Plasma transport in the magnetotail lobes

Abstract

Abstract. The Earth's magnetosphere is populated by particles originating from the solar wind and the terrestrial ionosphere. A substantial fraction of the plasma from these sources are convected through the magnetotail lobes. In this paper, we present a statistical study of convective plasma transport through the Earth's magnetotail lobes for various geomagnetic conditions. The results are based on a combination of density measurements from the Electric Field and Waves Experiment (EFW) and convection velocities from the Electron Drift Instrument (EDI) on board the Cluster spacecraft. The results show that variations in the plasma flow is primarily attributed to changes in the convection velocity, whereas the plasma density remains fairly constant and shows little correlation with geomagnetic activity. During disturbed conditions there is also an increased abundance of heavier ions, which combined with enhanced convection, cause an accentuation of the mass flow. The convective transport is much slower than the field aligned transport. A substantial amount of plasma therefore escape downtail without ever reaching the central plasma sheet.

Solar wind entry into the high-latitude terrestrial magnetosphere during geomagnetically quiet times

“…Additionally, event selection was made according to the particle energy flux in the lobe: we require that the energy band between 700 ev and 2 keV, and at least one order of magnitude for all energy bands, contain a particle energy flux greater than 8 Â 10 4 keVs À 1 cm À 2 si À 1 keV À 1 . Based on these criteria, only events with magnetosheath or cusp-like 35,36 ions with energy around 1 keV were selected, and the upflowing ions with lower energy 29,34 from the ionosphere were excluded.…”

“…A total of 104 events was found, with 45 and 59 occurring in the southern and northern hemispheres, respectively. Figure 3a shows that the plasma density of these events is greater than 0.05 cm À 3 , which is much higher than the lobe background level 29,34 . The bulk ion flow speeds are below 60 km s À 1 (not shown).…”

“…Previous observations have shown that the magnetospheric lobe 6,7 , which occupies the majority of the magnetotail volume in the high latitudes, typically forms a reservoir of magnetic energy 28 , consisting of tenuous, low energy ions of internal, ionospheric origin 7,29 . Although observations 30 and numerical simulations [20][21][22] have inferred that plasmas from outer regions, for example, compressed solar wind in the magnetosheath, may enter the highlatitude lobe regions, direct observations of these plasmas inside are rare, partly because high-latitude lobes tailward of the mid-altitude cusps have seldom been explored in situ, restricting our ability to gain an understanding of this region.…”

Detection of a plasmaspheric wind in the Earth's magnetosphere by the Cluster spacecraft

“…The here-calculated plasma transport rate due to the plasmaspheric wind ∼ 5 × 10 26 ions s −1 constitutes a plasma source for the outer magnetosphere which has to be compared to the other known plasma sources. The solar wind source is of the order of ∼ 10 27 ions s −1 and the high-latitude ionospheric source is of the order of ∼ 10 26 ions s −1 , varying by a factor of ∼ 3 as a function of the activity level and particularly dependent on the IMF orientation (Moore et al, 2005;Haaland et al, 2009;Li et al, 2012). The plasmaspheric plumes, which are a persistent feature during active periods, contribute during these periods by typically ∼ 2 × 10 26 ions s −1 to the magnetospheric populations (Borovsky and Denton, 2008).…”

Circulation of Heavy Ions and Their Dynamical Effects in the Magnetosphere: Recent Observations and Models

“…This suggests that some acceleration is at work in the direction perpendicular to the magnetic field in the boundary layer, with O + ions being transported into the plasma sheet by a strong electric field, on the order of 20 mV/m. combined measurements of ion velocity and density from Cluster (Engwall et al 2009b) with convection electric field measurements in the lobes (Haaland et al , 2009) to quantify the recirculation of cold upflowing ions. The recirculation is directly controlled by the convection electric field.…”