Investigation of the homogeneity of energy conversion processes at dipolarization fronts from MMS measurements

Abstract

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Two Classes of Equatorial Magnetotail Dipolarization Fronts Observed by Magnetospheric Multiscale Mission: A Statistical Overview

“…More importantly, the systematic and significant reversal in the current density pointed out in Alqeeq et al. (2022) as the cause of the reversal of the energy conversion process for the six analyzed DF events is confirmed by this statistical study as being a common signature of class II events. Although being small, we point out that the positive peak of the reversal of the current density after the DF crossing is obtained by three independent measurements (i.e., from pressure measurements ( J dia , Figure 7c), magnetic field measurements ( J curl , Figure 7d) and density and velocity measurements ( J part , Figure 7e)).…”

“…We have reported on a statistical study based on 132 DFs detected by the MMS mission during the full magnetotail season of 2017 (end of April to end of August). We found that the 132 events can be subdivided into two categories mostly according to their DF-shape (magnetic field profile): class I with 98 events (74.4%) for which the DF-shape shows a slow decrease of the magnetic field after the DF and is associated with smaller ion velocity, class II with 34 events (25.6%) for which the DF-shape shows the same time scale for the rising and the falling of the magnetic field (a bump) associated with minimums of ion and electron pressures and faster velocity as shown in Alqeeq et al (2022) for six DF events. These two classes can be considered as subcategories of the Schmid's DF category A (Schmid et al, 2015) as they both correspond to a decrease of the density and an increase of the temperature.…”

“…DF crossing time t 0 is defined by the maximum of B z in the selected time interval. Only DFs near the Earth's magnetotail equator are kept using the following constraint | B x | < 5 nT. Indeed, electron partial moment data computed by the FPI team are necessary due to the very low density values (and low counts) in the magnetotail (see Alqeeq et al. (2022), for more details). Due to these constraints, the new DF list is reduced to 132 DF events.…”

“…In this section, we present the results from the SEA of the energy conversion processes. For energy conversion, positive values of j ⋅ E correspond to an energy load or dissipation whereas negative values correspond to a generator or dynamo effect (e.g., Alqeeq et al., 2022; Birn & Hesse, 2005; Huang et al., 2015; Torbert et al., 2016). Figure 10 shows the results of the SEA of the energy conversion processes for our two DF categories.…”

Are Dipolarization Fronts a Typical Feature of Magnetotail Plasma Jets Fronts?

“…The right column of Figure 3 presents an example of a BBF front which satisfies the S11 criteria but not the F12-based criteria. This event was first reported by Alqeeq et al (2022) to show the non-homogeneity of the energy conversion due to electron-scale substructures attributed to lower-hybrid drift waves. Similar to the other example, t DF is accurately estimated as it corresponds to the ion energy enhancement (panel g), the ion density n i decrease (panel i) and the ion temperature T i increase (panel k).…”