Solar wind control of plasma number density in the near-Earth plasma sheet: three-dimensional structure

Abstract

Abstract. The plasma number density in the near-Earth plasma sheet depends on the solar wind number density and the north-south component of interplanetary magnetic field (IMF B z ) with time lag and duration of several hours. We examined the three-dimensional structure of such dependences by fitting observations of plasma sheet and solar wind to an empirical model equation. Analyses were conducted separately for northward and southward IMF conditions. Effects of solar wind speed and IMF orientation were also examined by further subdivision of the dataset. Based on obtained results, we discuss (i) the relative contribution of the ionosphere and solar wind to plasma sheet mass supply, (ii) the entry mechanisms for magnetosheath particles, and (iii) the plasma transport in the plasma sheet. We found that solar wind number density dependence is weaker and IMF B z dependence is stronger for faster solar wind with southward IMF, which suggests the contribution of ionospheric particles. Further from the Earth, different interplanetary conditions result in different structures of solar wind dependence, which indicate different solar wind entry mechanisms: (1) southward IMF results in a strong dependence on solar wind number density in the flank high-latitude region, (2) slow solar wind with northward IMF leads to lower-latitude peaks of solar wind number density dependence in the flank region, (3) fast solar wind with northward IMF results in a strong dependence on solar wind number density at the down-tail dusk flank equator, and (4) solar wind number density dependence is stronger in the downstream of quasi-parallel bow shock. These features are attributable to (1) low-latitude dayside reconnection entry, (2) high-latitude dayside reconnection entry, (3) entry due to decay of Kelvin-Helmholtz vortices, and (4) diffusive entry mediated by kinetic Alfven waves, respectively. Effect of IMF B z and its time lags show plasma sheet reconfiguration associated with enhanced convective transCorrespondence to: D. Nagata (nagata@kugi.kyoto-u.ac.jp) port under southward IMF. Duration of IMF B z effect under northward IMF is interpreted in terms of turbulent diffusive transport.

A case study of Kelvin–Helmholtz vortices on both flanks of the Earth's magnetotail

“…In the dense region the magnetosheath plasma flowed tailward with a speed of $ 2002290 km s À1 , while flows were stagnant or slightly sunward on the magnetospheric side, which shows the presence of velocity shear similar in magnitude to that on the dawn side. The magnetospheric plasma temperature on both sides was as low as 10-15 MK, which is much higher than the magnetosheath temperature but is lower than the typical magnetosphere temperature (several tens of MK), and the magnetospheric ion density on both sides ð $ 1 cm À3 Þ was much higher than its usual value ð $ 0:220:4 cm À3 Þ (Nagata et al, 2008). Because both Cluster and GT had opportunities to repeat encounters with the boundary layer ( Fig.…”

IMF effect on the polar cap contraction and expansion during a period of substorms

“…Densities vary between about 0.05 and 0.3, mainly below 0.2 cm −3 . These densities are rather low, since typical densities close to the PS flanks are 0.2-0.5 cm −3 (Tsyganenko and Mukai, 2003;Nagata et al, 2008). However, several SW parameters affect the densities in the geomagnetic tail: IMF polarity, solar wind speed and density.…”

Estimation of the eddy-diffusion coefficients in the plasma sheet using THEMIS satellite data

“…It was shown that the values of the eddy-diffusion coefficient increase significantly during the growth and expansion phases, being more pronounced in the later. The turbulent transport in the plasma sheet is also affected by the orientation of the interplanetary magnetic field (IMF) (Nagata et al, 2008;Wang et al, 2010).…”