The magnetospheric banana current

Abstract

[1] It is shown that the banana current, a current system in the inner magnetosphere closing entirely within the magnetosphere (i.e., not through the ionosphere or on the magnetopause) but not circumflowing around the Earth, is a regular feature of near-Earth space. Closure options for the eastward asymmetric current on the inside of a localized pressure peak were explored, with the conclusion that the current must close via westward current around the outside of the high pressure region. It is a current that encircles a pressure peak and, therefore, whenever there is a pressure peak in the inner magnetosphere, a banana current exists. If multiple pressure peaks exist in the inner magnetosphere, then multiple banana currents will also coexist. Its occurrence rate is equal to that of the partial ring current, defined here as westward magnetospheric current that closes through field-aligned currents into and out of the ionosphere. Its magnitude can reach a few mega-amps during the main phase of storms, but drops to <0.1 MA during extended quiet intervals. The magnetic perturbation related to this current is strong within the region of high plasma pressure that it encircles, but is otherwise very weak outside of the banana current loop because the oppositely-directed current flow on either side of the loop largely cancels each other. In general, its related magnetic field is a few nanotesla of northward perturbation for both ground-based and geosynchronous magnetometers, making it difficult to magnetically detect. The banana current is placed in the context of the other near-Earth nightside current systems.

A physical explanation for the magnetic decrease ahead of dipolarization fronts

“…In addition, the difference of magnetic field B z is almost the same at t 0 -10 s and t 0 + 10 s, which strongly suggests that these three current form circuits, which are independent from the background magnetotail current. We point out that although the plasma pressure variation supports the picture of banana current loop, it may be not exactly the same as described in Liemohn et al (2013) since the DF is a kinetic structure that can not be fully interpreted by MHD theory. For the third current structure in Fig.…”

“…However, the volume gradient of magnetic flux tube is extremely difficult to be accurately estimated in any magnetic field model in the perturbed magnetotail, especially accompanied with BBFs (Kubyshkina et al, 2011;Tsyganenko, 1995). Moreover, Liemohn et al (2013) suggested that current could flow in a closed loop around peaks in plasma pressure forming a banana current. This banana current is distinct from the other current systems in the near-Earth space.…”

Storm time current distribution in the inner equatorial magnetosphere: THEMIS observations

“…Numerical experiments carried out by Liemohn et al . [, ] indicate that the small‐scale eastward current can reach L = 5–6 at times (e.g., Figure 4 in Liemohn et al . [, ]).…”

“…[, ] indicate that the small‐scale eastward current can reach L = 5–6 at times (e.g., Figure 4 in Liemohn et al . [, ]). Our multipoint analysis shows that the eastward component can indeed extend beyond r = 5 R E for weak storm times.…”

“…According to the modeling result of Liemohn et al . [, , ], the tail current inner edge will move Earthward inside geosynchronous orbit during the early main phase, then retreats until the ring/tail boundary is beyond L = 10 in the nightside magnetosphere; this process completes by the peak of the storm interval. Our direct measurement is thus highly consistent with their modeling conclusion.…”