a similar WSA signature is observed in the northern and eastern hemisphere during June solstice by both the GPS‐TEC and the FORMOSAT‐3/COSMIC electron density observations. From the observed altitudinal structure of the WSA during 1800–2400 LT and the similar feature occurred in the opposite hemisphere suggest that the southward offset of the magnetic equator with respect to the geographic equator plays a major role for the WSA formation.