Response of Meteor Plasma Trails Observed by Meteor Radar to Geomagnetic Activity

From meteor radar observations typically measuring neutral winds and temperatures in the upper atmosphere, we showed that under‐dense meteor plasma trails respond to geomagnetic activity. Depending on the geomagnetic activity conditions, the parameters of the under‐dense trail echoes show substantial anomalies, and their responses are immediate. As geomagnetic activity increases, the decay time decreases up to about 10% at Kp = 8, while both the returned signal power and radial velocity error increase. In addition, the types of diffuse evolution vary with geomagnetic activity, resulting in strong geomagnetic activity that immediately affects the trail. The evolution of the trail is affected not only by the ambient mesospheric neutral atmospheric properties but also by electromagnetic effects, such as strong electric fields inside meteor trails. Furthermore, our findings suggest that the geomagnetic effect should be considered when estimating atmospheric parameters from MR during a geomagnetically active period. Plain Language Summary Through long‐term meteor radar (MR) observation (2007–2021) at King Sejong Station in the Antarctic Peninsula, we found that the diffusion process in the meteor trail immediately accelerated under enhanced geomagnetic activity. The backscattered‐returned signal powers, which are proportional to the square of the electron line density of the meteor trail, also instantly increased. These anomalous characteristics in meteor trails appear while the background atmospheric parameters remain constant. Therefore, we propose that the observed immediate responses in the MR may be associated with the strong electric field in the ambient ionosphere D/E region induced by the increased geomagnetic activity. The strong external electric field can stimulate an electric field and current inside the meteor trail, owing to the difference in electrical conductivities between the meteor trail and ambient atmosphere. Thus, the electric field, current, and charge separation inside the meteor trail can lead to faster diffusion and enhanced electron line density in the trail. The meteor plasma trails are observed in regions that are affected by electric fields caused by geomagnetic activity; therefore, when deriving neutral atmospheric parameters from MRs, the impact of geomagnetic activity must be considered. Key Points Under‐dense meteor echo parameters at a geomagnetic latitude of 50.2°S revealed an instantaneous response to geomagnetic activity Ge