The Dawn‐Dusk Tail Lobe Magnetotail Configuration and the Formation of Aurora Transpolar Arc

Abstract

Most of the disturbances in space environment can be explained under the framework theory of open magnetosphere and Dungey cycle (Dungey, 1961). This theory is sketched in Figure 1 which is similar to Dungey's original figure. Under southward IMF (SIMF) conditions, magnetic reconnection occurs first at the nose of the magnetopause (Figure 1c) where IMF field lines interconnect with dayside geomagnetic closed field lines. Such reconnection creates a northern set and a southern set of open field lines that consequently convect toward nightside and form into a north-south tail lobe magnetotail configuration (Figures 1a and 1b). Then the northern open field lines interconnect with the southern open field lines in the tail (Figure 1d), creating new closed field lines and new IMF field lines. These two magnetic reconnection processes thus form a Dungey cycle, during which the topology of involved geomagnetic field lines changes from closed to open in dayside and then changes back from open to closed in nightside. This cycle causes solar wind mass and energy to enter into the magnetosphere and the ionosphere, resulting in disturbances such as magnetic storm, substorm, aurora, and so on.

3D GUMICS Simulations of Northward IMF Magnetotail Structure

“…(2005) would be more consistent with the results of Li et al. (2021, 2022), which are in turn consistent with our results. Interestingly, very similar dawn–dusk open lobe populations and resulting closed wedge structures that form in the high latitudes are present in simulations using real events (such as those discussed by Li et al.…”

“…It is not clear, from an observational point of view, how closely this resembles the real magnetosphere under northward IMF conditions (when the magnetotail's structure will be influenced by earlier periods of southward IMF and the pre-existing high-latitude field lines are open). However, we note that the structure in Figure 1a resembles that expected for reconnection with initially closed high-latitude field lines (Cowley, 1981(Cowley, , 1983Crooker, 1992;Fuselier et al, 2015;Milan et al, 2022) and also that observed in other simulations that are initialized with northward IMF conditions (e.g., Li et al, 2021Li et al, , 2022.…”

“…Their results were consistent with the topological features observed within their previous study Li et al (2021), as well as the alpha-like configurations shown in this study. Like KJ04, Li et al (2022) interpreted their results as consistent with the Chang et al (1998) model and described their formation of a closed field line region as being due to field lines that were trapped between new and old lobe regions (shown in their Figure 12). We previously discussed the physical limitations of the model proposed by Chang et al (1998); we would suggest that a modified magnetotail reconnection mechanism such as that described by Milan et al (2005) would be more consistent with the results of Li et al (2021Li et al ( , 2022, which are in turn consistent with our results.…”

“…We do note that there is a key difference between our simulation results and observational interpretations, which is that the magnetotail reconnection occurs due to the "alpha-like" configuration of the magnetotail, which arises from the northward IMF initialization of the simulation, but bears similarities to dawn-dusk lobes which have been argued to form during northward IMF configurations by previous studies(Fuselier et al, 2018;Li et al, 2021Li et al, , 2022. A consequence of this "alpha-like" configuration is that the two twisted open field line regions are brought into contact by the rotation of the magnetotail.…”

“…They discussed how the varying IMF B y conditions can affect the occurrence and rate of reconnection, and how they compare to observations of substorms but did not explicitly discuss the possible link to global arcs and auroral features (although a more recent study by Li et al. [2022] discusses the model results in context to TPAs). Additionally, they found signatures of fast earthward flows which indicated reconnection was taking place.…”