Colocated Observations of the E and F Region Thermosphere During a Substorm. Issue 11 (20th November 2020)

• Record Type: Journal Article
• Authors: Billett, D. D.; McWilliams, K. A.; Conde, M. G.
• Is Part Of: Journal of geophysical research. Volume 125:Issue 11(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-11-20
• Subjects: Ampere -- Superdarn -- Scanning Doppler Imager -- Ion‐Neutral Coupling -- Thermosphere‐Ionosphere Coupling -- Substorms; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2020JA028165
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Two‐dimensional thermospheric wind fields, at both E and F region altitudes within a common vertical volume, were made using a Scanning Doppler Imager (SDI) at Poker Flat, Alaska, during a substorm event. Coinciding with these observations were F region plasma velocity measurements from the Super Dual Auroral Radar Network (SuperDARN) and estimations of the total downward and upward field‐aligned current density from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). This combination of instruments gives an excellent opportunity to examine the spatial characteristics of high‐latitude ionosphere‐thermosphere coupling and how a process which is triggered in the magnetosphere (the substorm) affects that coupling at different altitudes. We find that during the substorm growth phase, the F region thermospheric winds respond readily to an expanding ionospheric plasma convection pattern, while the E region winds appear to take a much longer period of time. The differing response timescales of the E and F region winds are likely due to differences in neutral density at those altitudes, resulting in E region neutrals being much more "sluggish" with regard to ion drag. We also observe increases in the F region neutral temperature, associated with neutral winds accelerating during both substorm growth and recovery phases. Plain Language Summary: At different altitudes in the polar atmosphere, how charged particles (the ionosphere) interact with neutral particles (the thermosphere) is of great importance. Primarily, this is because collisions between the two is the mechanism by which energy from the solar wind is ultimately deposited into the atmosphere, from the magnetosphere. Magnetosphere‐thermosphere energy exchange drives auroral displays and contributes to heating in both the E region (altitudes between 100 and 130 km) and F region (altitudes between 150 and 300 km). The neutral atmosphere is significantly denser in the E region compared to the F region, so its interaction with the ionosphere at those different altitudes is quite different. In this study, we examined the E and F regions during a "substorm" event, which is a large, sudden injection of energy into the nightside ionosphere. We found that the velocity of neutrals in the E region reacted much more slowly than those in the F region, so that the conditions imposed on the E region before the substorm persisted during the substorm. Key Points: Ionosphere‐thermosphere coupling is examined at E and F region altitudes during a substorm, postmidnight above Poker Flat, Alaska E region neutral winds are found to react slower to changes in the ionsophere due to substorm phases, compared to the F region F region heating is observed and associated with neutral wind acceleration during substorm growth and recovery