Polar Vortex Strength Impacts on the Longitudinal Structure of Thermospheric Composition and Ionospheric Electron Density

摘要

This work examines the weak stratospheric polar vortex event in late February 2008 and the strong polar vortex event in late February 2021 to understand the potential influence of polar vortex strength on midlatitude thermospheric composition and ionospheric plasma density. The weak polar vortex event shows a reduction in thermospheric O/N2 at all longitudes, changes in the ionospheric total electron content (TEC) that vary with longitude, and an intensification of the semidiurnal tides. The strong polar vortex event shows O/N2 elevated by up to 25% in the Asian sector and a 25% decrease in semidiurnal tidal amplitude. The TEC response during the strong polar vortex event is complex and shows enhanced TEC in the Asian sector where O/N2 is elevated. These are the first observations of anomalies in the thermospheric composition and ionospheric plasma associated with a strong polar vortex event. The stratospheric polar vortex is a belt of westerly winds in the midlatitudes that exists in the middle atmosphere during the winter months. The Arctic polar vortex is highly variable; sometimes it is weak and distorted, while other times it is strong. Vortex strength is known to impact weather in the troposphere and variability in the mesosphere, thermosphere, and ionosphere. The state of the polar vortex is predictable up to 2 weeks in advance, so knowledge of the vortex may increase predictability in other regions of the atmosphere. Here, we use two case studies to examine how a weak vortex and a strong vortex impact the composition of the thermosphere and the density of the ionosphere at midlatitudes. During the weak vortex case, the thermospheric composition is changed such that there is a decrease in the ratio of atomic oxygen to molecular nitrogen (O/N2). However, during the strong vortex case, there are longitude sectors with elevated values of O/N2. These regions of elevated O/N2 correspond to increased ionospheric plasma density. These are the first observations of anomalies in the thermosphere and ionosphere associated with a strong vortex event. For the first time, a strong polar vortex event is shown to have an impact on both ionospheric electron density and O/N2 at midlatitudesBoth strong and weak vortex events have an influence on thermospheric composition, possibly through modified thermospheric circulationRegions of enhanced O/N2 coincide with elevated total electron content in the Asian sector during the strong vortex event