Impact of 10 January 1997 geomagnetic storm on the nighttime Weddell Sea Anomaly: A study utilizing data provided by the TOPEX/Poseidon mission and the Defense Meteorological Satellite Program, and simulations generated by the Coupled Thermosphere/Ionosphere Plasmasphere model

This study investigates the evolution of 10 January 1997 magnetic storm and the nighttime space weather change created by the impact of the interplanetary shock wave and associated events on the ionosphere. Its aims are to trace the storm's energy flow dissipation and transportation processes and to learn about the response of nighttime ionosphere to these interplanetary events, focusing on the reaction of the nighttime Weddell Sea Anomaly (WSA). To track down the consequential space weather changes, multi‐instrument measurements and Coupled Thermosphere/Ionosphere Plasmasphere (CTIP) simulations were combined. As results show, the first response of nighttime WSA to the energy input in the magnetosphere, when BZ turned southward, was its ∼50% total electron content (TEC) and Ni increase maintained during the main phase, indicating long‐duration positive storm effects. At ∼0800 universal time (UT) the second such BZ event triggered the depletion of equatorial and northern midlatitude ionosphere, a signature of strong downward E × B plasma drift, and launched gravity waves. Following a period of very bright aurora, at ∼1200 UT, some southern midlatitude and subauroral plasma enhancements developed. TOPEX detected an enhancement between 45–65°S (dip), where the equatorward winds were most effective, with a sudden TEC drop‐off, a signature of the plasmapause. Particularly strong negative storm effects depleted the nighttime WSA's TEC‐Ni (∼45–50%) and O/N2 ratio (∼21%). The Bent model could simulate the WSA, but not the storm‐related ionospheric responses. CTIP simulations indicated equatorward winds causing downwellings and changes in the neutral atmospheric composition revealed by the O/N2 ratio. Joule heating and electric fields were the major geophysical factors observed changing space weather during this storm.