Superposed epoch study of PV^5/3 during substorms, pseudobreakups and convection bays

Abstract

We present a superposed epoch study to examine the entropy parameter PV5/3, for isolated substorms, pseudobreakups and convection bays observed by Geotail in the near‐Earth plasma sheet, by using a flux‐tube‐volume formula with coefficients adjusted to fit magnetic field models for a variety of conditions. It is found that the changes of PV5/3 for these three types of events are distinct: (1) for substorms, PV5/3 increases continuously during the growth phase, decreases after dipolarization, and maintains a low value of ∼0.08 nPa(RE/nT)5/3; (2) for pseudobreakups, PV5/3 changes in a way similar to substorms, but decreases more moderately and then gradually increases; (3) for convection bays, PV5/3 takes a nearly constant value of 0.06 nPa(RE/nT)5/3. These results suggest that the characteristics of the processes that violate conservation of PV5/3 play a central role in the temporal and spatial reduction of PV5/3 and thus determine the earthward plasma transport during active times.

Role of depleted flux tubes in steady magnetospheric convection: Results of RCM‐E simulations

“…Therefore, the manifestation in this case is that the magnetic field strength is larger than empirical models in the near-Earth plasma sheet and plasma pressure is well enhanced near geosynchronous orbit. There is neither largescale explosive reconfiguration nor strong injections of unambiguous bubbles in SMCs [Yang et al, 2010], though weak and short-lived injections have been observed near geosynchronous orbit [Sergeev et al, 2001]. To our knowledge, at least two scenarios are related to the formation of low PV 5/3 boundary used in our simulation.…”

“…The coefficient one half in front of the SMC term in equation (1) represents the degree of the depletion on the boundary in the SMC run compared with the substorm growth phase [Yang et al, 2010]. Therefore, PV 5/3 = 2/3 P s h s l s on the boundary in SMC is set to about one half of that in the growth phase run.…”

“…Primarily motivated by their work, we carry out numerical simulations to investigate how the level of PV 5/3 changes the large-scale configuration in the near-Earth plasma sheet and inner magnetosphere. [5] In this paper, we use an equilibrium version of the Rice Convection Model (RCM-E) to model an idealized SMC event and a substorm growth phase, showing that continuous feeding of substantially depleted flux tubes in the magnetotail is the key to having steady and strong magnetospheric convection. Section 2 briefly introduces the model and its setup.…”

“…[4] Yang et al [2010] recently estimated the value of PV 5/3 in the near-Earth plasma sheet by using Geotail observations for different modes of plasma transport. Their superposed epoch study shows that PV 5/3 at about −10 R E increases in the substorm growth phase as the magnetic field stretches and decreases abruptly and strongly in the expansion phase as the magnetic field dipolarizes, which is an indication of the plasma sheet bubble injection to the inner magnetosphere.…”

Energetic ions in dipolarization events

“…Dipolarization events consist of a rapid change from stretched tail-like to more dipolar magnetic fields and are identified most commonly to be the rapid increase of B z within the central plasma sheet. Magnetic field lines threading through the region of enhanced B z are characterized by reduced field line entropy [e.g., Wolf et al, 2009;Birn et al, 2009;Yang et al, 2010;Kim et al, 2010;Dubyagin et al, 2011] and commonly denoted as "bubble" [Pontius and Wolf , 1990] or "dipolarizing flux bundle" (DFB) [Liu et al, 2013a[Liu et al, , 2013b. Earthward moving short dipolarization pulses are typically associated with an earthward flow burst [e.g., Nakamura et al, 2002;Runov et al, 2009;Sergeev et al, 2009], whereas an increase of B z toward a more persistent higher level may be observed closer to Earth without significant flow .…”